What is Engine 'Break-in'??

[BRENT in 10-uh-C]

I engaged in a small post on social media where several people were recommending to a hobbyist that a rebuilt engine needs to go thru a 'break-in', ..and (more emphatically) during that time, the engine RPMs needs to be varied (-from idle to up & down the RPM range.). I asked "why" does this all need to happen, ...and no one could seem to give me an (intelligent) answer other than auto manufacturers suggested this.

So I'll ask here where I know the responses to my question will be much more accurate!!



Let me start by giving my theory as to why their advice is a bunch of nonsense on 21st century Model-A engine rebuilds;

• The term Engine 'break-in' is really just an old phrase justifying the reasoning for allowing an engine to use internal friction of mismatched components to prematurely wear to a specification instead of using proper machining methods to obtain that desired clearance specification. (See Point #4 below)
  
  
• The engine RPM does not need to be varied, -and it is likely preferable to run at a single RPM with enough RPM speed to provide splash oiling that all parts receive a constant coating. Altering this engine speed does nothing to increase longevity or better ring sealing on a properly machined & assembled engine.
  
  
• After initial start-up of a rebuilt engine, the engine only needs to run long enough where various metals and gaskets can thermally expand. If the deck surface of the cylinder case and the cylinder head have a good RA finish, -and if the head gasket is of quality, then upon the components cooled to room temperature, the stud nuts can be retightened to compensate for any gasket compression. The (mis)use of gasket sealers (Copper Kote, et/al) often hinders the thermal expansion & contraction of the gasket which will affect fastener torque ratings being met.
  
• Use of inferior machining techniques and/or worn machines causes cylinder bores to not be truly cylindrical. The use of 220 grit Diamond stones at roughly a 35° cross-hash will produce a finish that a cast iron ring can easily seal to. When poor quality machines and/or stones are used, the concentricity of the bore is compromised creating a need for the rings to scrub against that cross-hashing longer so the ring(s) can shape themselves to conform to the non-concentric shape of the cylinder bore. Additionally, a properly burnished cast bearing does not need additional run time for it become 'fitted' to a crankshaft journal pin. If a rebuilt engine requires a 'run-in' period for the bearings to clearance themselves, then either poor machining practices or machines themselves (crankshaft grinder or line-boring) were used.

The above are just my opinions, ...and I welcome theories that either corroborate or contradict my reasoning for Model-A engines not needing a rebuilt engine break-in period with the machining technology of today.

[Mister Moose]

My Model A engine rebuilder instructed me to run for short periods of 10 minutes and then a cool down. The explanation was the rope rear seal would burn if run for too long, that it needed to seat from wear over a longer period of time. If the engine was run too long the rear seal would carbonize from the frictional heat before the seal was worn in.

*Edit I was also instructed to use mineral oil for the first 500 miles for better seating, AD oils were too slick.

Aircraft cylinders have the diamond cross hatch pattern you describe. On brand new engines (I flew a lot of them) I was instructed by Continental to run at no less than 75% or even 80% for the first 10 hours. The explanation was the higher power settings gave higher cylinder pressures, and this would expand the rings to seat effectively. If the engine was "babied" when new, the cylinder walls would glaze and the rings would never seat. I'd expect an aircraft engine would be machined to state of the art. The engine was shipped with mineral oil, which would stay in for the first 50 hours, and then go to synthetic.

Outboard engines (2 cycle) were different still. OMC and Mercury instructed to run below half power for the first several hours, gradually increasing the power thereafter, and not to run at a constant power setting.

Obviously different machining methods and different materials lead to different instructions.

[Gene F]

Hmmmmm. I recently had my engine rebuilt. I know 2 things:

1) My rebuilder was very specific about me running it at varyed sppeds, and not on jack-stands either. 20 - 30 MPH for 20 to 30 miles to start with. He also wanted me to use very specific oil, but then he gave me a bottle of ZDP to add to that oil. I have already ran the engine around the neighborhoods for about 30 miles.

2) The reason my engine needed to be rebuilt to start with was because my crankshaft snapped. When you speak of machining techniques, I recall sending my crankshaft over to what I thought was the most notable shop for Model-A engines I knew of. That expensive place in PA. It was machined wrong. I had it turned, counterwighted, and balanced. It was also balanced and matchmarked with the flywheel and pressure plate.
Turns out there were 2 surprises to that machine work.

Brent, I'm interested to see the further comments to this thread since I am not a machinist expert.

[alexiskai]

Was this a case where someone had rebuilt the engine himself, or had bought the rebuilt engine from a builder? If the latter, you definitely follow the builder's advice, not random people on message boards (present company excepted, naturally). The builder has an incentive to minimize come-backs, so he should be giving advice that works on his engines.

[GerryAllen]

Not wanting to start anything . When should the first oil change be done. I am right now waiting for my oil to fully drain from newly rebuilt engine. Oil is cheap and I have the time, I am doing it at 250 miles then from this point on every 500 - 700 miles.
Brent and others what is your opinion on the mileage of the first oil change. I do enjoy and value the wisdom, thoughts of the group as whole.
Gerry Birch Bay Wa

[Stingray70]

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I agree with both Brent and Moose. In 1930, a model a engine probably required a break in period. In 2021 a new Corvette does not. My question would be: do/can modern parts and machining eliminate the need on our old engines? Are their any builders of these old engines that can do the work to the required precision?

[kawagumby]

My take is that break-in of engines from decades ago is solid. Heat cycles and moderate engine speeds are good to keep spot temperatures down until surface friction is reduced by the break-in process. My own experience has convinced me long ago that varying RPM's does help seat rings better. A corvette engine has the advantage of a modern cooling system, high pressure oiling, speed limits and gearing that won't strain engine parts, and especially the advantage of modern metallurgy that older engines do not. There is a huge difference between the life-span of modern crankshafts vs those made even during the fifties and sixties.
edit:
Regarding ring seating; the varying cylinder pressures associated with increased throttle and decreased throttle (esp under load) help the rings seat. Whenever I rebuild one of my bikes, the first thing I do is get riding in the hills. This is true for four-strokes but especially true for two-stroke engines which I have rebuilt countless times.

The cylinder honing process used today in new modern engines is a far cry from the old days..
Here's an article which explains plateau honing...
https://www.productionmachining.com/...cation-control

[Synchro909]

I'm in pretty much the same camp as Stingray70 and kawagumby. New engines these days are made to tolerances not possible when our cars were made and out of materials not available using techniques they couldn't dream of. An engine rebuilt by the best workshop today will only be to about the standard Ford attained in the day. I don't think it is reasonable to compare a new engine with a Model A engine, new or rebuilt.
The engineers of the day knew what they were on about and they were quite strong in their recommendations that an engine be run in properly. That'll do me when dealing with one of their engines.

[Ranchero50]

When did Ford start running the engines in on electric motors? I've seen the flathead V8's but what about the I4's?

[stevests]

Ford was "burning in" Model T engines in the teens with external sources.

[Jack Shaft]

I was maintenance supervisor for a 250 tractor/500 trailer fleet.During that time the fleet was in transition and I oversaw the rebuild of 40 CAT 3406E diesel engines.The truck would come in,we would kit it,slap on heads and bearings,inspect the rest and ship it..put the truck right back out spending 90% of its time fully loaded.no failures,no accelerated wear noticed in oil samples..build it correctly and run it.

[PotvinV8]

Modern engines and modern engine builds using modern components (IE roller cams, roller rockers, etc) don't suffer from the same issues as hydraulic or solid flat tappet cam setups. Incorrect break-in of a flat tappet cam is a notorious cause of flattened lobes. I've done it and have seen it done many, many times.

I worked in a machine shop with a cam grinder who had 50 years under his belt and he told every customer the same thing, break in the cam. Vary the rpm for 10-15 mins, don't let it idle. Keep the oil pressure up and the lifters spinning (flat tappet cam lobes are ground with a ramp to force the lifters to spin to prevent them from wearing a flat spot in them). The dyno shop we use does the same thing and they test motors day in and day out. They wouldn't waste 20 mins of dyno time if it wasn't necessary.

Now, how that concerns a Model A? If I was swapping in a new cam, I'd break it in. Rings, new pistons, etc. Probably not.

[nkaminar]

The Model T engines were indeed "burned in." The engine was assembled with the main bearings so tight that the crankshaft could not be turned by hand. The engine was mounted on the burn in machine up side down and oil was applied by an oil can to the main bearings. The crankshaft was turned over with a large electric motor until the bearings were literally so hot that the oil was smoking. When the bearings cooled down the babbett was fitted to the crankshaft with the right clearance. The rod bearings and the rest of the engine was fitted during the breakin period.

In my experience, the bearings will tighten up when hot and when cool again will have the correct clearance. For my newly rebuilt Model T engine, I could not crank it if I stalled it when hot. I had to wait until it cooled off. These were babbett bearings. I am not sure if the same thing is true of insert bearings.

[deuce5wndw]

The Corvette has been used in a couple of post as a comparison but I took a tour of the plant in Bowling Green, KY and the last thing they did to a corvette was put it on a dyno and open it wide open! Same with the Harley factory in PA. Don't know if its right or wrong but that is just what they do.

[Jack Shaft]

I've built flat tappet, roller lifter and hydraulic lifter cammed engines, with cast and forged camshafts, been in the trade 40 + years, have never seen a cam fail on break in.

The ones that amuse me the most is the snake oil salesmen selling zinc additives. Modern oil designs do work, additives to aide load and shear, as well as detergents help us...but the high dollar 'racing' additives you must have to break in a cam?.. its a myth perpetrated by those who profit off the product.

[BRENT in 10-uh-C]

Originally Posted by PotvinV8

Modern engines and modern engine builds using modern components (IE roller cams, roller rockers, etc) don't suffer from the same issues as hydraulic or solid flat tappet cam setups. Incorrect break-in of a flat tappet cam is a notorious cause of flattened lobes. I've done it and have seen it done many, many times.

I worked in a machine shop with a cam grinder who had 50 years under his belt and he told every customer the same thing, break in the cam. Vary the rpm for 10-15 mins, don't let it idle. Keep the oil pressure up and the lifters spinning (flat tappet cam lobes are ground with a ramp to force the lifters to spin to prevent them from wearing a flat spot in them). The dyno shop we use does the same thing and they test motors day in and day out. They wouldn't waste 20 mins of dyno time if it wasn't necessary.

Now, how that concerns a Model A? If I was swapping in a new cam, I'd break it in. Rings, new pistons, etc. Probably not.

Unfortunately you are leaving out several things in forming your opinion. When you factor in the quality of lubrication has changed immensely over time, the wear additives in modern engine oil alone allow for less chance of premature wear. We now have modern cam lubes that are meant to circumvent cam wear as it is very hard to wipe off this lube.

You also hit on one major thing that many Model-A rebuilders overlook. Tappet bores are often worn, and when a tappet is pressed against worn bore walls, it generally only has pressure contact in the extreme lower and opposite side upper. This generally causes a tappet to be unable to rotate. So when this machining step is omitted, the engine rebuilder is hoping that varying the RPMs will try to make the tappet rotate enough where the camshaft lobe will not be wiped out.

With all due respect to your camshaft grinding friend, there is MUCH in technology that has changed where his methods are obsolete. The engine machining tooling and supplies are different now. It isn't just engine machining that has changed in 50 years, ...look at paint & materials, battery technology, gasoline, fabrics, etc. and notice how much has changed.


I will also share with you that any performance Dyno shop that runs an engine for 15 minutes is doing that out of ignorance, -or you are mistaken. They have never done any of my engines that way, -and I have many close friends in the performance engine business and they don't dyno that way either. In the class we race in, a top quality engine is between $35-$40k, These engines are good for 1,000-1,200 laps. With lap times under 20 seconds, every 3-4 laps equals a minute. At an average cost of $35 per lap, I would not be interested in wasting $2,000.00 of run-time just sitting on a dyno listening to it run! Neither is anyone else!!

[BRENT in 10-uh-C]

Originally Posted by nkaminar

The Model T engines were indeed "burned in." The engine was assembled with the main bearings so tight that the crankshaft could not be turned by hand. The engine was mounted on the burn in machine up side down and oil was applied by an oil can to the main bearings. The crankshaft was turned over with a large electric motor until the bearings were literally so hot that the oil was smoking. When the bearings cooled down the babbett was fitted to the crankshaft with the right clearance. The rod bearings and the rest of the engine was fitted during the breakin period.

In my experience, the bearings will tighten up when hot and when cool again will have the correct clearance. For my newly rebuilt Model T engine, I could not crank it if I stalled it when hot. I had to wait until it cooled off. These were babbett bearings. I am not sure if the same thing is true of insert bearings.

This is a sign of poor engine machining where the journal pin is not truly round, -and/or has taper from a plunge grinding with a worn machine. Often times, engine rebuilders will assemble an engine tight like you are describing with the hopes that it will clearance itself.

[BRENT in 10-uh-C]

Originally Posted by Synchro909

I'm in pretty much the same camp as Stingray70 and kawagumby. New engines these days are made to tolerances not possible when our cars were made and out of materials not available using techniques they couldn't dream of. An engine rebuilt by the best workshop today will only be to about the standard Ford attained in the day. I don't think it is reasonable to compare a new engine with a Model A engine, new or rebuilt.
The engineers of the day knew what they were on about and they were quite strong in their recommendations that an engine be run in properly. That's do me when dealing with one of their engines.

This is not really an accurate statement. As I mentioned above, technology has changed immensely, so people should not assume anything. Ford engineers were dealing with several differences between their technological timeframe and today's. Ford was dealing with unseasoned cast which today's machine shop typically has seasoned castings to work with. Second, Ford engineers did not have near the quality of engine oils like today. The machines that we use today in the rebuilding industry can hold tolerances that even OE production engines do not try to meet. (This is why performance shops offer 'blueprinted' engines)

As mentioned above, the abrasives used for machining in the day vs. today are hugely different. Today, most rebuild shops are using diamond and CBN stones where the tolerances can be held to tenths measurements. Additionally, parts such as the alloys in modern pistons, the modern ring compositions, and today's valve & guide materials allow for much tighter tolerances to be used. Therefore we can (-and should) be producing a product that is much better than original with respect to longevity. We do this in other areas of the restoration such as the quality of paints, fabrics, tires, glass, etc. So why do we accept less when it comes to engines?

[JayJay]

I don't have sufficient theoretical nor practical knowledge to be able to comment credibly on this. However, I want to compliment Brent on his occasional thought-provoking comments calling into question many of our long-held but not necessarily re-thought practices.

So often we accept what have been traditional practices without going back to fundamentals and examining if the practices are supportable. For example, I was taught many eons ago to always dunk head studs and nuts in STP before torque. Why? Because "that's the better way to do it". We now realize that the friction of the threads on the nuts is a fundamental part of the torque spec unless we are given a "wet" torque value by the engineers. Wet torque to a dry torque spec may result in overstressing.

Rethinking the old saws is never a bad thing to do.

Respectful discussion is how we all learn, and this is a great forum for this. Keep it up, Brent!

JayJay

[Mikeinnj]

"The (mis)use of gasket sealers (Copper Kote, et/al) often hinders the thermal expansion & contraction of the gasket which will affect fastener torque ratings being met."

Brent, are you saying not to use any gasket sealant on a new head gasket?
What gasket do you recomend for Snyders 5.5 head ? Thanks !Mike

[johnneilson]

Yes, Brent does invoke some interesting conversations.

And while I do agree that technology today, as far as manufacturing is much better, it still has two limitations. The first is the operator of said machinery and tools, have you noticed the machinery is more complex and requires less operator input? But it still relies on an operator. (less crank handles and more switches and knobs)
The other factor are the materials that the parts are made from, at best, 90 year old metallurgy and quality. FWIW, it is pretty good, but a limitation.

I was having dinner with a very wise engineer from Cosworth some years ago and we were discussing materials and coatings. This was the time of ceramic coating everything and moly spray coatings, before cryogenic treatments. "If you have to rely on some sort of surface treatment to make the assembly live, you have the incorrect material in the parts". Since we cannot change the materials we have to make changes to design and accompanying parts, such as pistons, rings and bearings. A change to the oiling system makes a world of difference in the materials and construction.

The process of "break-in" today is a much different process than 80 years ago.

Best, John

[katy]

Originally Posted by Mister Moose

My Model A engine rebuilder instructed me to run for short periods of 10 minutes and then a cool down. The explanation was the rope rear seal would burn if run for too long, that it needed to seat from wear over a longer period of time. If the engine was run too long the rear seal would carbonize from the frictional heat before the seal was worn in.

Last time I looked, Model A engines don't have a "rope rear seal".

[Jordan]

Just food for thought- when someone asks for you to challenge their theory, they will find holes in your response just as you find holes in their theory. I've got better ways to spend my time. Both sides already "know" they are right.

[kawagumby]

Originally Posted by Jordan

Just food for thought- when someone asks for you to challenge their theory, they will find holes in your response just as you find holes in their theory. I've got better ways to spend my time. Both sides already "know" they are right.

I dunno, many of us respond based on our own experiences under varying situations - different perspectives - the majority of which are no-doubt valid based on particular circumstances. However, if you're already sure you know the answer, why do you ask the question?

The questions and responses are a great way to get to know personality types on this forum!

[bbrocksr]

Originally Posted by Jordan

Just food for thought- when someone asks for you to challenge their theory, they will find holes in your response just as you find holes in their theory. I've got better ways to spend my time. Both sides already "know" they are right.

Best and most accurate response!

Bill

[Jack Shaft]

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Originally Posted by Jordan

Just food for thought- when someone asks for you to challenge their theory, they will find holes in your response just as you find holes in their theory. I've got better ways to spend my time. Both sides already "know" they are right.

Funny, this is how i learn something new.. through discussion with folks who hold different ideas..

[john in illinois]

X2 Bill.

John

[PotvinV8]

I won't respond with my opinion, but I will post a couple interesting reads so folks can formulate their own. Now, if someone from the "break-in isn't necessary camp" could do the same, I think we could have an interesting conversation.

https://www.compcams.com/pub/media/w...chBulletin.pdf

https://help.summitracing.com/app/an...and-lifters%3F

https://www.melling.com/wp-content/u...Rev4-12-07.pdf

https://www.mahle-aftermarket.com/na...procedures.jsp

[bbrocksr]

Originally Posted by PotvinV8

I won't respond with my opinion, but I will post a couple interesting reads so folks can formulate their own. Now, if someone from the "break-in isn't necessary camp" could do the same, I think we could have an interesting conversation.

https://www.compcams.com/pub/media/w...chBulletin.pdf

https://help.summitracing.com/app/an...and-lifters%3F

https://www.melling.com/wp-content/u...Rev4-12-07.pdf

https://www.mahle-aftermarket.com/na...procedures.jsp

Good Job! Bill

[ronn]

While I have never rebuilt an engine, I have often thought of the same topic as you mention Brent and what comes to mind foremost is not that the technology isnt available today- to build a motor and not have to break it in. What my concern is - is that every builder has different methods- some truer then others and I believe, therein lies the problem.
One fella goes to one hospital for treatment and is supposedly getting the best treatment avail and dies- over some miner infraction. Another fella goes to a diff hospital for the exact same thing and gets another 20 years. Less about the knowledge available then those practicing the knowledge.
Does every shop rebuild an engine the same? no

[daren007]

Content also aircraft engines have half wedge rings. Cylinder pressure forces the rings against the cylinder walls. High power settings are required for the first few hours.

[Jack Shaft]

Of the four articles melling has it right in my opinion,the use of diesel grade engine oils is spot on..Mahle, makes superior engine parts has the fire up and rev up to hold at 1500 rpm advice..Ive spent the last forty years working in,and running mechanic shops..ive never seen a mechanic do that proceedure..we ran it warm,checked for leaks,test drove tuned changed the oil and shipped it was the routine in the gas powered fleets I've been around.

[Dave in MN]

Brent,
Specifically: Why raise and lower the engine rpm when breaking in? If done rapidly, from a high rpm by totally closing off the carb., it will draw oil into the rings and promote lubrication of the upper cylinder wall and rings thus reducing the heat being generated between these components.
I follow this practice.

All the rest? I basically agree with what you are saying.

I do have another purpose for running the long-blocks I build longer, as I am verifying them to be leak free well past normal driving loads by using a water brake/Dyno to load them. Doing this, I know when the customer picks them up that all is proper.
The customers also like the dyno report.

As to my driving and operating instructions when asked how to break it in: I tell them "Don't lug the engine" and repeat it two more times during the subsequent questions as we are loading the engine. Often, the last thing I say to them as they are departing is "Don't lug that engine!" rather than goodbye and we then both laugh. That's it!
Good Day!

BTW: I think Henry lied. I am seeing about 2 hp short on every engine I build that has close to stock bore, cam and original head. (Yes, I have had the Dyno calibrated.)

[GPierce]

Starting in the late 70’s we would put a brand new Diesel engine in the test cell and warm it up. When the water and oil was warm it went to full power, up to 400 hp loaded by the dyno and depending on engine model. The engine was instrumented with a blow by pressure gage in the crankcase vent which had a calibrated oriface. We monitored that pressure. You could see the crankcase pressure (blow by) drop within less than a minute as the rings seated. The whole test routine took less than 20 minutes. This brief run in was the result of cylinder sleeve machining and coatings as well as coated piston rings that didn’t need “breaking in”.

In 200O I put new cylinders on my Lycoming airplane engine. Running at 75% power I was monitoring the the cylinder head temps. After about 3 hours I saw the all 4 cylinder head temps start dropping within minutes of each other. They stabilized 20 degrees lower after about 5 minutes.
Fast forward to 2018; new cylinders again. Same routine, 75%+ power. This time the initial cylinder head temps were lower after the initial climb out, about 5 minutes. Again improved machining tolerances and coated piston rings instead of bare chrome rings on steel cylinders.
Some of these coatings are manganese phosphate. You can Google piston ring and cylinder coatings see a wide variety of processes that have virtually eliminated the need for break in.

[shew01]

Originally Posted by Dave in MN

BTW: I think Henry lied. I am seeing about 2 hp short on every engine I build that has close to stock bore, cam and original head. (Yes, I have had the Dyno calibrated.)

Henry was a clever marketer. Maybe he just rounded up. ;-)


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[GPierce]

Duplicate

[GPierce]

Originally Posted by Dave in MN

Brent,

BTW: I think Henry lied. I am seeing about 2 hp short on every engine I build that has close to stock bore, cam and original head. (Yes, I have had the Dyno calibrated.)

You have to correct the dyno reading for temperature, barometric pressure and MARKETING. 😀

[shew01]

Originally Posted by GPierce

You have to correct the dyno reading for temperature, barometric pressure and MARKETING. [emoji3]

[emoji23]


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[BRENT in 10-uh-C]

Originally Posted by Dave in MN

Brent,
Specifically: Why raise and lower the engine rpm when breaking in?

If done rapidly, from a high rpm by totally closing off the carb., it will draw oil into the rings and promote lubrication of the upper cylinder wall and rings thus reducing the heat being generated between these components.
I follow this practice.



I do have another purpose for running the long-blocks I build longer, as I am verifying them to be leak free well past normal driving loads by using a water brake/Dyno to load them.

As others have attested to above, I do like thought provocation as it does make me think of better ways of doing things.

Dave, I do like your thinking regarding snapping the throttle closed to induce oil movement however I am unsure if it will work that way. Work with me to establish how this works. If the piston is at TDC, the oil that is on the cylinder walls is typically below the bottom oil ring as slinging it around is always under that control ring. If a quality job of boring & honing has been done, the two oil rings should be the first to seal (i.e.: re-shape themselves) to the wall's cylindrical shape simply because of their thickness. Next I would want to figure the volumetric capacity of the bore & chamber at TDC and compare it to the capacity of the manifold draw tube, both sides of the upper tube section, and the port size of both the cylinder and the opposite port to see how much piston movement would be required to create enough vacuum to draw that oil past the oil rings. In other words, my initial thoughts would be that the amount of vacuum draw from the piston moving downward will first be used to pull the air/fuel mixture out of the manifold & ports prior to it creating enough vacuum to draw past the piston rings. Since volumetric efficiency numbers are low on a L-head anyway, I would think the oil would not be sucked by the new rings. Adding to this, one would need to consider the oil rings are already scraping some oil away from the walls as the piston is moving downward which would be less oil to draw anyway. What am I missing??

I guess my thinking is that the only oil that would reach the top rings is what oil is held in the cross-hash pattern on the walls since this would be below the surface of the compression rings and the oil rings. Do you think if compression ring lubrication is a concern, then maybe adding some upper end lube such as Marvel Mystery oil or 2-cycle oil to the gas would be a better option when you are doing the initial start.

One other thing for us all to consider is why do we hone the cylinders and put the cross-hash into the freshly bored cylinder?? In reality, if we could bore the cylinder to a truly perfect diameter, and install a piston with rings that exactly matched the shape of that perfect bore, we wouldn't need to hone. So in other words, the worse the shape of the bore, then the more the rings will need to be cut to meet that bore shape.


Now with that said, an engine rebuilder can put too much/deep of a cross-hash into the walls during the machining process. When this occurs, the mechanical honing away of the piston's ring's metal continues unnecessarily and shortens the life expectancy of that ring. It also causes premature wear on the piston. So how much does this premature ring wear shorten the engine's life? Good question but I am thinking that 15%-25% of the life shortened is believable. I wish Pete Samuelson, Bill Stipe, or Dudley Moordigan would jump in with their opinions on this topic.


Dave, is your running of the engine really a 'break-in' or just running it to verify there are not any leaks and put enough heat in it so you can retighten the head nuts??

[Bud]

I want to address a small item on engine rebuilding that I have noticed. When putting my own engine back together (the block had a crack stitched), I used new tappets. I noticed that an original tappet I had was machined with a central hole up from the face of the tappet, on center, which matched a cross drilled hole. I can only conclude this was meant to lubricate the tappet bore in the block. The reproduction tappets I bought and see that the vendors sell, do NOT have this feature.
When I had my 8N tractor rebuilt many years ago, the shop I used drilled the side of the tappet bosses with a small hole to introduce lubrication to this area. Same idea, different method. I can understand how Model A tappet bores can become out of shape especially if modern tappets without lube holes are used. The only way to get lube in this area is the oil fog that may circulate in the valve chamber, which may work OK, but I don't believe that was what was intended in the original design. Do modern builders bore and re-bush the tappet bores? I would think most do not, but I cannot be sure. Does anyone have a Ford detail of the original solid tappet showing if it were drilled?

[BRENT in 10-uh-C]

Originally Posted by Bud

Do modern builders bore and re-bush the tappet bores? I would think most do not, but I cannot be sure.

Former MAFCA Tech Director Jim Cannon and I were discussing this a week or so ago regarding someone he was helping on finding a noise. I have a special Go/No Go gauge made to check Tappet Bores diameters that is 0.5945 & 0.5960. The print calls for the bore size to be 0.5940" - 0.5945" and that was meant for about a 0.001 total clearance(-½ thou per side). As long as the .960 end does not fit into the bore, then I usually will let it go.

I would venture a guess that maybe less than 50% of the blocks I check are worn enough where the .596 will go in, -but many will have a lot of clearance with the .5945 portion of the gauge inserted.

Several of the Model-A vendors offer a 0.005" oversized tappet to use however set-up to accurately machine the block for these is a little labor intensive. Sure, it is not that hard to run a hand reamer thru the bore to "open it up", but if that is done without a fixture, then the bores can be out of alignment from each other and/or the camshaft. (You really need a fixture built to index off of the main bolt datums.) Like with most things, a good machinist can correct many of these problems if he has the budget to do so.

[Bud]

Is the original tappet drilled as I described, with the central drilled hole and the cross drill?

[GeneBob]

From reading through this I can see a few things that stand out:
1. Brent will always have a contradictory answer to anything and everything.
2. I am sure we are all impressed with the cost of the racing engines.
If the racing engines were properly broke-in, maybe they would last longer.
3. If you take your engine to a shop and ask them to apply their expertise and best judgement to the machining and assembly of your engine, LISTEN TO THEM. They put their blood, sweat and tears into becoming experts in engine rebuilding. When you get the engine back, it is a reflection of their work so they get to tell you how to handle the baby they just returned to you. Yes, you paid for their expertise but it is still their engine during the break-in period. If you do not listen to them and your engine craps out, see how far you get with "Well, I read a blog that said..."

[john in illinois]

Bud ,I think the tappets are continually oiled from the oil pump. It pumps oil out into the valve chamber , out the side drain pipe and to the timing cover.


John

[Mister Moose]

Originally Posted by GeneBob

From reading through this I can see a few things that stand out:
1. Brent will always have a contradictory answer to anything and everything.
2. I am sure we are all impressed with the cost of the racing engines.
If the racing engines were properly broke-in, maybe they would last longer.
3. If you take your engine to a shop and ask them to apply their expertise and best judgement to the machining and assembly of your engine, LISTEN TO THEM. They put their blood, sweat and tears into becoming experts in engine rebuilding. When you get the engine back, it is a reflection of their work so they get to tell you how to handle the baby they just returned to you. Yes, you paid for their expertise but it is still their engine during the warranty period. If you do not listen to them and your engine craps out, see how far you get with "Well, I read a blog that said..."

Fixed it for you.

It occurs to me that the degree of precision machining that goes on with your 90 year old engine overhaul will be a function of both how stock you decide to keep it and how much money you have the budget for modern improvements.

[BRENT in 10-uh-C]

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Originally Posted by GeneBob

From reading through this I can see a few things that stand out:
1. Brent will always have a contradictory answer to anything and everything.
2. I am sure we are all impressed with the cost of the racing engines.
If the racing engines were properly broke-in, maybe they would last longer.
3. If you take your engine to a shop and ask them to apply their expertise and best judgement to the machining and assembly of your engine, LISTEN TO THEM. They put their blood, sweat and tears into becoming experts in engine rebuilding. When you get the engine back, it is a reflection of their work so they get to tell you how to handle the baby they just returned to you. Yes, you paid for their expertise but it is still their engine during the break-in period. If you do not listen to them and your engine craps out, see how far you get with "Well, I read a blog that said..."

...........

[BRENT in 10-uh-C]

Originally Posted by Mister Moose

Fixed it for you.

It occurs to me that the degree of precision machining that goes on with your 90 year old engine overhaul will be a function of both how stock you decide to keep it and how much money you have the budget for modern improvements.

That shows how little he knows. Unlike rebuilt Model-A engines, racing engines do not come with any warranty expressed or implied.

I think your comment regarding a 90 year old engine overhaul is pretty accurate.

[Dave in MN]

Later....
I have a full schedule today, breaking down three engines and breaking in one!

Now it's later...And the engine is through with the "break-in"

"Dave, I do like your thinking regarding snapping the throttle closed to induce oil movement however I am unsure if it will work that way. Work with me to establish how this works. If the piston is at TDC, the oil that is on the cylinder walls is typically below the bottom oil ring as slinging it around is always under that control ring."......

Brent, I realize most of the oil on the cylinder wall is below the lowest ring. The assumption you make disregards or is not mentioning the oil deposited between and above the oil control rings and not factoring the machined slots and holes from the interior of the piston into the lowest oil ring groove. Oil is free to move in either direction through these lower ring groove openings. Excess oil removed/scraped from the walls is passed to the inside of the piston and oil from the oil mist in the crankcase is free to enter these areas in the reverse direction as well. The oil around the lowest ring is the oil I am trying to redistribute.

IMO: Blow-by past the top and middle rings will impact the oil within the lower ring assembly. Most often it will move the accumulated oil to the interior of the piston, would be my assessment. Quickly closing off the throttle plate on an engine at operating speed will change or maybe slightly reverse the oil movement around the lower oil ring(s).

My theory it that any change in the cylinder pressure, assuming there is some blow-by, will cause an interruption to the movement of the oil retained in the oil control ring assembly and could deposit some of that oil above the top ring of the assembly when the cylinder is trying to draw in air with the throttle plate closed. Doing so would provide a bit of additional oil to the middle ring and to a lesser degree to the top ring especially if these rings are not fully seated yet. My belief that I am redistributing some oil around and between the middle and top rings and is why I snap the carb closed a couple times early in the running.

My goal in snapping the throttle closed is to slow down the generation of heat being developed between the middle and top ring and the cylinder wall.

I can usually think of two reasons as to why I do something. While doing the "Snap the throttle closed" I am also listening to the engine perform. I am studying the result and listening for any errant sounds. I cannot say I have ever heard any but nonetheless, I am studying the result.

Thanks for your study Brent, it's always interesting.
Good Day,
Dave

[GeneBob]

There used to be 2 schools of thought on break-in; baby it for 600 miles to gradually wear in the parts and "run it like you stole it". I lean toward the baby it for a while but regardless of which you choose, you are breaking in the engine in the first few hours of operation. Simply stating that it doesn't need to be broken in does not change the reality of what is happening inside the engine. No amount of precision machining will change the fact that the engine is breaking in when first run.

[Flathead]

I think post #49 pretty much sums it up. Thanks GeneBob.

[daren007]

Do race car drivers and dragsters break in their engines.

[PotvinV8]

So the consensus says?

I haven't seen a single example in favor of the "anti-break-in crowd".

[alexiskai]

Originally Posted by Mikeinnj

Brent, are you saying not to use any gasket sealant on a new head gasket? What gasket do you recomend for Snyders 5.5 head ? Thanks !Mike

This question got overlooked in the melee. Gasket sealant should not be needed on a rebuilt engine, where the block and head have been milled correctly with the correct surface roughness.

[BRENT in 10-uh-C]

Originally Posted by PotvinV8

So the consensus says?

I haven't seen a single example in favor of the "anti-break-in crowd".

Ummm, I think you have. If you read in some of the links you provided, it speaks of running an engine at a constant speed. That was the intent of the first post was to discuss the mindset of why varying the RPMs. Starting an engine to verify leaks and to build temps to thermally cycle the engine so retighten head nuts and like fasteners can be done is not really "breaking-in" an engine as this is done in a much shorter timeframe. In a subsequent conversation with a Model-A camshaft manufacturer, he agreed that he does not break-in his own engines.

Originally Posted by alexiskai

This question got overlooked in the melee. Gasket sealant should not be needed on a rebuilt engine, where the block and head have been milled correctly with the correct surface roughness.

Colin, Mike also reached out to me via a PM and I answered him there.

[BRENT in 10-uh-C]

Originally Posted by GeneBob

There used to be 2 schools of thought on break-in; baby it for 600 miles to gradually wear in the parts and "run it like you stole it". I lean toward the baby it for a while but regardless of which you choose, you are breaking in the engine in the first few hours of operation. Simply stating that it doesn't need to be broken in does not change the reality of what is happening inside the engine. No amount of precision machining will change the fact that the engine is breaking in when first run.

Yes, I agree how you say this. Maybe 600 miles to accomplish the rings sealing is excessive but I see your point.

Originally Posted by daren007

Do race car drivers and dragsters break in their engines.

No. A top-fuel dragster is generally rebuilt between racing rounds. Once reassembled, the engine is generally started to check for leaks, verify spark plug wires are installed correctly, to set ignition timing, and to seat the clutch plates. All of this takes place in less than 60 seconds. The next time the engine is started is prior to doing a burn-out.

In the NASCAR world, engines are started on the dyno and run long enough to bring to operating temps before the first pull is made. After the first pull, they will generally 'leak' the engine and then use a bore scope to check cylinder walls for abnormalities. They may make subsequent pulls to see if changing timing or jetting changes makes any performance gains, but generally the engine has sealed-up by the time it has reached operating temps (generally a couple minutes)

Just for clarification, there is a difference between warming up a new engine vs. breaking-in a new engine. Yes, both engines are operating however the length of time is vastly different, and the purpose is vastly different also.

[PotvinV8]

You haven't provided a single example supporting your case. I provided three.

I'm just trying to save someone the headache of pulling out a brand new cam with a flattened lobe. As far as engine break-in goes, that's the single biggest factor. Gasket sealing, ring sealing, etc is what it is. You can retorqued fasteners but you can't relube a flattened cam lobe because the engine was fired up and idled for 20 minutes while the operating futzed with the carb settings.

[johnneilson]

The articles referenced previously are for a different application, completely.
Apples to rhubarbs.
Cam material(s) and the PV specification does require breaking in the cam in some applications.

Most Model "A" motors, even the hot rodded ones do not require much of a break-in.
Cams do get spalled or have the nose flatted off, usually caused by other factors.

Even aircraft engines have this issue, but it is only at major rebuild time or if a cylinder is a substantially low output.

FWIW, the race motors will use a very different pist/ring combination that requires very little time to seal properly.

Best, John

[PotvinV8]

An interesting thread over on the "hot rod" forum...

https://www.jalopyjournal.com/forum/...stion.1223452/