Engine failure - high speed running

[ppower]

I have a Ford Model A engine fitted in a light sports car. Because of the limited radiator size I use Evans waterless coolant. The coolant temperature is 220°F to 300°F (the coolant is good to 360°F).
I have recently fitted a Snyder 6.5:1high compression head. The coolant temperatures have not changed. The improvement in performance is impressive, particularly the high bottom end torque.
I was concerned about pre-ignition, so I use the retard lever at low revs.
However after running at 3000rpm for about 10minutes I lost power. The power returned. A few days later I repeated the high speed run, and again lost power accompanied with a tapping noise. I stopped, and the engine was seized. When it cooled everything seemed OK. I drove it again and after a few miles at lower revs, a rod came through the side of the crankcase.
The paint on the cylinder barrels below the water jacket has gone brown. The land above the top piston ring in number one cylinder has mainly disappeared. The big end cap on number four seems to have been pulled off (one stud pulled off and the other has its threads stripped, but it is not bent). The top and bottom rings are seized in number four cylinder. Number four big end journal has turned blue. I have not yet removed the other three pistons.
In my anxiety to avoid pre- ignition I seem to have restricted the advance to 24° BTDC. Could this be the cause of the failure? Or am I unreasonable to expect to be able to run at a constant 3000prm with the original gravity and splash lubrication system?
Thanks for any help you can give me.

[Mitch//pa]

you cooked your engine running temps upward at 300 ... combine that with a constant 3000 rpms and kapppoooowww. meltdown

the engine paint acted as a heat tab and melted

[ppower]

I realise I cooked the engine. The question is was the cause, sustained revs with standard lubrication, or was it the retarded ignition? I don't want to do it again.

[Big hammer]

300 degrees water temp #4 cly runs hot because poor water flow around it
At 3000 rpm's how much oil is in the dipper tray Get the water temp down and install a overdrive and use low end torque keep rpm's down IMO

[Jon]

What clearances are you running on the pistons?

[Kurt in NJ]

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I have gone long distances at about 3000 rpm with stock car65+mph-I did mixture testing up to 3200 on the emissions dyne--not at that coolant temperature though, and I once had the babbitt come off a rod at that speed but it didn't leave any marks on the crankshaft -it did feel like I drove over a telephone pole though--do you have babbitt or inserts in the rod big ends

I think many people run too little advance because they are worried about hurting the "babbitt", I mostly run full advance and have been trying to break it

the nut with the sttripped threads came off first and the other broke

how hot does the oil run when you have that coolant temperature---oil cools the lower part of the cylidnder walls ---

how is the engine mounted in the chassis, is the rear of the engine lower than the front

pistons too tight, temp too high, oil cooked into something else, perhaps ring gap too small for the temps you are running

try and post some pictures

[mcorrell]

This may be too simple an explanation, but the coolant may be good to 300+ degrees but the materials and clearances in the engine are not. Materials break down at given temperatures. Pistons expand faster and to a greater degree than the block. The clearances area usually set up for temps between 165 and 220 F. You were likely running on the ragged edge before the high CR head. Once you installed the head you went over the edge. You must install a larger (more cores) or a second radiator to get the temps down under 220 deg. The limitation is not the coolant. The limitation is the engine and the temps it was designed to work at.

[ppower]

Originally Posted by Jon

What clearances are you running on the pistons?

I checked that, the ring gap is .025" with +.060" pistons, so I though that would be OK.

[ppower]

Originally Posted by Kurt in NJ

I have gone long distances at about 3000 rpm with stock car65+mph-I did mixture testing up to 3200 on the emissions dyne--not at that coolant temperature though, and I once had the babbitt come off a rod at that speed but it didn't leave any marks on the crankshaft -it did feel like I drove over a telephone pole though--do you have babbitt or inserts in the rod big ends

I think many people run too little advance because they are worried about hurting the "babbitt", I mostly run full advance and have been trying to break it

the nut with the sttripped threads came off first and the other broke

how hot does the oil run when you have that coolant temperature---oil cools the lower part of the cylidnder walls ---

how is the engine mounted in the chassis, is the rear of the engine lower than the front

pistons too tight, temp too high, oil cooked into something else, perhaps ring gap too small for the temps you are running

try and post some pictures

Thanks for your post.

The engine has standard Babbitt bearings.

When you say full advance, what do you mean in degrees BTDC ?

You may be right about the sequence of failure for the big end; the cap bolt and nut seem to have exited through the window in the block.

I had not previously had need to check the oil temperature, but it does not smell burnt.

The engine is mounted horizontally.

As per my previous post, the ring gap is .025"

I will take some photographs and post them.

[700rpm]

In my personal recent experience, .025 is too tight for pistons, especially #3 and #4. Twice that was necessary for my engine.

OOOPS! EDITED! Reading too early. My piston clearance is .005, not .050, and not my ring gap. Sheesh. I gotta wake up before I post.

[ppower]

Originally Posted by 700rpm

In my personal recent experience, .025 is too tight for pistons, especially #3 and #4. Twice that was necessary for my engine.

That's interesting, I was told that the original spec was 0.012"gap.

When you say your experience is .050" is necessary, what were you doing and what happened to indicate the necessity for that gap?

[PC/SR]

FWIW, I have run 25 BTDC above 3000 with no problem, and best dyno power was 20 BTDC at 3600. I do not think timing is the problem.
Piston clearance is not the same as ring gap. It is the clearance between the piston and cylinder wall. It should be .003 minimum and closer to .004 for higher rpms. It also depends on the type of material the piston is made of. The burning you mention below the water jacket indicates tight piston clearance. Check for scoring of the cylinder walls as well.
Check with your ring manufacturer for correct ring gap.
I would like to know the piston clearance, as well as the rod/crankshaft bearing clearance, but it sounds like the engine was just too tight. I am also guessing it was a relatively new engine build?

[George Miller]

Originally Posted by 700rpm

In my personal recent experience, .025 is too tight for pistons, especially #3 and #4. Twice that was necessary for my engine.

You think 25 thousandth is to close. That would make a lot of piston noise. That is almost a 1/32 of a inch.

[BILL WILLIAMSON]

Pistons are ground "EGG SHAPED" to allow for expansion to make them "ROUND"---Past that point, THEY SEIZE!!
CATERPILLAR V-8 DIESEL engines have perfectly ROUND pistons, but they are "BARREL SHAPED" to allow for EXPANSION!!
Earlier Datsun B-210 engines ran hot in # 4 cyl & sometimes the valve seat would FALL OUT & most of the time, # 4 would be SCORED! That's why many cars had their TEMP gauge in the BACK of the head, there's an area in the Model A head, where this can be accomplished, SO, if you monitor the HOTTEST area, you can possibly SAVE your engine from DESTRUCTION.
Bill W.

[Bob C]

The OP said ring gap is .025 and others are talking piston clearance

Bob

[Tom Foster]

I believe full advance on a Model A distributor equates to about 45deg btc on the crank. The failure was caused by the combination of several factors, but the problem begins with the excessive temperatures. Is that the car in question in your attachment? That radiator looks waaay too small for a 200ci engine.
Fearless

[ppower]

Here are some photos showing the damage to No1 piston, No4 big end journal through the window in the block, the .025" ring gap, the scoring of the bore and the scoring of the piston.

PC/SR, the car has travelled about 1000miles since the new pistons were fitted.

Tom Foster, that is the car, and yes the radiator is smaller, hence the reason I am using waterless coolant, and generally the temperature remains at about 220 degrees, and I had hoped that at 75mph the extra airflow would if anything drop that temperature.

[ppower]

I am now going to continue the dismantling and measure the piston clearances, and will post the results tomorrow.

[Tom Endy]

PC/SR, "the car has travelled about 1000miles since the new pistons were fitted".


Could you tell us where the new pistons came from?

Tom Endy

[johnneilson]

That looks like a classic seizer from lack of proper piston clearance.

Rings should be fine @ .025 end gap.

I would bet the high temps were caused from the lack of clearance and oil.

Also, consider changing the water flow system to pressurize the block, it reduces the tendency to cavitate at higher speeds.

Good luck, time to source a good donor, J