Chevy Pistons

[nosbod]

Hi everybody ,
Yes I know this topic of using Chevy pistons has been explained in depth in other threads but I am still not clear on one point if somebody could please enlighten me.
I read that when using these pistons they should be inserted with the normal front facing side facing the rear . If so why and what harm could be done if they were not inserted in this way ?
Rgards
John

[colin1928]

Wow this is a can of worms there are 2 different schools of thought about this
here are a few facts for you to think about and make a decision
the A model crank is offset 0.125 inch
the chevy 283 piston is offset 0.060 inch ?
that said I fit them front to front never had a problem

[George Miller]

When you get to much off set it puts more load on the thrust face of the piston. That in turn causes more heat and more wear on the thrust side of the piston. It also takes away some power.

Most will put them in with the mark to the front, which will work fine. But in my opining they will work better in a Model A engine with the mark to the rear.

I'am talking about real chev pistons that are made for a 283 engine, not the ones John sells. I think he corrected the off set in his pistons, but check with him if that is what you are using.

[nosbod]

Many thanks for info. Sorry to show my ignorance but who is John as his pistons seem to be the ones I am looking for .

[George Miller]

Originally Posted by nosbod

Many thanks for info. Sorry to show my ignorance but who is John as his pistons seem to be the ones I am looking for .

Contact John at Pete's Auto Machine in New Mexico 505-836-3110.
He has good pistons that have the narrow 283 rings and the pistons are made like a 283. Call him and ask about the off set in the wrist pin. I think they are right for a Model A.

[George Miller]

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If you use real 283 pistons you have to use the rods that are made for them. If you use Johns pistons you use Model A rods.

[nosbod]

Many thanks George . I have the rods for the standard Chevy pistons so will have to think about putting them in back to front when I rebuild the block.

[tbirdtbird]

John's are ready to go (made for the purpose) and you install them facing in the usual direction. Use the search function on this forum it has been discussed in detail several times and even very recently. Do advanced search under me as username and 283 or John or pistons as search term. George has weighed in on this also

[MikeK]

Here's a set of full skirt/modern narrow ring Egge #1104 next to stock 283 pistons on the special A.E.R. rods. The rods are ~.100" longer and made for press fit/heat shrink 0.927" pins:

Calculating the thrust difference 90 crank degrees down from TDC (half way down the bore) with the 283 pistons forward vs backward (total ~.125"), a rod length of ~7.600", (A.E.R. 283 rod, slightly longer than stock), and a standard crank throw, the difference is 0.82%, less than 1%. Hardly an issue if you put them forward vs. backward!

I suppose you could discount a smidgeon of horsepower if you put them forward vs. backward, likely less than 1%, due to thrust x coefficient of friction of a piston riding on an oil film, but the picture is larger, as the varied offset changes the piston acceleration/deceleration curve and that changes the width of the torque/HP profile you would see in a dyno graph. Any lost peak horsepower is gained in a broadened torque curve.

Short skirted pistons like the 283 will exhibit less rock/slap when offset. I like mine forward, total ~.187" offset. This makes for a very quiet (no slap) cold engine. As explained above, with the extremely long rods, this offset is not an issue.

As for the unused 283 valve reliefs, about 4cc total/piston, they serve to add turbulence to the squish, needed if you are going to any decent increased C.R.

If you go 283 pistons, I would highly recommend the KB claimer racing pistons with the available lighter pins.
Here's why:

From my build records, +0.060 pistons:
Egge 1104, +0.060 747g, 745g, 748g, 746g
(Hypereutectic 390 alloy)

Silvolite 1412 +0.060 (std. 283 chev) 783g, 781g, 784g, 783g
(Std Al/Si alloy)

KB 165 +0.060 (283 racing piston) 503g, 504g, 501g, 503g
(Hypereutectic 390 alloy, this set also had lightweight 108g pins)

...I do not have any std A +0.060 pistons to weigh or build weight records...

Some errata for those interested:
Hypereutectic alloy pistons have the smallest thermal expansion coefficient,
Standard Al/Si alloys a bit more,
Forged Al alloy pistons have twice the expansion coefficient of the hypere's.
Piston compression height:
283 Chev- 1.805
Weight of AER/283 rods: 707g plus 52g for bearing shells.

[George Miller]

Just let me add that .1875 is way more than any engine manufacture that I know off uses. With 283 piston when put in back wards if memory is right is about .062 that is .125 difference that is a lot in my book. .062 is about the same as a 283. I know they will work ether way but why not do the best you can. Plus less risk of scoring pistons. It does not cost anything.

[van Dyck]

What was Ford's reason for off-setting the crankshaft in his engines if not for producing more low RPM torque?
MikeK: Thanks for sharing your research. The long connecting rod along with the lower combustion pressure on top of the piston is going to be much "kinder" on cylinder wall thrust loading than the 283 short (5.7") rod and 9:1 compression ratio.
It would be nice to know some full skirt piston weights from various manufactures for comparison sake.

[Browntudor]

What is the point of messing around with the wrong pistons when the pistons already manufactured for A's are perfectly good?

[tbirdtbird]

"What is the point of messing around with the wrong pistons when the pistons already manufactured for A's are perfectly good?"

Or not.

Start searching and learning on this forum about piston shrinkage, piston slap, etc. Be nice to your motor and it will be nice to you

[Browntudor]

I've thrashed the pants off mine on badger pistons and it's very smooth and sweet. One of my customers bought an engine with Chevy pistons and it has problems. What's to learn?

[MikeK]

Originally Posted by George Miller

Just let me add that .1875 is way more than any engine manufacture that I know off uses. . .

Quite true George! Keep in mind the A rods are way longer than any modern engine, reducing the offset effect. The thrust scuffing issue is related to maximum rod angularity during the power stroke. Just for kicks I did some calculations to see how much that wild 0.187 offset would affect the A.

The larger the number the better:

Bone stock 283 (Gen I, 3.000 stroke) 5.700 rods, 0.062" pin offset:
Compression stroke: 74.095 degrees Power stroke: 75.387 degrees

Bone stock A (4.250 stroke) 7.500 rods, 0.125 block bore offset:
Compression stroke: 72.542 degrees Power stroke: 74.534 degrees

A w/ 7.600 A.E.R. rods, 283 pistons backwards (0.062 offset):
Compression stroke: 73.276 degrees Power stroke: 74.257 degrees

A w/ 7.600 A.E.R. rods, 283 pistons forward (0.187 offset):
Compression stroke: 72.289 degrees Power stroke: 75.226 degrees

Errata:
Piston loading 283 vs. "A". How does it compare, roughly?-
a stock 283 is about 160 hp, 20hp per piston
a 'hot' 4 banger is about 80hp, 20hp per piston

[MikeK]

Originally Posted by Browntudor

I've thrashed the pants off mine on badger pistons and it's very smooth and sweet. One of my customers bought an engine with Chevy pistons and it has problems. What's to learn?

-That engine builders vary wildly in skill and ability !?!? With an "N" of 1 and mismatched independent variables with unequal controls any conclusion is invalid. Did you learn anything?
I did: Testimonials do not equal valid tests.

[George Miller]

Originally Posted by Browntudor

I've thrashed the pants off mine on badger pistons and it's very smooth and sweet. One of my customers bought an engine with Chevy pistons and it has problems. What's to learn?

Some one did the engine wrong. I have turned my engine with chev pistons and home made rods and a home made over head to well over 4000 rpms at the hill climbs and the pistons are still with us.

You do not have to use chev pistons, it is just another way of having a little better engine. There are several good pistons out there to chose from. I think most of us engine guys can agree that the ones with narrow rings are the best.

[Browntudor]

That does include towing a trailer hundreds of miles through France, and two years of use as my everyday car when the roads aren't salted. The engine doesn't rattle, slap or use any oil at all. I've found the correct pistons are very well suited.

[Browntudor]

-That engine builders vary wildly in skill and ability !?!? With an "N" of 1 and mismatched independent variables with unequal controls any conclusion is invalid. Did you learn anything?
I did: Testimonials do not equal valid tests.

As long as every thing is square, the holes are round, nothing that isn't meant to touch anything else does, and there's as little friction as possible then all should be ok. I think I've learned a fair bit in the last 37 years, fron Grand Prix Maserati engines to Aston martin. I think one or two are still actually running. No slap or shrinkage either. AFord engine will build itself if you put the bits in a box and shake it hard enough, they're really well designed and considering the period and numbers in which they were made are very good engineering. Standard pistons are fine.

[MikeK]

Originally Posted by Browntudor

. . . I've found the correct pistons are very well suited.
. . . Standard pistons are fine.

Then you've got a real problem! NO pistons are available that are an exact match for the originals! All the replacement 'full skirt' (if that is what you mean by correct/standard) pistons have differences. Most are cam profiled, not concentric, have reduced land diameters to prevent overheat seizure, use different (if any) expansion slot placement and profiles, some have gas vent holes in the lands, use different pin locking methods, and none are the original #12 aluminum alloy. Fortunately for you almost all the available "stock" A pistons use the wide original type rings rather than the narrow profiles the entire auto industry went to.

Take a look at the Egge 1104 full skirt pistons I show in post #9 above. They are over-the-top drop in replacements for original pistons with all the nasty improvements listed in the preceding paragraph plus another one- hypereutectic (390 alloy). I've used them in 3 builds.

[Browntudor]

I have no problems with pistons. So what if they're not the same as the originals? That probably means they're much better. If they were no good then why do they sell in such quantities without my hearing about mass failures! Materials and manufacturing are now better. The originals had split skirts because they couldn't control expansion and ford then didnt know what piston manufacturers know now? And since the thing will hardly exceed 3500 revs, I don't care how narrow the modern rings are they go just fine. The modern ones don't need to be the same as ford made. It was 80 years ago. We've all passed a lot of water since then!

[tbirdtbird]

go ahead and rev it to 3500 and then get back to us.
You are on the wrong forum
maybe you'll go away soon
insurance salesman?

[colin1928]

Originally Posted by George Miller

Just let me add that .1875 is way more than any engine manufacture that I know off uses. With 283 piston when put in back wards if memory is right is about .062 that is .125 difference that is a lot in my book. .062 is about the same as a 283. I know they will work ether way but why not do the best you can. Plus less risk of scoring pistons. It does not cost anything.

Not so many manufacturers are making Desaxe engines with huge offsets
Volkswagens latest has 12.5 mm Porsche 10mm Audi 10mm ? Honda motorcycle 5mm and the list goes on
note this cylinder or crank offset not piston offset
they do this to gain both power and torque
Henry Ford ahead of his time again
they also use friction reducing materials and very high quality materials due to the high thrust loading as you pointed out
the other thing that must be factored is con rod angularity which is a whole new story

[Browntudor]

I'm not on here to start a fight, a reasoned discussion would be good, but I still haven't read a good reason for using Chevy pistons over the readily available part made for the model A. Ring width is irrelevant unless you want the thing to spin up faster but it's a 90year old side valve design and you can only do so much. I've just Rebuilt a low mileage engine for a customer which had Chevy pistons and appropriate rods so we did the same again and it's no different to any engine with the correct pistons. The only conclusion I can make at the moment is that the Chevy pistons can be as cheap as $6 each while badger etc. are about $25 each so it's down to cost.
It's a lot of messing around to save a few $ when they're cheap enough already.
And no, I've never sold insurance and I live in England so I'm not after any business. I have no agenda and no vested interests. I do have nearly 40 years in engineering and vintage motor racing though so while I know a fair amount, there's always more to know.
Can anyone give me a solid reason not to use pistons made for the Model A engine?

[RobertB]

Originally Posted by tbirdtbird

go ahead and rev it to 3500 and then get back to us.
You are on the wrong forum
maybe you'll go away soon
insurance salesman?

Gee...way to make a new lister and Model A hobbyist feel welcome! What, no comments about his possible heritage or family?

We all have a different take on the hobby and in my humble opinion, anyone that is interested in Model As in any particular way should be welcome here.

I find it interesting that the Chevy pistons are an option. I know they have been used in old Triumph engines before.

If you hate the idea, why even open the post?

Just my opinion... "Can't we all just get along?" r.king

[tbirdtbird]

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"If you hate the idea, why even open the post?"

reading comprehension has always been a problem on this forum.

i assume the comment above should be directed to the gentleman who thinks he can rev an A to 3500.

If you bother to look at my extensive record you will see that I am an advocate of the 350 style pistons.

And surely you would not wish newbies on here thinking it was OK to rev to 3500. I am dead set against erroneous info on this board, which will be searched by newbies for years to come for assistance.

[Browntudor]

There are guys over here who race using an A engine, not necessarily in an A chassis and often with better cranks and breathing but they will see 5000 regularly and theyre on std pistons. One of my friends has revved his so high that he's broken three cranks because his flywheel is mostly made of air. I agree thats extreme but its a very fast car driven by a friendly nutter. If you get the porting right and balance it nicely, yes you can see 3500 with a counterweighted crank. The whole car gets a bit flustered so it's a bit pointless but I was just making a point.

My reading is coming along nicely, as an advocate of 350 pistons tbird, you must have very good reasons for using them, perhaps you could share?

RobertB, thanks.

[zzlegend]

Originally Posted by tbirdtbird

go ahead and rev it to 3500 and then get back to us.
You are on the wrong forum
maybe you'll go away soon
insurance salesman?

Sorry, but this was just a poor response. He has his own opinions as you do also, so what it is the big deal. He seems like a decent guy to post and ask questions. Just seems like this site has got a few more experts lately and that the average guy just trying to maintain his Model A are getting fewer. Just my 2 cents. Have a good day.

[MrTube]

Originally Posted by Browntudor

I have no problems with pistons. So what if they're not the same as the originals? That probably means they're much better. If they were no good then why do they sell in such quantities without my hearing about mass failures! Materials and manufacturing are now better. The originals had split skirts because they couldn't control expansion and ford then didnt know what piston manufacturers know now? And since the thing will hardly exceed 3500 revs, I don't care how narrow the modern rings are they go just fine. The modern ones don't need to be the same as ford made. It was 80 years ago. We've all passed a lot of water since then!

I've got mixed feelings about this.
I have 80+ year old refrigerators whos compressors are made with unbelievable tolerances even by todays standards and the materials are clearly just as good. GE claimed tolerances of a few ten-thousandths of an inch.

We're talking about pumps that often have over 100,000 hours on them and yet still have close enough tolerances to pump gas under pressure without rings!

My point being I don't know if the new ones are necessarily better than the originals. Seems like an assumption we cannot make based off of what was available in mass production in the 1920s-1930s.

While this is a 1933-34 rotary pump I still feel it gives an example of the close tolerances that were possible in mass production at the time. No cork or copper or rope gaskets needed. Just steel on steel.
http://youtu.be/gn0u7dFBCTk

[Browntudor]

Thats very impressive that it's still going after all these years, I think it's a different thing though. There wouldn't be much variation in temperature and if the piston and bore are the same material then expansion rates would be the same so clearances would remain constant. An engine has to cope with combustion which creates by-products contaminating the oil, temperature variations and whatever is in the air, all of which are undesirable.
An automotive piston has a shape that is similar to an oval, tapered barrel with the dimensions dictated by the diameter, stroke and material and they're made to micron tolerances. I'm not expert here but I've learned a bit when I've had pistons made for the cars I rebuild and it's a whole discipline in itself, but as they tell me, a piston is just a ring carrier albeit a complex one.

It's very nice to correspond with you guys, I've had my A for 10 years now and I enjoy rebuilding and servicing them, the quality of engineering and materials is very high and the cars are a hoot to drive. It's a fast as a three litre Bentley but you meet a nicer class of person!

[MrTube]

Originally Posted by Browntudor

Thats very impressive that it's still going after all these years, I think it's a different thing though. There wouldn't be much variation in temperature and if the piston and bore are the same material then expansion rates would be the same so clearances would remain constant. An engine has to cope with combustion which creates by-products contaminating the oil, temperature variations and whatever is in the air, all of which are undesirable.
An automotive piston has a shape that is similar to an oval, tapered barrel with the dimensions dictated by the diameter, stroke and material and they're made to micron tolerances. I'm not expert here but I've learned a bit when I've had pistons made for the cars I rebuild and it's a whole discipline in itself, but as they tell me, a piston is just a ring carrier albeit a complex one.

It's very nice to correspond with you guys, I've had my A for 10 years now and I enjoy rebuilding and servicing them, the quality of engineering and materials is very high and the cars are a hoot to drive. It's a fast as a three litre Bentley but you meet a nicer class of person!

Yes,
Huge temperature variations and garbage from combustion are two things a refrigeration compressor luckily doesn't deal with.


Try not to get offended too easily here. Many are very emotional about their cars but I think they mean well in the end.

[Browntudor]

I should add that I've taken original pistons out of ancient A engines and while the cranks can be several grinds undersized and the white metal(Babbitt) is falling apart, the pistons are standard without sleeves in the bores so they can't be bad. The modern ones in engines used by some of us get a lot of use and don't have an easy life because the cars are so usable and durable that we will take the ford out rather than the modern. That's why I asked the question.

[Browntudor]

Hello,
No, I'm not offended, I'm fine. I was slightly surprised by an earlier response but it's obvious it's not the majority.

[zzlegend]

Robert it's good that you are not offended. I will probably never get around to building an updated "A" engine, but if I did, I would follow all of George Millers post. He seems very knowledgeable on chevy pistons and has a way of explaining there use in a polite manner. He has a lot of good info to share. But you have choices. Just my 2 cents.

[hardtimes]

Originally Posted by zzlegend

Robert it's good that you are not offended. I will probably never get around to building an updated "A" engine, but if I did, I would follow all of George Millers post. He seems very knowledgeable on chevy pistons and has a way of explaining there use in a polite manner. He has a lot of good info to share. But you have choices. Just my 2 cents.

Hey zz,
I agree entirely !
Would this gentleman sound like someone that you would like to carry on conversation with, regarding things..Model A !
I re-read his input and my answer would be a resounding ..YES
On the other hand, disrespecting another member, be they newbie , or old timer, is to hazard the wrath of the owner of this FREE medium..Ryan. Ryan has stated emphatically that your butt WILL get the boot for disrespectful and/or uncivil behavior...and damn well should,eh !! This forum has become a nice place to visit , as most of the 'drama' creators have gotten Ryans message..but unfortunately not all yet !