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.