Need source for original pistons (396)

[Keith B.]

My brother in law is going to rebuild his engine in his 1969 Camaro 396/375. This is the same motor that is in the 1965 396/425. The motor has compression of 11:1 and he rarely drives the car. I have searched for the right pistons but have not had luck on google and ebay. If available I am sure he would like original (NOS) if they are out there. Can someone help me with this dilemma?

[Scott S.]

Re: Need source for original pistons (396)

My brother in law is going to rebuild his engine in his 1969 Camaro 396/375. This is the same motor that is in the 1965 396/425. The motor has compression of 11:1 and he rarely drives the car. I have searched for the right pistons but have not had luck on google and ebay. If available I am sure he would like original (NOS) if they are out there. Can someone help me with this dilemma?

Keith,

I suspect those more knowledgeable than me will recommend modern pistons (either OEM-equivalent forged-domed or Keith Black), but if I absolutely had to have NOS pistons for the same engine that was used in the big block '69 Camaro, I would start by calling Jerry MacNeish. If he doesn't have them, he may know who does.

[Scott M.]

Re: Need source for original pistons (396)

Why wouldn't you use either Speed Pro 2240NF or 2242NF forged pop ups?

[Joe L.]

Re: Need source for original pistons (396)

My brother in law is going to rebuild his engine in his 1969 Camaro 396/375. This is the same motor that is in the 1965 396/425. The motor has compression of 11:1 and he rarely drives the car. I have searched for the right pistons but have not had luck on google and ebay. If available I am sure he would like original (NOS) if they are out there. Can someone help me with this dilemma?

Keith-----


The search for NOS pistons is complicated by the fact that there were several over-sizes available and he probably needs a specific one. Furthermore, for 1969 there were two different piston designs used. The first design was used for applications using cylinder head 3919840 and the second design was used for L-78's using cylinder head 3964291.

Here's what he's looking for:

first design:

std--------GM #3878231
+0.001----GM #3875905
+0.030----GM #3875906
+0.060----GM #3875907

second design:

std--------GM #3969989
+0.001-----GM #3969990
+0.030-----GM #3969991
+0.060-----not available

Good luck. I think it will be extremely difficult to find any of these, let alone a set of 8-------7 just won't do.

[Scott M.]

Re: Need source for original pistons (396)

The 2242NF is the large pop up for closed chamber heads, the 2240NF is a small popup for the 396/325-350 HP piston closed chamber piston.

[Loren L.]

Re: Need source for original pistons (396)

In point of fact, isn't any .030 piston no longer NOS, but NORS?

[Dick W.]

Re: Need source for original pistons (396)

More than likely Speed Pro or one of it's predecesors furnished GM pistons when new. To me there would be no difference if they came in a Federal Mogul, Speed Pro, GM or what ever box. Same materials, machining, weight, etc

[Joe L.]

Re: Need source for original pistons (396)

More than likely Speed Pro or one of it's predecesors furnished GM pistons when new. To me there would be no difference if they came in a Federal Mogul, Speed Pro, GM or what ever box. Same materials, machining, weight, etc

Dick------


Well, there's no doubt the piston blanks were furnished by an outside supplier, TRW or otherwise. GM never had any internal aluminum forging capability that I'm aware of. However, I'm not so sure about the finish-machining. In general, GM engine plants machined the pistons, including those sold in SERVICE. In the case of cast pistons, most were cast at the GM aluminum foundry in Bedford, IN and then machined at the engine plants. The exact same thing could have been true for the forged aluminum pistons forged by outside suppliers. I've never been able to determine this one way or another.

I don't know if the GM engine plants of today still machine the pistons in-house.

[Clem Z.]

Re: Need source for original pistons (396)

i don't think you will find standard bore pistons if that is what you are looking for.

[Clem Z.]

Re: Need source for original pistons (396)

Dick------


Well, there's no doubt the piston blanks were furnished by an outside supplier, TRW or otherwise. GM never had any internal aluminum forging capability that I'm aware of. However, I'm not so sure about the finish-machining. In general, GM engine plants machined the pistons, including those sold in SERVICE. In the case of cast pistons, most were cast at the GM aluminum foundry in Bedford, IN and then machined at the engine plants. The exact same thing could have been true for the forged aluminum pistons forged by outside suppliers. I've never been able to determine this one way or another.

I don't know if the GM engine plants of today still machine the pistons in-house.

i do not know if GM still machines their own pistons but i do know they come to the engine plant with the rods and rings already on them.

[Clem Z.]

Re: Need source for original pistons (396)

the 840 head has 107 cc chamber and the 291 head has a 109 cc chamber that is the difference

[Joe L.]

Re: Need source for original pistons (396)

i do not know if GM still machines their own pistons but i do know they come to the engine plant with the rods and rings already on them.

clem------


Well, I'd say if the pistons arrive at the engine plants of today already fitted with connecting rods and rings, then it's a safe bet they're machined elsewhere.

[Dick W.]

Re: Need source for original pistons (396)

Dick------


Well, there's no doubt the piston blanks were furnished by an outside supplier, TRW or otherwise. GM never had any internal aluminum forging capability that I'm aware of. However, I'm not so sure about the finish-machining. In general, GM engine plants machined the pistons, including those sold in SERVICE. In the case of cast pistons, most were cast at the GM aluminum foundry in Bedford, IN and then machined at the engine plants. The exact same thing could have been true for the forged aluminum pistons forged by outside suppliers. I've never been able to determine this one way or another.

I don't know if the GM engine plants of today still machine the pistons in-house.

It was my understanding that Alcoa did the forging of the blanks for all the manufacturers of those pistons.

[Steve B.]

Re: Need source for original pistons (396)

Try posting a want ad on yenko.net. I'll bet that you will find them there.

[Domenic T.]

Re: Need source for original pistons (396)

More than likely Speed Pro or one of it's predecesors furnished GM pistons when new. To me there would be no difference if they came in a Federal Mogul, Speed Pro, GM or what ever box. Same materials, machining, weight, etc

Dick,

I have found the weights to differ when I weigh tafter market pistons.

They don't weigh the same as the original factory pistons.

The pistons sets are matched weights but they don't match the factory weight which requires another engine balance.

I weighed factory small block pistons years ago and the dish, flat top, and dome were exactly the same weight (within a gram or 2).

That makes sence because the factory could balance all the cranks the same and not have to worry about what pistons were installed in what engine.

I had to prove this to a speed shop owner in Santa Fe Springs CA. when I bought a replacement piston. It was 53 grams light and he said it was because it didn't have a high compression dome. The other gur behind the counter said it was lighter because it was high performance?

I brought 3 pistons (all original factory) and let them weigh them and their jaws dropped.

If i were going to mass produce engines I would want to do it that way and reduce the chance for error in weight between engines.

The after market boys will give you a number of different reasons why their piston weights vary, but the only truth is that the engine has to be ballanced to their pistons.

It is a good idea for us to record our piston weight when rebuilding so we can go in and change one if needed.

some how the screw off a cresent wrench found it's way past the intake valve in my chevelle and broke the top ring land . That happened on a fresh engine while breaking in the cam . I had to take it apart and try to find a piston the same weight. Not in this day and time. I had to get a lighter piston and press a weight in the wrist pin to equal the total weight mass. In the old days when I bought GM pistons it would only be a trip to the parts dept.

DOM