348 pistons

[djohnson1937]

Newbe here...in the process of tearing down a 348 (7655). Wondering if a person can visually see the difference between the low compression pistons (truck block) and the car pistions. This motor has been recentley gone thru so I do not think that its stock. I pulled one piston, measured up, it appears stock with "camz18 av" stamped on the top. thanks for any help.

 

[Ronnie Russell]

dj, I am not familiar with that piston number. Possibly , if you could post a picture , someone may be able to help you with identity.

 

[SSpev]

that casting is a late truck 348. car pistons, 9.5, have a top shaped like a roof. the truck is almost flat. there is a step then a small angled part to the side. I will try to remember to get pics tonight.

 

[djohnson1937]

Thanks for the info guys. here is some pictures of that piston....I got a kick out of the bolt impression. Here is another question... the cylinder head that is pictured is a truck head (3815857) but with a "closed chamber"?

 

[models916]

333

only the 333 truck head got the small chamber.

 

[johnnyrod]

Thats ruck piston. The car 9.5s are a dome looking type you can see them on one of the 409 parts sites. John

 

[Bungy]

The head you have pictured would be the "small" chamber (about 7cc) The 333 head has the larger chamber (not sure but I think about 15-20cc) And yes, that is definatly the low compression truck piston.

 

[djohnson1937]

Thanks guys. what a great website!

 

[CDNpontiac409guy]

Thought I would mention too, Djohnson....
Those low compression truck pistons... if they are the original ones from the the "truck" engine... then you have a car block .
The truck 348 was built in 2 diffiferent configurations. The first ones use the regular 348 car 9.5:1 piston ( like the guys have been talking about ), but the block has TWO(2) GIANT machined valve reliefs in each cylinder in the combustion chamber. I think ALL of the "655" 348 blocks are the "car" design.

Anyhow, it looks like you have a good core for building

 

[djohnson1937]

This block did just have the one cut-out in the cylinder wall.
Wondering...would 59-61 heads work on this block?
I have one 333 head and one 5857 head (goofy-odd-duck head) wondering if I should look for another 333 or a set from a car?

 

[models916]

offset pin

Does anybody know if the new cast pistons for the 348 still use the factory offset pin location? The 409 pistons were straight up on the pin and the 348 forged pistons come from a straight up W blank, but I am wondering about the current batch of CAST pistons out there. Would be something to be concerned about during installation.

 

[Ronnie Russell]

models, I have used 2 sets of cast pistons recently for low perf. re-builds. Both sets were EGGE,,,,, both sets had the steel inserts, but I did not check for pin location. Did not realize there was a differance. Both engines are great running engines, so I guess this was not an issue.

 

[1958 delivery]

The blocks with a single ex valve cutout is which, pass or truck?

 

[Ronnie Russell]

As I understand it, One relief = 348 pass. block and some trucks. two reliefs = truck only.

 

[models916]

Wear Issues

Chevrolet offset the pin on the 348 to offset the lopsided weight issues of the cut top of the piston. By the time the 409 came around they decided it wasn't an issue. I wonder what the wear pattern is if you put a Left offset piston in a Right hole. Low milage use 348 engines today would probably never notice it. But then again the new cast pistons might have done away with it anyhow.

 

[CDNpontiac409guy]

Not for weight issue, Models. Most cast pistons are manufactured with a pin offset. 99% of the reason is to reduce piston "slap" / noise when the engine is cold. The 340 horse 409 car engine has the pin offset... meaning, there are actually four(4) different pistons in them !:eek:

High performance engines generally don't have an offset.

 

[models916]

ok

I knew there was a reason. Still wonder what is being done today for Cast 348 pistons?

 

[Ronnie Russell]

4 part numbers!!! Glad they did away with that. I have enough problems getting machine shop to install pistons on rods correctly with 2 part numbers.