What is wrong with my motor? Figure this one out!!

[VintageMusclecar]

Rich;

Bad news...I think that may be your problem. Those pistons are the L78 style replacement pistons. While they are listed as "closed chamber" pistons, note that the chambers are not the same between rectangular port and oval port heads. The L78 pistons are known to just slightly hit the corners of the chambers on an unmodified oval port head. I've ran into this issue myself in the past, and another member on here ran into it a few years ago as well.

Read this thread over on the Chevelle site.

Eric

[Mr. Chevy]

[ QUOTE ]
Rich;

Bad news...I think that may be your problem. Those pistons are the L78 style replacement pistons. While they are listed as "closed chamber" pistons, note that the chambers are not the same between rectangular port and oval port heads. The L78 pistons are known to just slightly hit the corners of the chambers on an unmodified oval port head. I've ran into this issue myself in the past, and another member on here ran into it a few years ago as well.

Read this thread over on the Chevelle site.

Eric

[/ QUOTE ]

Boy, thats great news.. I hope this is not the issue.. Wouldn't there be more problems, or the motor would not run right if the piston was hitting???

Rich

[VintageMusclecar]

Rich;

Normally the pistons don't hit very bad, just enough to leave witness marks in the domes that are maybe .010-.020" deep...but that's still more than enough to create a h*lluva racket when the engine's running. Needless to say this isn't good for the engine, so I would strongly advise against running it any further. I would advise discussing this issue with your builder before doing anything else.

If there is any "good news" to the situation, it's that the problem can be alleviated by slightly relieving either the domes or the chambers at the point(s) of interference. Other than that, the only choice is to remove the L78 pistons and install the correct L34 style units with a smaller dome which is designed for the oval port heads.

One other thing to consider is that the L78 pistons will give you close to 11-1 compression, so you'll have to run good gas should you decide to leave them in.

Give me a call monday if you wish and I can give you some more details.

Eric

[Mr. Chevy]

Thanks Eric...

Rich

[Mr. Chevy]

What is the part number for the stock L34 pistons and where can you get them????????? I thought this was what I had.. I expressed to the builder that is what I wanted..

Rich

[VintageMusclecar]

L2383F .030

Note how short the domes are:

http://store.summitracing.com/partde...p;autoview=sku

[Donnie]

my bet is the top left corner on the radius of the dome and bottom right are just barley touching the head.