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

[Mr. Chevy]

Cam bearings are a good place to start.. But I can't believe the builder would have done that.. But I guess anything is possible and we are all human and make mistakes.. The pushrods were listed as the correct ones via the part # on the box. We checked to make sure that they were not obstructed when installing them..

Unfortunately I am not that video/computer literate to video the noise and install it...

Rich

[VintageMusclecar]

Rich;

What brand and part # are the pistons? Which heads (casting #) are on the engine?

Did you check for dome to chamber clearance?

Eric

[P.J.]

Rich;
What kind of lifters did you install in the motor.?
I had the same problem when I installed anti pump up lifters
on my hydraulic cam and used 20-50 oil.The oil was not inflating the lifters
and making a hell of a racket.I changed the oil to
10w 30 and it stoped.
PJ

[Mr. Chevy]

[ QUOTE ]


What brand and part # are the pistons? Which heads (casting #) are on the engine?



Eric, here are pictures of the head casting numbers and the new pistons (Federal Mogul) with the part numbers... Everything is basically stock and there were no issues with clearance.. The lifters are just regular hydraulic lifters as far as I know...

[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