327 SBC - piston carnage - thoughts?

[fullahotair]

Some of you might have recalled some issues a friend of mine was having with a 327 that he just had rebuilt. Well we found the problem....just not sure what the cause is. Keep in mind this motor has 30 miles on it tops.... The builder is speaking with the manufacturer to get their input.... Pistons in the #5 and #8 cylinders were busted. I imagine one broke up first and then transferred over to the other cylinder....

Would you expect to bust up a piston like this with predetonation or ignition knock for a normally aspirated motor considering it was never wide open on the throttle? It has edelbrock performer rpm heads. I think i remember being told the compression ratio was 10.5 to 1 - i might be wrong on that..i'll have to check

Bad piston?

engine ate something?

Just curious as to what your thoughts are...


Thanks,
Nate

 

[dr_frankenstein]

considering the motor has only 30 miles on it.... the bores look way tooo shiney.

to me it looks like improper piston to wall clearance.

got to tight..... busted the piston crown off.

A.j.

 

[fullahotair]

thanks for the reply...it'll be another possibility to discuss with the engine builder as possibe causes...

the builder is sending photos to the piston manufacturer to get their input. I find it interesting that they both broke in the same way...

the engine was broke in at the machine shop, and then we drove not more than 30 miles, mostly trying to trouble shoot things....

Any other thoughts?

Thanks,
Nate

 

[bison]

considering the motor has only 30 miles on it.... the bores look way tooo shiney.

to me it looks like improper piston to wall clearance.

got to tight..... busted the piston crown off.

A.j.

My first thought too

 

[STGMAN]

Piston ring end gaps too tight, rings butted together and pulled the piston top off. If this is a Keith Black piston, or the hyper piston, top end gaps need to be about 28 to 30 thousandths or this is the end result.

 

[fullahotair]

Thanks guys, I'll run these by the builder to get his opinion on the matter. This helps out a lot. These are in fact keith black hypers. I am not as concerned that there was an issue as much as that mistake is corrected and all is made right....


Thanks
Nate

 

[Randy Greenoe]

Piston ring end gaps too tight, rings butted together and pulled the piston top off. If this is a Keith Black piston, or the hyper piston, top end gaps need to be about 28 to 30 thousandths or this is the end result.

My thoughts also. I don't believe the piston manufacture is going to eat this one.

 

[Chuck Leeper]

Piston to wall is?
End gap is?
Deck hgt is?
30 mi, + a "break in" @ the shop, and the valve area is black, but the rest of the piston is shiny clean??
What's the corresponding cyl head look like?
" " " " head gasket look like?
What do the rest of the pistons look like?
What do the rest of the plugs look like?

 

[fullahotair]

Piston to wall is?
End gap is?
Deck hgt is?
30 mi, + a "break in" @ the shop, and the valve area is black, but the rest of the piston is shiny clean??
What's the corresponding cyl head look like?
" " " " head gasket look like?
What do the rest of the pistons look like?
What do the rest of the plugs look like?

Chuck, thanks for the reply.....I don't know the answer to all those questions, but the other pistons looked similar if i recall. I don't recall any oddities, however admittingly I don't really know what a piston with that many hours should look like. The other plugs looked decent - chocolate brown in nature. The head gaskets looked decent, no blown out portions, but the head must have lifted or something on Cyl 5, as when spun the motor around, with the plug out, a little antifreeze squirted out of the cylinder....(this was prior to knowing the piston was busted and head removal)

I would expect 1 of 3 outcomes to occur out of this situation...1. He puts the blame on my friend for something he allegedly did, 2. He chalks it up to part failure and may or may not ask my friend to split the bill, or 3. He recognizes it was something he did and makes it right.

It certianly seems by the feedback here it was a build issue, which again I'm OK with as long it is made right by the builder....as we all makes mistakes.... I just wanted to be a little educated on the possible causes so as to not be snookered by the builder if it comes to that...

Thanks
Nate

 

[Chuck Leeper]

Could be..

"but the head must have lifted or something on Cyl 5, as when spun the motor around, with the plug out, a little antifreeze squirted out of the cylinder....(this was prior to knowing the piston was busted and head removal)"

I'd be looking for a split cyl wall, cracked head. A/f in the cyl could have broken the pistons. It would also account for some of the "clean up" of the piston tops.
It could also be the result of the head getting "jacked up" when the piston chunk got on top of the piston.
A look in the oil pan could reveal a/f being the problem.
Some of the early engines had some core shift. Over bores could have resulted in a thin wall/cracking.

Will be interesting, once the engine is disassembled. I'd be there when it happens...

 

[dr_frankenstein]

it really sounds like you need a new engine builder.

if the guy cant get a SBC right.... imagine the carnage to a buick!!!!

A.j.

 

[STGMAN]

Read the instructions that came in the piston box, it will plainly say the top ring "MUST" have extra clearance because the top ring groove is so much higher on the piston and runs much hotter than a normal piston. Again, READ the instructions. If they were thrown away, check the web site for Keith
black pistons and you will see it. There is even a picture of the exact problem that will occur as a result of too little ring gap. Looks exactly like your pistons.

 

[fullahotair]

My friend never got the box from the builder, but i did go the KB website and found the article you spoke of. I'll be printing that out and taking that with me to the machine shop and see what the builder thinks.

Thanks for all the help...

Nate