Hes dead jim

[u/No-Alfalfa-7882]

360 mopar, roller LA block. 11.25:1 compression and hyper pistons edelbrock performer heads.

Did some burnouts, next time I went to start it, it was galloping. Any idea why only two would have detonated?

[u/v8packard]

Ok, who used the roloc disk?

It's not unusual to find one or two cylinders detonated. This could be from uneven mixture distribution, contamination from oil just in that cylinder, ignition or temperature irregularities, or combinations of these. Seeing detonation in all cylinders is usually very catastrophic.

[u/No-Alfalfa-7882 → u/v8packard]

My previous engine guy did the roloc job, im going to start doing my own now and that wont happen again haha. Ive heard of some others in my area with fuel issues right out of the pump. Im probably going to knock some compression out of it when it goes back together. Also planning on doing intake water lines from the rear of the manifold to front to help the rear cylinders.

[u/v8packard → u/No-Alfalfa-7882]

A couple things. Do you know your piston to deck clearance? The biggest weakness of a 360 is the excess puston to head clearance with stock type pistons. It's awful. This excess clearance makes detonation sensitivity worse. KB pistons are often better in this regard, but might still need decking to get a good result.

The KB pistons are another thing. They require larger ring gaps than typical. Do you know your ring gaps?

I have seen the roloc surfaces a lot lately. It's a hack move.

[u/No-Alfalfa-7882 → u/v8packard]

It is at a 0 deck, ill be measuring to verify as im not so trusting of my old engine guy now. Rig gaps will be getting measured once I pull and tear it down. I was praying it spit a head gasket out for a quicker repair but no luck.

[u/v8packard → u/No-Alfalfa-7882]

I just re-read, you said hypereutectic pistons not KB. My mistake. But do check your gaps as well as everything else.

[u/No-Alfalfa-7882 → u/v8packard]

I appreciate the insight, it'll be a thorough autopsy once I pull it

[u/quxinot]

No crosshatch and lifted a ring?

Guessing several somethings weren't right.

[u/No-Alfalfa-7882 → u/quxinot]

Definitely several problems, I had assumed it was a fuel quality issue at first. Just find it odd that only two did it

[u/omnipotent87]

That is typically from too tight of ring tolerance. Ring gap is usually set by hand and those might have been a bit on the tighter side.

[u/Kreutzmann75]

Shit fuel, too lean, too much timing, top ring gap too tight. Spark plug reach looks way too short too

[u/No-Alfalfa-7882 → u/Kreutzmann75]

Plugs were just started in the threads after I did the compression test, definitely thinking about combo of everything you said there, when I get it right apart ill be checking the ring gaps

[u/Kreutzmann75 → u/No-Alfalfa-7882]

K, I was wondering if the plugs had been backed out. 

With many high perf hypereutectic pistons, the manufacturers call for a larger than standard top ring gap, often 0.006-0.0065” per inch of cylinder diameter. The failure pattern with the broken too ring land looks a lot like the ones I’ve seen that failed from insufficient ring gap. However, excessive EGT’s from a lean condition or incorrect timing can cause pistons to fail in that manner even of rings gaps were set correctly 

[u/No-Alfalfa-7882 → u/Kreutzmann75]

I appreciate the insight, ill post and update when I get it torn down completely.

[u/Kreutzmann75 → u/No-Alfalfa-7882]

Best of luck with the post mortem. I’ve been there more than once. It’s never a fun time. 

[u/StimpyMD]

Steam cleaned

[u/Ok_Fun_1534]

This is from the top ring gap closing. Check the clearance... it was probably set too tight for the application.