this is what i found when i pulled my motor apart. i think the damage happend only a couple minutes before i shut the engine off for the last time, i was driving home and heard a rattle like a bolt getting kicked around and the engine bogged so i gave it some gas and it stabilized, the noise stopped and i got it home. i'm getting the cylinders bored so damage to the walls isn't an issue, nor for the pistons. one of the combustion chambers got chewed up pretty good and a couple others got minor damage. they are aluminum L98 heads. can i grind/sand the chambers smooth so i dont get hot spots? any ideas on what happened?

 

Lunch was had in your motor bro!

 

You cant just sand and grind that one chamber because you will off the compression a little in it. You can have the cylinder welded up and then milled flat again. Worst case is that after the welding the seats might come loose from the heat, just have new seats installed in that chamber, and your good to go! There is no damage in the tub part except right above the plug that would need to be hand grinded, the rest would be done by a surface mill!

 

If that's the worst chamber you can just polish out the sharp edges and it will be fine, it won't affect compression enough to worry about.

 

Send them to the machine shop and have them surface them and check for cracks. If they cant get them totally clean use a thick composite head gasket like nitro seal you might be alright.

 

so what really caused it?

 

Looks like you had some detonation going on.

What happened immediately prior to this? How much spray?

I don't really see anything serious enough to need welding. Looks to me like a little polishing would take that out. Clean the heads up first, then you can actually see what you've got.

 

how the hell did that happen??? NOS? anyways send them out to a mill shop they can fix them. but when you brake somehitng its just more of a reson to put in better parts

 

This might have been the end result of the saga I've been having with my engine. About two months ago I blew a head gasket at the track, I think because my carb was untuned and the cylinder temps got too hot. One or two of the rings on each head gasket were destroyed. So, I replaced the head gaskets but ever since then I was burning oil really bad so I replaced the intake gaskets a couple times to no avail. So I drove the car home from college, 220 miles, and made sure the oil was full before I left. I was driving around my hometown and noticed the oil pressure was low so I drove it home, a couple miles maybe, and checked the oil. It was 3.5 quarts low! So I refilled it and took it for a spin to make sure it was running ok. I did some donuts at the local high school and was on my way back home when I heard the aforementioned rattle in the engine. I've never used nitrous, by the way. I think I will try to clean up the heads and if they still don't look too good I'll just have to get new ones.

Could detonation sound like a bolt rattling around? It was VERY noticeable, the one time I heard detonation (on another engine) it was very quiet and you really had to listen for it.

 

Detonation sounds like marbles rattling around in a coffee can, loud.
What you heard before was probably "pinging", the lead in to true detonation.

 

I won't claim to be an expert, but it looks like something was in there. Would detonation leave distinct marks like that? I see a few rectangular marks. The bowl part of the chamber looks untouched, but all the lower, flat areas are beat to hell. Except for a couple spots, the valve reliefs on the pistons look good. Just something I noticed.

 

Yes, it does look as if there was something metallic in there beating the piston and head.


Was the spark plug in one piece when it was removed?

 

yea those look like pure scrape marks instead of heat killing it., look around and see if you have a bolt missing on your intake manifold, if so, i bet i know where it went .

 

Detonation caused that.

I'll bet it's on the side of the piston that would be right under the spark plug.

What happened first, was the ring lands cracked from the impact of the detonation, allowing the rings to flop around; combustion gases leaked through the cracks, and eroded the hole in the piston; and fragments of rings got loose and wandered around all in there.

Combustion gas acts like a very fast-acting abrasive when it encounters a leak like that. Anybody that's ever seen a burned valve knows exactly what I'm talking about.

Detonation is usually pretty noticeable in a car with an exhaust on it. It sounds like hitting things in the engine with a hammer, rather like an extreme case of pinging.

A bolt won't get past the valve. They'll usually get stuck in the valve and hang it open. Then of course the car runs absolutely terrible, spits back through the carb etc.

This is a clear-cut case of detonation from what I see. I've seen it too many times.

 

weird, my car sounded like something was literally inside my engine rattling around then it cleared up for some reason.....wonder if it was my timing

 

Okay, I see what RB is saying. There eventually was something in there, but the detonation caused "that something". I didn't think about the piston fragments doing that.

 

I would think that the fragments were what you heard combined with the detonation noise. I would guess it went away when either the aluminum melted, and went out the exhaust, or it went through the hole in the piston, and landed in the oil pan.

 

Well the old rods and pistons are at the machine shop right now so they can press the new pistons on and recon the rods but I'll call them and ask them to save the old pistons so I can check out the rings. I haven't looked at them closely but the only rings that I saw with damage were the ones on the piston with the hole in it. I wonder why it would detonate, the engine was idling without any load on it (I was stopped at a light).