Any guesses?

Any guesses what would have went through the motor?

Little backstory. I ran this motor in my puller for 2 years before I quit pulling. There wasn’t anything wrong with it then. This was 2009 I think. I would start it 1-2 times a year and at one point when I went to start it there was compression coming back out of the intake. I finally pulled it apart today and this is what I found. #4 and there are a few marks on #7.

First thing that comes to mind would be a screw that holds the throttle blade. I'm sure you've looked already and their all accounted for.

are the heads aluminum?they should have dents on them as well.maybe even cracked.

Ground strap on the plug?

Yes throttle blade screws are still there.

Yes the heads have dents in them also. Don’t think there’s any cracks but they will be checked before they go back.

The ground strap is what I was thinking also but I don’t remember ever pulling a plug that was missing one. But it looks right to be one.

I’m wondering if it could possibly be a piece of the valve seat. There is one intake valve that lets compression back in the intake like it’s not even there.

Hopefully when the heads get taken apart there won’t be any major damage done.

The only other parts in the engine would be bleeder screws used in the metering block main wells. The main jets would have to be large enough to allow them to pass thru.

I assume that an air cleaner was always used. Probably a stupid question.

Yes it’s always had an air cleaner on it.

From the looks of the damage I would have to say that you have a broken ring or two. Looking near the edge of the piston also looks like you broke the top ring land as well.

jmarks99 wrote:From the looks of the damage I would have to say that you have a broken ring or two. Looking near the edge of the piston also looks like you broke the top ring land as well.

I missed that when looking at the photo on my cell phone. You are absolutely correct. I doubt that the other impact marks were from aluminum but most likely from a broken top ring.

Message to the poster
That section of ring land is the weakest and most hottest on the piston top due to its thin section from the valve relief cut. Lean and hot is the cause of this. If its a corner hole they are typically leaner. If the runner for this hole is used for a PCV or other vacuum demand its another cause.

Chicken dinner for Mark?

You have peaked my interest. I sure didn’t think there were any ring lands missing but I will now tear it completely down this weekend to see if he’s correct.

Small update. Top ring lands are still fully intact and the top rings all look to be in good shape. I didn’t have enough time to tear it on down but looked it over a lot closer.

jmarks99 wrote:From the looks of the damage I would have to say that you have a broken ring or two. Looking near the edge of the piston also looks like you broke the top ring land as well.

YES, it looks like that piston has melted, detonated or both around the intake notch; maybe small pieces of piston ring land.

I pulled all the pistons and checked today, all rings are good and all the ring lands are good. I cleaned up the spot on the piston in question. There are some minor signs of detonation but I think the lighting in the first pic was making it looked worse than it was. I plan on taking the heads to the shop in the next week or so to see what they find there.