5 replies to this topic

[Richard Pressman]

Well, here's the story.

Found a 92 with 112K and an owner wanting to swap it out with a 1.8 to supercharge it. He wanted a very fair price for the 1.6 - cam cover to oil pan and intake to exhaust. Said he bought it from the original owner and used it for the last few months. Had no reason to doubt him. Overall the car was in very nice shape, obviously well cared for. The engine was still in the car. My son (the race car driver) took the car out for a 20-30 minute drive and said it felt solid, strong, with nothing to raise any red flags. I listened to the engine when he got back and heard nothing unusual. No smoke from the tail pipe. It was dripping oil in all the usual places - but I was going to replace all the seals and rubber anyway so no problem.

Decided to buy the engine, clean it up, use it to replace our 245k stocker and see what it would do on the dyno (for SSM). Didn't bother to compression test it since if it dyno'd really bad we'd freshen the head. I felt much more comfortable putting a nice head on a 112k bottom end rather than on a 245k bottom. Worst case we'd have a good head and next year freshen up the bottom end, maybe.

So, I finished the "build" and had it dyno'd. It was couple, three hp better than what it replaced but not close enough to the 96 hp spec that MARRS uses that it could be a winner at VIR or Summit Point. Definitely a contender at NJMP -- but I digress.

Thought about it and decided to shoot the budget and give the head a shave and valve job to maybe get to the 96 hp spec.

Now for the "Houston, I think we have a problem", bit.

Removed the head and found this:

Cylinder #1 piston

Cylinder #1 head


Cylinder#2 piston

Cylinder #2 head


Pistons #3 and #4



So, detonation?? Right?
Recent? Ancient? Does it even matter?
Go ahead and do the head anyway and just race it?
Or, is it just so much scrap metal??

[Graeme]

Looks to me like something went through it, the shape of the deperssions are too consistent.

[Ken SM94]

Looks like someone but bbs in it to me.

Ken

[Keith Novak]

I thought that's how they lighten and balance the pistons.

It does look more like FOD than detonation. It also looks pretty old since the pits have as much carbon in them as everything else. Here's a link that has a few pictures of detonation, and describes circular pits...

http://www.theultral...com/pistons.htm

If it's FOD, I'd question what other issues might be lurking in there.

[Richard Pressman]

Yeah, the more I look at it and read up on the subject (thanks for the link, Keith. I learned something) it appears that at some point "something or somethings went through the engine.

Keith, good point about the carbon in the pits.

Anyone with an opinion on how long ago this may have happened? I'm thinking along the lines of...well, if it happened 50k miles ago chances are there is no other damage or it would have shown up by now. OTOH, it's probably not a good move to put a new head on top of that piston. I guess even refreshing the existing head is risky.

So... let's ass-u-me the engine will continue to hold together and I have a shave and valve job done. Will that amount of pitting in the piston and head have a significant effect on the cylinder volume and thus effect the compression ratio relative to the other cylinders enough to matter?

Does it mean anything that it just dyno'd reasonably well (92+ over an 800 rpm range) for a bone stock 112k engine, multiple pulls bouncing off the rev-limiter w/o coming apart?

....or do I need to stop beating a dead engine?

[Ken SM94]

I wouldn't put too much money in that head. It would probably last forever like that but a new core is only $100 or so. Buy a new head and have it rebuilt. I'm sure the lower end would be fine too but I would replace it (or at least the pistons) when you're ready to go deeper into the engine.

A leak down test after the head rebuld/replacement would tell you how much you're giving up in the lower end.

Good luck,