DanD

I finally took apart my spare engine to see what shape it was in. Here are a couple of photos.

The questions are, what pistons are these? Are they oversized? The car had 118k on it and was blowing white smoke, (the headgasket on #4 was blown).

The engine looks to be recently rebuilt, the other cylinders were perfect no ridges.



And, how bad is this scoring. What can be done to fix it?



Thanks,
DanD

david fracolli

First oversized. Spec is 100.48mm to 100.52mm.
Dave Fracolli

OZ951

100.48 is probably for first oversize pistons. My klobenschmidt's (Sp?) did not have those same markings though.

Wayne

Perry 951

Dan -

1st over pistons as everyone else said. I cannot tell how deep the scoring is from the photo. Run a fingernail across them, and if they are deep enough to snag, or are very rough, it should be re-finished.

DanD

[quote]Originally posted by perry951:
<strong>Dan -

1st over pistons as everyone else said. I cannot tell how deep the scoring is from the photo. Run a fingernail across them, and if they are deep enough to snag, or are very rough, it should be re-finished.</strong><hr></blockquote>

Thanks all for the replys.
Does refinishing mean reboring or just hone and re-treat the cylinders? In other words, do I have to replace the pistons?

951and944S

There's something seriously wrong with that cylinder.......!

Notice how the piston traveled high enough to score the wall even above the maximum stroke, which in your picture should only be the carbon ring around the top....

Have you checked the bottom end yet.....

For a stretched/damaged rod...?

Cheers

DanD

The thought crossed my mind. The other cylinders are perfect. Reciently rebuilt I would guess from the oversized pistons. I haven't got the pan off yet..
DanD

951and944S

DanD,

The cost of boring, then honing machine work with pistons can run into some serious $....

Let me know what your plans are, your rods should be in good shape, since they should have the forged versions, if they're original....

I have a complete '86 engine longblock, with perfect cylinder walls, rods, pistons, etc., if you are interested.
I can also assemble the engine to factory spec., on some type of exchange basis..., with new bearings, rings, gaskets and seals.

'86 engines are in a class by themselves as far as the turbo goes, they have different balance shaft bearing caps, and covers, forged connecting rods..
Also engines '87 and up have self adjustable timing belt tensioner bolt holes in the blocks front area.

Bri Bro

DanD
Pull the rod bearing for that cyclinder and post it. You can oversize only one piston ie fix one and leave the other ones along. I bet is you measure that cyclinder it will be way out of round.

I tend to side with getting everything back to spec while I have it all apart. It is all a matter of risk and cost.

DanD

Good suggestions. I'll take the bottom apart and see what it looks like. I might go the way of the one cylinder fix. Like I said the others are perfect.

BTW, what is the standard bore?

mmmbeer

If the warped cylinder is your #4, that would be the reason why the headgasket blew. When the piston travel that high it would create an enormous compression in that cylinder causing the headgasket to shatter.

Eirik Kvello-Aune
<a href="http://www.diateam.no/porsche" target="_blank">www.diateam.no/porsche</a>

Geo

[quote]Originally posted by beab951:
<strong>I bet is you measure that cyclinder it will be way out of round.</strong><hr></blockquote>

Actually, if you want to measure a bore for being in or out of round, you should do it with a torque plate in place.

Without it a cylinder that is perfectly round with the head bolted in place will likely be out of round.

951and944S

Geo, while what you say is true in most engine designs, the 944/51/68 engine have cylinders that are raised from the block's mass like smokestacks, for lack of a better word.
Also the stress from headbolt torque you refer too, is passed along to the studs which are attached to the main bearing "girdle" effectively compressing the engine between the cylinder head and the girdle.
These engine are thus less effected by headbolt/stud torque effects than your average cast iron head bolt design..

AFAIK, the factory workshop manual makes no reference to bolting a stressed plated to the block when check for cylinder dimensions..

DanD

[quote]Originally posted by beab951:
<strong>DanD
Pull the rod bearing for that cyclinder and post it. </strong><hr></blockquote>

#1 cylinder is the scored one.

I pulled #1 and #2 roods off. They both were standard and looked like they were just replaced. &lt; 10k miles.

Sorry, no picts.

So, I'm not sure why the #1 cylinder was like that. The #4 cylinder was the one with the blown head gasket. If it didn't blow, the engine would have eventually seazed or gotten real noisy.

I'm preparing for the Parts Heaven swap meet, so I'm debating what to keep and what to sell. If nothing else, I'll keep the head, and sell the short block. That's still up in the air.

With 2 951s to care and feed, I need all the spare parts I can. But, there has to be a balance of what to keep around for 2 or 3 years and what to part with and repurchase when the time comes. Ah.. the delema.

Thanks for the help.
DanD