What wears out first?
 

My 82 Euro S has 150k miles on the original engine. The heads were pulled and reworked, but the bottom end is still original. If, someday, I want to rebuild the bottom end, do I dare even have it bored? It seems like the aluminum block is unusual enough that I should leave the bores alone. How do the cylinders wear in comparison to the pistons and rings? Would new rings alone provide significant improvement in reducing blow by? Pistons and rings? Anyone know a good source for rebuilt short blocks?

No wear is normal wear for short blocks. Some do have problems, but I suspect they could be traced to owner abuse. I am debating right now on whether or not I should put in new rings or bearings in the short block I have (85/86 for a Euro hybrid motor).

Very few people rebuild 4.5 or 4.7 short blocks. A good used short block is cheaper than a set of new pistons, and you need to either buy genuine Porsche or have the block Nikasil coated after boring.

With a Euro S I would find a good low mileage 85/86 5.0L short block and build a hybrid.

I've seen stock engines that were very healthy at 300k, if yours has lasted 150 then it will probably keep lasting.
It would be worthwhile to "rebuild" one simply by replacing gaskets but leaving the pistons and crank alone, spend real effort on the heads. You could slip some new rod bearings if you feel you need to do *something* while it's apart:)

I think a PO overheated the engine. I get significant blow-by under heavy throttle. This makes me think that new rings would be helpful. I have other things that need attention before the bottom end. I just started pricing things and noticed that rings + a gasket set already would put me at $1000. Thanks for the replies!

Many use 944 rings, gasket set is I think about $460 if you shop around.

One of the reasons for going to a 5.0 L block is the lower cost of the more common 100mm parts.

You'll have a much better feel for block condition after the heads are off. Inspect the bores and make a decision then. The bocks are pretty durable but they also don't do well with abuse. The boring and lapping process is unique to the silicon-aluminum material. Boring isn't that big an issue, but the lapping process is very specific. It involves a hone with straight supports for lapping felts, and a honiong paste that relieves the aluminum around the silicon particles in the metal. The plated piston then rides on the barely-proud silicon so the aluminum never sees wear from the skirts or the rings.

From what I remember with Americam engines, if it smokes while on the gas, the rings are worn, if it smokes letting off the gas, its worn valve seals / valve guides. If it smokes on & off the gas, its rings & valves.

my blowby issue was 6 broken compression rings and 7 busted pistons.

the air pump (smog pump) made the situation worse, not to mention that these engines are notorious for having oil consumption issues due to loose piston to wall clearances and a lousy, non-existent crankcase breathing system....

run a compression check and a leak down test for each cylinder.

if your readings are steady (near the same) for each cylinder, leave the short block alone. you should see comp numbers up around 175 psi. anything significantly less or one-maybe two or more much lower than the rest......plan on boring/Nikasil coating and a new piston ring set using domestic pistons/rings. Otherwise, your looking at very expensive Porsche stuff.

Short of all that----do as Danglerb suggested: build a 5.0L hybrid and be done with the broke/worn out 4.7L engine.


--Russ

you can get them for $100 cheaper on ********. Also when shopping around, take into account that the cheaper sets will have some gaskets missing, and other stuff.

Are there different sets, or do some sellers pull some gaskets?

Some of the sets I see have valve cover gaskets separate from the main gaskets, which is better for hybrid builders since you need a 32v 5.0L bottom and 16v top.

Hi Gang,

I made a 600 mile round trip to California yesterday in the 928 and it really didn't consume any oil. I'm going to credit the oil control kit I bought from 928motorsports. I was doing about 80 the whole way, so I'm comfortable that the bottom end is sound enough to leave alone for a while. I think my "smoking" around 4500 RPMs is telling me that my timing is too far advanced as I'm hearing detonation too. Th smoke is more black than that white oil consumption smoke.

Isn't black smoke too rich?

yep. black/blue haze

I think it would be your wallet and your patience....if I had to pick just two.