recently "rebuilt" 2.7

[sww914]

I just bought a 2.7, almost complete. I paid so little that I could sell the carbs alone and make money on the deal.It was allegedly rebuilt by a non-porsche mechanic. The only good thing is that the case has been time-serted. Everything that I can see on the outside so far is screwed up. They used wave washers and steel washers under an assortment of different nuts on the valve covers and cam chain covers. They sealed the cam housings to the heads with copper RTV. They obviously forgot the O rings on the case through bolts because they RTV'd the outside of some of the nuts.
I'm starting to pull it all apart because we all know that everything that I can't see is equally stupid. My question is- if I pull the case apart, must the main and rod bearings automatically be replaced? Even if by some miracle they happen to be the right bearings, installed correctly, and with little or no wear? The thing was supposedly driven only a hundred miles or so before it was replaced with a used 3.0. The way the engine looks supports this claim so far.

[304065]

A well respected, but anonymous, engine builder says that one should never preassemble the case because the bearing shells bend when the case is torqued.

That said, the factory workshop manual for the 3,2 talks about re-using bearings in the event an engine is torn down prior to rebuild.

In your case I would throw them out-- how would you know they weren't oversize when standard are called for? Somebody who assembles with copper RTV isn't exactly the type to mic the crank and post the results in a scatter graph. Not worth the risk for the price of a new set IMHO.

[Bobboloo]

When you get the motor apart you need to check the main line bore. If it's out of spec and wasn't corrected before the rebuild then the bearings have been worn out of round and should be tossed.

[Steve@Rennsport]

A word about 2.7's (and even 2.4's) that have been running for awhile,................

One can loosen all the case through-bolts & nuts, retorque everything back up, and the crank will no longer turn easily (if at all) due to case warpage. This only affects mag cases (all).

One must either line-hone these or in most situations, machine the mating surfaces and line-bore the mains back to standard size.

[sww914]

Thanks, Steve, I think that settles it, I'll send the case out to a well respected Porsche machine shop and have the mating surfaces machined and the bearing bores put back to stock diameters.
Must you then space out the cylinders an equal amount to compensate for the pistons rising higher in the cylinders, or would you check all of the clearances and use the extra compression to your advantage if possible?
This will be a race only engine, and if I must buy P's and C's, cams, or do any head work I'll go bigger wherever possible.

[Bobboloo]

The short answer is yes but more specifically deck height should always be checked. This will determine what size cylinder copper base gasket is to be used for clearance and desired compression ratio. The deck height is not only affected by shaving the case for a line bore but also by machining the spigot lands for the cylinder bases flat.