nose bearing

[quattrorunner]

Should I replace the no 8 nose bearing in a rebuild or reuse? Don't have any answers on a search.

[cgarr]

Is it in spec?

[quattrorunner]

I don't know, but it looks cute
I'm new to the 911 building thing, what would I meaure or is it a wobble thing? Seems nice and smooth but I just don't know.

[cstreit]

I reused mine for several builds (race engine) untill a spun bearing on #2 boogered it. Safety says don't cheap out, but have your machinist check it.

[Walt Fricke]

For a "normal" rebuild (replace main and rod bearings regardless of wear because you are in there, or because they are worn but crank is OK), the #8 doesn't get replaced. It just doesn't see the forces the other ones do. No rods and pistons flying around on it. Just the IS shaft gears trying to move it apart from the IS shaft (and vice versa). And what little sress the distributor gear might supply (almost nothing, I'd think). So it doesn't wear much.

And hasn't changed much. The early ones had a full OD, but at some point Porsche decided to add an axial slot along the OD to help let oil drain back. One can add this slot with a hacksaw on an early #8.

Which is one reason why a set of new mains does not include the #8 (packaging would be another reason, and cost yet another).

There is a spec for its ID (should be in Wayne's engine rebuilding book, which of course you have), and if you have a bore gauge that small, or just snap gauges, you could easily check it out. Maybe calipers would do?

If it is boogered I assume a visual inspection would reveal scoring even if checking for out of round would not? I've had rods let go (breaking lots of stuff, including the case each time) on three motors now - twice because valve heads fell off, and once because a rod bolt failed, but haven't noticed issues with #8 (not that I measured carefully, but it went back in and worked).

I think that on crank regrinds (where needed) that crank journal also usually still in spec and left alone. Expensive enough as standard/standard.

I made a bad mistake long ago in having a case line bored to first over, and including the #8 in that. I hadn't realized it doesn't get replaced usually, and even in the 2.7 mag case its case bore is seldom, if ever, affected. A first under #8 is expensive enough, but a first over is worse. Nowadays, of course, the good shops trim the mating surfaces and line bore to standard. But you get the point, which is leave it alone if at all possible.

It is possible to damage it by buttoning up the case with the locating pin not in its hole in the bearing. You learn of this because the crank won't rotate as it should while you are tightening the case fasteners. But such iatrogenic damage is evident.

Walt

[Flat6pac]

Walt, You should have been there in 82 when a friend did his own build after having the machinist cut the crank. The machinist cut the #8 and we didnt know it. The man built the engine, 2.7RS and couldnt get oil pressure. opened the bottom and the iol pump seal fell out.
I took it apart and all back together started up and low oil pressure. I called G Fairbanks and he suggested taking a piece of a check and seeing if it would slip into between the crank and bearing. It did, cut 10. I called west coast and got a bearing in, never another lesson there, just lots of reflection..
Bruce