HELP! I-5 crankshaft end-play problem

[Ameer Antar]

Thanks for responding guys. I too am normally on the cautious side, especially since I have no real experience rebuilding bottom-ends. I took the bearing shells over to the race shop and talked with the owner. I told him how everything now has the perfect clearance, but my concerns over having the copper showing. He told me he sands the thrust bearing shells for all the engines he builds. He's been in the race engine business for over 20 years and never had a problem with that. He even showed me a race engine he was building that had the copper showing on the thrust surfaces of the bearing shells.

At first, I was a little worried myself, but now with all his assurances and experience, I'm going to go with it as is. I figure if a race engine, which will see much more rpm's than mine ever will, can handle sanded bearings, mine will too. Now that I think about all those metals, copper is a bit harder (not much) than the babbit coating on the shells, and the original thrust washers are some sort of steel, so actually the OE design dictates an even harder surface than babbit or even copper. I guess that means w/ the new design there will be more wear in the bearing shell thrust surfaces than the crank's. I guess thrust surface wear is not a huge issue... certainly not as big an issue as journal surface wear which directly affects oil pressure. I hope everyone knows I only sanded the thrust surfaces on the side and not the journal surfaces of the bearing. The shop owner did the machining on the bottom-end, and he's guaranteeing it. So, doing this is sorta like doctor's orders. I'm planning on running the motor in this body for a while, then transplanting it to a nice clean quattro shell (if there is such a thing) when funds and a good opportunity turn up. So I guess I'll found out how much difference in wear there is then. I really appreciate all the advice and concern; really shows people care on this list... I'll be sure to let you know of any future troubles.

-Ameer


---Original Message---
From: "Fred Munro" <munrof at sympatico.ca>
Date: 2/4/04 7:59:53 PM
Subject: RE: HELP! I-5 crankshaft end-play problem

I'm with Mike, Ameer.

Typical bearing construction is a steel shell covered by copper plating
which in turn is covered by a soft babbitt type metal.

The crank is never meant to contact the bearing surface - in an ideal world
there is always a layer of oil between the crank surface and the bearing
surface. In operation, the crank is supported hydrodynamically on a high
pressure "wedge" of oil constrained between the bearing surface and the
crank surface. In our non-ideal world, the soft metal on the bearing
prevents damage to the crank on those occasions when they do touch, but more
importantly allows any hard particles in the oil to sink into the soft
bearing metal, keeping them from scoring the crank. If you look at bearings
from a high mileage engine, you can sometimes see these particles embedded
in the bearing material, particularly if the owner wasn't too particular
with oil & filter changes.
You have just sanded off this protection.

I'd be inclined to find a bearing that fits or surface the crank to fit the
bearing.

HTH

Fred Munro
'94 S4