HELP! I-5 crankshaft end-play problem

[Fred Munro]

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


-----Original Message-----
From: quattro-bounces at audifans.com
[mailto:quattro-bounces at audifans.com]On Behalf Of Mike Arman
Sent: February 4, 2004 8:37 AM
To: quattro at audifans.com
Cc: Ameer Antar
Subject: HELP! I-5 crankshaft end-play problem



>Ameer Antar <antar at comcast.net>
>Subject: Re: HELP! I-5 crankshaft end-play problem
>To: Quattro List <quattro at audifans.com>
>Message-ID: <20040204061951.CF1145F5C4 at audifans.com>
>Content-Type: text/plain; format=flowed; charset="iso-8859-1"
>Well, I talked it over w/ the race shop where I got the block machined and
>they told me I could have the crank ground down or just sand the bearings.
>They said they always sand the thrust surfaces of the thrust bearings when
>building a race motor to take any inconsistancies out of the surfaces.
>Grinding the crank would probly cost another $50 and maybe 3-4 wks as
>there's only one crank grinder here in CT. With all that I took my chances
>and sanded down the bearing shells on the thrust surfaces. I used the
>bearing cap to support the shell and wet sanded w/ 600 grit paper. After
>putting it all back together, I'm right on the money w/ .006" end play.


>  Even though the silvery surface was removed and copper showing
underneath,


This is _wrong_ - the silvery surface is the bearing material and the
copper underneath is the backing.

There's an error here somewhere - if these are the crank and block that
originally came together, and just the rod bearings have been ground, it
sounds like someone gave you some incorrect thrust bearings (too thick).

Don't assemble the engine this way - this one is NOT going to last. Find
the error - the copper usually only shows up AFTER the bearing is *already*
worn out.

I'm not trying to make you unhappy, either - but you'll be a LOT unhappier
if you put this engine into the car and it fails quickly and expensively.


Best Regards,
Mike Arman