HELP! I-5 crankshaft end-play problem

[Ameer Antar]

I'm not going to argue that race engines are anything like street engines. They do go through a lot more stress, but over a shorter period of time, so it's hard to compare. I will definitely get a second opinion (more like 7th or 8th!) before I run the motor. After talking to the dealer and Rod at TPC, I'm now wondering if this is an MC/KH issue. My KH originally came w/ the 4-piece steel thrust washer set. Rod says he thinks the MC originally did not come w/ the 4-piece t-washer set, but used the current design of thrust surface built into main bearing #4. Can anyone who's rebuilt or opened up an MC bottom-end verify this? I wonder if this is the issue, b/c using the old style t-washer set takes the clearance within spec. Anyway, I have left some comments to your comments below...



---Original Message---
>According to Federal Mogul's book "Engine Bearing Service Manual" - and I'm 
>willing to bet that Federal Mogul knows a LOT more about bearings than your 
>race guy, on page 114 they have a fabulous picture of a set of bearings 
>assembled with insufficient clearance - and it is not pretty.

what type of clearance was this.. journal or thrust? Also what I've done is to actually avoid having insufficient clearance. Not having enough clearance would quickly heat up and destroy the bearings and possibly the crank. Initially the crank was too tight. Now that the thrust surfaces are sanded, the crank spins nicely.

>The babbitt metal not only provides the bearing surface, but it "catches" 
>bits of abrasive material (grit, sand, metal), and "heals" over it, keeping 
>the crankshaft from being scored. In severe cases, the grit is too big to 
>embed into the babbitt, and the crank will be ruined anyway. If you have 
>removed the babbitt, anything that gets in there will be held by the 
>copper, just like a cutting tool in a lathe, and it will ruin the crank in 
>short order.

I'm pretty sure that copper and babbitt are not very apart on the hardness scale. Anything that can score steel, such as a grit of sand, will be hard enough to "sink" into copper as well as babbitt. In fact there was almost no layer of babbitt on the thrust surfaces, b/c it was removed after only a few passes w/ the sand paper, so the particle would be sinking into the copper mostly anyway. Also, I'd think it is much easier for a particle to get caught in a horizontal surface, like the journal area, than a vertical surface, such as the thrust surface; and also the rotation of the crank will push most of the oil and particles back into the oil pan to be filtered out. Keep in mind the original design used steel thrust washers which would cause even more wear if a particle got caught in between.

>
>There are several bearing technologies which use different combinations of 
>different metals, but if the bearing is sized correctly, you will NOT need 
>to sand anything to fit - someone has given you the wrong parts, or the 
>crank was cut incorrectly or SOMETHING - but this is NOT right!!!!

I double checked w/ Rod at TPC and it's definitely the right part... the crank was not touched on any thrust surface. Even if the crank grinder nicked it and ground it to smooth it out, I'd have the opposite problem... too much clearance.

>
>If you want this engine to live, find out why it didn't fit together 
>properly the first time. And engine that won't turn, won't run. Besides, if 
>the extra coating wasn't needed, why does the Audi accounting department 
>let them get away with it? It costs money to apply, and more money later to 
>remove. And it slows down production if each thrust bearing has to be 
>hand-fitted.

The bearings are plated w/ the babbitt coating. It would cost more to only coat certain areas of the bearing, and I think it would also cost more money to remove the coating once applied on the thrust surfaces. Although I agree the intention is to have all surfaces coated, I'm not sure how important this is on all surfaces.

>
>The thrust bearing takes the entire load of the clutch springs (when you 
>depress the clutch, think where the effort goes!), and it locates the 
>crankshaft fore and aft in the block. If the bearing fails, the entire 
>engine will become scrap pretty quickly.
>

BTW, this is an auto. I don't think that makes any difference in clearance tolerance; at least I don't see anything in the Bentley.

Thanks again for the interest and concern.
-Ameer