Good Source For Oversized Rod Bearings?

[Cinnabar325is]

Just yanked the bearing caps out in my M20 (was able to buy the car b/c of the rod knock) and discovered a very high mileage block. The block isn't original to the car, so the mileage is technically unknown. Cylinder 4 was doing the knocking, but cylinder 2 was very close to doing the same. 3, 5, and 6 were also pretty beat. Cylinder 1 was the only acceptable bearing.

Either way, I'll be replacing all the rod bearings. I haven't measured the crank journals yet to find out what size bearings I need, but I thought I'd ask about the best place to buy bearings. Hopefully a place that won't make me buy complete sets in one size. I'm thinking 2 and 4 might need bigger bearings then the rest.

Any particular brands to get or stay away from?

Thanks.

[whodwho]

If the crank does not measure up to standard then the crank has to be pulled and all the journals cut under size.

If it comes down to that I have a set of Glyco .25 over rod bearings for you for $25.

[Cinnabar325is]

Visually, the crank journals look pretty good. We'll see for certain when I measure them.

[nando]

Do yourself a favor, junk that crank and find one with lower miles that only needs a polish and can be used with std bearings.

[MR 325]

Do yourself a favor, junk that crank and find one with lower miles that only needs a polish and can be used with std bearings.

Exactly what I was going to say. Internals are cheap for these things.

[whodwho]

LOL, Damn it...I'm never gonna get rid of these bearings :D

[Cinnabar325is]

If the crank does not measure up to standard then the crank has to be pulled and all the journals cut under size.

If it comes down to that I have a set of Glyco .25 over rod bearings for you for $25.

If I need .25 over bearings, I'll come to you first.

Do yourself a favor, junk that crank and find one with lower miles that only needs a polish and can be used with std bearings.

To pull the crank out, I'd have to pull the motor. This is a quick fix and I still have the motor in the car. I just lifted it and pulled the pan. If I can find a set of oversize bearings that match the crank, I should be fine going that route. If I can't, then I might source another long block. This isn't supposed to be a lifetime fix, just something to get the car on the road so I can sort the rest of it out.

[riceh8r]

so i guess plastigauge to check oil clearance is out of the equation. it seems aweful difficult to do this under the car. how are you gonna clean rod saddle and install bearing ? engine stand...easy. on your back, cramped and upside down seems...no bueno.

[nando]

You cant just use oversized bearings, the crank needs cut for that. And if its damaged enough that they physically fit, this isnt even a short term fix. The crank is many times harder than the bearings, it doesnt wear under normal circumstances.

[Cinnabar325is]

You cant just use oversized bearings, the crank needs cut for that. And if its damaged enough that they physically fit, this isnt even a short term fix. The crank is many times harder than the bearings, it doesnt wear under normal circumstances.

You're right, I'm not disagreeing. I know for a lot of American cars (probably older V8 stuff at this point) you can get "oversize" bearings that were made to account for natural wear of the crank. For example, 1, 2, or 3 thousandths oversize. I was looking for something like that when I made this thread.

I've searched around and the least oversize bearing I could find for the M20 was 10 thousandths. So, like you say, that won't work unless I cut the crank.

I measured all the journals today and all are between 2 and 3 thousandths undersized. Visually, they are all okay.

So, I just ordered standard bearings for the car. Won't be as tight as factory spec, but far better than before. Again, I'm not counting on this to last me 30k miles.

[Cinnabar325is]

so i guess plastigauge to check oil clearance is out of the equation. it seems aweful difficult to do this under the car. how are you gonna clean rod saddle and install bearing ? engine stand...easy. on your back, cramped and upside down seems...no bueno.

It really isn't that bad at all, the only one that's tough to reach is the #4 cylinder b/c of the subframe/steering rack. I shouldn't have much trouble cleaning up the journals and saddles. All the pistons are up in the cylinders, so if I rotate the crank, I can reach around it to clean the upper half of the rod bearing surface.

Yes, it would be easier on a stand. But overall, this is far easier than yanking it out to put the motor on a stand. Besides, I already have one motor on a stand and that's enough for me!

[MR 325]

If you're doing this in the car and the crank is not visibly damaged, throw in a set of stock rod bearings.

Don't expect it to last forever but you'll be fine for a while I bet!

[jlevie]

You cant just use oversized bearings, the crank needs cut for that. And if its damaged enough that they physically fit, this isnt even a short term fix. The crank is many times harder than the bearings, it doesnt wear under normal circumstances.

Rod bearings are available in two "standard" sizes (red & blue). From memory the blue bearings are about 0.0003" larger than the red. Main bearings are available in three sizes (yellow, green & white) with about 0.0003" difference between each color. The main purpose of the choices is to account for manufacturing variations during production of the crank shaft. But if indicated by measurement, a larger bearing can be used to compensate for wear.

Note that measurement of a crank journal requires a micrometer that reads to one tenth of a thousandth, i.e., not your ordinary micrometer. And on a high mileage engine you have to check for out of round wear and the crank probably requires polishing before fitting new bearings if the wear is within spec. If a journal is out of round, the crank will have to be re-ground for 0.25mm or 0.50mm oversize bearings.

[nando]

I thought red and yellow were the standard sizes? it's been a while since I bought bearings.

also, as far as I know - all BMW engines are built for the "std" bearings, none of them used oversized from the factory. Red are for early blocks and blue (or yellow?) are for later blocks.

looking up the part #s isn't all that helpful either..

[jlevie]

I thought red and yellow were the standard sizes? it's been a while since I bought bearings.

also, as far as I know - all BMW engines are built for the "std" bearings, none of them used oversized from the factory. Red are for early blocks and blue (or yellow?) are for later blocks..

There is a table in the TIS or Bentley manual that tells you which color bearing to use for the journal diameter. The ideal bearing clearance is 0.0001" per inch of journal diameter. While modern manufacturing techniques good, they aren't that good. So after grinding of the journals the diameters are meausured and the bearings chosen to match. Usually, but not always, one color bearing will work. But occasionally more than one color will be required.