Rumbling noise from main bearings?

[Seek]

Hi guys, I'd like your opinion on this one. I am, rebuilding my R69 engine. Crankshaft was professionally done in Germany because the rear main bearing seat was worn out. Big end bearings were deemed to be perfectly allright.

When cold the crankshaft rotates very nicely. When heated up it makes sometimes(!) this weird rumbling noise. It seems to come from the rear main bearing. I used a NOS 20207M C3 bearing. There is no unusual amount of play in the bearing, radial something like 0.01 to 0.02 mm when cold.

What do you guys think? The noise is not always there. Will it disappear? Just some dustspecks in there? Or pull everything apart again and try again with a new bearing?

Link to video. Heated up to 100 degrees. Bearing well oiled. https://www.youtube.com/shorts/8Kkzg9s5ipE

[Seek]

And this is today. 100 degrees again (Celsius). I can hear the gears which have allready been installed but the weard rumbling noise of the bearing is not there. Call me confused....

https://www.youtube.com/shorts/UsuzmyJdMOQ

[vechorik1373]

When assembling an R69 - R69S and R50S engine, with the barrel roller bearing it is very important to get the outer race of the bearing positioned exactly over the inner race during assembly. Because of the design of the barrel roller bearing, one can physically push and pull the inner race, with the captive rollers in and out of the outer race quite far. If the bearing is carelessly installed, and the inner and outer races are not aligned, it will cause the barrel rollers to to pinched from this misalignment, the bearing will feel rough when hand turned,and will cause premature bearing failure. This is the tool that must be used to insure that both races are in line with each other, when the crankshaft is drawn forward in the case, after it has been installed in the empty case. After one gets the crank laying in the case, but not yet installed in the rear main bearing carrier, you slip this tool through the carrier, and install it on the end of the crankshaft, and use the bolt that holds the flywheel on the crankcase, to hold the tool in place.
Then the case must be heated, and the crank installed in the case, too deep, on purpose. After the front main bearing carrier is installed, the crank must to drawn as far forward as it will go, and the tool will keep both races exactly in the correct position.

You may want to consider removing the flywheel, and do a depth measurement in the case of the outer race versus the inner race. I they are not both at the same depth in the bearing carrier, you may have to disassemble the whole engine and start over with the reassembly.
If the outer race is higher than the inner, it can be driven deeper tot he correct position without tearing the complete engine back down.
However, if the outer race is found to be in the carrier below the inner race, you have no choice but to take the engine apart and start over.
This is the tool I am talking about.

[Seek]

Yes I have such a tool, made from brass way back in the IBMWR mailinglist days.

But I used a slightly different installation method. Your method seems more logical for the barrelbearings. Overhere in Europe it is now more often advised to use a different method: Put the crank in the case with the rearbearing not in the bearing carier yet. Then first heat up the front bearing carrier with front bearing and install it fully on the crankshaft. Then with a very hot case push the crank back into the rearbearing carier and at the same time the front bearing carier is inserted into the case. This method puts less stress on the front bearing. But it could indeed slide the 20207 bearing out of alignment!

Anyway, I meassured and both races are equally deep (within 1 thou). Maybe they were out of allignment and all my heating and pushing and turning pulled them back into the right position? I don't know, they are precisely alligned now, not the result of sheer luck I'd say.

Greetings and thanks for the good advice as always Vech!

Kees.