Assembly lube on main crank bearings before dropping in?

Greg Narvas · Joined: 31 May 2012 Posts: 50

Currently rebuilding my cr125 stock moto. I'm about to install my crank bearings but do I need to apply assembly lube on the outer bearings before dropping them in or do they drop in dry?

Chris Reinhardt · Posted: Fri Dec 21, 2012 4:48 am Post subject:

If your rebuilding a stock moto, then you're using OEM Honda bearings, right? They have a chunk of lube inside them, I usually flush that out. A 2 stroke motor carries oil in it's fuel, it can't run without fuel, so if the motor fires, that means that fuel/lubrication has already washed the bearings.

CR
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Sam Zavaglia · Posted: Fri Dec 21, 2012 6:42 am Post subject:

Bill Pyles · Posted: Tue Dec 25, 2012 6:26 pm Post subject: crank installation

I always have the crankshaft bearing journals sanded down on a lathe to the point where a main bearing slip-fits onto the journal at room temperature. You will of course have to heat the case halves and cool the bearings to install the bearings into the case halves, but with the crank journals sanded, the crank will drop into the bearings easily so you can torque the case halves together without bending the crank.
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andy graham · Posted: Wed Dec 26, 2012 5:00 am Post subject:

put the bearings in the freezer overnight, they'll drop right in.

Greg Narvas · Joined: 31 May 2012 Posts: 50

ok thanks guys. But from what I'm understanding, there should be no lube on the outer part of the bearing (where the bearing meets the case itself)?

Benn Herr · Joined: 18 Jul 2001 Posts: 1579

Right, clean and dry on the outside of the bearing. Make sure the case is free of debris too.
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Sam Zavaglia · Posted: Wed Dec 26, 2012 7:30 pm Post subject:

J.R. Clasen · Posted: Fri Jan 04, 2013 12:49 pm Post subject: to lube or not to lube

Lubricating the bearing outer surface is always a good idea, espceially when the two mating surfaces are dis-simular metals (alum & steel in this case). This will make it a lot easier when you have to press the bearings out the next time you rebuild.
As suggested earlier, put the bearings in the freezer over night; heat the cases to the point you have to pick them up with a shop towel, and then drop the bearings in. Make sure you have a soft mallet standing by just in case you get one crossed up when you drop it in, they can get stuck pretty quickly so sometimes you need to give 'em a tap in. No metal hammer though!
JR