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Crank Main Roller Bearing Fit
Posted: Sat Sep 01, 2018 9:03 am
by Martin.S
Hello, The drive side main Roller Bearing is I believe a LRJ 7/8 or CRL 7 but do we know what the spec of these bearings should be - C2 C3?
Cheers
Re: Crank Main Roller Bearing Fit
Posted: Sat Sep 01, 2018 6:50 pm
by Martin.S
Did a little more reading - C rated bearings have a different clearance between the inner and outer races - std being in between C2 and C3.
C2 is a little tighter than std - would that be OK for the Cranks Main Roller bearing?
Re: Crank Main Roller Bearing Fit
Posted: Sat Sep 01, 2018 7:38 pm
by clanger9
I wouldn't go any tighter than C3. The oil in these engines isn't especially clean...
Re: Crank Main Roller Bearing Fit
Posted: Sun Sep 02, 2018 12:28 am
by Martin.S
But a C3 is looser than a standard bearing
Re: Crank Main Roller Bearing Fit
Posted: Sun Sep 02, 2018 7:41 am
by Mick D
Hi
The clearance should be indicated on the edge of the bearing outer race as a suffix 'C digit', how is your current bearing marked? The absence of a 'C digit' suffix indicates it is a standard clearance bearing.
In the absence of any reference to a specific clearance I'd opt for a standard clearance bearing.
Regards Mick
Re: Crank Main Roller Bearing Fit
Posted: Sun Sep 02, 2018 8:33 am
by Martin.S
I haven't got an old bearing - just empty crankcases.
Re: Crank Main Roller Bearing Fit
Posted: Sun Sep 02, 2018 9:23 am
by Ozmadman
Martin.S wrote:I haven't got an old bearing - just empty crankcases.
Buy one from club spares or AMC classic spares by AMC part number if you are not sure and that will be the correct spec
Re: Crank Main Roller Bearing Fit
Posted: Sun Sep 02, 2018 9:29 am
by clanger9
Martin.S wrote:But a C3 is looser than a standard bearing
If it's slightly looser than standard, you can be certain it won't seize. If it's tighter, you can't be sure.
Re: Crank Main Roller Bearing Fit
Posted: Sun Sep 02, 2018 12:41 pm
by Mick D
clanger9 wrote:If it's slightly looser than standard, you can be certain it won't seize. If it's tighter, you can't be sure.
Hi
In a roller bearing there is an increased tendency for the elements to skid rather than roll as the clearance and rotational speed increases - it's very unusual in my experience for a roller bearing to seize.
I stand by my recommendation of a standard clearance.
Regards Mick
Re: Crank Main Roller Bearing Fit
Posted: Sun Sep 02, 2018 1:14 pm
by clanger9
Mick D wrote:In a roller bearing there is an increased tendency for the elements to skid rather than roll as the clearance and rotational speed increases - it's very unusual in my experience for a roller bearing to seize.
Agreed. Seizure is unlikely.
I'd usually associate C2 bearings with high precision, high speed applications. I was thinking more about possible damage to the bearing from the grotty dirty oil/high temperature environment in the crankcase. A C3 bearing should be well below its maximum RPM in this application (always check with the manufacturer, etc).
How tight were the clearance tolerances on "standard" bearings anyway?