Mag Side Bearing Race Issue

[RManson]

Check the pics. Very few miles on this motor and the mag side crank race is looking pretty beat. I have a few ideas as to what could have caused this but before I go down another rabbit hole, thought I'd ask and see if there's a common issue that might be arising. My bet is on the bearing not being centered on the race but I would have thought the race to be hard enough so as to resist the damage that is being seen. Thoughts? Naturally it's going to take a new mag bearing as they're mated to the race from what I understand, but would like to try to solve the issue before it goes back together.

Bearing was an NU2205 from a reputable dealer.

IMG_6244 by PotvinV8, on Flickr

IMG_6243 by PotvinV8, on Flickr

IMG_6242 by PotvinV8, on Flickr

IMG_6241 by PotvinV8, on Flickr

[garry inglis]

There dosent appear to be any heat build up on the race could just be a crap bearing worth getting the crank checked for balance and twisting which can pull the piston more over to one side

[Muppet]

NU2205 C3?

[HxPaul]

You say you got the bearing from a reputable dealer,but is the bearing a reputable make ?.................Muppet said NU2205 C3.The drive side bearing is the C3 bearing,not the mag side.

[steve c]

did anyone heat the bearing inner to get it on, looks like the surface may be blued from overheating and softening the hardened surface. Heat from a flame can damage hardened surfaces. The other thing could be dirty grease carrying grit or the one in a million bearings with a bit of metal debris or a pitted roller.

[Adam_Winstone]

With the big-end eye protruding so far beyond webs, did you have the back of the casing welded and trenched for the back of the rod to clear the casing? I've had this done to a number of cases and have frequently found that the heat distorts the alignment across the casing so puts the drive side and mag side bearings out of alignment. This misalignment would end up with the components stressing each other to try to be the determining alignment factor and I wonder whether this could cause such damage?

You may not have had the casing welded so this might be easily discounted.

If you have had the cases welded, the alignment issue often shows itself in a misalignment of the engine mounts, difficulty lining up the engine mount bolt, premature failure of engine mount, or rear wheel being off centre to the back of the frame when viewed from behind.

Adam

EDIT!!!! Sorry, Ryan, I've only just noticed that you posted this, which gives me an idea of which motor it is from! As such, heavy casing welding is likely. Have you checked for misalignment/warping of the cases? If your's is suffering this then I'm very likely to suffer it on a couple of motors that I have some warping on.

[Daggs]

Obvious I know, but you did grease the bearing after installation?

[RManson]

Thanks for all the replies!

I can't remember heating the race during installation, but I may have had to and that could very well have softened the race. I don't recall the installation being an issue, but that doesn't mean it didn't take a little heat to drive it on. I will definitely keep this in mind for the next one!

Bearing was an SKF/FAG brand. Greased before going in.

Adam,

You share my thoughts on the alignment of the crank bearings. I need to chase that down and investigate further for sure. As you know there was a large amount of welding on the case, though I was very careful to keep the heat down and used jigs and fixtures in the hopes of keeping things in line. Doesn't mean things didn't move slightly however so I will be looking at that very closely. I never noticed any indicators of things being out of line and the crank installed nicely and turned over very smooth once installed. I would think that an alignment issue would display itself in a knackered bearing and increased vibration, but the bearing looks brand new and the engine ran smooth. But what do I know? Looks like I'll be getting out the dial indicator to check the alignment at the very least before swapping out the bearing and seals.

I'll update as soon as I find anything out. Thanks!

[Muppet]

is the mag bearing an NU2205 “C3” ? only ask as I have seen this happen to bearings that ran too tight a clearance; the mag bearing dont like to run tighter than a C3 clearance; more so on higher powered engines that make more heat with the extra loading on the bearings;
hx paul is right the standard drive bearing is a 6305 C3 a lambretta also runs the same C3 clearance at the mag bearing sometimes marked as C3 or on some bearings a series of dots after the bearing number
think adams right with the welding distorting the cranks bearing journals
muppet

[RManson]

Muppet,

Looks like the bearing is an NU2205EG15J30. I don't think it's C3 with the larger internal clearance. Is the C3 designed for slight misalignment?

Looking at a NU2205-E-TVP2-C3. Anybody use one?