Engine main bearings

[kostean]

As part of preventive maintenance, I got to open up the lower end of the engine and big was my surprise when I saw the condition on the clutch side of the crank bearing were :O

Anyone seen such sort of damage before? For me it looks like the bearing material has been over hardened or defective and had chipped off some bits of itself. These bits actually were at their place as they only separated together with the crank and there is no visible damage at the crank rolling surfaces as far as I can say.

Now though the million-dollar question- what is the spare part number of the main bearings for 390? The parts catalogue enlists separately every bolt and pin- but it can't be true KTM considers as essential part as main bearings not to be serviceable?!

 

[Superpacman13]

You have found my absolute #1 issue with these motors. No replacements I have found, new cases required.

 

[kostean]

I wonder if at new these journal bearings also have some special coating on them or are they just plain metal?

Talked with the local machine shop and they have the rig to mill matching size from hardened material, though it might be tricky. Then again, knowing KTM parts quality, they might not be any special formula/coating even to start with. At least when I am looking at that cracked bearing, I have seen more reliable looking stuff going to my yard tractor, and that things if from 70s.

 

[kostean]

Some guy at the Duke forum actually decided to press out the parts and found these to have a Baja spare code JY541023 even at them and sharing the same spare as Dominar 400 engine.

https://www.ktmduke390forum.com/threads/main-bearings.43765/page-2