Should I reuse these main bearings?

I'm in the middle of replacing a shift fork and rounded off dog on my transmission, which required case split. Engine has 15k miles on it. Maybe 2k miles worth of track days.

Looking at the main bearings, the cloudiness is gone in certain places. I'm not sure if the cloudiness is just a coating that goes away over time, and certain areas being slightly polished is normal wear, or should I consider replacing them? These are the lower main bearings, didn't remove the crank yet as I wasn't planning on disassembling the top end. As far as I know lower bearing usually have more wear than the upper, so this should be about as bad as they all are. This is not a race bike, 80% street / 20% trackdays.

 

What's the condition of the journals? If they are good and money is not an issue I'd replace since you've done all the hard work already. Truth is they don't look bad. 15k miles is peanuts if they weren't abused.

 

Bearings are cheap, cranks are expensive. I'd recommend replacing them while you're in there.

 

crank journals are perfect. Looking at Mahle's wear guide, it looks like the matte coating wear is normal, if it's limited to the center of the bearing, though I do agree with you on the "while you're in there" factor. I suppose it's going to come down to whether I can remove / slide out the upper halves with the crank insitu. I really don't want to tear the top end apart now. My biggest issue is the escalading costs. I can find good low mileage engines for between $600-1000, while just replacing the 2 affected 4th gears (dog and receiving gear) and shift fork on the gearbox is already totalling up to $550, including no reusable items. If I add bearing onto that that's another $300, so if the bearing are OK I'd rather keep them. Again, probably gonna come down to whether I'm able to slide the old upper bearing out without any struggle.

https://www.mahle-aftermarket.com/m...b-2-1114-engine-bearing-failures-brochure.pdf

 

I would rather buy a used transmission, with good forks and gears and replace the bearings. Although I have no experience trying to replace main bearings with the top end still on.

I would guess you could pop off the valve cover and zip tie the sprockets to the chain, to try and keep from messing up the cam timing?

Then you could remove the cam chain tensioner and possibly give you enough room to spin the main bearings out?

 

Personally I’d run those mains. That’s totally normal wear and very light wear at that.

 

I'm in the group of people that are saying, while you're in there...





...might as well "speed it up!"

 

if you can find good replacement motors for $600, and bearings are $300, I wouldn't bother. If you hate dropping motors and doing work, sure it makes sense to replace em. Just grab a spare engine and run it til it blows- if it ever does

 

I’m not sure why this is even a question.

 

If you were going to replace them would you install the same size?

 

I would start with the same size (if you can still see the paint marks) and then measure oil clearance, adjust if necessary. In most cases, the original sizes generate clearance within spec.

 

Thanks was wondering about that.

 

Those things look mint!

 

Part out. You've already disassembled it.

 

Yet I know you would be replacing those if it was your race bike. SMH.