Crank bearing conditions?

Going to go grab some plastigauge tomorrow before progessing further with my rebuild and was examining the crankshaft shell bearings. My crank looks great, but I'm wondering how the shells look for a bike with nearly 40k miles. What overall condition would these appear to be?

 

in my automotive experience, I would say those look great.

FU

 

Bike hasn't shown any issues in this respect, so I'm hoping the plastigauge is satisfactory.

 

If you can feel any roughness with your finger then replace them. I'm mainly concerned with the two that have visible scratches. Otherwise they look good.

 

Yeah, those were the ones I was more concerned with.

 

Yes, that bearing in the first picture looks iffy, AT BEST.

 

What is this this number on the rear of the shell? Are these numbers specific to a bike or an actual item number?

 

Those are the manufacturer markings that ultimately correspond to the Yamaha part number/ color. DO NOT mix your bearings up as there is (to my knowledge) no comprehensive cross refrence for those numbers (I have seen different numbers on the same size and type of shell). The journal size numbers are engraved in your crankcase, and the crank journal sizes are inked onto the end of the crankshaft. The method for determining bearing shell size for your case/crank combo is covered in the Information Overload Hour (or in Len's catalog page for engine parts; I forget which), as well as in the factory service manual.

The "easy" way to tell shich shells you have is to look for a band of color along the edge of the shell at the midpoint. Usually the color is mostly gone after sitting in oil for 30 years, but you might get lucky.

 

Yeah, unfortunately my upper engine case has been repainted, covering the etched in writing. Bottom crankcase has "324" and nothing more etched in.

 

See my edited post, and get some paint stripper handy in case you can't find color on the bearing shells.

 

Believe I got lucky. Kind of difficult to see, but 34324.

 

So based off this, my crankshaft shells would be the result of 42343-21222, with 42343 being the sequential reverse of 34324. That would give me 21121 = black, blue, blue, black, blue.

 

You got everything correct!

 

Perfect. I can sleep now...

 

No rest for the weary.........it's time to calculate your rod bearing colours.

 

When reinstalling the shells should you oil the rear of the shells too or just the front? Wasn't sure if the additional oil would make any difference.

 

I use cam lube, only on the bearing surface and not the rear which seats in the journal.

 

I pre-lube the backside just to help the shells roll into place better.

 

Plastigage came out great. All clearances within spec. Outsides a touch "thinner," but still good. Nice feeling.

The two shells have a scratch, so would replacing them be a bit touch and go? I'd hate to replace a shell with a slight scratch and risk messing up the clearance, despite replacing with the same color...

 

It's your call. Clearances increase with wear, so new shells in those positions will bring things closer to being within spec. The only concern with the scratches is if they stand proud of the shell, or are deep enough to let too much oil get pushed away from the bearing. In both cases you will have accelerated crank journal wear (which costs a lot more to fix).

The one in the first photo is concerning because of it being angled. It will act as a channel for the oil film to be squeezed out too quickly, which may cause contact between the bearing and the crank journal.

 

I can't be the only one that thinks "pre-lube the backside" is funny!
Anyone?

Damn. I got problems.