Replacing Main bearings - any ideas?

[DAVINCI]

Guys, (and gals). I'm posting this because i got a response on my parts for sale posting. This member is asking questions about main bearing selection and replacement.

Not wanting to steer him wrong, please post your knowledge about this subject. My own experience with replacing mains is also part of this message trail. Top message is the most recent. Thanks.

HIM: Bearings.
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What are NOS Blue? I've saw the term but have no idea what it means. I'm interested, I get paid Tuesday so if you have what I need consider it sold.
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ME: Bearings are sized by color code, with BLUE being the tightest ever available for these motors. If your motor is worn, these are the only choice. I put a set into my motor three winters ago and this set is extra, and I'll never use them. I also have two rod sets, also BLUE.

IF you could get these ten bearings, the set would cost $250, I'm asking $100. If you want the two rod sets, make it $120. If that suits you, my paypal is:

HIM: Well, my current bearings didn't show much wear, but they had gouges in them, so I don't think blues would be right. When you say tight, how tight?

ME: How tight. Hmm. Well, All I can say is that my motor had 60K miles on it and originally had BLACK main bearings. I got a suggestion from Tod, (TRBIG) that if you're changing bearings the only way to go is with the BLUE. He was right, I plasti-gauged these and they fell right in spec.

If your bearings have gouges in them, they are toast regardless of the color or clearance. Gouges usually point to filthy oil, too few changes or running without a filter. Could also be the bearing flaking and chewing itself up.

[Yard Dogg]

I found a section in my XJ service manual which tells me how to identify the factory bearings installed. It says to subtract the numbers on the journal from the numbers on the upper case half. My case numbers are 55 555, my crank numbers are 11222. So I come up with 44333. Which means I need 2 greens and 3 browns. The bearing colors are listed as this: Yellow, Green, Brown, Black, Blue
Other sources I've read have indicated that yellow is the thinnest bearing and blue is the thickest. If you're reading this post for info, keep in mind that your case and main numbers will be different than these, so use your own numbers to order bearings.

[DAVINCI]

Those numbers were stamped when the motor was new and only tells you what was installed then. You will have to measure the clearances to know what you need to install today.

[DGXSER]

That is the fact. You have to know what the gap is now. An option might be to clean up the bearings that are in use now, plasti-gage them to see what the gap is, measure the bearing. And now you have the total picture, at least where you gauged them. Then you can add the two thicknesses together, subtract the spec clearance, and know the thickness bearing you want to put in.

[DAVINCI]

Yup, no different than any crank or rod, there's no magic here, but Yamaha DID make a confusing mess out of it with the whole color and stamp crapola.

[Rasputin]

My thought is that if I had a motor that far apart and wanted it to be like new, I would order the blue bearings. Then after checking everything out, if it was too tight you could always get the crank turned. That way you could have "as new" clearances on all the bearings. Any good machine shop should be able to have a bike crank ground the same as any car motor is done. After all many cars have smaller engines in them than these bikes.
On another note, I have heard that the Ford Focus 2 litre engines have rings that will fit our bikes. I have yet to check it out but if they do it would mean we can get stock and oversize rings for our bikes. Doing a ring job plus new bearings in the rods and crank would be awesome. Just need to find new pistons that are available if the Ford Focus rings work.

[Yard Dogg]

I'm just going to order some browns. My other bearings weren't bad at all as far as normal use, and the crank journals are great.

[DAVINCI]

Well, alrighty then. I'm glad you've come to a logical conclusion based on good engineering practices. Good luck with that.

[Yard Dogg]

My crank journals are not in question, at all. Yes, you can order standard sized bearings that came in your bike if your previous bearings show little wear. If I buy a set of blues, they will more than likely be too tight, so why would I waste the time? They are not the standard size that came in my bike. If your bearings are worn out, then you may need to plasti-gauge them to find the right clearance, in my case, it's a waste of time.

[crazy steve]

...Yamaha DID make a confusing mess out of it with the whole color and stamp crapola.

I'll wholeheartedly agree with that. After reading the 'procedure' in the FSM, several things come to mind. One, if you have any crankshaft journal damage, throw the crank away and get another one. As a practical matter, I doubt if you could have any machine work done on the crank other than possibly having it micro-polished and even that may be iffy given that the allowable clearance 'range' is only .0008". Ask a machinist if they can take off a couple of ten-thousandths only, I suspect the answer will be no.

Two, Yamaha isn't showing any of these bearings as being 'undersize replacements'. The entire procedure is to ensure that you reinstall the same bearing as original. Note that there's no explanation of which size bearing to use if the clearance is out of spec either loose or tight.

Three (and this is most intriguing of all) is Yamaha identified the bearing saddles. This tells me that the holes the bearings fit into aren't all the same size by some unknown amount. If a particular placement uses a thin 'yellow' bearing, is that a 'large' journal in a 'large' hole, or a small one in a small hole?

Bottom line IMO? At least make the calculation for bearing size; going from yellow to blue may be too big a step. Definitely check the 'before' clearance and absolutely check the 'after'.

[petejw]

there was a large write up on the uk site,
i think it was shapps, the bearing colours only came
into play when the engine was new,
from memory they did a check using plasti guage
with the difference size bearings and it was determined
to go with the thickest. apparently theres not that much of
a difference between sizes,
hopefully some1 on the uk site will confirm and chime in.

[TomB]

The different colour sizes of shells are nothing to do with being able to regrind the crank, they are for selective fitting of the same size crank that has been machined to machining tolerances. As Steve has said, you will not find a machinist who will offer to reduce your crank journal in diameter in so small differences, (I used to be a machinist people went to)

If you have a used crank the best shells to use are the ones with the smallest diameter, as your crank will be under the machining tolerance from use. Machining tolerancing is the plus or minus sizes given to a size I.E. if you had a 2.00" journal + 0.00" and -0.02" you could end up with a crank 2.000" up to 2.002" so different size shells would be used for selective fitting.

There is a much more detailed explanation on the UK site.

Tom (Toolmaker for 18 yrs, now Mech Fitting Tech at GlaxoSmithKline)

[DAVINCI]

The different colour sizes of shells are nothing to do with being able to regrind the crank, they are for selective fitting of the same size crank that has been machined to machining tolerances. As Steve has said, you will not find a machinist who will offer to reduce your crank journal in diameter in so small differences, (I used to be a machinist people went to)

If you have a used crank the best shells to use are the ones with the smallest diameter, as your crank will be under the machining tolerance from use. Machining tolerancing is the plus or minus sizes given to a size I.E. if you had a 2.00" journal + 0.00" and -0.02" you could end up with a crank 2.000" up to 2.002" so different size shells would be used for selective fitting.

There is a much more detailed explanation on the UK site.

Tom (Toolmaker for 18 yrs, now Mech Fitting Tech at GlaxoSmithKline)

Could not have said it better myself, but that's how Todd explained it.

[DGXSER]

If you have a used crank the best shells to use are the ones with the smallest diameter, as your crank will be under the machining tolerance from use.

Meaning the thickest actual bearings? Assuming the outer diameter of the bearing remains the same, increased thickness giving a smaller inner diameter.

Now, I would still maintain that the best solution would be to take the measurements and know the real answers which may only confirm this suggestion, but you will know and not be guessing. However, if your going to take a SWAG (Scientific Wild Azz Guess) at it, this would seem to be the safest approach.

[Yard Dogg]

The bearings are a much softer material than the crank journals, so if the bearings are barely worn, then just put the factory size in. If my bearings were worn out, I would feel inclined to plasti gauge them to make sure the bearings will work. I am not guessing. I know what came in the bike, substantial evidence suggests that I am safe to use stock bearings, there is no guess work here. If I were to order the thickest set, that would be the guess work.

If my bearings were worn out, I would feel inclined to order thicker bearings and go from there.