Engine bearing help

[AlanB]

Hi Trbig,

The bearing "sizes" in the colour codes are NOT designed to take up wear; they are "tolerances" on the one size, to allow the original builders to set the bottom-end up as close to pefection as possible..... to "blueprint" it; That is why these motors will last for over 100,000 miles.... so long as you keep decent oil in 'em!

This discussion started over here when one of our members got a full,new set of all of the colours of bearings to rebuild his engine. He had great difficulty in measuring ANY difference between the colours...... and he IS an engineer. He then found the chart which I copied above.

Oversize (+0.010") shells would need a reground (undersize!) crankshaft, and the factory never offered specs or parts for that......

Over on this side of the pond, I have heard of specialist engineering companies who WILL regrind cranks, and match up (or manufacture?) shells to suit, But I would attempt to just find a decent bottom-end and run it; The guys at Yamaha were better at building these than I will ever be!

Hope some of this helps someone!

AlanB

[79XS11F]

I did my bearings as per the original colors /sizes. If there's anything Japan could and still can do ... it produce high quality steel. Japan was and still is a world leader of steel production of very high quality.
The bearings are rather soft compared to the steel so unless a bunch of grit made its way into the bearings the crank will have taken very little if any wear. Replacing with original size bearings will therefore return the setup to as close to factory specs as anyone could ever hope for in their garage. You can't go wrong replacing with stock sizes.
Rob

[AlanB]

Hi Rob,

I have certainly found in the past that "stock" sizes on a high-mileage motor comes out right at the top (or just outwith!) the recommended tolerances........ Nothing to worry about (much tighter than most cars!) but not right........

In each case (with ALL Japs..... not just XSs!) the bigger shells have given better results (measured by plastigauge!)

The sizes are so close to one another that the running-in process will just about move you up a size!

AlanB

[mro]

That's what the plastigage is for

Have rebuilt a few lower ends.
Used color code as per manual and checked em.
All were in spec and as far as I know are still running strong.

To NOT check after installing new bearings is asking for trouble even tho mine worked out just fine it's always worth the time and peace of mind. Would not count on a "too tight" bearing fit to wear in. Might just gaul and self destruct.


mro

[AlanB]

Hi mro,

You are right; too tight a bearing fit will NOT wear in. However, my experience has been that most engines need a heavier shell once run; You may either have worked on better engines than me, or be better at measuring! LOL

AlanB

[Bullet]

For what it's worth ..

I got into looking over the cranks and rods yesterday to see which ones I was gonna use for my rebuild.. ( got 3 engines now )

Out of the 81 engine , all 4 rods are stamped "5G6"

The matching crank is stamped

2-2-2-1

The first 3 rods contain original green bearings, the 4th is not readable by colour, but should be yellow by the info given in the manual , so my guess is they used the "6" as the correct number for the rods and not the 5 ..

[79XS11F]

Originally posted by Bullet
For what it's worth ..

I got into looking over the cranks and rods yesterday to see which ones I was gonna use for my rebuild.. ( got 3 engines now )

Out of the 81 engine , all 4 rods are stamped "5G6"

The matching crank is stamped

2-2-2-1

The first 3 rods contain original green bearings, the 4th is not readable by colour, but should be yellow by the info given in the manual , so my guess is they used the "6" as the correct number for the rods and not the 5 ..

Hey ... Where's Hockey Valley Ontario?
Rob

[mitch]

New Bearing Set on Ebay

Check this out
http://cgi.ebay.com/ebaymotors/New-O...em380008904632
Good luck
Doug

[trbig]

Shhhh... leave this one alone! I am needing it and have bid on it a bit already! lol

[trbig]

Holy Crap!!!

Apparently I didn't need those crank bearings THAT bad! Has anyone ever seen a set go so high? $141.50!!! I can go to Yamaha and buy a motor full of them for cheaper than that. I realize it's a whole set... but crap!

Tod

[DiverRay]

Tod,
I was also bidding on them, but it went to rich for me as well. I have two engines that I'll be going through. One soon, and the daily ride in about 20K, once it has 120K on it!

[blue giant]

Originally posted by trbig
Holy Crap!!!

Apparently I didn't need those crank bearings THAT bad! Has anyone ever seen a set go so high? $141.50!!! I can go to Yamaha and buy a motor full of them for cheaper than that. I realize it's a whole set... but crap!

Tod

So you think I paid too much for them?

[randy]

I don't think you paid too much at all. Take a look at the over-the-counter price on those bearings. When you're done with the ones you need, you can sell the leftovers and you'll come out ahead of the game.

Bikebandit: $274 to do the whole crank. Ouch.

$32 per rod

$25 per main

$46 main/thrust

[blue giant]

Originally posted by randy
I don't think you paid too much at all. Take a look at the over-the-counter price on those bearings. When you're done with the ones you need, you can sell the leftovers and you'll come out ahead of the game.

Bikebandit: $274 to do the whole crank. Ouch.

$32 per rod

$25 per main

$46 main/thrust

I'm just joking around. I was out of the running as soon as they went over 50 bucks.