Rod bearings

Hello every one:

I need too replace my rod bearings in my Kz650 1977. The repair book is telling me too look for numbers on the crank and the rods. Where do i find the Numbers? Does the number on the back of the rod bearing have any useful meaning? The book also gives the spec for the rod bearing size. How do you go about measuring for that size? I bought some plasti gauge but the bearing have too be replaced first. I have all the tools to do it. I'm just not sure what dimension that I'm looking too measure.

Is there only one size main bearing? As these will be replace at the same time. I seen that on the back there is a stamping on the back of a number and Std. So i was not sure if there was other sizes.

The bike has low miles on it around 12000. I never heard it run but I plan on racing it next year so I want to know whats going on with every part of the bike.

Thanks for all your information thanks Scott

I alse recall the manual talking about the numbers on the crank to denote soecific thicknesses but I never looked for them.

I can't imagine a KZ would have measurable wear on the main bearings at 12k miles, but I suppose it's possible. If I was doing it, I would plastigage the journals first to see if there is any wear. If not, keep the originals intact.

Hello there is a little bit of scoring at or difference in color, I would keep them but i did scratch them with my caliper when i was trying too measure them.

I have done rod bearing on older BMW's with those bearing you have too make sure you do not touch them with your fingers. Be cause the oil on your skin will etch the bearing surface, I have seen it. It will leave a finger print on the bearing surface. Any one encounter that with kz bearings?

Thanks Scott

plastigague them since you are blueprinting a hammer

babbit bearings etched?? without acid or base chemicals? I say NO
they are soft but not that delicate

man what does old engine oil do to them if finger oil ruins them?? (don't answer that, it's retorical)

you are worrying about things you don't need to.

4 different sizes each so you'll need to buy 16 different sets to get this done.
good luck

The "std" means "standard", as in factory installed. Kinda like a "standard" piston as opposed to an oversize one. As far as bearing clearance spec's, I don't know where to find that.

I have the FSM and it gives all info on rods and mains, what do you need to know?

Post edited by: Bluemeanie, at: 2008/02/19 15:34

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Post edited by: Bluemeanie, at: 2008/02/19 15:44

Post edited by: Bluemeanie, at: 2008/02/19 15:48

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I dont trust plastigauge, I prefer to mic the crank, the rod and the rod with the bearing, this will give you the best results, plastigauge can lie to you.
Also, you are not going to ruin the bearing surface with a finger print, the clevite coating on the bearing surface is very durable.

plastiguage sucks. it doesnt give you accurate or reproducable results. measure everything and set the clearance to what it is supposed to be. you cant do this with a set of calipers. you need a micrometer (actually 2) with special tips and a bore guage
measure the crank, measure the cases, measure the rods, then install the correct thickness of bearing inserts to get the proper clearance accross the board
do yourself a favour and get the proper tools to do it correctly
have a look at the following list, it will make your life easier, then you wont have to worry about guessing at what insert to put in

Harbor Freight:

item 94873-2vga
1.4-6" electronic bore guage

item 95918-0vga
mic stand

McMaster-Carr:

economy electronic outside micrometers:

0-1" accurate to plus or minus 0.00016"
item 2091a5

1-2" accurate to plus or minus 0.00016"
item 2091a6

tips:

item 2313a12

oh i allmost forgot, match up bearing inserts that are the same thickness, dont go by colour as every now and then they can be painted wrong. dont mix bearings of different thicknesses to get a clearance. match up the thicknesses and find a matched set that gives you the proper clearance.

use plastigauge to check your clearances afer your machine work if any is done to make sure youve got right pieces as you start final assembly;)i know the oil from fingerprints will cause bare metal pieces to rust,polish a piece of steel and touch it with your fingers and watch rust fingerprints apear