KZ650 Crankshaft Bearings & Con Rod Bearings Identification

Hey all,
Long time KZ lurker.

Rebuilding the bottom end of the KZ, wanted to get new bearings, but found that.. whoa. There are different sizes, and its seemingly difficult to find out what part numbers you need to replace bearings with if you dont already know which bearings are in the bike.

Ive got a KZ that I cannot seem to identify the needed bearings for the connecting rods or the main bearings.
Information I do know:

• On one of the connecting rod journals I see a black mark on the side, others are worn.
• I dont seem to see any distinguishing marks on the upper or lower crankcases front side (looking for a 1 or a 0 somewhere, or maybe no mark?)
• Existing main crank bearings when measured with a caliper measurement tool read about 1.46mm across the board
• Existing main crank journals read out about ~36mm with the exception of one being ~35.97mm.
• There is a #28 stamped on the crankshaft, not sure if this means anything

Information I dont know:

• Any color markings are completely worn off on the main crank bearings, so unable to identify
• Am I looking in the right places for these/any marks on the crankshaft or case? Ive looked on the crankshaft and on the front side of the lower and upper cases
• Since I do see a black mark on the side of one of the con rod bearings, does that mean that they are all the same black part number, or do the installed part numbers vary by journal?
• Are there marks on the con rods themselves I am missing?
• when selecting bearings, is it a mixture of a marking on the con rod and a mixture of a marking on the crankshaft?
• 35.97 seems awfully close to wear limit, should I just get another new crankshaft? Can other crankshafts fit in the case, or are they matched?

Anyone have any pictures of these markings (0 or 1)? Or any good diagrams? Its my intention that once I get this figured out, I am going to make a video/article explaining this so that future nubs like me can figure this out a whole lot easier.



Are those embossed circles markings or just some sort of machining remnant?

Topics I've read:
KZ650 Rod & Main Bearing Source?
How see the color codes on crank and rod bearings?

How are you measuring the crank? With a micrometer that reads down to .0001"? If not, you need to get one. And get a ball bearing attachment for measuring on a curved surface (you can make one by using a .250" ball bearing taped to the anvil.) Then measure the con rod bearing you have that shows the black color and compare the thickness against the other bearings. Good chance they will be the same. Not sure what to suggest about the main bearings though. Do you have a factory manual?

I have THIS CALIPER for measurements.
Looks like its .0005, so seems like it doesnt cut it, eh?

The ball bearing thing: I think I see a pic of @MkC doing this in the mentioned post. Ill do that to get an accurate measurement of the con rod bearings and compare them.

Ive got a factory manual sure, but i cant seem to gauge how to figure out which bearings id need. Ill report back here with my measurements.

I just inspected the connecting rods and i do see a faint "1" on the large end. Pic here:


I remeasured three of the con rod bearings with a round "bb" between the caliper, and got a measurement consistent across of ~1.46mm

You must have a micrometer, not a pair of calipers, to measure a crank. And again, get one down to .0001". Many only go to .001" and that's not good enough.

ok.. looks like im taking this crank to a shop for some real measurements with a device thats a bit on my expensive side.

My first question would be how do you know you need to replace the crank bearings? Are they making noise? Do they have some flat spots? I don't know 650's very well but 900 cranks are pretty much bullet proof. As long as the bearings are quiet when you roll them they should be fine.

hardrockminer wrote: My first question would be how do you know you need to replace the crank bearings? Are they making noise? Do they have some flat spots? I don't know 650's very well but 900 cranks are pretty much bullet proof. As long as the bearings are quiet when you roll them they should be fine.

I had been rebuilding the bike ground up. Wanted to touch every point needed. So checking the bearings and crank tolerances is on the list of touch points. They very well may be in spec, but i didnt want to get down to the bottom end and then just skip the bearings while im down there.

Can you post up some photos of the crank side bearing surfaces? Assuming there is no bad wear they can be reused, along with the crank.

This thread might be of some help:
www.kzrider.com/forum/2-engine/332879-ho...ank-and-rod-bearings

Why not plastigauge them then decide?
Steve