Topic: Rear comstar, CB750F 1978, bearings and spacer

[70CB750]

I took bearings out frqom the hub because the threaded retainer (on the brake disc side) was not fully seated.

I cleaned the thread on the retainer and in the hub, it threads all the way in, but the numbers dont add up for me.

The bearing spacer is 106.5mm and the hub distance between bearings is 104mm.

The only way to assemble it and have the retainer threaded fully in would require to leave the other bearing (on the chain side) not fully seated?

What am I doing wrong?  The bearings are 15mm wide, maybe they are aftermarket and they should be narrower?

Any suggestions appreciated.

[andrewk]

What bearings are you using? (the brand should be on the seal)

Also, was this ever together correctly since you've owned it?  Could be the wrong spacer in there from the word go.

[70CB750]

Bearings read SKS Argentina - 15mm wide and 52/20mm - fully sealed and in good shape.

I bought it as part of a deal - engine, wheels, etc - from 1978 F2.  The retainer was screwed out about 8mm; that's why I took it apart in the first place.

The spacer looks original.

[trueblue]

Bearings read SKS Argentina - 15mm wide and 52/20mm - fully sealed and in good shape.

I bought it as part of a deal - engine, wheels, etc - from 1978 F2.  The retainer was screwed out about 8mm; that's why I took it apart in the first place.

The spacer looks original.

There will be a number on the bearing, I can't remember what it is meant to be off the top of my head, I'm sure there will be someone on here who will know.  It will be a 4 digit number, for some reason I keep thinking 6206 but that could be wrong.  If you have a bearing that is too wide then that will probably be your problem

[70CB750]

Yeah, it could be.  The PO tried to replace them and they were too wide, I don't think SKS produced bearings in Argentina in 1978

[raymond10078]

If I'm reading this right, you have an expectation that both bearings will be fully seated.  That is incorrect.

Per the service manual, the bearing with the retainer is installed first.  This bearing is installed firm against its seat, and then the retainer installed/locked into place.

The spacer is installed, and then the opposing bearing.  The opposing bearing is installed just far enough until the spacer is lightly "caught" - with essentially no side preload.

I made this mistake last year (fully seated the non-retained bearing) - and then had to pound the non-retained bearing out, bought a new one, and did it again - the right way.

The bearing and retainer are the parts that position the wheel left to right - in other words, that counterbore is a critical dimension when machining the wheel/hub.  The opposing bearing counterbore has no real critical depth tolerance (other than it can't be too shallow).

[70CB750]

Thank you!

My bad, I should have read the manual.

I know exactly what you are talking about,  bearing and retainer first and the second bearing snug against the spacer.  The left (sprocket) bearing ledge in the hub is also much smaller comparing to the right one.

That is the only way I could imagine to assemble it, but I wanted to hear what people have to say before I write my theories.

Yesterday, I was about ready to start pounding on it, but the spacer was sticking out too much and that made me get the other bearing out and measure distances.

Thanks again 

[70CB750]

I just got an email from All Balls, the bearing kit for the rear wheel consists of 2 different ball bearings:

2 of 20-52-15 - that's for the main hub
1 of  25-62-17 - this must be for the sprocket hub/insert

Just recording the information here, the kit number is 25-1355, my bearings and seals are in good shape and i will reuse them.

[70CB750]

Looks like the PO - or somebody, let's not point fingers - farked up the bearing retainer.  It was actually one piece with the left side collar, because the retainer was bent into the collar groove.

That made the collar stick way out of the collar on the bearing side.  After I took this new and innovative assembly apart, I was able to line up the wheel, swing arm and brake bracket to full satisfaction. 

I will replace the retainer and the 35x45x7 seal before the final assembly.

[Black 750K8]

http://www.cmsnl.com/honda-cb750f-750-super-sport-1978-usa_model7240/partslist/F++12.html#results

You should have two #31 bearings the small ones and one # 32 the large one If you get the AllBalls kit the big one is KML6305 the two small will be KML 6304 they are all double sealed. I'm not clear if you put them in and took them out then I would not use the one you had to drive on the inner ring of the bearing no matter how good it feels.

[70CB750]

I took them out and put them back in.