Main Bearing identification

[r1_pete]

Is there a way to measure and identify main bearings once the colour has worn away? I know the outers are B, but I didn't het the crank with the cases.

I have a set of perfect bearings, which I'd like to identify...

[AshimotoK0]

I guess Plastigauge on crank. Assemble and check compressed width of Plastigauge after dis-assembly again to determine crank/shell clearance.
Cheers ....  AshD

[Bryanj]

If I can find it there was a table of figures once that included shell thicknes, but that only really workred when new and you had to be able to measure accurately to 0.001mm

[r1_pete]

Thanks, yes I'd not thought of plastigauge....

Bryan, that's the sort of thing I had in mind...

I have 2 complete bottom ends, cases are As and Bs, and a set of empty cases which I've prepared for use, which are all Bs with perfect bearings, I'm hoping to get a set of bearings without resorting to buying new sets at £9 +VAT a shell.

I've internal and external mics so I guess I could bolt the empty cases together and measure the bearing ids.

[archmill]

Definately Plastigauge. Did an article for Practical Sportsbikes magazine last year which explains how it works so from that, you could measure the crank diameter, add the Plastigauge clearance and therefore determine the shell sizes. Its a word document just short of 5Mb so give me your E-mail address and I will send. And anyone else who want it.

Archmill

[Bitsa (Ralph Wright - RIP)]

Hi Guys.
A while ago when I could not match the crankcases with the crank, the etching on the crank was not visable I thought what the hell and rang Haynes.They were very nice and put me through to a Honda racing mechanic who told me after 30 or 40 years or so just buy the biggest shell fit them and re run it in gently.I have to say it shook me a bit and did just that.Fitted them the crank span after torquing down and so far touch wood no problems.As always leave it to you, in the past had good advice but also some shit advice.
Cheers
Bitsa

[philward]

I had the same problem but after checking under different lights, I saw the marks on the crank - really looked like a 2 year olds writing, almost a scribble! Having a real look might save you a some work with the plastiguage - took me ages to spot the marks on my crank
Phil

[Trigger]

Bitsa is right on this one. Between the smallest which off the top of my head is Yellow, to the largest which is Black. The difference is 0.0015 off the top of my head. I always use black but, do apply some running-in compound.  And as Bitsa says: Take it slowly.

[AshimotoK0]

I had the same problem but after checking under different lights, I saw the marks on the crank - really looked like a 2 year olds writing, almost a scribble! Having a real look might save you a some work with the plastiguage - took me ages to spot the marks on my crank
Phil

+1 those marks are hard to read and you need the right light level as there is very little contrast between the marks and the crank. They look like they were done with a wax crayon or lipstick!! obviously not, must be some kind of special marker pen the Japanese had.  I have convinced myself in the past that they had worn off but after a mug of tea and a re-examination they have always been there!

Link to Service bulletin #14 is useful (prices for the shells are a bit out of date though  ).

 http://manuals.sohc4.net/CB750SB/750_14.pdf

Cheers..... AshD

[Trigger]

60p a shell, trade price. The ones i got last week were coming up near a tenner.

[Bryanj]

You need a mic with rounded anvils to measur a shell, and accuracy to 0.001mm is not asily done---its normaly done using air gauges.

I also have fitted all black shells and just run them in for about 1,000 never had a problem yet