SOHC.co.uk Forums > CB350/400

Crank Finally Measured by Engineering Firm but I'm confused

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waffey:
I must admit now that i'm a little of of my depth.

Firstly I had a local engineering firm measure the crank up but when i look at the manual it looks likes it's too worn. Is that correct?

I also had connecting rods measured with the bearings (at least 3 anyhow!) but i'm not sure where this leads me.

I'm think bolt the connecting rods on, plastigauge for clearance for bearing size???

McCabe-Thiele (Ted):
You need to look at the chart in the parts book - I'm a relative beginner but at a glance there's not much wrong with your mains they are all within the maximum tollerance of 32.00 minus 0.03 that would make the minimum diameter allowed as 31.97 mm so all yours look good.

Your big ends are also looking good minimum journal size is 32.00 minus 0.03 mm  so minimum diameter is again 31.97 mm.

Are the journals scored if not you will be able to look in the manual and check your crank case codes & con rod codes to work out what shells you need.

If you look in Ash's dropbox the shell sizes & colour codes are there Page 8- you might be lucky & find some markings on your old shells likewise the crank codes. Mains are fairly easy as the code is stamped on the lower casing at the back.

Subtraction my maths  amended!

K2-K6:
I've got those above from Honda tolerances at

Crank main bearings left to right on drawing
C C B C C
You'd now need crankcase id to work out main bearing shell's colours.

Crank pins for rods at
5 (-0.001 outside) 5 (-0.003 outside) 5 (exactly on tolerance) 5 (+0.002 inside)  making two of them just outside tolerances.

Rods, I'm curious as the bore is not ordinarily a wear surface (shells are taking the work here) but seem too big.

Will look again at the numbers.

K2-K6:
"I also had connecting rods measured with the bearings (at least 3 anyhow!) but i'm not sure where this leads me."

Oops, didn't see the proviso "with the bearings" there.

Honda protocol is to measure the rod bores without bearing to then agree bearing thickness to fill that gap between the measurements of pin and hole.

Will look at those big end numbers again to give view.

K2-K6:
OK, you'd need either the big end shell colours at minimum, and or preferably the measurement of con rod big end bore to determine how to proceed with sizing of any new big end shells.

If there's some Latitude to be had in the machined size of the rods, then that 0.001 and 0.003 error can potentially be accommodated by selecting a shell colour that's wrong in "book terms" but makes up the running tolerance to function correctly.

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