Author Topic: Crankshaft Bush Clearance  (Read 186 times)

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Offline Ian Foote

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Crankshaft Bush Clearance
« on: January 01, 2019, 02:40:46 pm »
Hello,
I have stripped down my C11 motor for a rebuild. New valve guides, bored first oversize, new piston, new crank drive side bearing, but what about the crankshaft timing side bush?? What clearance do we allow here? Or is it false economy not to install a new bush out of hand? Any thoughts gents?
Ian

Offline Owen

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Re: Crankshaft Bush Clearance
« Reply #1 on: January 01, 2019, 03:16:29 pm »

Service Sheet 702. states the crank shaft Journal bush dimensions should be 0.983-0.982 based on a standard journal.
1940 C12 (350cc)
1945 C10 & C11
1953 C10 & C11
Anyone want a B20 in need of a lot of tlc

Offline ianinglis

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Re: Crankshaft Bush Clearance
« Reply #2 on: January 01, 2019, 09:19:16 pm »
2 thou should be enough


ian
BSA C10L 1956 - JFO 588
BSA C10L 1954 - MVE 107
RM6 RALEIGH RUNABOUT
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Offline timsdad

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Re: Crankshaft Bush Clearance
« Reply #3 on: January 02, 2019, 06:06:37 am »
Unless it's quite badly worn, or damaged, just leave it alone, Ian. You'll never live long enough to wear it right up and a bit of oil pressure loss there makes little difference to the over-engineered pre-unit Cs. The crank can be shimmed to keep the gap down to a  thou' or two end-float on its side.

The timing-side crank to bush fit is only really important in the bikes that have shell bearing big ends, that rely on a good, steady feed of oil. That's just my opinion, of course, - no doubt others will tell you I'm a Philistine!


Ray
Just a motorcyclist.

Offline Ian Foote

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Re: Crankshaft Bush Clearance
« Reply #4 on: January 06, 2019, 09:30:01 am »
Hello again,
Back to the crank bush. I set up the cases with the crank inside and used a feeler guage on the bush, I have a gap of two thou, the specs say one thou. The bush and the crank journal are in quite good shape. So I am inclined to take "Timsdad's" good advice as the bike will realistically only get used, what.... two, three, four rallies a year and maybe a little bit of running around in between.
Any howlers out there who think I am doing the wrong thing, I would appreciate and treasure all input.
Cheerio boys
Ian

Offline timsdad

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Re: Crankshaft Bush Clearance
« Reply #5 on: January 06, 2019, 09:57:30 am »
It will be fine, Ian, there's at least 50,000 miles of hard use there. It's a credit to the old boys in brown coats who first put it together.


Ray
Just a motorcyclist.

Offline Owen

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Re: Crankshaft Bush Clearance
« Reply #6 on: January 06, 2019, 10:07:55 am »
You could do more damage removing and replacing the bush for one thou in my opinion.
1940 C12 (350cc)
1945 C10 & C11
1953 C10 & C11
Anyone want a B20 in need of a lot of tlc

Offline Ian Foote

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Re: Crankshaft Bush Clearance
« Reply #7 on: January 06, 2019, 10:33:30 am »
Thank you men...... I will look forward to those hard won 50,000 miles.

Ian