69/70 Bonneville rebuild

Like many of the Coventry makes, Triumph had their roots in the bicycle industry, beginning motorcycle production in 1902.

69/70 Bonneville rebuild

Postby guzzibat » Sat May 29, 2010 9:21 am

I'm rebuilding my 69 bonnie with a new 70 drive side crankcase - the 69 cc was broken - problem the casing is slightly different - breathers, blanking plates, etc.

Does anyony have any warnings, tips or tricks before I start the rebuild?

Thanks in advance
All the best.......

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Re: 69/70 Bonneville rebuild

Postby L.A.B. » Sat May 29, 2010 11:45 am

You'd be better off trying to find a set of matching crankcase halves in my opinion.
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Re: 69/70 Bonneville rebuild

Postby Tman » Sat May 29, 2010 11:55 am

I agree with that. It can be done, as many engine builders will say, but as the cases were machined as a bolted-together lump, renewing one half only can lead to problems as diverse as shaft alignment to deck heights and dowels.
Most likely it will be fine, but a detailed check and/or dry build with crank and cam shafts would be sensible. Nice bike, by the way... :209
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Re: 69/70 Bonneville rebuild

Postby MOUSE » Sun May 30, 2010 12:53 am

"My arthritis has gotten so bad I can hardly grip anything, my cataracts seem to get worse every day, I have gout in my right leg and can't bend my knee and I can't hear anything.
But thank God I can still ride
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Re: 69/70 Bonneville rebuild

Postby Stuart SS » Sun May 30, 2010 1:27 am

Definitely agree with LAB and TMan ~

After all there are heaps of crankcases appear regularly on EBay ~

I think you creating a hassle for yourself by using mismatched halves right from the get-go ~

Good luck ~

You could also get a copy ~ "A Bike is Born" All depends if you are novice ~ there are a few Videos around which would be of use . there are always a few tips to be gleaned from these vids ~ rock
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Re: 69/70 Bonneville rebuild

Postby Welsh Wizard » Sun May 30, 2010 3:58 am

non matching half are not a good idea, cases are inline bored putting to non matching halve will put undue strain on the alignment of the crankshaft bearings, causing premature failure.
only way round this is welding the bearing areas of the cases and getting them rebored, expensive, and of questionable use as heat generated in the welding is likely to affect the cases by causing distortion,
Best find a matching pair, if numbers are important to you, browse the Internet, new unstamped cases ( NOS ) are still to be found and any registered motorcycle shop can stamp the cases with the numbers from yours, provided the destroy the old cases.
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Re: 69/70 Bonneville rebuild

Postby MOUSE » Sun May 30, 2010 5:23 am

This is better for motor rebuild than Bike Born mentioned ...

http://www.fouracescycle.com/merch.html
"My arthritis has gotten so bad I can hardly grip anything, my cataracts seem to get worse every day, I have gout in my right leg and can't bend my knee and I can't hear anything.
But thank God I can still ride
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