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Pre unit cranks #773821 05/15/19 7:01 pm
Joined: Dec 2016
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Xavier Devars Offline OP
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Hi everyone,

I bought what was supposed to be a 56 t100 but the engine obviously had mismatched cases, and I was almost sure it was to use big bearing timing side. Turned out it was not, and I have now the correct 56 cases but a small bearing crank. Is there anything preventing the use of this crank in these cases ?
(Am reluctant to discard it as big end bearings are perfect) what are the other options ? Is there a one piece crank fitting ?

Regards

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Re: Pre unit cranks [Re: Xavier Devars] #773830 05/15/19 8:50 pm
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koan58 Offline
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So you seem to have got an earlier engine in a later frame.
Presumably the engine and frame numbers do not match. Can you give an indication of those numbers to help identify years of origin?
It is even possible that an earlier timing side case has been used to replace a damaged later case. Engine number and stampings low on the cases will help.

I assume that you wish to build a bike, not worried about originality? If so, you can use either set of cases.
The small bearing cases would be the simplest to use with that crankshaft. I am assuming your rods have separate shells?

If you wish to use the small bearing crank with the big bearing cases you will need a sleeve (1/16" thick) on the journal, and possibly a spacer (as I'm not certain that the bearing widths are the same). This wouldn't be a cheap thing to do, unless you can do it yourself.

I don't know if/when 1-piece cranks came in for P/U 500s. I've had a 3-piece crank in my 650 for nearly 40 years (obviously nearly 20 years old when I started with it), with my ordinary road use it has given no problems, the B/Es are still std. I don't believe they have a reputation to break (assuming correct assembly and bolts). They are just less convenient in that to clean the sludge trap it has to be split, rather than the plug/tube of the 1-piece crank.

The standardisation of the later P/U models allows some "mix and match" between 500 and 650, with minor adjustments to head height, pushrod length etc.

I think HT Bill would know much more detail.

Re: Pre unit cranks [Re: Xavier Devars] #773835 05/15/19 9:20 pm
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HawaiianTiger Offline
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I'm a bit out of my dept with the 500's. I've only built one and that was a rigid frame Trophy. Now, I've always wanted a T100 of any pre unit vintage. Oh so cool.
I'm afraid I would just drop a 650 unit crank in it with a spacer for the cylinder and call it good.
The one piece pre unit 500 cranks seem to be rocking horse poo. that is, if you can find someone who can tell the difference between them and the 650. I'll bet there aren't ten guys on this forum that could spot the difference, especially at a swap meet.
Getting a vendor, especially on eBay to identify it? Probably not gonna happen.
Now I've heard that the 650 cranks of the day have 6T stamped on them. I don't know. I never looked....I always slot in a 60's crank in my bikes. Well except for the Trophy I built. I kept the bolt up crank. Wasn't much else to do at the time. I had to send the rods to some Model T restoration guys to have new Babbitt poured. That old stuff is a pain in the butt.
Cheers,
Bill

Last edited by HawaiianTiger; 05/15/19 9:26 pm.

Bikes
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Re: Pre unit cranks [Re: Xavier Devars] #773877 05/16/19 3:18 am
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Bob Buchanan Offline
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Bill- I have seen several 500cc 80mm, both small and big bearing 3 piece cranks that all had small 5s on cheeks instead of 6T. I just bought another big bearing crank last month with the 5 on it. I'm also working on a 1950 6T with also a small 6T on the flywheel too.

Re: Pre unit cranks [Re: Xavier Devars] #773896 05/16/19 8:56 am
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Xavier Devars Offline OP
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Thanks guys, yes Koan , the drive side has the correct engine numbers regarding frame and year, but not regarding the other half. And I found the « small » roller bearing in it. Must have been damaged at some point, and considering the huge amount of dirt I found in this crank, I supposed the previous owners were not to keen on opening and cleaning these, nevertheless, the big end jounals are like new (well at +0.20).
I have in stock a big bearing drive side, and seems to me it would be more period correct, and easier to find big bearing for.

Thought of the sleeve, perhaps the cheaper way. The cylinder spacer seems a little bit out of reach, never seen one for sale. Or try to find a correct crank on eBay...

Regards


Moderated by  John Healy 

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