Smallframe Crank

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storkfoot
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Wed May 17, 2017 10:40 pm

A mate had a "dealer" build him a small frame engine. His instruction was to build it as standard top end but with a race crank and decent bearings as the long term plan was to fit a Polini kit.

Anyway, the engine never got fitted and the mate has now bought the Polini Kit. I think it's a 130 but I haven't opened the box yet.

I said I'd fit the top end for him, albeit that I have never worked on a smallframe engine before. Having taken the top end off, I have some doubts about how this engine was put together.

My question relates to this crank. I know it's hard to tell without me splitting the casing, but does this crank look like a suitable race crank?

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GeorgeS
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Thu May 18, 2017 7:18 am

Is this going to be using the rotary intake or reed on the barrell? Assuming rotary as it's not a full circle crank.

Can you post a picture of the crank intake cutout & perhaps measure the open timing?

You'd get best results by matching the casing transfers to the barrel & openning up the intake, but that would mean a casing split as you'd not want the waste ally getting in the crank.

storkfoot
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Main scooter: '70 GP150 [TS1 225]
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Thu May 18, 2017 11:31 am

I'll have to open up the parcel he has given me but I suspect it may be reed valve. I'll get back to you. Cheers.

225worb
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Thu May 18, 2017 9:19 pm

Looks very much like a standard type crank or yes maybe a cut crank but if it were a reed type there would be signs of chamfering on the on all of the right side web and the inlet port wouldve been properly fettled !!!!

storkfoot
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Joined: Thu Jan 08, 2009 12:08 am
Main scooter: '70 GP150 [TS1 225]
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Sun Jul 09, 2017 12:38 pm

Only just getting back to this. Stripping engine down to get at the crank.

My question is about the clutch. A large frame clutch will just prise out once you have taken the nut off under the thrust plate. I have done this but clutch doesn't seem to want to move. Should it prise off now?

Boreham
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Sun Jul 09, 2017 1:34 pm

The small frame clutch is on a taper, similar to the flywheel, requires the correct tool

storkfoot
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Posts: 1283
Joined: Thu Jan 08, 2009 12:08 am
Main scooter: '70 GP150 [TS1 225]
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Sun Jul 09, 2017 1:37 pm

Thanks, mate. Just found reference to it in the Haynes manual, finally.


storkfoot
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Posts: 1283
Joined: Thu Jan 08, 2009 12:08 am
Main scooter: '70 GP150 [TS1 225]
Location: Merseyside
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Sun Jul 09, 2017 2:59 pm

Thanks for those links. I'll re-register on the Smallframes forum too ;-)

storkfoot
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Posts: 1283
Joined: Thu Jan 08, 2009 12:08 am
Main scooter: '70 GP150 [TS1 225]
Location: Merseyside
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Sat Aug 12, 2017 10:56 am

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Not even a new conrod :shock:

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