Author Topic: Crankshaft measurements  (Read 839 times)

Offline Gavin

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Crankshaft measurements
« on: 23.07. 2016 07:37 »
Hi, I am having a great deal of fun building my first plunger A10 motor. There must be a better way to do research than I can find, so can someone please tell me what was the original size of the main crank journal which takes the bush please? (I can then work out how undersized etc I need the bush to be.. I hope)

While we are there can someone also tell me the original size of the hole in the timing side casing too please?

Armed with this info I think I can mull over what kinda bush I will need.

Many thanks for anticipated replies.


Offline muskrat

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Re: Crankshaft measurements
« Reply #1 on: 23.07. 2016 09:06 »
G'day Gavin.
1.375" timing side main, drive main 30mm, crank pin 1.461".
Can't help with the hole size. I had the primary off two days ago. Bugga.
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Muskys Plunger A7

Online KiwiGF

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Re: Crankshaft measurements
« Reply #2 on: 23.07. 2016 11:42 »
Hi Gavin, ref the I.D. Of the crankcase for the bush is usually academic as the hole is often worn oval, in which case (pun  ;) ) the hole should be bored to round and a non standard bush made.

The generally accepted advice is to have the crank journal ground the minimum to make it round and then get a non standard bush made to suit the crank, if the case is not worn oval a standard bush of maximum undersize can be bought as a starting point for the non standard bush, but note the first comment on the use of a standard O.D. bush, if the case is worn.

New Zealand

1956 A10 Golden Flash (1st finished project)
1949 B31 rigid “400cc” (2nd finished project)
1968 B44 Victor Special (3rd project,in progress)
2001 GL1800 Goldwing, well, the wife likes it
2007 KTM 950 Adventure, cos it’s 100% nuts

Offline Gavin

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Re: Crankshaft measurements
« Reply #3 on: 23.07. 2016 13:20 »
Thanks Musky. I think this helps me work out what amount of under sized bearing I need to be chasing.  Not sure if that makes sense but I am guessing the inside "bore" of the bush needs to be undersized from standard. my Journal us 1.360" and i understand needs 1 thou clearance.

Thanks KiwiGF. this is also where I find the forum helpful. I get bogged down on a detail and someone else's idea starts another thought process for me. I understood your thinking, but I had no idea what a standard size the OD of the bush would have been. My casing has already been line bored to take out the oval and another blemish. However I have no idea what the standard OD size was. Once I read your post I went down to the shed, found 2 other casings and am now using the smallest size of those (thus bypassing any oval aspect in those casings) as the original OD. 1.6775"

Now if i can find an off the shelf bearing of relative size... they seem to go for +20, - +80 and so on... i can try and supply our good friend Orabanda with a close fit that he can tweak in his shed. And so the fun will continue.

Many thanks.