The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: roadrocket on 22.09. 2017 13:00

Title: Crank identification
Post by: roadrocket on 22.09. 2017 13:00
Hello

In the belief that I was confronted with a nice large journal crankshaft for my A 10 I bought the item hopefully depicted here. It was advertised as BSA 650, and I was happy to see the absence of provision for an alternator, so had to be for A 10. The journal was measured by seller as 42 mm (and since no A 7's were large journal, to the best of my knowledge, again had to be for A 10). Hooray, large journal! However, I can by crude means only measure the stroke to about 70 mm, and not the desired 84 mm. The casting bears the number 68-175-4001.

Can anyone help me to identify this crank, many thanks in advance?

Title: Re: Crank identification
Post by: JulianS on 22.09. 2017 13:32
68 175 is an early A50 A65 crankshaft number. But that does not look like an A50 A65 crank. I think you need to measure the main journal and the stroke and let us know what you get.

Below from A65 parts book dated November 1961.

Ignore the first three numbers, dont know what the 1 stands for but the 86 is a price code.

Title: Re: Crank identification
Post by: roadrocket on 22.09. 2017 13:37
OK, but should these not have the drive side with a smooth portion for the alternator rotor?
Title: Re: Crank identification
Post by: roadrocket on 22.09. 2017 14:04
Hi, stroke is 74 mm to the best of my measuring skills (by caliper), journals measure 43 mm, timing side journal is 38 mm and drive side axle measure 28,5 mm. But it puzzles me that the drive side axle clearly doesn't have provision for alternator, and instead is fashioned like the A 7-10 crank.
Title: Re: Crank identification
Post by: JulianS on 22.09. 2017 15:16
Interesting - A65 timing side journal = 1.5 inches or 38 mm standard size - A10 = 1.375 inches or approx 35 mm standard size.

A65 Drive side bearing inner diameter = 1.125 or about 28.56 mm. A10 drive side bearing = 30 mm inside diameter or about 1.18 inches.

A65 stroke = 74 mm

So it will not take A10 main bearings.

So it is an engima!
Title: Re: Crank identification
Post by: Angus on 22.09. 2017 17:17
Was there not a picture about recently of an A50 based racing bike with a magneto, perhaps a crank for something like that.
Title: Re: Crank identification
Post by: chaterlea25 on 22.09. 2017 20:20
Hi,
Have a close look at the photo,
The remains of the alternator keyway can be seen in the threaded part
So it looks like it was modified for some reason? Flat track racers often had a shortened crank

John
Title: Re: Crank identification
Post by: roadrocket on 25.09. 2017 16:48
Anybody in the market for a modified A 65 crank  ;)
Title: Re: Crank identification
Post by: muskrat on 25.09. 2017 20:53
Could be the start of a large journal, stroked A7, with A65 rods and A75 pistons  *pull hair out*
Cheers