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#433230 - 05/04/12 7:53 am BSA C15 1965 crankpin dimensions and B40 crank  
Joined: Nov 2001
Posts: 98
Jacco van D. Offline
BritBike Forum member
Jacco van D.  Offline
BritBike Forum member

Joined: Nov 2001
Posts: 98
Netherlands
To all who can help with my 1965 C15.

C15 crankshaft
The crankshaft is at the moment at my engineer/machinist for a new big-end.
I supplied a new bigend/conrod assembly with correct 1" diameter at flywheels. I think it was no. 41-234.

But now he said that the bearing or pin is to long.
Ruperts book tells that you must machine something of the flywheels. It's just a note. So I am not sure if I understand this correctly.

Anyone ideas regarding the machining (with dimensions) or a new correct bearing?

B40 crankshaft
I also have a very good B40 crankshaft, but this is heavier than a C15 crank. I want to built a trail bike, so maybe this isn't a bad idea. As far as I know, I must only fit a new small-end for the C15 piston or should it also be rebalanced?
If rebalancing is neccessary, please give some hints. Overhere I don't know anyone who can rebalance it for a normal price or has the skills. So I am hoping that someone did this before without rebalancing.

Well, thanks in advance.


Triumph T100T 1969
Triumph TR6R 1972
Triumph T25T 1971
BSA B25 Fleetstar 1968
Laverda 750SF 1971
TWN Boss 1954
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#433232 - 05/04/12 8:05 am Re: BSA C15 1965 crankpin dimensions and B40 crank [Re: Jacco van D.]  
Joined: Dec 2004
Posts: 8,889
kommando Online content
kommando  Online Content


Joined: Dec 2004
Posts: 8,889
Scotland
C15 crankshaft
The crankshaft is at the moment at my engineer/machinist for a new big-end.
I supplied a new bigend/conrod assembly with correct 1" diameter at flywheels. I think it was no. 41-234.

But now he said that the bearing or pin is to long.
Ruperts book tells that you must machine something of the flywheels. It's just a note. So I am not sure if I understand this correctly.


Anyone ideas regarding the machining (with dimensions) or a new correct bearing?

Give the old assembly to the engineer, 2 mins with a mic will tell him how much he needs to take off. The new assembly is wider but I have no idea how much.


B40 crankshaft
I also have a very good B40 crankshaft, but this is heavier than a C15 crank. I want to built a trail bike, so maybe this isn't a bad idea. As far as I know, I must only fit a new small-end for the C15 piston or should it also be rebalanced?
If rebalancing is neccessary, please give some hints. Overhere I don't know anyone who can rebalance it for a normal price or has the skills. So I am hoping that someone did this before without rebalancing.

You can do your own static rebalance using knives,

http://www.youtube.com/watch?v=HbsGGSjmpko

#433355 - 05/04/12 8:57 pm Re: BSA C15 1965 crankpin dimensions and B40 crank [Re: kommando]  
Joined: Nov 2001
Posts: 98
Jacco van D. Offline
BritBike Forum member
Jacco van D.  Offline
BritBike Forum member

Joined: Nov 2001
Posts: 98
Netherlands
Thanks Kommando,

My engineer has the old bearing. Am I right that its just a bit of machining from the flywheels? Just a circular part?

Kind regards, Jacco


Triumph T100T 1969
Triumph TR6R 1972
Triumph T25T 1971
BSA B25 Fleetstar 1968
Laverda 750SF 1971
TWN Boss 1954
#433419 - 05/05/12 6:59 am Re: BSA C15 1965 crankpin dimensions and B40 crank [Re: Jacco van D.]  
Joined: Dec 2004
Posts: 8,889
kommando Online content
kommando  Online Content


Joined: Dec 2004
Posts: 8,889
Scotland
Never seen the two versions to compare, a roller replacing plain bearing will be bigger and this could be in width and/or OD. I am surprised with your engineer, if he has both parts it does not take much to work it out for himself.

#433424 - 05/05/12 7:34 am Re: BSA C15 1965 crankpin dimensions and B40 crank [Re: kommando]  
Joined: Nov 2001
Posts: 98
Jacco van D. Offline
BritBike Forum member
Jacco van D.  Offline
BritBike Forum member

Joined: Nov 2001
Posts: 98
Netherlands
The old big-end bearing was a roller or needle. Not a plain one.
In Ruperts book is written at the conrod assy 41-234 (that is a roller from 1965-on) "Flywheels not allready fitted with the needle roller assembly will need to be machined to accept it due to it being 1/16" wider then the caged roller assemblies".

I think that this is happening with my assembly. Therefore I want experiences from other C15/B40-owners who did this before.


Triumph T100T 1969
Triumph TR6R 1972
Triumph T25T 1971
BSA B25 Fleetstar 1968
Laverda 750SF 1971
TWN Boss 1954
#433440 - 05/05/12 11:35 am Re: BSA C15 1965 crankpin dimensions and B40 crank [Re: Jacco van D.]  
Joined: Dec 2004
Posts: 8,889
kommando Online content
kommando  Online Content


Joined: Dec 2004
Posts: 8,889
Scotland
The old big-end bearing was a roller or needle. Not a plain one.

What was fitted before as you have not mentioned this?

In Ruperts book is written at the conrod assy 41-234 (that is a roller from 1965-on) "Flywheels not allready fitted with the needle roller assembly will need to be machined to accept it due to it being 1/16" wider then the caged roller assemblies".

41-234 is a roller bearing not a needle, the needle was a further upgrade introduced to use the B50 needle roller bearing on B40WD's so you need to re read Rupert Ratio with this in mind and concentrate on the comments refering to larger con-rod big eyes.

#433483 - 05/05/12 6:16 pm Re: BSA C15 1965 crankpin dimensions and B40 crank [Re: kommando]  
Joined: Nov 2001
Posts: 98
Jacco van D. Offline
BritBike Forum member
Jacco van D.  Offline
BritBike Forum member

Joined: Nov 2001
Posts: 98
Netherlands
Hi Kommando,

I dismantled my 1965 engine and think that the bottom end was never dismantled before. So I think the original roller bearing big-end was still inside.

I sent the complete crankshaft with conrod to my engineer.
I gave him a new bigend-conrod assembly. I think it was a needle type (but could also be a roller). It had the correct diameter at the flywheels of 1".
I never knew that there were differeces in width of the bearing.
I now have 3 options:
1. Buy a correct roller bigend.
2. Modify the flywheels. Just grinding away a circular part at the big-end bearing.
3. Fit my B40 crankshaft.

I think option 2 is the best, so if someone did this before, I would welcome experiences, dimensions etc.

Kind regards, Jacco


Triumph T100T 1969
Triumph TR6R 1972
Triumph T25T 1971
BSA B25 Fleetstar 1968
Laverda 750SF 1971
TWN Boss 1954
#433493 - 05/05/12 8:01 pm Re: BSA C15 1965 crankpin dimensions and B40 crank [Re: Jacco van D.]  
Joined: Oct 2007
Posts: 1,272
Wilfred Offline
BritBike Forum member
Wilfred  Offline
BritBike Forum member

Joined: Oct 2007
Posts: 1,272
Nanaimo, B.C. Canada
Jacco. If you need one I have a NOS alpha bottom end bearing. It is a B25K for 1965/66 engines. I also have a NOS conrod for the 1965 engines 40-0570 with casting on the rod of 41-234 MF A2 and the letter G on the other side. This is the same as was in both of my 1966 C15 engines when I had them. 65 and 66 engines were pretty much the same except for some small details like available gears. Bearing is $ 100 and the conrod is $45 plus shipping. The bearing is still in it's original sealed packaging. I recall that the B40 crank was a little bigger and heavier. This info was probably in the Rupert book. Cheers, Wilf


"It's about the ride..."
#435281 - 05/16/12 12:14 pm Re: BSA C15 1965 crankpin dimensions and B40 crank [Re: Jacco van D.]  
Joined: Nov 2001
Posts: 98
Jacco van D. Offline
BritBike Forum member
Jacco van D.  Offline
BritBike Forum member

Joined: Nov 2001
Posts: 98
Netherlands
Hi Wilfred,

Thanks for your offer.
But I prefer to modify the flywheels as also "simply" written in the Rupert-book.
But in the book are no dimensions given.
I still want some info about this, so if someone can help?

Thanks, Jacco


Triumph T100T 1969
Triumph TR6R 1972
Triumph T25T 1971
BSA B25 Fleetstar 1968
Laverda 750SF 1971
TWN Boss 1954

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