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#91
Twins / Re: Keyway repair
Last post by DAVE BRADY - 14 Oct, 2026, 20:08Hi,
Crankshaft is parallel rather than tapered. With a bit of work with a file an over wide key can be fettled to fit the worn shaft and the rotor. The key should be protrude enough so that the rotor needs to be tapped on rather than a sliding fit and if the rotor has been loose for while it may not be the tight fit it needs to be so use some bearing retainer and then make sure the nut is tightened to 60lb/ft with a torque wrench.
Dave.
Crankshaft is parallel rather than tapered. With a bit of work with a file an over wide key can be fettled to fit the worn shaft and the rotor. The key should be protrude enough so that the rotor needs to be tapped on rather than a sliding fit and if the rotor has been loose for while it may not be the tight fit it needs to be so use some bearing retainer and then make sure the nut is tightened to 60lb/ft with a torque wrench.
Dave.
#92
Singles / Re: Thinking about a B40
Last post by limeyrob - 14 Oct, 2026, 20:03Not a bad plan. At the risk of offending some, I had a B40 many years ago and was glad to see the back of it, but the cycle parts are tough and it has a reasonable amount of power.
B40s come in various varieties - standard, SS90 tuned (mine was an SS90 and the thought of 90 on it is terrifying) and quite a lot of ex MOB ones with some different cycle parts and every colour so long as its NATO green.
I think the ex MOD ones are a good buy, they are often quite low mileage and sat around in warehouses then got sold off and sat around in sheds.
Personally I would not recommend the SS90, mine had the feel of a bike that would have been much nicer with less compression and softer cams.
Now I'm going to commit heresy as a lifetime BSA owner - take a look at the Matchless G3 / AJS 16, a lot of bike for your money. Very similar in performance and build to the B31 but about 60% the cost.
B40s come in various varieties - standard, SS90 tuned (mine was an SS90 and the thought of 90 on it is terrifying) and quite a lot of ex MOB ones with some different cycle parts and every colour so long as its NATO green.
I think the ex MOD ones are a good buy, they are often quite low mileage and sat around in warehouses then got sold off and sat around in sheds.
Personally I would not recommend the SS90, mine had the feel of a bike that would have been much nicer with less compression and softer cams.
Now I'm going to commit heresy as a lifetime BSA owner - take a look at the Matchless G3 / AJS 16, a lot of bike for your money. Very similar in performance and build to the B31 but about 60% the cost.
#93
Singles / Thinking about a B40
Last post by NClark - 14 Oct, 2026, 18:52Hello Everyone!
I've just joined this forum because I'm considering buying a B40, and need a bit of advice.
Let's get the hard bit done first... I'm a big fan of Triumph twins. I hope this admission doesn't result in me being cast into outer darkness!
However, I would really like to try a typical light/middle weight British single from the sixties, and the idea of a B40 appeals, as it's seemingly a fairly light machine with adequate power.
'Adequate for what?' you may ask. I would be planning to use it mainly for country lane and B road pottering, probably on local bike club ride outs where we seldom exceed 50-60mph. Brief dual carriageway excursions may be necessary, where I would need to be able to cruise at 60mph for 10 minutes or so, simply to keep up with the trucks and avoid being pushed along by said juggernauts.
I don't imagine a 250 would have the performance for this type of use, hence the 350cc B40 appears a better bet, with the added bonus that prices of these machines seem quite reasonable.
So my question is 'will a B40 have the performance and capability I'm looking for?' Or am I barking up the wrong tree?
Thank you in advance for your insights and experience.
Nigel
I've just joined this forum because I'm considering buying a B40, and need a bit of advice.
Let's get the hard bit done first... I'm a big fan of Triumph twins. I hope this admission doesn't result in me being cast into outer darkness!
However, I would really like to try a typical light/middle weight British single from the sixties, and the idea of a B40 appeals, as it's seemingly a fairly light machine with adequate power.
'Adequate for what?' you may ask. I would be planning to use it mainly for country lane and B road pottering, probably on local bike club ride outs where we seldom exceed 50-60mph. Brief dual carriageway excursions may be necessary, where I would need to be able to cruise at 60mph for 10 minutes or so, simply to keep up with the trucks and avoid being pushed along by said juggernauts.
I don't imagine a 250 would have the performance for this type of use, hence the 350cc B40 appears a better bet, with the added bonus that prices of these machines seem quite reasonable.
So my question is 'will a B40 have the performance and capability I'm looking for?' Or am I barking up the wrong tree?
Thank you in advance for your insights and experience.
Nigel
#94
Twins / Re: Keyway repair
Last post by V500 - 14 Oct, 2026, 17:40I would be unhappy to use any compounds on the taper (not the nut), a) because at some point it'll need to come off again, and b) the strength of the "taper grip" will be compromised by anything which sits between the taper faces.
#95
Twins / Re: Keyway repair
Last post by limeyrob - 14 Oct, 2026, 17:32As above, lap it, clean the threads and tighten with Loctite and it should be OK. What makes you think its a loose rotor? It is (as said above), possible to file up a slightly wider key and that is a good fix since it leaves the crankshaft alone.
#96
Twins / Re: Keyway repair
Last post by JulianS - 14 Oct, 2026, 16:12There are various hi spec Loctite industrial strength retaining compounds which might assist, could be worth researching.
#97
Twins / Re: Keyway repair
Last post by V500 - 14 Oct, 2026, 12:53Not just the "tightness" of the nut, but the well-fitting taper as well.
Often a custom-filed up key plus a gentle lapping with fine grinding paste will do the job.
Often a custom-filed up key plus a gentle lapping with fine grinding paste will do the job.
#98
Twins / Re: Keyway repair
Last post by iansoady - 14 Oct, 2026, 12:17There was a discussion on the C10/11 forum about using jbweld in a similar situation. I know not an "engineering" solution but some found it to work. Personaly I've used JB weld with success for damaged castings and the like.
The rotr is held in place more by the tightness of the nut (as you've discovered) than by the key itself.
The rotr is held in place more by the tightness of the nut (as you've discovered) than by the key itself.
#99
Twins / Keyway repair
Last post by Chriss750 - 14 Oct, 2026, 10:46Hi all. Can anyone recommend a repairer for a damaged crankshaft keyway. Cause I think running with a loose rotor.
Thanks Chris
Thanks Chris
#100
Singles / Re: 441 Victor Spark Plug Evol...
Last post by scifi - 13 Oct, 2026, 10:15Have you changed your cool N4 to the hotter N6Y,? It should clear some of the soot.
I used to have a Rover 6 cylinder car, that used N5 plugs, but cylinder 5 was oily and needed an N8.
Edit..... My mistake.. the N6Y is not hotter, it is the extended tip version, which may or not foul the piston.
So maybe try the N5 or even N6, to get a hotter plug.
I used to have a Rover 6 cylinder car, that used N5 plugs, but cylinder 5 was oily and needed an N8.
Edit..... My mistake.. the N6Y is not hotter, it is the extended tip version, which may or not foul the piston.
So maybe try the N5 or even N6, to get a hotter plug.