Belt drive run offUp to Heavy Twins
Belt drive run offPosted by james_chapman at February 26. 2012
I have a 56 Dominator 99 which I am attempting to get back on the road, I purchased a belt drive kit from Norvil which I have fitted according to the instructions, however when as suggested I manually trun the engine over the belt runs off the engine drive sprocket by about 1/4".As my engine is the dynamo version there is no alternator, the kit is supplied with a gold plate which mounts on the front of the engine drive sprocket, with this fitted the belt stays on.My question is will I get away with this?, or what do I need to rectify on the engine/gearbox alignment which I assume is causing the problem.Advice appreciated. many thanks.
Re: Belt drive run offPosted by robin_goddard at February 26. 2012
You will probably get away with it but you will prematurely wear your belt. I have seen one of the gold end plates worn away by half its thickness as a result of a belt trying to run off.
Some say the original gearbox clamping arrangement is not rigid enough to retain correct alignment for a belt. You can overcome this by buying a gearbox top mounting bolt with adjusters on both sides (you will need to drill a hole in your drive side engine plate for the extra adjuster). I got mine from RGM. Alternatively, as a belt does not require adjusting, you can weld up the adjusting slots in your engine plates and cut holes in the appropriate places in order to provide a fixed location.
Re: Belt drive run offPosted by james_chapman at February 27. 2012
Thank you for your reply Robin, I will try the double adjuster to see if I can get a better alignment.
Again many thanks James.
Re: Belt drive run offPosted by don_constable at February 28. 2012
I was advised by a supplier that the double adjuster was difficult to use and not always needed. I used a 'fillet' inserted in front of the shaft on the left side of the gearbox which I adjusted to fit, by trial and error, then brought the gearbox forward against it a then pulled the gearbox round to the correct orientation. Very cheap and seems to work!
The fillet(s) I filed up using some old alloy I had. Picture attached.
Re: Belt drive run offPosted by james_chapman at March 04. 2012
Thank you for the advice Don, I am still working on the problem!
Re: Belt drive run offPosted by phil_hannam at March 04. 2012
Robin is quite correct about the need for a second adjuster as the chances of the engine and gearbox shafts being parallel to each other after nearly 60 years are very slim.
But before you take the plunge and splash out a small fortune on this piece of kit please check out whether it will fit your engine plates and still be adjustable. Some of the early Dommies seem to have extra tinware under the carb and this makes any spanner work in this area difficult.
An alternative used by some of the race boys is to lock the top gearbox bolt in place on the left engine plate and then then use the adjuster on the oil tank side to pivot the gearbox about to get a good shaft alignment.
This can be achieved by filling the space in the plate in front of and behind the top bolt with some welded metal fillets. Of course you have to get the belt tension spot-on before welding.
I did not want to mess up the plates on my bike with welding and so instead cut and shaped some small Aluminium fillets to fit in the gap in the engine plate. I was going to peg these in place but found that this was unnecessary as the head of the top mounting bolt pinched them in place against the gearbox lug.
I then ran the engine and adjusted the gearbox position until the belt only moved in the centre of the front pulley.
One point I would add about fitting a belt drive. All of your gearbox bearings must be as-new otherwise any play in them will allow the gearbox shaft to whip about. This instantly takes it out of parallel with the front pulley and this in turn starts to shred the belt on the alternator mount or pulley keeper plate.
Re: Belt drive run offPosted by james_chapman at March 10. 2012
Thank you for the advice Phil, I have sorted the problem, indeed by locking the left gear box mounting in place, I was able to pivot the gearbox, it took a few attempts to get it right, but knew I was on the right track when the belt started to travel the opposite way towards the engine!
Thank you all for your valued advice.