[quote name='SquiddlyDiddly' date='15 Nov 2007, 21:54' post='39618']
Thanks everybody for the replies. I think my use of English must be wanting as I clearly didn't really explain myself properly.
The motors I have are to replace the old Hornby Triang X03/X04 motors. Unfortunately the height of the shaft from the base of the motor is higher by 1.5mm on these new motors so the existing worm will not do. I need a larger worm. I don't think the shaft diameter is a problem, I just need a supplier of a larger worm so I can find one that fits with the new motor firmly seated.
Does this make things clearer? I hope so.
you are looking for a worm that is 3mm larger in diameter then the original Triang Worm. That is far bigger than ANY stock worm I have seen in the last 20 +++ years of scratchbuilding / kitbuilding and reworking/re-powering loco's of every brand except the BACHMANN worm that is used on their split-chassis loco's.
It may fit BUT it will almost certainly have the wrong pitch and tooth angle - a worm and axle gear require accurate matching to work effectively so if they are not perfectly ight, you will have a problem.
I think you will have to find a machine shop that will make them specially for you. Make sure you specify the length of the worm such that it positions centrally on the drive gear). It would be better to give the machine shop the chassis and motor so they can create accordingly.
To be honest my instincts say that a new axle gear (slightly larger) will be a better and safer bet - try Markits for a combined set as they DO make the gears to fit triang/hornby knurled axles as part of their range. You'll have to be specific in sizes though......
No matter which way you go, it won't be cheap.
ALSO: if the motor is 1.5mm higher at centreline than the XO-4 then you will have problems getting the body back on some loco's - not all have a lot of clearance above the original motor. (Given the height, width may also need checking...)
Perhaps you've already covered this then you'll be OK of course, but if not, its Worth checking this thoroughly before you spend too much.