I’ve just noticed that on both my V65 and the V50 II, after a run the bevel box feels quite hot. Not too hot to touch by any means, but more than just warm. In both cases the wheel still spins freely and there are no ominous noises. Since the bevel box only contains gears and bearings, I am a bit concerned - why should it generate heat? So, either the heat is normal, or they are both faulty, but which is it?
Any ideas / comments?
Both my big block Guzzis used to be practically too hot to touch until, in the latter case, I started using SAE 85-W140 oil plus a dash of molyslip, from a recommendation on this forum (which was a few years ago).
Typical gear pair will waste about 1% of the power it transmits in friction etc, so will get a bit warm depending on how fast/hard you ride it.
Metal gets too hot to touch at surprisingly low temperature. About 60C depending on surface finish etc.
All in all sounds quite normal to me, although I think the small-block bevel drive runs a bit hotter than big-block hence Guzzi specified 140 grade oil for it. I think 85W-140 or 90W-140 but would need to look it up.
Many thanks for the replies, I feel a good deal more confident!
The V65 came to me last year as a box of bits ( well, several boxes!) and part of the restoration involved rebuilding the bevel box, which is a right old palaver, involving checking the meshing of the gears with engineers blue while pulling the crown wheel away from the pinion to try to get the gear teeth into the position they’d be under load. I did what I could to the best of my ability, but needless to say, I was less than 100% confident in the result. When I eventually got around to a test ride, I nervously checked the temperature of the bevel box and found it fairly hot as I said before. I don’t think I’ve ever checked this before on any shaft-drive bike. I was somewhat relieved to find the V50 was the same but I still thought it worth asking the question.
By the way, as anyone who has used engineers blue will know, it’s very easy to get too thick a coating and the result is blue everywhere - hands, clothes, workbench etc. Someone told me to use a “Sharpie” instead (felt pen) and in fact it works quite well so long as the gear teeth are pretty oil-free. Much less messy and very easy to apply. A nice even and thin coat of blue is still preferable and shows a clearer contact patch, but the sharpie is so much easier and it works pretty well.
If anything goes wrong in small block bevel drives, it is a pinion rear taper bearing. That’s why older small block have them same at both ends, and bit younger ones have that particular one bit bigger. My bevels get “too” hot as well as yours, but, although not 100% sure about my job as you, I am pretty confident old technique will survive.
Dismantling pinion setup for brief check is relatively easy and all job can be done in an afternoon. You won’t catch description in pics below, but crucial thing is a precise washer between the bearings, to give 0.1mm play on the races, otherwise, doing the 27mm nut with 100Nm force, you apply it in fact directly to the races, which will kill the bearings in few hundred miles. This is not exactly the answer for your doubts, but apart from above mentioned bearing, I have never heard about other serious failure in bevel drive dept.
involved rebuilding the bevel box, which is a right old palaver, involving checking the meshing of the gears with engineers blue while pulling the crown wheel away from the pinion to try to get the gear teeth into the position they’d be under load. I did what I could to the best of my ability, but needless to say, I was less than 100% confident in the result.
When I did mine, albeit, again, a big block, I used same shims (I was just replacing seals) so all I did was make sure there was some play at all positions of the crown wheel, this means rotating the pinion 33 times and recheck. Surprising how much variation there was, best could be done was make sure no point was tight. To try be more fussy than that, forget it!