Scooterotica

Just fitted a new BGM GP crankshaft too an SX, couldn't find the flywheel nut so I ordered another one.
Of course as soon as the second one arrived I found the first one
However, neither of the BGM nuts fitted, they both tighten up after only a thread or two (and I didn't want to force them and bugger up a new crankshaft), the old SX nut goes on as smooth as silk so I know the thread is ok.
Anyone else experienced this problem?

Just because the SX nut works does not mean the crank threads are good. It sounds like you have a rolled thread on the crank but that's easily fixed with a die or thread file.

If it were me I'd run a tap through the nut and a die over the threads, then clean both. This way you know both are as good as can be.

12mm LH threads I believe.

Thanks for the reply, I had considered that, but as both the BGM nuts do the same on the SX crank I figured too much of a coincidence.

hello,

the thread on our bgm flywheel nut is intended to be a proper fit. you can't get it on by hand like the sloppy 40 year old one. but the thread is accurate and there is no problem.

but you should be careful when fitting it on a n non GP flywheel. there are different outer diameters of the flywheel nuts. and on LI/SX one you can be unhappy that it doesn't fit. in the worst case you tighten it down and is seems to be locked, but is only on two or three pitches of the screw threads.

Philipp wrote:hello,

the thread on our bgm flywheel nut is intended to be a proper fit. you can't get it on by hand like the sloppy 40 year old one. but the thread is accurate and there is no problem.

but you should be careful when fitting it on a n non GP flywheel. there are different outer diameters of the flywheel nuts. and on LI/SX one you can be unhappy that it doesn't fit. in the worst case you tighten it down and is seems to be locked, but is only on two or three pitches of the screw threads.

Thanks for your interest Philipp.
I understand the issue with trying to fit a SX flywheel to an SX crank with a GP nut, I was just trying the BGM nuts on the SX crank to check the thread.
So an interferance fit nut?
With forty years experience working on bikes, cars, scooters and commercial printing equipment that's the first time I've heard of that! (Excluding nylocks etc).
I don't accept that the original (Italian) flywheel nut is "sloppy" just because it goes on both crankshafts smoothly, it just feels like every other correctly fitting nut I have ever used.
If the BGM nut is so tight that you can't get it on more than a couple of threads by hand, surely that will effect the torque reading when tightening properly.
The BGM crankshaft looks lovely by the way, hope it works as good as it looks.
I'll be interested in any further comments regarding the flywheel nut.

Cheers

John

It'd be nice if £250 + cranks came with a nut and washer as standard.