When tightening up crankpin nuts, very tight, is it common to have the threads in the nuts shear, or is it advisable to only fit new good quality nuts?
Thanks Keith

email (option): Atkinson

Hi Kev...Occassionaly you will find a nut with a damaged/tight thread and they can have problems when tightened. The original nuts are of pretty good quality and reusing them isn't normally a problem.
Generally if the nut is too tight to turn by hand onto a clean, undamged crankpin thread it is best to replace it with another..Like any nut they can be overtightened. There is no torque setting laid down for the crankpin nuts so it is difficult to describe how tight to do them. What tooling are you using for tightening?
The assembly works by 'pulling up' on the pin taper and shoulder. When the pin is inserted by hand into the flywheel there should be approx. a .010" gap between the flywheel face and the shoulder on the crankpin. The nut then pulls the taper into the flywheel, stretching the hole until the pin shoulder comes up against the flywheel face. The pin is then 'locked' on both the taper and the face of the shoulder. Once there the nut needs to be tight but there is no point going too far beyond that point... .Ian

email (option): ian@wright52.plus.com

I tend to tighten them to 100ft/lbs, I tried doing them in the past by "feel" then I tried my torque wrench bit by bit until it just started to turn it and I came up with the figure. I have had no problems with genuine nuts, but I've had a few Alpha ones that the threads have gone on despite being a nice fit on the pin. If you look on the technical section there is a whole thing on how to help you do them

email (option): davmax@ntlworld.com

I am using a suitable sized socket with the chamfered end ground flat, so the socket fits right down over the nut. I have a piece of flat bar about 800mm long, with the socket welded in the middle. So yes, with this tooling, and the flywheel cheek clamped firmly in the vise, I can get the nuts very tight.
When I dismantled these flywheels, I found the nuts incredibly tight, also very difficult to break the taper once the nuts were undone.
I noticed the 100ft/lbs figure in the excellent article in the tech section.
I was just trying to nip the nuts up tight, as before, but 2 original second hand nuts I have tried, have sheared out the thread. Luckily not the pin thread.
Keith

email (option): Atkinson

Hi Kieth (not Kev!)..It sounds like you may be overtightening them..I use a 3/4" drive socket bar with an adaptor to fit the 1/2" drive socket..over the end of the socket bar I put a piece of thick walled stainless tube. This gives a lot of leverage but it is there more for improving 'feel' than for swinging on the end of. What was the fit of the nuts you used like over the new crankpin thread before tightening?....Ian

email (option): ian@wright52.plus.com

I used the peice of flat bar with the socket welded in the middle, so I could get the 6 sided socket to stay perpendicular to the nut when tightening. Before when I done a flywheel rebuild, I only had a single bar, or single sided leverage, and the socket tended to skew off causing damage. These nuts and pin are the same. They are not replacements. I refurbished the bearing using the same pin. Thats why I though it might be good policy to buy a set of new nuts.
Anyway
The threads looked in good condition, and clean.
I could hand screw the nuts onto the pin, about 1/2-3/4 the distance, then they would get progressively tighter until they contacted the face of the flywheeel.
I think I may be overtightening them as you say, as I now have the perfect tool for wrenching them up very very tight.
I was just concerned because when I dismantled the assembly, the nuts took considerable effort to crack undone, and I don't think I am doing them up again any tighter than before.
Thanks keith

email (option): Atkinson

I think when the BSA ones were made, they were copper plated on the threads this was to allow them to be hardened without hardening the threads (Harley used to do this too) I think Alpha's ones didn't use this method, which allows the threads to be hard enough to damage the threads on the nuts, I've noticed that when you tighten Alpha ones there is usually a thin sliver of the thread comes out of the end of the nut like a thin piece of wire, even if the nuts were hand tightenable on the pin before fitting. So many people have made the big ends in the past that you may have a mix and match of components that aren't always compatable under load, or you may have "stretched" threads on the pin which is giving the nut a variable pitch to contend with when tightening them, do you have thread guage to check if the pitch to see if it dosen't vary?

email (option): davmax@ntlworld.com

I have a selection of crankpin nuts, they all look the same type though. Maybe some are non BSA. Hard to tell.
I have a thread gauge, so I'll check for any stretch in the pin threads.
Interesting about the copper plate coating.
I suppose if the shoulder on the pin is hard up against the inside flywheel cheek, and the nuts done up firm, as against very tight, and with the locking washer and screw installed, then the whole assembly should stay together OK.
I have to order in some other parts, so I might buy a couple of sets of nuts. No doubt these would be after market, but if made in England and sold by Draganfly (for example) then I shouldn't go wrong.
Keith

email (option): Atkinson