I bet one of you knows

[Itsme]

why manufacturers now feel the need to tighten gearbox sprocket nuts so tight that they can only be undone by a fully grown gorilla with an impact gun. I remember sprocket nuts being easy to remove on a variety of bikes over the years when I've changed chains and sprockets, after all they normally have a tab washer to stop them coming loose unexpectedly.

However the last three I've done (two Suzukis and my current Royal Enfield) have needed between them a large impact gun loaned by my son, a four foot tube on a fixed socket handle and cutting down the length of the nut with an angle grinder. All of them were the first sprocket change so had all been torqued at the manufacturer.

My question is why is his necessary? Is there an engineering reason for such immense tightness? Seems a bit overkill to me given, as I said earlier, that all three nuts were held on by a security washer anyway. I would be interested in your thoughts gents.

Ian

[iansoady]

Many of the ones I've taken off over the years have been so loose they almost came off by themselves. But I agree factory torque settings seem inordinately high, even for case screws and the like - hence the frequent complaints at one time that such screws were made of cheese. Of course it didn't help we were all using the wrong screwdrivers.

I'm lucky(?) in that my bikes tend to have been dismantled many times in the past. The problem is they've been put together as heinz 57 varieties. I'm currently engaged in making wheel spindles, spacers and nuts for the little Beeza. To replace lengths of metric studding some previous owner thought were a good idea.

[Itsme]

I laughed to myself there Ian as I have had my share of finger tight sprocket nuts in the past. Cutting this one off has cost me £16 for a replacement which is a price I would have thought more appropriate for the sprocket itself! Modern world modern prices I guess.

Ian

[themoudie]

MMMmmmm! Ducati singles final drive sprockets are torqued to 50 ft/lbs and have a tab washer to secure them. Advice is to clean the threads on the shaft and the nut, using brake cleaner, apply a small amount of nut lock to the shaft thread, then tighten to 50 ft/lbs, afore bending the tab washer against a flat of the nut. 

Torqueing the nut any more than 50 ft/lbs, causes clearance problems between the gears on the gearbox output shaft, likely to cause binding and the incorrect alignment of the gears!  It is a Ducati after all!

If I remember right, the torque for the SRX twin shock gearbox sprocket, for the screws holding the eccentric plate, retaining the sprocket is only 10 Nm or 7.2 ft/lbs and a touch of nut lock on the threads. Whereas the SRX/XT monoshock drive sprocket nut requires 120 Nm or 85 ft/lbs and the lock washer bent over against a flat of the nut.

Just making sure it's "Reet tict lad!" could cause all sorts of problems, use the torque advised by the manufacturer, or depending upon the shaft diameter and pitch of the thread, together whether the thread is lubricated or dry.

I'll now return to my cave for a period of shut eye! 

Good health, Bill

[Itsme]

Hi Bill

Royal Enfield figure is 130 - 160 Nm which to me sounds ridiculous. I understand what you say about why manufacturers specify torque values, but I will be setting my torque wrench at 130 Nm and then bottling out when I feel uncomfortable. I know that I am no engineer or mechanic but for 50 years I have done my own rebuilds and maintenance and didn't even own a torque wrench for 30 of those.

I'm grateful for your reply Bill and I'm not ignoring you and I will let you know how far I get towards 130 Nm before I bottle out.

Ian

[Itsme]

Bill

I did in fact torque the nut to 130 Nm as it didn't feel excessive when I actually did the job.

Thanks chaps.

Ian