Sump Plug Torque

I see that the list of torque settings in the Workshop Manual doesn't offer any value for the sump plug (perhaps because of the different possible designs?)

My suggestion is restraint-plus-lockwire … 

Of interest to some people.......the revised Dominator Service Notes also do not mention a torque setting for any of 4 types of sump plugs fitted to those engines.

The nearest in terms of BIG threads was the exhaust rose which had a recommended 50 ft lbs. This is similar to the large sump plugs in that it also has a crushable washer under its head. However, I think that 50 lbs of torque is probably far too high for a sump plug and half that amount of pull would suffice. These are often pigs to loosen once over-tightened.

If its a 72/73 750 then they don't have the large sump plug, only a 5/16 or 3/8 plug which will be a lot lower than 50 ft lbs. That small thread is easily stripped so I just go by feel, lockwire would be good insurance. 

I now know from bitter experience that the recommended torque setting for a magnetic sump plug is rather less than might be imagined - I sheered the top off mine whilst trying to torque it to, what I thought was a conservative, 15ft lbs.

The magnetic plugs seem to be constructed by drilling out the centre of a standard bolt and gluing a magnetic insert into the well that is created.   The net result is a plug which has an inherent weakness at the base of the drilled section.  The recommended torque setting is apparently 5ft lbs.  Now I just need to figure out a way to get the old one out!

Regards to all

Left hand twist drill?

Thanks David,yes, that’s my Plan A.  My concern is damaging the crankcase and I really want to avoid removing the engine if I possibly can.  My plan is to drill a hole through the centre of the top of the plug that sheered off and then use it as a drill guide for a left handed drill….

Plan sounds good but start off with a small drill first, you can then see if its off centre and then use the next size drill up to re-centre by starting off at an angle, straighten up when back on centre. Or chuck it in a lathe and centre drill.

I'd be constantly worried it would unscrew itself and drop out, especially on a Commando where although the rider doesn't feel the vibrations they're still there.

I just nip it up and have not had one fall out yet. Reality is that I doubt if anyone has heard of one coming undone.

Don`t be tempted to use a cheap or old uncalibrated torque wrench on your bike, better to use feel and common sense rather than having to repair busted crankcases.

Just nip it up and leave it at that I have had MK2 from new in 1974 and had no probs. Torque wrenches can be wrong, even quality ones

My attempt to drill into the broken magnetic plug sadly failed - the core is too hard even for my cobalt drills, so I may have to bite the bullet and pull the engine after all.  Interestingly the replacement magnetic plug came with a health warning - max torque 10ft lbs!

If you want to be certain:

With care and patience I was able to remove the broken plug in situ using a modified M8 tap extractor and a car scissor jack!  Needless to say the new plug was fitted very carefully and wire locked in place.  Thank you to everyone for their ideas and suggestions.

Regards to all

Richard

so for the benefit of others, the jack was ?? used to apply upward force as you engaged the tap?

I used the Jack, leant over at the appropriate angle, to apply upward pressure on the tap extractor to force it to engage in the broken plug.  I shortened the prongs and “castellated” the top of the extractor with a dremel to give it teeth and made a small aluminium base plate with a recess to stop the tap extractor slipping out of place as I applied upward pressure with the Jack.