Mk3 Crank Drive Side Oil Seal Circlip

Pre-Mk3 didn't have a circlip so there's every chance the oil seal will stay in place without.

Commandos had no circlip until the 850 MK3, it was added to stop the seal being pushed out if the engine was started with a sump full of oil. An alternative is to put a spacer between the main sprocket and the seal so stopping the seal moving outwards.

What the hell has ground that outer face away ? Norton introduced quite a number of new problems with the Mk3 which were never addressed as there was effectively no development once the model was in production. However, there is a fair amount of metal missing from the outside of the bearing / oil seal housing in this case.

Earlier models had a lip behind the oil seal which meant that the seal could at least be pushed in square. With the Mk3, it seems to be a case of enter the seal, then the circlip and gently ease the clip in, until it springs...hoping that the seal will still be square behind it. I prefer the steel-outer seals with a wipe of Loctite.

I also had problems with a damaged circlip grove on the Mk3 that I bought in 1983 after seven previous owners and probably as many blow-ups. Norman White machined out the circlip area and faced the casings then made a steel top-hat bush with two grooves that sits outside of the bearing so I now have a circlip behind the seal and one in front.

That was about thirty-five years ago and it's still good...I'd suggest having another word with Norm. It's worth getting it right as a seal that pops out in use, while not disastrous will fill the case with oil and give a clutch that slips and drags at the same time. You'll get home, but you won't be smiling !

JS Norton are selling an O ring to put outside the seal ( possibly only for pre mk3?) to prevent wet sump ejection. Dimensions have been mentioned somewhere.

That's not a commercially-produced Commando front pulley...something taken from an industrial belt supplier's stock I think. The previous owner was probably so proud of himself for having saved £50 on the conversion.

Mk3s can be fitted with belts without that butchery but there are limitations on pulley sizes.

Looks more like the results of a shredded belt to me (been there, back on chain now). The reinforcing cable inside the belts gets wound around the crank, tightens up and is forced outwards into the adjacent components. You could have it built back up with weld and machined back to standard dimensions.

Best of luck, Al.

Belt pulley looks similar to stuff that was available in the '80s.

To offer a response to your "Some people should not be allowed near motorcycles!" comment, I'd remind you that in the '70s and '80s a Commando was a cheap old banger not a rare and valued classic (still is to some of us :)). Going racing? - Mk3 cases were stronger. Belt drive pulley doesn't fit? - file a bit off the crankcase. Need to adjust the primary tension? - slot the engine plates and inner cover. Don't like LHS gearshift? - fit earlier covers. What does it matter, you're probably going to smash it up anyway.

Think of it as archeology and enjoy.