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Questions while removing engine


I’m having to open the engine crankcase to replace the cam because of a split in the tapered section where the ignition rotor fits, which was resulting in much oil loss out of the ignition cover breather hole. Engine is now on the bench.

Firstly the primary sprocket puller has some L shaped threaded adaptors which I didn’t use: anyone know what they’re for?

The cable sheath at the point where it enters the stator has cracked open (and the remainder of the cable is rather stiff). The charging was fine prior to the current work. I’m wondering whether to leave the cable as-Is or repair it (or replace the stator but the bills are adding up :-(  ). Any advice welcome.

The bike has an additional adjuster for primary chain tension which I found I couldn’t adjust with primary case fitted because no room to turn a spanner. Any suggestions for improvement other than removing it?

I’ve bought front and rear vernier engine mounts. With the engine out, what’s the quickest way to replace the rear mount. I’m going to take the gearbox cover off to fit a new kickstart shaft seal and hopefully to be able inspect the kickstart ‘pawl’ with a view to replacing if worn: I might remove the gearbox for this work, so perhaps that changes access to the rear mount?


Job of adjuster is not to tension primary chàiñ, but to stop final drive chain pulling gearbox back and overtensioning primary, as such you extra tenioner in of no use, so I would bin it.

Probably too late, but no need to dismantle top end to swap cam,  remove nuts from cylinder base, then lay engine on it's primary side, then raise barrels clear of studs, hopefully base gasket lifts too, otherwise if welll stuck down nick it with a blade where cases separate. Now you can dismantle timing case and once that timing pinion is pulled off remove crankcase half with cam. As cam is scrap you can hold it in a vice to achor it while removing it's nut which will be well stuck!

If you really want a new base gasket cut it in one place to fit it round con rods and use Wellseal.

Regards Martin


My 850 Mk2A was fitted with a belt drive primary and I fitted a second adjuster to help keep the belt run as straight as possible but, as you have found, it was a PITA to adjust with the ability to turn the nuts about 1/8th turn with each spanner movement, but it did work. If you have a standard triplex chain primary, as Martin has said, it may be easier to remove (and perhaps sell?) it. One of your photos shows some sort of flat(ish) aluminium cover over the gearbox (which is absent in the final photo) which obviously obscures access to one adjuster (or perhaps both) - what is the cover for?


Graham, I fitted an adjuster to my Atlas gearbox. In order to adjust the my belt drive primary I cut the end a ring spanner so as it would fit over the threaded shank. This could be slid along to the nut for adjustment. This worked on the Atlas not sure about a Commando. As long as you don't lean on the nut too much it seems to work.

I think the aluminium cover is cosmetic only: I’ve not seen one for sale. It does protect the subframe plate edges from paint damage when removing the awful air filter, as witnesssed by the scratches on the plate :-)


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