primary chaincase questions

My '74 850 is nearly done and I am hoping to be on the road this weekend....

I am at the point of re-assembling the whole Primary side.

the guy guy who did some work on the bike before me obviously left out washers and shims on the center stud...should I measure the gap behind the inner cover and shim exactly or is it a guessimate situation?

also, is there anything else I should take care about while re-assmebling the Primary side?

should I use gasket sealer on the chaincase to crankcase gasket?

what about primary chain and drive chain tightening? anyone have a straight forward procedure for this?

thanks........Eric

DEFINITELY fit up the chaincase with gasket, measure the gap, then shim as close as possible.

I like Permatex gray RTV sealer.

Loosen tranny adjuster & rear axle hardware; adjust drive chain to "snug" with rider sitting on the bike and centers of front sprocket, swingarm pivot and rear sprocket as nearly in alignment as possible. At this point, primary chain should also be quite snug; hold this setting and nip up all hardware.

Check into http://www.oldbritts.com/ob_clutch_info.html referencing the "optimal clutch stack height" for easy lever pull. Well worth the short time and very little effort that it takes to get it right.

Yes, shim the chaincase with washers after measuring the gap with crankcase gasket in place. On final assembly I use Permatex red spray stuff on that gasket (high tack?) and a light bead of clear RTV o the rubber o-ring. I also use RTV on the alternator stator wire where it exits the back of the chaincase, and on the mating surfaces where the inner and outer primary meet (around the stud bolt). I'll let it all set up over night before adding 7 oz of ATF to the case.

Factory procedure for primary chain is to use the gearbox adjuster screw to pull the chain "dead tight", then back it down until there's 3/8" total movement in the center. Rear chain is adjusted after all that is tightened up.

thanks guys for the quick responses and thanks to Jerry....this is such a great site.

Eric

Don't forget the rotor to stator gap clearance. That requires a minimum of .008" all round between them. Use a brass feeler gauge for true feel as the magnet seizes a steel gauge. Sometimes theres more gap on one side than the other. There are some "non-standard" ways of adjusting that ranging from machining down the rotor a few thou to ovalising the studs to knocking the studs with a drift and mallet in the required direction.

Also some people use a Belville washer against the centre of the rotor as these when older, can get sloppy. Pay careful attention to the alternator cable run as it exits the inner primary case. Make sure its not going to get hacked by the chain. I lube the cable with a bit of RTV as it slips through the sealing grommet.

I prefer to use a light coat of Castrol Rubber Grease on the rubber band when fitting up the outer case. Tap the case all round before tightening the centre bolt. Most leaks I think come from the Medieval Age felt "seal" in the back of the clutch cover. There is a later cupped sleeve seal holder that eliminates that, but you won't find it in the parts book. It was a very late update to the MK2' and you need a special tool to fit it. Works good.

Mick

Mick,
Since the rear seal holder is not in the parts book, do you have any pictures? Does this replace the entire double sheetmetal sliding disc?

Hi Ron,

Wish I had some pics of this rare seal holder, but I don't so I'll try to describe it as best as I can. The cupped seal holder is one new clutch side steel disc, that has the same concentric arrangement , with 4 spot weld points. The cup is a slighly curved sleeve protruding from the lip around the seal boss. It is about 6mm to 8mm tall and the back of the clutch basket sits just off it. The oil running down the face of the inner primary case no longer runs directly onto the seal as it is diverted by the cupped sleeve. Any oil flung off the back face of the basket has minimal gap to enter and the cup shape prevents flow back into the seal.

You only need the new inner cupped disc. The gearbox side can be re-used. You'll have to drill out the existing spot welds and seperate the discs. Then a shouldered mandrel has to be inserted through the 2 discs to hold then concentric when fitted either side of the inner case. You can then re-spot them or if possible, pop rivet. Refit the felt seal by first soaking it in oil and clamping it in flat plates in a vice to squish it flat. With a prod you can gently fit the seal into the boss. It will gradually expand.

I guess you could try genuine Norton parts dealers and cite that it was fitted to the very last series of MK2's. The MK3 of course was a different set up. I got mine from a good mate who used to have the Norton shop in West Australia, and he admits they are rare, most likey to found as fitted to the inner case at the factory.

I have zero leak from my primary, but I do miss that fragrant odour of burning ATF from the left pipe!

Mick

I didn't have easy access to spot welding or riveting capacities and used four (or five?) incredibly small bolts and nuts to hold those felt-seal retaining cups/plates in place (loctite on the bolt threads). An added benefit is you can fit the seal in first before tightening up the bolts, saving the delicate operation of installing it after the cups/plates are fastened together.

Seems to have worked fine, several thousand miles later. Credit for that idea goes to Matt Rambow at CNW, with thanks again Matt for saving my bacon yet again. Have placed more than one "Help me Mr. Wizard...!" call to Matt; never in vain. (Frizzle, frazzle, frozzle, frome....)

Old Britts have carried that seal cup affair in stock for some years now. Very handy, easy enough to pop rivet.

BrianK said:

Credit for that idea goes to Matt Rambow at CNW, with thanks again Matt for saving my bacon yet again. Have placed more than one "Help me Mr. Wizard...!" call to Matt; never in vain. (Frizzle, frazzle, frozzle, frome....)

Click to expand...

He's saved mine too on numerous occasions. I swear I owe that guy about 100 pints of beer by now. I'm tempted to make the 2000 mile trip down there someday just to say thanks in person.