Solving primary chaincase oil leaks

I thought I would share this with others who have irritating oil leaks from the primary case. No matter what I did, I could not get mine completely oil tight. I checked for leaks from the felt seal behind the clutch, the alternator wire grommet and the crankcase/inner primary joint, and all OK, so it had to be from the inner/outer case joint.

The standard rubber band is a sloppy fit in the inner chaincase groove. I got some O ring cord of 5.7 mm diameter from a specialist seal supplier (Norton item is approx. 5 mm). The 5.7 mm cord is pressed into the groove dry with moderate thumb pressure, and it should stay put when the outer case is removed. With a smear of silicone gasket on the face of the outer case, so far no leaks (touch wood). It is only necessary to cut the cord with a blade so that both ends are just touching when pressed into the groove, with the gap in the middle at the top, since oil tends to leak only from the bottom. Or you could splice and Loctite it. The outer case tends to distort a little when the sleeve nut is tightened (assuming the inner case is also shimmed properly). The larger diameter cord may be just enough to compensate for this.

If anyone wants to try it, you should state the application so you get the correct O ring material. 3 metres should be enough for one seal plus a spare.

Congratulations on your fix Dave.

I found a solution to the dreaded drips as well. After fitting a new seal to my fully cleaned up case and cover with the joint at the top all done proper it still leaked. Then seated the new seal in silicone and tried again and it still leaked.

I gave up and fitted a belt drive (no leaks).

This also has the added benefit of by using a high ratio belt kit I can now kick the bike over a million times easier than it used to be. (I'm not one the worlds heaviest Commando owners!!)

Mike — Yep, that's a good way to sort your primary leaks permanently! After reading many posts on Commandos belt drive conversions, I realise their value. I even have one on my classic racer, but I find it difficult to justify the cost for my Commando. I'll persevere with the chain for the moment, but a belt is a long term aspiration.

mike916sp said:

This also has the added benefit of by using a high ratio belt kit I can now kick the bike over a million times easier than it used to be. (I'm not one the worlds heaviest Commando owners!!)

Click to expand...

Is the kick difference really that noticable,? I dont have a leak but find i mostly need to put the bike on the centre stand to start it, not ideal if i stall at the lights or am parked in a kerb at an angle , I am practising starting with out using a stand at all but an easier kick would make life much better

Yep does make a difference. Probably about 25% less effort needed to kick the bike over so I would recommend giving a belt a try if your having problems - but make certain you get a high ratio kit!

I have had no worries with the stock rubber band, but I use Castrol Rubber Grease when fitting up the outer case. However, I had another popular irritating leak issue, from that poxy inner felt seal, running down the back of the inner case then along to the front and dripping onto the hot left header pipe.
The standard felt seal holder is 2 flat concentric sheets of panel steel with 4 contacts welds holding the inner panel to the outer. Oil in the case just gets past the seal about 100 miles after replacing it. But to my surprise, the factory actually recognised this and did something about it!

Sometime toward the later series of 850 Mk2's they added a circular sleeve protroding about I guess 5 or 6mm outward from the inner panel to just off the back of the clutch hub. The idea is that oil running down the case now flows around the sleeve and the felt seal is somewhat protected from constant immersion.

If you can find this inner panel, it is worth fitting. Note you need a mandrel to fit into the seal hole to align the panels when you either spot weld or pop rivet them back together held in the inner case. Wipe some high temp grease on the mating faces as well to act as barrier to oil migration.

As usual, with odd changes to production parts, they did not record a new part number! The only part no' through 750 to 850 Mk2 is 06-0769 "Chain Case Oil Seal Disc". The word "Temporary" could well be inserted.

Mick

ML — interesting. If I understand you right, the circular sleeve you mention is a modified version of the flat disc in two halves that is pop riveted to the inner case. So the inner half of the disc (facing the gearbox sprocket) is the same, but the outer half (facing the clutch hub) has this protruding sleeve you mention?

I wonder if a lack of ventilation exacerbates leaks from this spot? We know that lack of ventilation in the gearbox causes oil to migrate along the path of least resistance, through the clutch pushrod tunnel in the mainshaft, because Norton fitted a breather on the Mark 3 to cure this.

Dave,

Yes, the disc facing the back of the clutch hub has the protruding sleeve, the opposite one facing the gearbox is the same flat disc. I would recommend anyone re-assembling the primary to chase up the upgraded part as it is well worth it. I literally have no leaks from the primary.

As to ventilation, it may be a issue, but theres lots of room in the primary case. I have never had gear oil running through the mainshaft into the clutch on any Norton, Triumph or BSA as I apply axle grease to the pushrod which seems to act as a barrier to oil migration and I park the bike's sidestand on a 2 inch wood block so its not so angled over to prevent gear leakage out the drive seal.

Mick

Thanks for the clarification, Mick. Interesting that you use axle grease in the pushrod tunnel. Hadn't thought of that.

Dave