Inner Primary main shaft seal

I have the primary apart on my 72 750 to cure a really bad leak. Putting ATF in there wasn't helpful as it just comes out even faster than thicker oil. What I found is the felt seal is worn out and the steel plates are a very loose fit. Thinking of using a rubber o-ring rather than the felt seal. Any reason why this might be a bad idea?

I think the rubber will not cope with turning shaft. it will heat and melt very quickly.

I wonder if you could modify that to accept an oil seal like the 9815 being used on kick start shafts. Do you have the diameter handy? Of course going to a belt drive...yada yada yada...

Russ

I blamed that seal for a lot of leaking I used to have. However, now I'm still using the same seal and felt and it's not leaking. I'm sure the oil was coming from lots of other places. If I were you, I'd repair the disks, you could probably screw it together with #2 or 3 machine screws and judicious use of loctite. Get a new felt seal and see how it goes. There are plenty of other places that show up as a leak in the primary. For some reason all the oil likes to go to the bottom most point, the primary.

Install the large o-ring with silicone inside the inner cover trough and a very thin skim of silicone on the outside flat surface, or on the top of the o-ring itself.

Apparently the newest version of the inside metal disk had a shape to it that was supposed to help with leakage, but I've never seen one. I did look for it while I was rebuilding.

Dave
69S

Thinking about it, the o- ring would likely go away quickly. Guess I'll get a new felt. Already have the discs fastened with 4-40 screws. Thanks

I washed mine with solvent really good, smeared black RTV around the perimeter of the sheet metal sliding holder (after setting the chain tension) and the existing old felt remained. Nary a drop leaks out. Way overfull with ATF. YMMV

concours said:

I washed mine with solvent really good, smeared black RTV around the perimeter of the sheet metal cliding holder (after setting the chain tension) and the existing old felt remained. Nary a drop leaks out. Way overfull with ATF. YMMV

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I like the RTV idea. Even if the chain needs future adjustment the RTV will likely give enough.

Replaced mine with a like sized disc cut from a 3/16 rubber sheet... never melted, wore away or caused problems otherwise. Shaft moves freely and the disc creates a good seal... others in the ONO have been known to use a similar disc cut from leather

You may want to put some sealer on the stater wire hole in the back of the inner chain case. Iv had some nasty leaks from there in the past.

Phil

rvich said:

I wonder if you could modify that to accept an oil seal like the 9815 being used on kick start shafts. Do you have the diameter handy? Of course going to a belt drive...yada yada yada...

Russ

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One thing I just realized, timing belts on cars are something that need to be replaced roughly every 100,000 miles. When I see an engine with a timing chain, it's a relief. So why is a drive belt better than a triple row chain? Weight, quiet yada yada yada.

illf8ed said:

rvich said:

I wonder if you could modify that to accept an oil seal like the 9815 being used on kick start shafts. Do you have the diameter handy? Of course going to a belt drive...yada yada yada...

Russ

Click to expand...

One thing I just realized, timing belts on cars are something that need to be replaced roughly every 100,000 miles. When I see an engine with a timing chain, it's a relief. So why is a drive belt better than a triple row chain? Weight, quiet yada yada yada.

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Dave
Bits from a few different stories about commando primaries:

In about 1970 or early 1971 when I had my first 70 "roadster"... I had beat the hell out of it like a ninja. I finally blew the chain off the front sprocket and it trashed the steel felt oil seal carriers. At that time I did not know the carriers were available. My dad, a highly skilled toolmaker/machinist, made some thin tapered aluminum discs with a bore to hold the felt. It was made in two halves and was had maybe .015 of seperation that was closed up by 3 or 4 little #4 screws to make a sealed and secure, but sliding carrier, against the machined inner and outer surfaces of the primary. It could have easily been made with a "real seal" built in instead of the felt. In a wet environment I don't see the tranny shaft speed as being high enough to not be entirely effective and long lasting.



In the late 80's when I was at a Lotus rally in Corning NY near Watkins Glenn. There at the track I met Carl Hockinson a Norton race guy. His belt drive story goes as follows. He used to drag race a commando for many years before going to road racing. He would go to New England dragway and with a triplex primary chain would trash a gearbox almost every weekend. He finally put a belt drive in it as they were fairly new on the market at the time...

From then on he would then go the whole season on one gearbox......

He was so enthused about them he gave me a Fair spares catalog. and urged me to try one.
I did get one and in addition to a full gearbox rebuild, I tried it. This is the ocassion that prompted me to make my clutch rod seal that I read about in the norton news, since no one was selling them.

I am absolutely convinced the MASS of the chain and clutch basket along with the energy of resonant chain whip is the cause for much gear face brinnelling/sprauling and not the shock of drag race starts. If you look at many gearboxes you will see gear face damage on commandos but much less on featherbed bikes with only light single primary chain.
Drive a bike with a belt right after installation and most alert riders can sense a huge difference by the elimination of the heavy chain whip. I pit crewed for almost 10 years for vintage racers and this is also very evident when you go to a race track and observe the open primaries and actually pay attention to the chain/belt motion.

I would pretty much put a belt drive on any commando I plan to KEEP and RIDE... trailer queens don't need them.

Dave, I just put a Newby belt drive on my 650SS. The stock setup there is as you mention, not as heavy as the Commando. Even so, there is a different feel to the bike after fitting the belt drive and clutch, it felt lighter somehow and a bit quicker to pick up.
Unfortunately after about two hundred miles the clutch no longer functions well, it is contaminated with gear oil. Now I know why the original clutch wouldn't hold!
One of each type of your seals are on the the way, might as well do the Commando too, it likely has the same problem. I believe that running type F ATF in the Commando chain case masks the problem by washing away the trans oil before it can cause a problem. When I first got the Commando it had the a dragging and slipping clutch. I put type F atf in there a recommended by an old time Norton man. After two weeks of running, no drag, easy neutral selection and no slip. The downside is as Les mentions, the hydraulic tensioner of the MK 3 doesn't really work properly with atf.
Perhaps with the seal in place I can go back to motor oil.....or bite the bullet and go belt drive.

Glen

Any chance this P/N 06-5956 (reference #5 seen here - http://www.oldbritts.com/nor_mk3_75_10.html), for a 1975 Mk III 850 would work in earlier models in place of the felt and metal disc.

Hullsfire said:

Any chance this P/N 06-5956 (reference #5 seen here - http://www.oldbritts.com/nor_mk3_75_10.html), for a 1975 Mk III 850 would work in earlier models in place of the felt and metal disc.

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Hello Hullsfire, welcome. The MKIII transmission is stationary, where the earlier bikes need to allow for for and aft movement of the trans to allow adjustment of the primary chain. MKIII uses a chain tensioner instead. Hope this helps.
Or do you propose fabricating a holder for this seal, to replace the sheet metal felt holder?

Gathering info as of right now. Riding season is coming up here in Canada and I will be opening up my chaincase for the first time.
I want to clean up the clutch plates and begin using ATF type F in there. Using this fluid will also help in determining where my only leak is from.
I'm suspecting the current felt seal. I have not overfilled the case before, always use the centre stand yet the leak does come from the counter sprocket area and run down to the bottom of the assembled primary in that traditional fashion.
I will clarify that I do fill it 'till oil runs out the fill hole and have read on here that that may be even too high.

Thus the reasoning for cleaning them up and beginning with a lower ATF fill just enough to allow the chain to lap in it.
I've purchased a new felt and 1 disc to replace while in there.
This is a point of confusion for me as I've read of needing 2 discs and spot welding or using approx. 4 small screws to squish the felt?
What's the deal there?

I appreciate the welcome. Owner since '08, first year riding '12. Long time lurker, first time poster.

Thanks all

The two steel discs mentioned are sheet metal holder for the felt, allows sliding in the (oversize) hole in the inner primary to allow the assembly to move. You'll see when you take it apart... kinda like a shield, not exactly a "seal" lol :roll:

Leak? There ain't no leaks.

Dave

Hullsfire said:

Gathering info as of right now. Riding season is coming up here in Canada and I will be opening up my chaincase for the first time.

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Yes, here too in Michigan.

The felt sandwich a good system and has little to go wrong. It serves its purpose well. The felt is easily replacable and so are the discs that hold them. Just drill out the spot welds to remove the old ones if needed and replace with the use of pop rivets. Be sure to clamp the discs together when drilling so the pop rivet hole will be aligned when assembling.

Really, unless you are simply inclined to fiddle with this, there is really is no practical need to try and update this system.

I should be more explicit. I thought the mainshaft seal in the primary was leaking, but after rebuilding and fixing a lot of other leaks, the gearbox to primary seal was not the problem. The problem is most leaks show up at the bottom of the primary cover and I always assumed it was either the primary or the seal to the GB, but I don't have that problem now. Still the same GB to primary seal and no leaks. So, it was something else.

Dave
69S

I had ordered one of each. DogT, from your previous post you mention the inner disc. I have in front of me the felt and a disc. Only the one P/N from Old Britts for the disc.

It does have a recession on one side that would seam to accommodate the felt (albeit the felt doesn't seat perfectly in there - dry anyways. Greased maybe a different story). Two discs with the recesses facing each other would seem to make sense. Again the felt would have to be manipulated to sit directly in the recesses.

Questions: (editing due to newer posts). So it will currently be a two disc set up? I might as well order a second new disc and go from there. Thanks pvisseriii.

My Haynes states to grease this "oil seal" prior to fitting the inner case onto the main shaft. Will greasing the felt make it pliable to fit properly within the recesses? It is rather dense (which also leads me to believe it should be an adequate oil seal in its location).

Lastly what type of grease to use for this?

I hope this is clear.
Thanks