New saying: "If it 'is' broke...

....don't fix it ". We've all heard the original version. I'd like to ad this one to the lexicon. Here's the story:

Trying to fix a couple of the usual oil leaks on my '72 750 Roadster, kick shaft on one side and the sleeve gear bearing seal on the other (leaking behind the drive sprocket).

Sent the gearbox outer cover to Phil Radford at Fair Spares to do the Mk3 cover mod (milling the cover and installing standard seals for the kickstart shaft and gear selector shaft holes). Phil does a nice job at a very reasonable price. Installed the cover, still leaking around the kickstart shaft, but much less at least.

At the same time I had pulled the primary case off to switch out the old sleeve gear seal with a new one. (was also thinking of replacing the 19t drive sprocket with a 20t, but ended up sticking with a new 19t that I had lying around.)
While I had the primary drive off I noticed a very slight oil leak (tiny smear of oil when wiped with fingertip) on the crank seal. I had a new crankshaft seal on hand, so I thought I might as well replace the old one while the primary was apart.
Reassembled the primary case and took the bike out for a run. The new sleeve gear seal still leaked, but, again, not as badly.

Additionally some small leakage that I was getting from the crankcase joint in the flattish area behind the cylinders was now much worse, presumably from the increased pressure caused by replacing the crankshaft seal.

I have 2 questions: For the crankcase joint leak I was thinking of springing for the CNW crankcase breather reed valve that Matt sells for 1972 only that can be installed (with patience) with the engine and gearbox in place. It's pricey, so I wondered if anyone has any opinions or direct knowledge of the valves efficacy in relieving crankcase pressure?

Secondly, regarding both the kickstart shaft and sleeve gear seals (which still leak after installing new seals), is it possible that eccentricity of shaft rotation, possibly caused by some bearing slop on the kick/layshaft ass'y. and mainshaft, would ensure that the leaks will never stop without rebuilding the gearbox with new bearings, bushings etc.?

Regarding your kick starter oil leak, is the kick start axle perfectly smooth in the area where the Mk III seal contacts it? If it is, check to make sure you are not getting a pressure build up in the gearbox case. Some folks say this can be an issue. Others say it's an urban legend. Norton created a small brass vent for the Mk III models. It screws into the top of the inner cover. This can be easily retrofitted to earlier gearboxes.

Gearbox Vent Pipe

Regarding the oil leak at the engine to inner primary cover gasket, check the shimming on the inner cover support stud. If you do not have that shimmed correctly, the inner cover will not be parallel to the the engine crankcase, causing a leak. Items 8 & 11 linked below. The shims sometimes are lost or thrown away by previous owners.

Commando Primary Exploded View

Improving the crankcase breathing is always a great idea to eliminate/minimize oil leaks.

For the counter-shaft gear leak, verify that the outer diameter of the spacer which the oil seal lip rides on is not grooved. During gearbox assembly, I like to apply a thin layer of RTV [silicone sealer] between that spacer and the counter gear. This insures that the oil is not actually leaking between these two parts, rather than the oil seal. I also seal the threads between the gearbox shell and the shift fork shaft, to prevent any minor leakage through those threads.

Phil told me it’s kind of a secret that he is still in business. No more spares sales, but he still works on customers machines. Over to the left in the avatar is my ‘72 roadster bought from Phil in 1997.

chaztuna said:

Regarding your kick starter oil leak, is the kick start axle perfectly smooth in the area where the Mk III seal contacts it? If it is, check to make sure you are not getting a pressure build up in the gearbox case. Some folks say this can be an issue. Others say it's an urban legend. Norton created a small brass vent for the Mk III models. It screws into the top of the inner cover. This can be easily retrofitted to earlier gearboxes.

Gearbox Vent Pipe

Regarding the oil leak at the engine to inner primary cover gasket, check the shimming on the inner cover support stud. If you do not have that shimmed correctly, the inner cover will not be parallel to the the engine crankcase, causing a leak. Items 8 & 11 linked below. The shims sometimes are lost or thrown away by previous owners.

Commando Primary Exploded View

Improving the crankcase breathing is always a great idea to eliminate/minimize oil leaks.

For the counter-shaft gear leak, verify that the outer diameter of the spacer which the oil seal lip rides on is not grooved. During gearbox assembly, I like to apply a thin layer of RTV [silicone sealer] between that spacer and the counter gear. This insures that the oil is not actually leaking between these two parts, rather than the oil seal. I also seal the threads between the gearbox shell and the shift fork shaft, to prevent any minor leakage through those threads.

Click to expand...

Thanks for your comments. I think you may have inferred a leak that I don’t have, that being the engine to inner primary cover gasket. That seals fine. I have the correct shims and knew about that aspect.

On the other two, the kick start shaft is smooth (not scored) but there’s a fairly abrupt taper on the shaft, as it turns into the splines, right in the area where the seal is. It seems like the seal is on the right side of the taper to seal correctly, but there is some end play in the shaft so maybe it doesn’t quite seal all the time.

On the seal behind the countershaft sprocket I did replace the spacer (which was scored) with a new one. I think I see your point about possible leakage between what would be the inner diameter of the spacer and the sleeve gear itself, but doesn’t the spacer spin independently of the shaft? Not quite sure how or where the sealant would function.

Any opinions from anyone on whether eccentric rotation of the gearbox main shaft would contribute to oil
leaking past the seal??

The gearbox already had a breather, the clutch cable hole, why they added the brass plug when they already had a breather is a mystery.

The '72 style reed valve breather is a good mod, Don Pender @madass140 also sells a very similar product at a better price than CNW - that is where I got mine. It is not too bad to install - replace the 4 button head screws that hold the body together with hex head screws, and then use a ratchet wrench to tighten. Removing the upper and lower transmission bolts so that you can pivot the trans out of the way is key. Having the bike up on a bench makes the job a lot more pleasant as well.

Hope this helps!

The leak between the cases behind the cylinder was there from the first day with my new Norton in '72. The CNW or most any breather should cure it and other leaks like the tach drive. I have the CNW on mine and it was a close fit but I didn't have to move the transmission.

luckyed said:

snipped

On the other two, the kick start shaft is smooth (not scored) but there’s a fairly abrupt taper on the shaft, as it turns into the splines, right in the area where the seal is. It seems like the seal is on the right side of the taper to seal correctly, but there is some end play in the shaft so maybe it doesn’t quite seal all the time.

On the seal behind the countershaft sprocket I did replace the spacer (which was scored) with a new one. I think I see your point about possible leakage between what would be the inner diameter of the spacer and the sleeve gear itself, but doesn’t the spacer spin independently of the shaft? Not quite sure how or where the sealant would function.

Any opinions from anyone on whether eccentric rotation of the gearbox main shaft would contribute to oil
leaking past the seal??

Click to expand...

Are you referring to end play in the kick start axle? Does your gearbox have a ball or roller bearing on the left side? Sounds like you need to limit that end play to keep the seal in the proper location.

Once you tighten up the nut which retains the front final drive sprocket, that spacer is locked to the sleeve gear. There is on seal between the ID of the spacer and the OD of the sleeve gear. Apply your favorite sealant either between the spacer ID and the gear OD, or the spacer inner wall and the outer side of the sleeve gear face. Either will ensure you get no leakage at that point.

The Triumph 5 speed gearboxes, unlike the Triumph and Norton 4 speed boxes actually have an oil seal between the main-shaft and the outboard end of the sleeve gear. An orbiting main-shaft would make short work of the bushing inside the sleeve gear. Even if gear oil were to leak from this area, you would not find it around the final drive front sprocket. That oil would leak into the primary cases. You can see the Triumph 5 speed oil seal mentioned above in the link below. It is item #1

Triumph T140 Gearbox Exploded View

Thanks all for the informative replies. You gotta love the Forum. Looks like I'll be installing a breather. I'll look into Don Pender's version. I've purchased some parts from him but hadn't noticed the breather.

Thanks Chaztuna for clarifying the interface relationship between the spacer and the sleeve gear. May be worth removing the primary case again to see if addressing that cinches up the remaining leak. As I mentioned the leakage was way less after putting in just the new spacer and seal.

Yes the endplay in the kick start shaft/axle appears to be causing the seal to not be riding on the optimum location on the shaft some of the time. I thought of putting some kind of spacer on the end of the shaft between the outer cover and the kick start lever thereby drawing the shaft outward from that end, which would keep the seal positioned on the main diameter of the shaft. I wasn't sure what effect that would have inside on the connection of the kickstart shaft and the layshaft.

I've read a number of threads on layshaft bearing replacement and the need for adjusting the endplay when a roller bearing is used. I haven't been into the gearbox yet, so I don't know what type bearing is on the end of the layshaft. I guess it might be time to tackle that inspection.

Anyway, thanks again guys for directing me to some possible solutions. Maybe some day I won't have to do my oil wiping ritual after every ride on one of my favorite bikes!

luckyed said:

Thanks all for the informative replies. You gotta love the Forum. Looks like I'll be installing a breather. I'll look into Don Pender's version. I've purchased some parts from him but hadn't noticed the breather.

Thanks Chaztuna for clarifying the interface relationship between the spacer and the sleeve gear. May be worth removing the primary case again to see if addressing that cinches up the remaining leak. As I mentioned the leakage was way less after putting in just the new spacer and seal.

Yes the endplay in the kick start shaft/axle appears to be causing the seal to not be riding on the optimum location on the shaft some of the time. I thought of putting some kind of spacer on the end of the shaft between the outer cover and the kick start lever thereby drawing the shaft outward from that end, which would keep the seal positioned on the main diameter of the shaft. I wasn't sure what effect that would have inside on the connection of the kickstart shaft and the layshaft.

I've read a number of threads on layshaft bearing replacement and the need for adjusting the endplay when a roller bearing is used. I haven't been into the gearbox yet, so I don't know what type bearing is on the end of the layshaft. I guess it might be time to tackle that inspection.

Anyway, thanks again guys for directing me to some possible solutions. Maybe some day I won't have to do my oil wiping ritual after every ride on one of my favorite bikes!

Click to expand...

There are also these:

My saying - if it ain’t broke, break it.

also - don’t force it, use a bigger hammer.

luckyed said:

....don't fix it ". We've all heard the original version. I'd like to ad this one to the lexicon.

Click to expand...

A few years ago, I came up with "If it ain't broke, fix it till you are".