Oil in my primary drive...

Your guesses about the crankshaft oil seal leaking are probably correct.

Like tyres, this item does eventually wear out and then lets oil blow past it into the primary chaincase on each downstroke of the pistons.

Then on the upstroke of the pistons a partial vacuum occurs in the crankcase which, in turn, sucks air through the seal from the primary chaincase. This in turn causes partial vacuum in this area which can suck oil through the gearbox mainshaft. Doubling the original problem.

Replacing the crankshaft oil seal is done from the primary drive side and is fairly straight forward in your case.

Youjust have to remove the front pulley (on your bike) and alternator then this will give access to the seal. Those of us still using a chain usually have to remove the clutch drum/sprocket as well.

The old seal can be levered out with a small screwdriver by first carefully punching throughits face. Make certain that the replacement has a dollop of grease on its inner lip and more on the crankshaft before sliding it into position. The open side of the seal faces in towards the crankcase. A piece of tubing that matches the size of the seal can be used to drift it into place. It should sit correctlyin place almost level with the edge of its housing.

One other sensible job to complete before reassembly of the all the bits is to pull out the 3 bolts that hold the inner chaincase to the crankcase. These have a coarse thread which can allow oil to seep them into the primary drive area. Clean up boththe bolt and crankcase threads and then replace with a tiny amount of sealant on each. Either a heat resistant silicone or gasket paste will do.

The hardest part of this whole job is torquing up the crankshaft nut. You will probably need some extra bodies to help with this.

Previously wrote:

Hi all,

Which I guess would normally be OK - but my bike ('72 Roadster) has a belt drive, so every 1000 miles I take off the primary drive cover and mop out a few cc's of engine oil.

I think its coming from the crank seal.

Has anyone else had this issue and if so what was the fix?

If it is the crank seal can it be replaced from the primary side, without major engine strip?

Regards - Paul.

Hi Paul

Iwould also check the crankcase breather.The none return valve mod works well

Regard Kev.

Paul,

Before you replace the oil seal check if the key for the primary sprocket (#06-7595) is a half moon shape or a half moon with the corners cut off. The full half moon ones, of which I have seen several over the years, tend to dig into the oil seal with the pointed end and ruin it. This happens as you put the sprocket on- i.e. behind the sprocket, out of sight- so you are not likely to notice straight away.

Justonemore thing.While you're at it, you could replace the clutch centre nut 040373 with a modified version fitted with aninternal O-ring to slide over the clutch rod. This will stop oil seapage along the clutch rod. This is a cheap mod, they are sold from various suppliers, I think I got mine from Andover Norton.

Previously wrote:

Previously wrote:

Paul,

Before you replace the oil seal check if the key for the primary sprocket (#06-7595) is a half moon shape or a half moon with the corners cut off. The full half moon ones, of which I have seen several over the years, tend to dig into the oil seal with the pointed end and ruin it. This happens as you put the sprocket on- i.e. behind the sprocket, out of sight- so you are not likely to notice straight away.

I agree with Joe as that turned out to be the same problem I've had for years. I also run a belt drive and the drive seals never seemed to last too long, especially after major engine work. For various reasons I've removed the crank twice in the last three years, for bearings and a cam change. If the seal is already installed and the crank inserted the keyway can easily damage the seal. With the crank installed and the seal then replaced it is much less likely. Thesealing is, however, notgreatdue to it running on an old worn crank. Ideally the crank needs building up and machining. If installed carefully mine lasts 6000 miles before it starts to weep.

I got fed up with replacing the crankshaft oil seal on my 750. The problemfor me was the amount of oil seeping past the oil pump into the crankcases. Ifound that if I didn't drain the oil out before starting the engine the extra pressure would force the seal off its mounting face â yet again. The cure, for me, was to fita Hemmings anti-drain valve into the oil line. A lot of people say these aredangerous and I'd agree normally but I trust Mick Hemmings to do a good job. Ifitted one a couple of years ago and have not had a drop of engine oil in theprimary drive case. Another benefit is that the clutch doesn't get too much oileither which means it frees up instantly.

I need to point out that I religiously serviced the oil pump at the lastrebuild but the oil draining continued. Also, the Hemmings valve is well madeand comes with easy to follow instructions so do the job properly and it will beOK.

Finally, if this post comes out under the name ann_nicholls itâ because Annis Solent Secretary and for some reason that means I donât get my own log-inID! Thatâs the thanks the NOC give me! Ha, couldnât really care less! Itâsactually Jem Nicholls here finally getting around to putting something onto themessage-board and (more importantly) still enjoying thundering around on theCommando.

Previously wrote:

Hi Paul

Iwould also check the crankcase breather.The none return valve mod works well

Regard Kev.

Kev, which non-return valve mod are you referring to?

Allan.