Oily rear tire

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May 19, 2006

I'm new to the forum but have been checking it out for several weeks and appreciate all the knowledge that is available from this medium. I have owned my 74 Commando for about 13 or 14 years, I purchased it as a totally disassembled basket case. I put it together without really restoring anything other than fixing or replacing broken or missing pieces and have enjoyed it off and since then riding it once or twice a week during the summer. This summer with the help of the forum I got it running, charging, starting like a new bike with all original equipment except new Amals from about 4 years ago, the last time it was registered.

Any how I've ridden it to work a couple of time this week, 20 miles highway one way it totally covers the rear wheel with oil and seems to be coming from the bottom of the primary, I have taken the primary off and the oil seal is buggered it's overfilling the primary causing clutch slippage.

How does the oil get out, it is not getting past the seal behind the clutch, The oring seal is new from a few years ago,also the chain is rubbing the inside primary case, is this due to incoorect spacing of the inside cover or a warpage issue or something else, I have not "glassed the covers" due the stator studs & locating dowesl are they both pressed in or screwed in.

Any info would be appreciated.


Daryl, It sounds like you have a number of different problems here and ought to address those that you have already identified before proceeding. Oil can get on the rear tyre from a number of sources including the chain oiler (if fitted), a wrongly routed breather pipe from the oil tank or sundry other leaks from various oil pipe junctions.
I recommend that you check the oil filter pipes down by the rear wheel and also the oil tank banjo bolt where it enters the tank there should be a sealing washer either side of it. I also suggest that you clean the bike down thoroughly and take it for a short spin round the block and see where the oil starts to leak first.
Oil can get into the primary case from the engine due to a leaking crankshaft seal which can be changed insitu by using a couple of self tapping screws to grip the seal edge and then pull it or lever it out carefully. Oil can also leak through the holes where the three bolts attach the inner primary cover to the crankcase if one is loose or has come out, and oil can leak past a good crank seal if the engine internal pressure is too high due to poor breathing or starting a bike with the sump full of oil due to wet-sumping.
Gearbox oil can creep down the clutch push-rod tube and contaminate the clutch plates and in extreme cases also add to the oil in the primary case. Norvil motorcyles in the UK sell a seal that goes on the end of the clutch shaft to prevent this.
Regarding your chain hitting the case. The clutch drum is positioned on the gearbox mainshaft using a circlip, a recessed washer that goes over the circlip and a number of shims to allow you to get the chain lined up correctly. The inner chaincase itself is also shimmed by washers under the centre mounting stud to ensure that there is no undue pressure on the case. If you had no washers there at all when you tightened up the centre mount the case could be pushed in towards the gearbox and distort. If you put your outer primary case on without the large O-ring/sealing ring you should be able to identify any gaps with a thin feeler blade. The O-ring is compressed a fair bit when installed and quite forgiving of some degree of poor fit. Good luck and keep us posted.
Thanks Dave,

The crank seal is definitely out, the first thing I checked was the oil filter lines, I replaced them as cautionary items although they looked and pressure tested fine, I have no wet sumping, I have a check valve installed. How can I tell what is too much crank case pressure, If I kick it over with the dip stick loosely set over the oil tank there is sufficient pressure to lift it. The inner primary bolts were definitely not overtight .The oil getting into the primary is not gear oil, So that side of it should be ok. As far as the shims behind the centre primary cover bolt there were two, this is possibly not enough, the chain is lined up in front with a straight edge across the sprockets. I'll do some more digging and let you know what I find.

Daryl, When you say the crank seal is definitely out do you mean you have ruled it out as a source of the leak or it has come out from it's position. If you are sure that it is engine oil then it has to be coming from the seal or the bolts. Why not try running the bike without the outer primary case fitted for a short trip up the road. The primary case oil is only there to cool and lubricate the chain so a moderate ride should not be any problem. There is some consensus amongst Commando owners that crankcase pressure is often too high. Some people add additional breathers to the timing chest where the distributor used to be on the first Commandos, others fit a PCV positive pressure valve from a GM catalogue in the breather line and this is supposed to stop the engine sucking pressure back in through the line and adding to crankcase pressure. I suppose if this fault has only surface after a recent recommisioning then it has to be the interface between the engine and the primary that is at fault somewhere.
Sorry, when I said the oil seal is out I meant literally, out of comission,
it has somehow separated itself. when I pryed it out , it came out with the rubber separated form the metal ring.I can see how it is overfilling the primary I just can't see how it is getting out. I took and sanded down the outer case of the primary, checking it on a piece of glass, the middle of the cover is about 30 thou clearence while the ends are tight. This probably pulls itself in as the center cover bolt is tightened. Also wouldn't less shims on the centre bolt behind the inner primary cover allow more clearance between chain and cover. I wil order a new seal and a spare and let you know how I make out. I will also try the PVC valve. Do you just install it inline in the breather line. How about additional venting, do guys drill an additional hole in the timing


Daryl, Given that you have identified the source of the leak into the primary cover that is the first thing to fix. The problem may then be completely cured and no further action necessary.
If the seal is shot to the extent that you describe you will also get crankcase pressure venting into the primary cover which under normal circumstances is only subject to atmospheric pressure, this extra pressure may be forcing oil out of what would otherwise be a perfectly oil-tight assembly.
The PCV valve should be attached to the crankcase vent tube before it enters the oil tank. I would not recommend drilling additional holes at this stage unless you have clearly identified a problem. The PCV valve costs only a couple of dollars and should help alleviate excess crankcase pressure.
Regarding the primary case mounting, the three bolts mounting the case to the left side of the crank case define the position and line of the inner cover all the way back to the gearbox as it is theoretically non flexible. The washers behind the inner casing should just be able to be rotated by hand but not have any discernable clearance between them and the case with the outer cover off, such that when you tighten up the centre bolt through the outer chaincase you are merely compressing the inner cover onto a mounting that more or less allows it to be stress free. The outer cover boss and the inner cover boss should clamp together on the mounting stud without warping the chaincase at all.
Is it your primary chain that is hitting the case or the final drive chain? There is a thick washer on the top adjuster/mounting bolt between the left side g/box mounting plate and the top mount of the gearbox is this present on your bike?
Finally are you sure that you have lined up the front and rear primary sprockets when fitting them? What did you use as a reference point to assess alignment?

The seal behind the clutch is made of felt and doesn't really seal the oil inside the primary. With a bad crankshaft seal as you mentioned I'm sure the oil is filling the primary quickly and going out this seal. My '72 has been over filling the primary and the crankshaft seal is new. I just put loctite on the three bolts under the alternator (holding the inner case onto the crankcase). Hopefully this will finally stop the primary from getting over full.
I was wondering about the crank pressure also building up in the primary and blowing out the oil , it does look like it is coming out between the crank case & inner cover and also between inner & outer cover, definitely not out the transmission opening, the prrimary chain is rubbing inside the primary cover. I am ordering the correct shims & spacer for the clutch locator as well as a new oil seal today. I will let you know what is happening when I get it back together.

Thanks again
Sounds like you have a handle on all the seal issues. Worry about the crankcase pressure after replacing seals and gaskets. Having a missing or bad crankshaft seal is the major factor here.
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