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Leaking Oil....breather problem?

Avery

Forum Website User
VOC Member
I have developed quite a serious oil leak from my Comet, intermittent drip about one every 30 minutes increasing to a drip a second when the engines running on tick over - it looks like it is coming from the area around or above the drive sprocket, initially I thought it was the chain oiler was open the full way but this is 1/2 turn open. If the breather is at fault could someone please suggest a fix and how to accomplish this......I have read that taking the breather pinion anti clockwise by two teeth at BDC alleviates the problem but don't know if this is just a twin fix or is this the same for the single. Could it be another problem?.....anyone have any ideas?
 

Avery

Forum Website User
VOC Member
Would excess oil in the tank, i.e. from overfilling, vent into the primary raising the level in the clutch?

The problem started between services so presumably engine oil would have been consumed in the normal way reducing the level - I'll give that a look at though.
 

nkt267

Well Known and Active Forum Website User
VOC Member
Would excess oil in the tank, i.e. from overfilling, vent into the primary raising the level in the clutch?
Short answer is ..No
If the oil level in the tank is dropping when you are not using the bike then the bike could be 'Sumping' ie the oilm is getting past the pump and filling the sump.
If your engine is bog standard,no cranckshaft oil seal mod, the any oil that sumps into the engine will eventually fill the primary case and you will get oil issuing just about everywhere,plus the bike will disappear in a cloud of smoke.
I run my Comet with the chain oiler screw,the one in the oil tank, screwed down and I do not get any oil around the gearbox sprocket.
Before you start getting worried about this oil please have a good look round to assertain where it is coming from,degrease the area and run the bike again..John
 

Hugo Myatt

Well Known and Active Forum Website User
VOC Member
Just a thought - If one habitually uses the drive side prop stand on the Comet there is a tendency for oil to seep through the main bearing into the primary chaincase and overfill it. From there it escapes from the back of the chaincase through the hole for the gearbox main shaft.
 
Last edited by a moderator:

Avery

Forum Website User
VOC Member
Bad news....for me is the primary was level, yes the machine did sump over the winter but I experienced this problem before the oil change, I drained the bike overnight before refilling and the problem was still there after the change. I have always stood the bike with the rear wheel stand.....it leans over too far with either of the prop stands unless on a steep hill or serious camber.
 

Avery

Forum Website User
VOC Member
Thanks for that John, I did give the underside a good clean and had my head underneath looking for any where the oil was coming from, the oil seems to be gathering on the casing 'ledge' on the back of the chain case. With it being a relatively new engine after rebuild I have 'nipped' the fastenings of the most likely suspects, engine bolts, head, etc but not much if any movement - checked the valve timing after checking the head all the basic stuff but the oil leak was the same as before...... bit stumped really....
 

nkt267

Well Known and Active Forum Website User
VOC Member
I removed the chain oiler pipe and blanked off the outlet.Although screwing down the chain oiler screw in the oil tank 'should' stop the flow it doesn't always.You can always oil the chain now and again..
Oil leaks on these old bikes can be a bit of a problem to cure but not impossible.Do you have grease in your gearbox or oil?.John
 

Hugo Myatt

Well Known and Active Forum Website User
VOC Member
Having had several Comets over 40 years these are the common leaks I have experiencd. Chain oiler taper screw in the UFM becoming shouldered. No matter how much it is tightened it will still leak. A new one is the only cure. Valve lifter cable needs a lot of slack or it will leak at the timing chest. Sometimes it is necessary to shorten the external sleeve a mite to obtain this. Leak from the dynamo. Rotating the dynamo to get ideal meshing of the pinion with the large idler distorts the oil seal. It is better to have less than ideal meshing but with the dyno pinion centralised in the seal. It is often possible to fit two seals. Corrosion or uneveness of the dynamo pinion where it bears against the oil seal will cause leakage. Grease filled gearboxes are often topped up with oil. This is good for the blind layshaft bearing. Unfortunately most of the oil seems to find its way out on to the garage floor. There is a sort of core plug at the back of the gear box or should be. Sometimes this is missing and will cause a leak. One that foxed me for a long time was the oil return banjo on the crank case was undersized across the depth. It seemed to be done up tight but in fact it wasn't. It was only when compared with other banjos that I discovered it. On the back of the inner chaincase is a cast in shroud that is intended to stop chain oil flying forward. Sometimes part of this shroud is broken away due to chainbreakage at some time and the chain winding up on the sprocket. In this situation chain oil is flung forward into the recess between the crankcase and the front of the chaincase where it forms a reservoir and a mysterious dripping of oil.
 
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