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Comet Oil Use

Martyn Goodwin

Well Known and Active Forum Website User
VOC Member
I have noticed at as my average speed of my Comet increases so does my oil consumption - mostly I suspect via the breather.


If I keep my speeds below 50 mph there seems to be almost no oil usage. When I run at speeds in excess of 70 mph the oil use goes thru the roof!

A recent 1/2 hour blast in the 80+ mph range ( so some 30 to 40 miles covered) resulted in almost a 1/2 pint of oil being consumed/lost.

My next step is to install a oil catch tank on the breather outlet.

My question however, is this level of oil use/loss normal??

Feedback welcomed.

Martyn
 

Garth Robinson

Well Known and Active Forum Website User
VOC Member
Where is the oil going,out the breather or into the chaincase?I fitted a seal between the main bearings and it stopped oil getting into the chaincase at higher speeds.
 

Martyn Goodwin

Well Known and Active Forum Website User
VOC Member
none into the chaincase and there is no sign of oil laks on the exterior of the motor - Its all going out the breather. The timed breather was removed some time back by a prior owner. I have a PCV valve in the line from the timed breather outlet. FWIW a complete rebuild was performed 3,000 miles back - bottom end, all bearings, new barrel and liner and new piston and rings
 

nkt267

Well Known and Active Forum Website User
VOC Member
Was the old breather hole blanked off?
I was wondering that if it wasn't could you get an air flow through the crankcase and force oil out the new breather..John
 

clevtrev

Well Known and Active Forum Website User
VOC Member
none into the chaincase and there is no sign of oil laks on the exterior of the motor - Its all going out the breather. The timed breather was removed some time back by a prior owner. I have a PCV valve in the line from the timed breather outlet. FWIW a complete rebuild was performed 3,000 miles back - bottom end, all bearings, new barrel and liner and new piston and rings
Run your finger, round the inside of the exhaust pipe.
 

rapide049

Well Known and Active Forum Website User
VOC Member
Is the Oil Exiting the Breather ? I would think the rear of the Bike would be well Lubricated
What piston to Bore clearance ?
Where is the Oil Feed hole in Relation to the oil Ring?
Check your exhaust pipe (as Trevor says)
1/2 pint in 30-40 miles , buy some shares in a Oil Company
 

davidd

Well Known and Active Forum Website User
VOC Member
I have to put my money on Trevor, but doesn't Charlie or Laurie have a leak-down tester? It will tell you right off where the problem is or isn't.

Best of luck,

David
 

Martyn Goodwin

Well Known and Active Forum Website User
VOC Member
Run your finger, round the inside of the exhaust pipe.
Checked the interior of the exhaust - tactile digit methodology - and there was nary a trace of oil there = just a thin film of dark grey soot. Also checked the plug, likewise no trace of oil and as expected for the motor so mu conclusion is that the oil is not getting into the combustion space.

I am rather certain the oil is coming out of the breather and am starting to wonder if the PCV valve has failed and is staying open all the time.

I do have a "D" type breather cover on the shelf and am wondering just how it was set up on the "D" series to be effective. Was it used in conjunction with a PCV valve or some such?
 
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