Comet Oil Use

Martyn Goodwin

Well Known and Active Forum User
Non-VOC Member
Gday Martin
Block the Timed Breather off , Fit a Breather to a Rocker Cap ,dont worry about a PCV valve for the exercise and Ride.
See what happens
Greg
Tried it - oil all over the place. Then fitted a PCV, not so much oil but still a mess.

Went back to the earlier setup but fitted an expansion chamber between the breather outlet on the side of the motor and the PCV. Result was much reduced oil loss, but not eliminated. Work on this continues.

Still finding it impossible to source an "elephant trunk" cover to go over the ATD - that's the next thing I hope to try, if only I can find one.

Martyn
 

Howard

Well Known and Active Forum User
VOC Member
Martin, as I hinted earlier, I think the engine is throwing too much oil at the inlet to the breather. In your situation, I'd take off the timing cover, and fit a tube into the hole where the breather was, with a slot from 6 to 8 o'clock, so that the oil is flung onto an "umbrella" and any oil separated in the breather pipe can leak back into the timing chest. If you also fit a non return valve in the end of the pipe it should form a partial vacuum in the crankcase, and the air/gas flow will be reduced (assuming your piston hasn't got a huge blowby problem).

The elephant's trunk outlet is in a vortex formed by the ATD keeping oil away from the outlet .... or at least that's what I read many moons ago.

H


Tried it - oil all over the place. Then fitted a PCV, not so much oil but still a mess.

Went back to the earlier setup but fitted an expansion chamber between the breather outlet on the side of the motor and the PCV. Result was much reduced oil loss, but not eliminated. Work on this continues.

Still finding it impossible to source an "elephant trunk" cover to go over the ATD - that's the next thing I hope to try, if only I can find one.

Martyn
 

Martyn Goodwin

Well Known and Active Forum User
Non-VOC Member
Current Situation:
The timed breather spindle ET159 is in place but the timed breather pinion ET141/n is missing. At the timed breather outlet on the side of the motor I have installed a modified banjo that provides a 1/2" od copper pipe outlet connected to a short length of 1/2" ID hose that in turn connects to a home made damping chamber consisting of a 2 1/2 inch length of 1 1/2 inch bore PVC pipe. The pipe is loosely filled with stainless steel spiral scouring pad material and the end caps on the pipe have a 1/2 inch OD pipe fitted to them. From the banjo the hose and damper run vertically (up behind the carb) with the outlet of the damper then connecting to a Bunn (or if you prefer PCV) valve. The outlet of this is connected to a hose that eventually exits at the rear of the bike. Theory is that the damper diameter slows down the gas flow and then the scouring pad stuff knocks the oil out of suspension. The Bunn only opens in response to positive crankcase pressure when the piston is descending then seals tight creating a partial vacuum in the crankcase when the piston is ascending.

This works as intended and the oil is indeed removed from the gas stream by the home made damper - but the tight sealing Bunn valve prevents the oil being drawn back into the motor by the partial vacuum. If I run the bike for less than 3/4 hour no oil escapes from the breather outlet - instead it accumulates inside the damper. If I run it for much longer than 45 minutes I start to get some oil loss out of the end of the breather.

Next Steps:
I am attempting to source an Elephants Trunk breather - Kemps' no longer supply them but I am (very) hopeful of obtaining one from Mac Read (see MPH #502). If that fails I will put a leak down tube into the line between the Bunn valve and the Damper chamber. The leak down tube will have a bore no greater than 1/16 inch and will run vertically upwards for a few inches to atmosphere; the idea being that the leak down tube will be too small to allow oil out when the piston is descending but will be of sufficient size to allow the vacuum caused by the piston moving up to draw in some air allowing any oil in the damping chamber to return to the motor.

M
 

chankly bore

Well Known and Active Forum User
Non-VOC Member
Begad! you are getting more and more elaborate here. Congratulations on your monomanic perseverance. No doubt the next step will be to weld on another crankcase with a slave cylinder geared precisely to offset your Comet crankcase pressure. While you're at it you could incorporate a balance shaft to get an even more "vibrationless" Single. On the other hand, you could just keep below 65 m.p.h. like a good law-abiding citizen you old tearaway! On the other hand I have five fingers. Keep us informed, this is a gannet-bemusing Thread.
 

Martyn Goodwin

Well Known and Active Forum User
Non-VOC Member
Begad! you are getting more and more elaborate here. Congratulations on your monomanic perseverance. No doubt the next step will be to weld on another crankcase with a slave cylinder geared precisely to offset your Comet crankcase pressure. While you're at it you could incorporate a balance shaft to get an even more "vibrationless" Single. On the other hand, you could just keep below 65 m.p.h. like a good law-abiding citizen you old tearaway! On the other hand I have five fingers. Keep us informed, this is a gannet-bemusing Thread.

Egad! What a good idea. I could fit a "slave piston" (in its own separate, but internal to the crankcase, barrel) sans spark plug and valves to operate 180 degrees out of phase with the real piston - this would mean that no matter how fast things happen the pressure in the crankcase will always be neutral. All I would then need do is fit some small air filter onto the existing breather outlet to ensure equilibrium with atmospheric pressure. Now why didn't Phil think of this :)?

Hmmm - actually I think Yamaha have already done this with their XP500 motor. Bugger, another idea gone west (or should that be east?)

Just kiddin - the real work continues.

M
 

redbloke1956

Well Known and Active Forum User
Non-VOC Member
Current Situation:
The timed breather spindle ET159 is in place but the timed breather pinion ET141/n is missing. At the timed breather outlet on the side of the motor I have installed a modified banjo that provides a 1/2" od copper pipe outlet connected to a short length of 1/2" ID hose that in turn connects to a home made damping chamber consisting of a 2 1/2 inch length of 1 1/2 inch bore PVC pipe. The pipe is loosely filled with stainless steel spiral scouring pad material and the end caps on the pipe have a 1/2 inch OD pipe fitted to them. From the banjo the hose and damper run vertically (up behind the carb) with the outlet of the damper then connecting to a Bunn (or if you prefer PCV) valve. The outlet of this is connected to a hose that eventually exits at the rear of the bike. Theory is that the damper diameter slows down the gas flow and then the scouring pad stuff knocks the oil out of suspension. The Bunn only opens in response to positive crankcase pressure when the piston is descending then seals tight creating a partial vacuum in the crankcase when the piston is ascending.

This works as intended and the oil is indeed removed from the gas stream by the home made damper - but the tight sealing Bunn valve prevents the oil being drawn back into the motor by the partial vacuum. If I run the bike for less than 3/4 hour no oil escapes from the breather outlet - instead it accumulates inside the damper. If I run it for much longer than 45 minutes I start to get some oil loss out of the end of the breather.

Next Steps:
I am attempting to source an Elephants Trunk breather - Kemps' no longer supply them but I am (very) hopeful of obtaining one from Mac Read (see MPH #502). If that fails I will put a leak down tube into the line between the Bunn valve and the Damper chamber. The leak down tube will have a bore no greater than 1/16 inch and will run vertically upwards for a few inches to atmosphere; the idea being that the leak down tube will be too small to allow oil out when the piston is descending but will be of sufficient size to allow the vacuum caused by the piston moving up to draw in some air allowing any oil in the damping chamber to return to the motor.

M
Hi Martyn, what about connecting the 1/16" inch hose to a tiny hole drilled in the carb adaptor as is done in many vehicles to counter crank case pressure? and burn off any oil that does escape. Regards Kevin
 

vibrac

Well Known and Active Forum User
VOC Member
Egad! What a good idea. I could fit a "slave piston" (in its own separate, but internal to the crankcase, barrel) sans spark plug and valves to operate 180 degrees out of phase with the real piston - this would mean that no matter how fast things happen the pressure in the crankcase will always be neutral. All I would then need do is fit some small air filter onto the existing breather outlet to ensure equilibrium with atmospheric pressure. Now why didn't Phil think of this :)?


Hmmm - actually I think Yamaha have already done this with their XP500 motor. Bugger, another idea gone west (or should that be east?)

Just kiddin - the real work continues.

M

What am I missing? why do all my Vincents perform without any oil from the breather with a much quoted 1 1/2*3/4" DIA pcv valve stuck in the 3/4" pipe from cap to dry catch tank
(and that funny old timed breather plugged up)
I am trying to source another box full at the moment
 

Martyn Goodwin

Well Known and Active Forum User
Non-VOC Member
What am I missing? why do all my Vincents perform without any oil from the breather with a much quoted 1 1/2*3/4" DIA pcv valve stuck in the 3/4" pipe from cap to dry catch tank
(and that funny old timed breather plugged up)
I am trying to source another box full at the moment

Just what cap is that 3/4 inch pipe stuck into/onto?

M
 

Martyn Goodwin

Well Known and Active Forum User
Non-VOC Member
Hi Martyn, what about connecting the 1/16" inch hose to a tiny hole drilled in the carb adaptor as is done in many vehicles to counter crank case pressure? and burn off any oil that does escape. Regards Kevin


Rather than burning or loosing the oil, I am trying to find a way to have it returned to the motors oil system

M
 

nobby

Well Known and Active Forum User
VOC Member
I used this on a Comet once, wasn't necessary anymore after replacing piston and liner.
It is made by Hartmut Weidelich, here's his website.

oelabscheider.jpg
 
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