Comet Oil Use

[Martyn Goodwin]

Hi MartynG, I really do not want to seem to be rude but ask yourself what is different in your engine from the engines in many other Comets! By all means add tubes to tubes to breather valves to feedback tubes etc. etc. ad nauseam if that is what you would prefer to do rather than look in the engine and find out what is wrong but be sure that there is something wrong. Of course many people have fitted elephant trunk breathers but many have not and do not suffer from your bike's incontinence. As davidd writes knowing and believing are different. I might believe that there are fairies at the bottom of my garden but knowing that they are there is a very different thing. Have a look and let us know what you find; broken rings, tapered bore or whatever. You will find something is wrong.

My Comet has always been an oil guzzler - remember there is no timed breather pinion within the motor. After the recent rebuild that included new bearings - all of them inc the big end, new piston (8:1) and rings (with a 3 piece oil ring) new muff and liner etc but still no breather pinion it remained a oil guzzler even with compression so high generally the only way I can kick it over is using the decomp lever.

But the breather spindle IS in place with its slot wide open all of the time - that is why the oil finds a ready path out of the motor via the normal timed breather outlet, to which I have fitted a PCV valve - but the motor is pumping an oil rich mixture right up to that valve. And when the valve closes the vacuum created between the valve seat and the oil face prevents the oil in the line being drawn back into the motor - ergo - it ends up exiting via the breather pipe onto the ground.

I have been trying to avoid opening up the timing case to install a timed breather pinion and thus my (futile) attempts with PCV valves, elephant trunks, damper chambers and the like.

With just 2 weeks to go to a 6 day 2,000 mile rally I have just about run out of options so am now sourcing a breather pinion assembly and getting ready for yet another dive into the bowels of the beast.

According to Richardson the timed breather pinion should be installed so that it opens at 35 to 41 degrees ATDC and closes 2 degrees BBDC; Some time in the past Big Sid suggested that this should be advanced by around 8 degrees, so that the closing happens around 5 degrees ABDC. As far as the "official" riders handbook is concerned I was unable to find any information about breather opening and closing points

So - what are the ideal settings?

 

[Chrish]

Martyn, is the breather spindle slot facing up or down? if up then turn it down. The oil path will find it hard to go up very far!

Chris

 

[davidd]

Sent two articles by PM to Martyn.

Irving on Breathers: 252 MPH at 15

Higgins on Breathers: 608 MPH at 19

Both are pretty good if you have you MPH's handy.

David

 

[b'knighted]

I am still seeking to locate a suitable "elephant Trunk" as these mount over the ATD where a vortex, created by the spinning ATD keeps oil out of the breather path. M

Try running the engine with the ATD cover off and you'll find oil sprays out of the hole. The Mac Read breather has a shuttle valve just above the ATD cover and a baffled condensing chamber above the engine. Any condesed oil is sucked back through a capiliary tube connected to a D breather cap on the front exhaust valve. No oil gets past. I have only ever seen them used on twins.
The Kemp pattern appeared to be a deep ATD cover stuffed with wire wool - not the same creature at all.
Try making a cover from a piece or two of 10swg ally plate copying the gasket shape to hold a flat cover clear of the ATD. The flat cover can be steel to have your trial breather pipe soldered to it. All the layers can be sealed with paper gaskets.

 

[Martyn Goodwin]

Martyn, is the breather spindle slot facing up or down? if up then turn it down. The oil path will find it hard to go up very far!

Chris

I should know the answer within 2days as a strip of the timing case is planned for this weekend. Martyn

 

[Martyn Goodwin]

I should know the answer within 2days as a strip of the timing case is planned for this weekend. Martyn

The breather slot is facing DOWN.

Today I managed to obtain a timed breather pinion assy and I modified it as suggested by PEI in MPH 252 in that I filed the flat on the breather bush till the slot was 3/8” wide, thus extending the opening duration, with knife sharp edges then I blended the edges of the flat into the circular portion of the bush with a generous radius. I also installed a larger bore banjo and a larger bore hose, extending up, then to the rear of the bike. I have set it up so that it opens at 22 degrees ATDC and closes at 3 degrees BBDC.

All the other (rubbish?) I was trying has been removed.

Test ride this weekend.

Martyn

 

[clevtrev]

Breather slot facing down, negates the shrouding. Means that the breather is getting the maximum oil to it, not the minimum, which will happen if the slot is positioned UP.

 

[Martyn Goodwin]

Trev,

Richardson says that on a single the slot in the breather spindle should face down.

I am confused.

Martyn

 

[chankly bore]

Yeah, but whatever oil gets into an upward facing slot is going to pool eventually to the height of the spindle bore, innit? Thus hindering effluxion of compressed air.

 

[clevtrev]

Yeah, but whatever oil gets into an upward facing slot is going to pool eventually to the height of the spindle bore, innit? Thus hindering effluxion of compressed air.

Tell that to a twin.