Who makes this breather?

clevtrev

Well Known and Active Forum User
VOC Member
Oil on the mag cowl has probably come from the head the front left hand cylinder stud (looking from astride the bike) has two threads by which it screws into the crank case, the grove between the two threads is an oil way. When putting in the stud the upper stud the top thread should be coated with jointing compound as oil can make it's way up this thread and cause a mysterious leak onto the mag cowl. I found out the hard way many years ago and in fact it is mentioned in Paul Richardsons excellent bible. Could be the rear l/h stud been a long time since I did it and old fartdom is catching up!!.

It`s the right hand rear stud. Old fartdum has certainly caught up.
And it does not affect the mag cowl, most of those come from oil blowing out of the exhaust nut, or through the head joint.
 

minivin

Well Known and Active Forum User
VOC Member
Sadly it is coming out of the exhaust port, details as follows from an email I have just sent to Trevor:

"Latest news on the Comet is that I have fitted a crankshaft oil seal to the primary side, the engine no longer pumps oil into the primary chaincase and all over the back end of the bike. This is at least one step in the right direction.

After riding the 50 miles down to the Dorset rally this weekend, I had smoke bellowing out the exhaust when pulling away and it generally smoking when riding. After getting to the event I had to put an additional 1 pint of oil into the engine after those 50 miles. The exhaust pipe inside is saturated with oil.


After taking the 25 mile for the concours this morning, the bike was practically dangerous for anyone who was behind. A WW2 Destroyer has nothing on this bike at present. After some deliberation and putting the last 1 pint of oil I had into the oil take (that topped it up nicely over the beam within, for at least the ride home), we decided to drop the sump plug. Considering the bike had only been sat for 15 minutes after the run, a good cup of oil pissed out the sump plug hole!. Those who witnessed this are now of the believe that the engine is not purging the sump while it is being ridden. I took the decision to head straight home at that point, going straight up through Templecombe and up to Wincanton to join the A303. Initially the exhaust was not bad, but after two miles, pulling away from junctions would give a faint hint of smoke, but after five miles it was bellowing smoke once again when pulling away. Having been cut-up twice by cars who were unwilling to sit behind, I am questioning whether I wish to ride this bike any more........

Fifty miles home down the A303 and I pulled the sump plug and measured 3/8 pint of oil out of the sump, which was then put in the UFM and another 5/8 pint was required to bring the oil level over the beam.


The oil pump is now of high suspicion, however, what with the engine breather being another possibility I have now installed a Mac Read engine breather (loaned from Norman Lord) and have blanked off the engine breather by tapping the A22 banjo bolt for the breather pipe, 5/16 BSF down its inner bore and fitting a 5/16" BSF length of stud to blank it off.


I will also leave the sump plug out over the next 24 hours and see if any additional sumping happens. At present, not much was obvious, but I may even leave it till Popham this weekend, so as to see what happens over a number of days."
 

Martyn Goodwin

Well Known and Active Forum User
Non-VOC Member
Sadly it is coming out of the exhaust port, details as follows from an email I have just sent to Trevor:

I have been down this EXACT path with my Comet. In my case I found that a prior owner had rebuilt the head but had NOT correctly installed the valve guides meaning excessive wear on one side of the valve stems - in fact, in cross section the valve stems resembled the letter "D". Fix was new valves and new valve guides and those new valve guides MUST be line reamed after installation to ensure that the upper and lower guides are in alignment. While at it be sure to check the valve spring free length and if short, replace them.

The sumping is a separate matter
 
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