Comet Oil Loss after 100mile run

manxman

manxman

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Non-VOC Member
It’s a continuing/recurring problem for me with the Comet. After a good ride, say 50 miles, the oil level in the primary has risen significantly and the oil level in the UFM tank is correspondingly significantly lower. If the bike stands for any period of time, there’s really no change. So my thought is that it’s a seal problem, aggregated by the revs and engine pressure which push oil into the primary.

If left unchecked, the primary level will keep rising until the bike bleeds a river of oil as it drains from the rear of the primary behind the clutch.

In any event, will try the seal route this winter as a project. Would greatly appreciate someone forwarding me copies of the articles from MPH 998!
 
Martyn Goodwin

Martyn Goodwin

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Non-VOC Member
Resolving Oil leaks in a Comet.
  • Sort out the breathing: set up the timed breather with PEI mods; and fit a oil catch tank;
  • Timed breather to close at 3 to 5 ABDC
  • fit a primary case oil seal to the mainshaft.
  • ONLY If low on compression, fit new rings and hone bore.
  • Ensure proper sealing of the main hold down studs
  • Proper oil seal on the Alton or generator shaft
  • Full set of Cometic gaskets – including that under the magneto/grosset ignition
  • Use the complete Neal Videan seal kit
  • Latest Neal Videan push rod tube seals – and NEW pushrod tubes if there is ANY doubt as to their roundness
  • 10W30 oil in the motor; Motul TransOil in the primary case
  • Confirm and if needed rectify primary chain alignment
  • Fit the Ken Phelps oil sling behind the clutch assy in the primary case
  • Replace the phony ribbed oil hoses with ‘proper’ modern ones; same for line clips
  • Neal Videan Paper oil filter (replace every 5,0000 miles)
Just my opinion - it works for me.
 
Martyn Goodwin

Martyn Goodwin

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For "How To' subscribe to OVR - its free https://ovr270.wixsite.com/ozvincentreview

then go into the OVR archives and read the following editions: 4, 16, 18, 44, 45 and 50. There may be other editions that will interest - but these ones have the specific info you are after.

FYI OVR came into being in 2014, after I ceased being editor of 998 (which was the newsletter of a now defunct VOC local section)
 
manxman

manxman

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Non-VOC Member
Thank you, Martyn. This is very helpful.

Do you happen to still have copies of the MPH articles you mentioned earlier in this thread? Regarding the seals and their installation? If not, is there a resource for members to obtain digital copies of earlier editions?

The Alton oil seal is another on my list, but my issues with the primary are, so to speak, primary...
 
Bill Thomas

Bill Thomas

Well Known and Active Forum User
VOC Member
As Standard the is no seal, Just a scroll that spins inside an alloy disc, On the Flywheel main shaft.
Sounds like you have a breather problem or use too thin an oil ?,
Must admit my Comet is a bit worn out now and I use 50 oil in summer in UK,
My other Vin's I use 30 in winter and 40 in summer, UK.
Has it got the standard breather ?. A lot of us use a bigger breather, Cheap to set up !.
Does it smoke out the exhaust at normal running ?.
A worn Piston can give too much crankcase pressure, But it would smoke out the exhaust all the time.
 
Martyn Goodwin

Martyn Goodwin

Well Known and Active Forum User
Non-VOC Member
MartynG said:
For "How To' subscribe to OVR - its free https://ovr270.wixsite.com/ozvincentreview

then go into the OVR archives and read the following editions: 4, 16, 18, 44, 45 and 50. There may be other editions that will interest - but these ones have the specific info you are after.

FYI OVR came into being in 2014, after I ceased being editor of 998 (which was the newsletter of a now defunct VOC local section)
Click to expand...
Also look at OVR 37 for detail on an oil sling to help stop oil being flung out from the rear of the clutch drum
 
N

Nigel Spaxman

Well Known and Active Forum User
VOC Member
Not many people believe me about this, but having the breather timed at around bottom dead center is not optimal. If it closes around BDC it is closing right when the pressure in the crankcase is at it's very highest, which is exactly when it should still be open. Of coarse the pressure does start to go down as the piston starts to rise but it is still at a higher pressure than when the valve would have been opened. It should open and close later than the standard timing. It is better if the valve opens about the same number of degrees before BDC and it closes after BDC.
 
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