Comet Oil Consumption

Matty

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VOC Member
Hi
I started a query a few years ago on this subject and it went on for many pages, though much of the comment was not related to my problem
In the meantime I have done around 10,000 miles since raising the problem after a rebore and it is still using around a pint in 200 miles, but with no problems except black oily plugs which sometimes oil up.
Many checks including sumping, the cylinder oil hole position (the hole has been blanked) , return pipe possible blockage, the rings, bore (not glazed), valve guides etc. have been carried out to no avail and I have come to the conclusion that my cylinder head is porous from the valve area into the inlet tract.
In fact if I put paper towelling down the inlet port with the carb. etc. removed, it comes out oily from the area round the far end of the port.
I do not think the oil is coming down the valve guide because this is fairly new and seems within spec. In any case the bike has always used a lot of oil and the guides have been changed at least 3 times over the 60 years and 80,000 miles I have had it.
I now feel that at last I should fix this oil problem because it is beginning to annoy me !!!
I am thinking of having the head impregnated which is a common fix for porous castings and having a sealed inlet guide fitted. This is a bit belt and braces but I do not fancy rebuilding the top end twice just to find which modification has fixed the problem ( assuming it does fix it).
Does anyone have any comments on my way ahead please - though I know really if it "ain't seriously broke perhaps I shouldn't fix it "at all.

Matty
 

nkt267

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VOC Member
One of our local members has this problem, it is so bad the engine smokes due to the porous front head. We are waiting to see what cure he goes for..John
 

chankly bore

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Non-VOC Member
I had the same problem when a re-bush on the exhaust rocker tunnel broke through. A thorough clean and a dob of weld fixed it. I suppose on the inlet side, being cooler, Devcon or similar stuff might avail.
 

vibrac

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VOC Member
I certainly would fit a valve seal PCV would have done if they had been invented he had enough trouble with inlet valves and oil
 

Martyn Goodwin

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Non-VOC Member
Are you loosing any oil out of the breather? A quick test for this is to replace the breather pipe with a banjo and a length of hose and run it into an old clear plastic drink bottle, sans lid - then go for a run and inspect then bottle contents.

This helped me track down then eliminate oil use; err loss!
 

Len Matthews

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VOC Member
One of our local members has this problem, it is so bad the engine smokes due to the porous front head. We are waiting to see what cure he goes for..John
Inded. A spare head solved the problem. The porosity only became apparent when the carb stub was removed thus allowing a clear view down the inlet port.
 

Matty

Well Known and Active Forum User
VOC Member
Hi All
Thanks for the very rapid replies.
Firstly my breather works very well and little puffs come out of it as the timer opens and shuts the breather pipe - the bike is virtually oiltight with only a five pence sized drip sometimes.
Think I will have the head resin impregnated and have a sealed inlet valveguide fitted.
It is nice to see that Len Matthews has fixed the same problem using a spare head (presumably a Shadow front one) Do you have any more second hand heads Len ??
I have heard of several others who have had an oil consumption problem and fixed it with another head, so it seems like some of the old head castings were probably porous from the start.
Will add to this Post on what has happened with the impregnation and guide replacement which would be MUCH cheaper than a new head.
I have lived with the 200 miles per pint for 60 years however, so if the above fixes do not work will probably just keep topping up the oil.

Alan Matthews (Matty)
 

Matty

Well Known and Active Forum User
VOC Member
PS
My Comet definitely burns the oil because as I said the plug is black and oily and grows a build up of carbon. Also it smokes a bit, particularly when opening the throttle after ticking over or going down a hill.
The colour of the insulator of the plug is about right if the soft carbon deposit is cleaned off, so I think the mixture settings are OK.
Thanks again Matty
 
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