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Comet Smoking After Rebore Is the Bore Glazed ?
- Thread starter Matty
- Start date
Thanks - the oil consumption is certainly much better now, but just once it had sumped a bit overnight and blew out some smoke for a while after start up.
However it has done this sometimes since the 50s and I think it depends where the oil pump is after the engine stops.
I remember on one occasion in the Isle of Man about 25 years ago it seemed low on oil so I filled it to just over the bar in the tank and then when I started it, it pumped the sump contents back into the tank, which overflowed all over the engine !!!
The real solution to this is to change the oil pump which is not easy to do, particularly if it needs to be lapped in after fitting, which we had to do for my friend's twin because the new pump was very tight after pressing the new sleeve into the crankcase.
So it ain't broke, and I shall not fix it !! I shall just check the oil level for a mysterious drop in level if I have left it for a few days, but normally use the bike once or twice a week so there is not often a problem and the pump normally scavenges perfectly well.
Matty
However it has done this sometimes since the 50s and I think it depends where the oil pump is after the engine stops.
I remember on one occasion in the Isle of Man about 25 years ago it seemed low on oil so I filled it to just over the bar in the tank and then when I started it, it pumped the sump contents back into the tank, which overflowed all over the engine !!!
The real solution to this is to change the oil pump which is not easy to do, particularly if it needs to be lapped in after fitting, which we had to do for my friend's twin because the new pump was very tight after pressing the new sleeve into the crankcase.
So it ain't broke, and I shall not fix it !! I shall just check the oil level for a mysterious drop in level if I have left it for a few days, but normally use the bike once or twice a week so there is not often a problem and the pump normally scavenges perfectly well.
Matty
Hello Matty, How about a Conways antisump valve, For a quick fix, Cheers Bill.
Thanks Bill
I knew it was a common cure for Velocettes but did not know if it would work for a Vincent.
Presume it goes into the pipe from the tank to the engine.
Was not sure if the "pressure" would be enough to open the valve, because the feed is only working from gravity, so had not thought seriously of fitting one.
One of my friends had a tap (which of course does not then rely on pressure to open a valve) in the supply for his Matchless twin and once forgot to turn it on.
He left bits of crankcase and con-rod on the M11 on the way to the Isle of Man, but it ran for 40 miles or so before the bang !!!
Will have a chat with Conways - though I have lived with very occasional sumping for a long time and at least know the oil is still getting round OK.
Matty
I knew it was a common cure for Velocettes but did not know if it would work for a Vincent.
Presume it goes into the pipe from the tank to the engine.
Was not sure if the "pressure" would be enough to open the valve, because the feed is only working from gravity, so had not thought seriously of fitting one.
One of my friends had a tap (which of course does not then rely on pressure to open a valve) in the supply for his Matchless twin and once forgot to turn it on.
He left bits of crankcase and con-rod on the M11 on the way to the Isle of Man, but it ran for 40 miles or so before the bang !!!
Will have a chat with Conways - though I have lived with very occasional sumping for a long time and at least know the oil is still getting round OK.
Matty
Hello Matty, I have not used one , But there has been talk on the Forum about it, Mine do it only after a lay off, So I just use it as for putting fresh oil in. The late Alan Dodsworth, West London, Had a D, And rigged a tap with his D ign' key, He had to turn the tap on to get the key out to put it in the ign', Very clever, Cheers bill.
That sounds a good idea, but I do not have an ignition key like a D on my virtually standard, magneto ignited Comet.
Thought a while ago about an anti-sumping tap and considered attaching a switch to the tap which shorted out the magneto, thus preventing starting with the tap shut.
However I never did fit this, because it is just another thing to go wrong and reduce the reliability - some of the work I did on military radar designs involved reliability calculations and I know that the more bits there are, the worse the reliability !!
Matty
Thought a while ago about an anti-sumping tap and considered attaching a switch to the tap which shorted out the magneto, thus preventing starting with the tap shut.
However I never did fit this, because it is just another thing to go wrong and reduce the reliability - some of the work I did on military radar designs involved reliability calculations and I know that the more bits there are, the worse the reliability !!
Matty
I think you could fix a fault with a wire, Like you are saying, Easy, Better than what happened to your friend !!. Brother Ron, Had a tap on his A twin, I think I remember him forgeting to turn it on a few times, But only for a few seconds. I don't think it's worth the risk, Cheers Bill.
Have now done around 900 miles and the smoking is much less and have done 300 miles on the last pint of oil which I think is acceptable.
Leaving the engine parked at or near TDC also has a dramatic effect on reducing smoking due to possible sumping.
This is because at TDC the crankpin is left nearly at the top and so the oil does not drain so easily from the oil filter through the big end quill, upwards and out of the crankpin to the sump.
I prefer to do this rather than fit an anti-sumping valve which is just another thing to go wrong
I do not think I have a porous head casting which lets oil from the valve gear into the inlet port - thank goodness !!
Matty
Leaving the engine parked at or near TDC also has a dramatic effect on reducing smoking due to possible sumping.
This is because at TDC the crankpin is left nearly at the top and so the oil does not drain so easily from the oil filter through the big end quill, upwards and out of the crankpin to the sump.
I prefer to do this rather than fit an anti-sumping valve which is just another thing to go wrong
I do not think I have a porous head casting which lets oil from the valve gear into the inlet port - thank goodness !!
Matty
Sorry a pint of oil in 300 miles has not fixed anything ,fill it with oil and check the Petrol
I have just fitted New CP 8.1 pistons and new liners ,to a Rapide , used just on 1/4 pint in 1200 miles , I would expect this to get better , standard breather , riding at 60-70 mph
I have just fitted New CP 8.1 pistons and new liners ,to a Rapide , used just on 1/4 pint in 1200 miles , I would expect this to get better , standard breather , riding at 60-70 mph
