Cylinder Oil Feed on Comet

[robin]

The quick cure for your oil feed problem is to take the liner out , turn it through 180 degrees and re-insert the liner, then slot and drill the oil hole as low as your crankcase will allow. You will need a rebore, probably.
The slot dimension, for your Comet should be from 5/8ths below the muff to 1 1/32ths below. Drill at the end of the slot at the most acute angle downwards that you can achieve with your drilling facilities
Most racers tend to use larger clearances than road bikes, which is why they do not seize.
As regards two piece head studs-- If the brass insert, inner stud and the outer hollow stud are all scewed
in with sealant there should not be a leak.
Robin.

 

[davidd]

I find this reassuring. You are the second successful racer I have heard say this. Does this include both your road bikes and racers? (Different amounts of oil being splashed about.) Then there is robin's experience above that seems to contradict that, plus anecdotal evidence and the wisdom of the collective and even warnings from the designers over the years about blocked oil feeds. It seems as though if done right the extra oil does no harm, but done wrong all kinds of oiling problems can happen. I think, especially with the early two piece head bolts like I have, that getting oil tightness is difficult, even if the oil ends up correctly inserted below the rings.

Ron

Ron,

I have never used the cylinder oil holes in a street engine or racing engine. I am not sure what this data means. I would not be insistent on the subject one way or another. I liked the fact that the oil would likely be diverted to areas that could better use the oil. On modern racing pistons there is not much piston skirt to oil. Most singles and racers would do much better with an oil jet squirting oil on the underside of the piston crown, but that is a tough one on a Vincent.

It is difficult to know if the Comet seizures and the presence of the oil hole are correlation or causation. There certainly have been many seizures with the oil hole in place. I had urged in Martyn's post that most Comets are built with too little piston clearance, although in Martyn's case the damage appeared to be caused by detonation. I think if the clearances are done carefully, then the skirt oiling may not be necessary. On the racers, the liners are Nicasil coated with no oil hole. All the street engines I have done have been plain liners with no holes.

David

 

[Matty]

Hi All

I had blanked off the oil feed to the Comet Cylinder by putting a plastic disc behind the feed in the timing cover. Do not do this on a twin - you will cut off the oil supply to the cams etc.
I dd this many years ago to try to cure a smokey exhaust problem but it had no effect and neither did I have any siezure problems.

Have now had my rebore and new piston and at first there was no smoke. However now after around 4X 20 mile runs at 40/50mph, it smokes badly (the weather is frosty, salt on roads, and I am 79 so I only did short runs) !!!

Tried disconnecting the oil return and taking it via a pipe to the oil tank, to miss out the valve gear for a few minutes and it still blows out smoke,
so conclude problem is with the bore/piston not valve guides, which in any case looked very good and have only done 3000miles or so.

Compression is very good, but I think the bore must have glazed up (I took great care that the piston circlips were in correctly so do not think this is the problem)

Obviously I do not want to pull it apart again if possible, but if it is glazed, are ther any magic cures or should I just drive it harder for while to try to bed the rings in.

If it is glazed and I have to have the bore honed to de-glaze it how should I run the bike in to avoid this problem happening again ?

Will post this again as a separate item because Glazing may be of general interest. I think I had the same problem about 10 years ago after a rebore but can not remember the details.

Matty

 

[BigEd]

Here is the link to the "Glazing" thread:
http://www.vincentownersclub.co.uk/...smoking-after-rebore-is-the-bore-glazed.7285/

 

[Gene Nehring]

Ron,

I have never used the cylinder oil holes in a street engine or racing engine. I am not sure what this data means. I would not be insistent on the subject one way or another. I liked the fact that the oil would likely be diverted to areas that could better use the oil. On modern racing pistons there is not much piston skirt to oil. Most singles and racers would do much better with an oil jet squirting oil on the underside of the piston crown, but that is a tough one on a Vincent.

It is difficult to know if the Comet seizures and the presence of the oil hole are correlation or causation. There certainly have been many seizures with the oil hole in place. I had urged in Martyn's post that most Comets are built with too little piston clearance, although in Martyn's case the damage appeared to be caused by detonation. I think if the clearances are done carefully, then the skirt oiling may not be necessary. On the racers, the liners are Nicasil coated with no oil hole. All the street engines I have done have been plain liners with no holes.

David

When I bought my Comet a year or more ago it was smokey. I pulled the head off because I thought it might be leaky inlet valve guides. It turns out that at some point the machine had been soft seized and the inlet seal was fine. I did note that there was bluing and heat colouring around the liner oil holes as if it was lacking oil.

 

[Kevin Fowler]

I am in the process of rebuilding a comet series C. I need to know how the oil pipe gets past the battery stand. Is there a sensible drawing for this.

 

[chankly bore]

Spares List drawing M066 helps, but note that Comet pump feed pipe must be wangled through the gap between the gearbox and the frame tie. Not only that, but current manufacture 12mm. o.d. pipes won't present a flush face at the banjo mount as the lowest bend is wrong. Twin feed pipe looks similar but is angled in the vertical plane to clear the unnecessary width created by the redundant cylinder. If you have an original pipe, 7/16" o.d., you'll not have a problem as long as you're a triple jointed midget. Comet rubber hose is 1/2" shorter as well, 8 1/2". The Comet pictured in "Richardson" does not have the correct feed pipe fitted at all. If you're talking about the return line, A52/3AS it just snugs in inboard of the pump feed pipe, it is 27 1/2" long.

 

[erik]

I have blocked the oil feeding to the liners on my three vincents. without any problem.Clamping the muff with the crankcase is no good idea to my mind because the cylinder bored round will be anything but true round.The camshaft will have more oil which is an advantage.The cylinders get their oil from the crankshaft big ends.If you think about modern 2-stroke engines with oil/petrol mixture of 1/100 this is enough oil to lubricate the whole engine! Erik

 

[Bill Thomas]

I am in the process of rebuilding a comet series C. I need to know how the oil pipe gets past the battery stand. Is there a sensible drawing for this.

I wonder if you have a twin pipe , Which is is not right, As Chankly says,
It came up a short while ago.
Cheers Bill.

 

[Kevin Fowler]

I am in the process of rebuilding a comet series C. I need to know how the oil pipe gets past the battery stand. Is there a sensible drawing for this.

Thanks for the information , I had just finished re-bending the tube from the banjo to the length of the bends and pushing through the frame member to miss the battery. When I remembered my 55 years as a gasfitter, so I ignored the book and did my own thing. Thanks for the advice .