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Cylinder Lubrication

Matty

Well Known and Active Forum Website User
VOC Member
Some time ago I had a new piston (low expansion) and liner in my Comet.

There was some discussion about weather it was necessary to drill the cylinder/piston lubriction hole in the liner, but after some problems with the exact positioning of the sloping hole to ensure that it came out below the lowest level of the scraper ring and mated up properly with the feed from the crankcase, I had the hole drilled.

After this the Comet always used a bit of oil (pint every 200/300 miles) with puffs of blue smoke sometimes and as an experiment - bearing in mind some said it was not necessary - I blanked off the oil feed in the timing cover to the cylinder.

If anything the bike seems mechanically quieter - probably because there is more oil for the crank and cam followers, and I have had no hint of the piston nipping up in the few thousand miles since - I also seem to be using a bit less oil at 400mpp.

So is it a case that with modern oils when the bike is only used for touring, this cylinder lubrication is not necessary any more ?

I am using Miller 20/50 grade oil by the way.

Matty
 

Matty

Well Known and Active Forum Website User
VOC Member
Thanks - but what problem was this cylinder lubrication meant to solve or was it simply overdesign. Maybe there was a problem with the older style pistons or the poor lubricants of 60/70 years ago which it was meant to fix?

Also is it OK just to blank off the oil feed in my timing cover. I can't see any way this can be a problem and as I said above should provide a bit more oil for the cams and bottom end of the engine !!

Matty
 

davidd

Well Known and Active Forum Website User
VOC Member
Matty,

I think I supplied a photo in the earlier posting on this subject showing that the oil feed hole in the timing cover can be peened shut. I leave the cylinders intacnt with no holes which, once the spindle is filled, does the same thing.

The original design had to deal with non detergent oil. Also, the piston runs very low inside the cank case, which makes cooling a problem.

David
 

passenger0_0

Well Known and Active Forum Website User
VOC Member
I agree fully with David's comments but with my twin I simply installed rubber seals that I'd punched out of the appropriate thickness viton sheet to blank off the cylinder oil feeds - no irreversible peening required. Additionally I completely removed the jet regulating oil feed to the cams and supplied main oil supply to the cam bushes. The idea here being the crank really sucked all it needed and the oil had to lift the 8" up to the cams so there was still oil in the crank oil gallery at all times. Morris R40 oil was used, 0.0065" piston/bore clearance on original NOS E7/11 Specialloids and not a problem after 4 racing seasons. I know we all have different ways of dealing with percieved 'problems' - this was mine but I'm sure you'll hear strongly from others. Good luck whatever way you go - David.
 
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Matty

Well Known and Active Forum Website User
VOC Member
Thanks David - your replies are reassuring and it seems I have done the right thing. All I have done to blank off the feed from the timing cover, is to put a disc of thin plastic sheet behind the "rubber" washer (ET183) which presses onto the feed spindle.

As a matter of interest (perhaps), I have just had a problem with the exhaust valve guide working loose in the head, pushing out the retaining ring and wrecking the thread.

Bob Culver suppiled and fitted an oversized guide, bored out the head to suit, made a new 1" diameter retaining ring and tapped out the head to suit - all for a very reasonable price.

Have put it back together and am now going for a ride to bed things down in between the showers.

Matty
 

davidd

Well Known and Active Forum Website User
VOC Member
I agree fully with David's comments but with my twin I simply installed rubber seals that I'd punched out of the appropriate thickness viton sheet to blank off the cylinder oil feeds - no irreversible peening required. Additionally I completely removed the jet regulating oil feed to the cams and supplied main oil supply to the cam bushes. The idea here being the crank really sucked all it needed and the oil had to lift the 8" up to the cams so there was still oil in the crank oil gallery at all times. Morris R40 oil was used, 0.0065" piston/bore clearance on original NOS E7/11 Specialloids and not a problem after 4 racing seasons. I know we all have different ways of dealing with percieved 'problems' - this was mine but I'm sure you'll hear strongly from others. Good luck whatever way you go - David.

I think this is a better solution than peening for a total cut off of oil. I was more afraid that a metal disc that could break up be avoided at all costs. The previous owner of my Flash used peening to make the hole smaller and he retained the cylinder oil feed, but he was racing in the late 60's.

Nice to know that the twin jet can be removed with no ills. The Comet jet has always seemed to be less of an issue because there is no rear cylinder cam. On the track, the rpms of the single are so high that the oil pump moves an amazing amount of oil with the single start pump.

David
 

Tug Wilson

Well Known and Active Forum Website User
Non-VOC Member
I understand that the 170 jet supplies oil to the cylinder liner, is this what you blocked off? I have done this temporarily and there was less smoke from the exhaust. Does anyone out there recommend this on a Comet?
 

davidd

Well Known and Active Forum Website User
VOC Member
I understand that the 170 jet supplies oil to the cylinder liner, is this what you blocked off? I have done this temporarily and there was less smoke from the exhaust. Does anyone out there recommend this on a Comet?

Tug,

No, DO NOT BLOCK OFF THE JET! We were discussing blocking off the oil supply feeds on the inside portion of the timing chest cover and are identifiable because they have rubber seals which need to be installed to seal the cover to the spindles. That being said, the oil supply that flows through the jet supplies the cylinders as you said, but also the camshafts. So if the jet is blocked, the supply to both the cylinders and the cam shafts is blocked. The reason to do the blocking downstream in the timing chest cover is that is where the oil supply splits so you can block only the spindle suppling the cylinder and leave the cam spindle alone.

The pressure side of the oil pump goes right to the oil filter. From there it goes into the timing cover passages and supplies the crank (below the jet) and the cylinders and cams (above the jet.) The jet is there so you can alter the bias to above or below, namely, the crank or the cams. The accepted advice is on a twin you can go from 170 to 200 to enhance the oiling of the cams when racing. This is usually considered unecessary on a Comet as the flow of oil is servicing only one cam and cylinder.

Additionally, the chamber behind the sraper in the crank case (called the recess in the diagram below) supplies the scavenge side of the pump and pushes oil up one of the exterior lines to the clinder heads where it supplies the rockers. Some of this oil dribbles down the pushrod tubes to the cams and the rest stays in the oil line that goes back to the bottom of the oil tank. Thus, even with a temporary blocking of the jet the cams and followers will recieve some oil.

I think the best way to block of the cylinder feed on a Comet is to use a solid rubber disc instead of a seal in the timing cover on the rear lifter spindle supply. This ensures full supply to the cam.

Here is a diagram from MPH:

Oil Diagram.jpg


David
 
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passenger0_0

Well Known and Active Forum Website User
VOC Member
If you run your Comet without any oil it should stop (smoking) completely. :D
Best not to change anything from standard unless you fully undertand the effect and consequences.
 
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