E: Engine Is the cylinder oil jet needed on a Comet?

CoreyL

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I've heard two conflicting opinions from Vincent gurus: one saying that the cylinder oil jet is not really necessary (he runs his race motors without the jet) and another guru saying the cylinder oil jet is absolutely necessary. Is there a consensus among this group?
 

chankly bore

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Why risk departing from standard? Modern fuels also burn hotter, run .005" bottom skirt clearance and about 35 degrees B.T.D.C. advance if single plug. Just my opinion, which is priceless, and since price is a function of worth, draw the obvious inevitable conclusion.
 

davidd

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I don't think there is a consensus. I am in the "no oil hole" camp. Never put one in any machine over the 50 years I have been tinkering. None of the race bikes have used them. I did not put one in the bike on the cover of this month's MPH, either.

On the other side, Patrick Godet insisted on them, among others. Greg Brillus probably put it best, by saying "It can't hurt." (This assumes you get it in the correct place.)

Finally, I tend to run more clearance on the crankcase mouth to liner dimension than most. No sense sending the oil down the gap. I would rather that it go to the cams.

David
 

vibrac

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It's. Not always possible to arrange a feed on a modified motor anyway the last big motor I built would have a long bypass slot to join the point below the rings to the crankcase hole that would easily lead to the oil leak down the jacket that David refers to . Cylinder wall oil feeds are not a common feature of motorcycle engines that I have come across
 

Bill Thomas

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And yet there was a bloke in "Featured Resources", A few days ago, Who said that is why his locked up !,
But we can never be sure, About anything ??. Cheers Bill.
 

davidd

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And yet there was a bloke in "Featured Resources", A few days ago, Who said that is why his locked up !

We have all done some misdiagnosis over the years. The fact is that there a lot of variables at play. The advent of low expansion pistons, the use of pistons with much smaller skirts, the use of super slippery oil (so slippery the rings may not seal), and the use of short liners and/or aluminum liners. I would think that at present, 110% of all piston seizures are a result of incorrect clearancing of the skirt to cylinder. Running small piston clearances robs the most power from the engine, more than any other component and has no obvious benefits (for me).

I think most careful builders would not find the cylinder oil feed "necessary" today. If you are doing something out of the ordinary it might be advisable to use the feeds. If you are careful with the placement of the hole and the crankcase fits, it should not hurt anything.

David
 

Cyborg

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And then there is the question of where the oil hole lines up in relation to the rings. How many liners are out there with the hole drilled too high? It seems like every one I’ve measured is too high... enough to cause extra oil consumption.
 

Gerry Clarke

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Rudge used a rear feed to the cylinder wall on the high performance Rudge "Ulster". For the 1937 season they left it out. In 1938 they put it back!

Gerry
 

Nulli Secundus

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Rudge used a rear feed to the cylinder wall on the high performance Rudge "Ulster". For the 1937 season they left it out. In 1938 they put it back!

Gerry
Indeed. I think the Specials had an oil feed too that was dropped and reintroduced. My 1938 Special race bike has the feed. Of course the plumbing is simple to line up on the Rudge. With Vincents it is somewhat harder, saying nothing about a liner that rotates unnoticed at some point, which my Rapide must have done when I stripped the top end down after purchase.
 
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