Im away from home at the moment and this tablet has a mind of its own on the forum but Bill is right to remind people of what I posted some time ago. Many cylinder muffs do not have their bases perpendicular to the bore. From a few I have checked five thou is a typical value. If this is in a fore and aft direction you might get away with it but if it is sideways you will not get away with using the low clearances. Davidd and several others on here know what they are doing with this problem but do not fit lo clearance pistons without getting someone to check for this problem first.
E: Engine Damaged quill
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I was supplied with a new barrel, And looking at the bore, You could see it was wonky Just by eye, Also the holes where the studs go though were smaller !, I asked a bike dealer in London where I lived, To check it and he said it was OK !.
I don't have the tools or the skill for this sort of thing, So I fitted it.
Didn't last long, So back to 10 thou for me !. Cheers Bill.
I don't have the tools or the skill for this sort of thing, So I fitted it.
Didn't last long, So back to 10 thou for me !. Cheers Bill.
Bill,
Yes, those clearances can be used on water cooled modern engines. I believe John Healy discussed this with me years ago when supplying cylinders and pistons. He felt too many of the automotive machinists were quoting modern water cooled numbers for piston clearances.
And, those are typically the numbers that companies that do Nicasil use. When I asked for .0035" they told me that was too big for Nicasil on aluminum. I insisted as that was the number that Carleton and I used on the racers. That cylinder has run for 10 years, has worn out three pistons and is still stock. I like the idea of small clearances, they just cost to much in time and money.
David
Yes, those clearances can be used on water cooled modern engines. I believe John Healy discussed this with me years ago when supplying cylinders and pistons. He felt too many of the automotive machinists were quoting modern water cooled numbers for piston clearances.
And, those are typically the numbers that companies that do Nicasil use. When I asked for .0035" they told me that was too big for Nicasil on aluminum. I insisted as that was the number that Carleton and I used on the racers. That cylinder has run for 10 years, has worn out three pistons and is still stock. I like the idea of small clearances, they just cost to much in time and money.
David
Thanks David, This is all much too clever for me, I have had some good performance from my bikes,
So that will have to do me.
Been watching some youtube stuff on Drag Racing, The Bikes are in the 6 second band now, I don't have a clue how !!. Keep up the good work, Bill.
So that will have to do me.
Been watching some youtube stuff on Drag Racing, The Bikes are in the 6 second band now, I don't have a clue how !!. Keep up the good work, Bill.
I always got the racing cylinders bored to the specific piston at 5 to 6 thou
David is right about comets on two of my road comets have sized both on long uphill climbs my Trials outfit did but I caught it and carried on ( it was a long way home) as the weeks went on my resolution to strip it got less and it ran for years with no problems.
David is right about comets on two of my road comets have sized both on long uphill climbs my Trials outfit did but I caught it and carried on ( it was a long way home) as the weeks went on my resolution to strip it got less and it ran for years with no problems.
Maybe the advance/retard is a bigger issue than overall advance. So if an engine tends to seize assuming it is ignition more than carburretion, If the spark is too early it could detonate and if too late it could overheat from the flame continuing down the exhaust pipe for too long. I have no doubt that a lot of engines seem to go to more advance too quickly, this explains the detonation when pulling up a hill with too slow an engine speed. A rich mixture might help overcome this, but then the engine will be too rich most of the time which can wash the bores and wear prematurely. It may also be a bigger issue now due to modern faster burning fuels..............With all that in mind, perhaps we could actually run more overall advance approaching the factory settings, but alter the advance rate of change so full advance is higher up the rev range. Easy to do with a mag and an ATD (springs) not so easy with electronic .......No moving parts............worth experimenting with, especially if you have a couple of spare pistons on the shelf...............
Can we get a consensus as to the Comet ignition timing people use for everman?
I use 34 degrees BTDC fully advanced. What are you all running? Not one person has mentioned it for the poor bloke.
Best,
E.
I use 34 degrees BTDC fully advanced. What are you all running? Not one person has mentioned it for the poor bloke.
Best,
E.
As for me, I did not question the 34 degrees full advance, seems about right , BUT I question the wisdom of full advance before reaching at least 3500 rpm, maybe even better at 4000 rpm. That could be one reason for hot running Comet engines. No other discussed details of that engine are really compelling to this fact as other engines are even less optimal cooling-wise but without that problem.
Vic
Vic
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