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#834975 12/31/20 2:33 am
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650 Triumph race bike. To get the piston/ head squish where I want it with the head gasket I have (.040) I'd need to remove the .008 copper base gasket. I've never run without a base gasket- is it likely to leak with just yamabond sealing?
Or- Is there such an animal as a .035 head gasket?

Thanks

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Mike Baker #834982 12/31/20 5:00 am
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It will not be a problem.
I use 518 but any decent sealer will do.
Watch the valve/piston clearance though....................................

Mike Baker #834989 12/31/20 11:55 am
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Thanks, Nick.
Re: clearances, This setup is going to uncharted territory and not forgetting the pile of parts that had previously looked like a motor that I made a year ago, I intend to err on the safe side this time.

Mike Baker #834990 12/31/20 12:41 pm
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knuckle head
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Mike, my T140 street bike has .032..My race junk about the same....I use 518 with no gasket, no leaks.J Healy likes Yamabond # 4 if things might flex a bit. There are several places in the US that will make custom copper gaskets...


79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
Mike Baker #836075 01/09/21 11:32 am
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If the bore has done some miles been untouched then check for a ridge at the top, the barrel is going to be lower by 8 thou and so the top ring will go 8 thou higher in the bore and could crack. Not an issue on a freshly bored or honed barrel.

Mike Baker #836738 01/14/21 9:20 pm
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When I was racing, I often used Copper Gaskets Unlimited in Phoenix, for custom gaskets, https://coppergaskets.us/ or you can google them. They do a nice job, and if you want to retain your thin .008 copper base gasket, the deck height equivalent would be to use their .032 head gasket instead of your .040. They have a ton of patterns in their computer and can make custom gaskets quickly. Their website says,

"Copper thicknesses we offer are:

.016" .021" .026" .032" .042" .050" .063" .080" .093" .125"

We also cut aluminum."

On the other hand, using no base gasket, and instead using Yamabond 4, is common on Norton engines--I did that on my street Commando, which seems very happy with the result -- but I also did experiment with no base gasket/Yamabond 4 instead on my old T140 race bike, and so long as you watch all the clearances, and keep at least .032 squish (mine touched using stock aluminum rods if you went any tighter), and adequate valve-to-piston and valve to valve clearances, and adequate crush (circa .030) on the pushrod tubes, it worked okay.

But, if you are taking the engine apart often, Yamabond is sort of a pain, since it requires some effort to get off the gasket surfaces with a scraper and solvent, but it will most probably not leak --I did have a few minor leaks doing this. On the other hand, a very thin coat of red silicone on both sides of copper gaskets (squeezed between your fingers until it is slightly transparent, like .005 or so, wiping of the excess) works fine--especially for race engines that come apart often because it is quick and easy to clean and you can do this at the track -- and seals very well. However, alone, with no gasket, red silicone can sort of walk out of high pressure joints like the base gasket and case seam after a while, so I wouldn't use it without a gasket.

Personally I had the best luck with, and I prefer to use, a base gasket with a thin coat of red silicone, instead of only gasket sealer, because you can be sure that with the gasket, it is more likely to seal any irregularities. And I had very good luck over many years using copper gaskets on the Triumph cylinder base surface, with a thin coat of red silicone. I've never used 518 to replace a base gasket, but the company literature says it is "medium strength", FWIW.

To the other warnings above about careful measurement of all relevant clearances, such as adequate squish clearance ( at least .032) and valve to piston and valve to valve clearances, and any possible ridge at the top of the cylinder, I can only add, when you are modifying deck heights, pay attention to the crush on the pushrod tubes when you dummy it up to measure.

Last edited by linker48x; 01/14/21 9:24 pm.
2 members like this: Stuart Kirk, kevin
Mike Baker #836811 01/15/21 12:34 pm
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I received a .032 head gasket from Gaskets Unlimited last week. Squish measures up at .035 at this point with the copper base gasket.
I'm currently considering something else. Part of the problem that I had last year that led to my motor failing was too little valve/ piston clearance. The new motor, mocked up is better, .070" intake and .080" ex, measured with soft solder. I will have the piston valve pockets cut so I have .090" everywhere. What I'm pondering is what effect does piston/ cylinder clearance play on the v/ p measurement? I could never get good consistent measurements with clay. when I switched to solder, I get repeatable results, probably because the piston is positively forced against the cyl wall. .050" clearance, BTW. But when the motor is running, I'm wondering where exactly in the bore is the piston likely to be when at it's closest proximity to a valve? Maybe that's why a racing motor with it's sloppier piston fit needs more v/ p clearance than a street motor with a closer piston fit? Or am I completely missing something?

Mike Baker #836839 01/15/21 5:48 pm
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knuckle head
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From what I'm told ,piston rock is a factor but when the engine is warmed up the piston clearance is less. My single and double engine racer have MAP 10.5 pistons at .006 clearance, valve to piston is about .060 in, .070 ex, squish is .032 or therabouts.. The single engine has R&R alloy rods, the double uses steel rods...Your engine oil get hotter but that shouldn't matter with steel rods.....You're not running the engine beyond the valve train limits? Tested the valve springs?


79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
Mike Baker #836875 01/15/21 11:13 pm
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Originally Posted by Mike Baker
I will have the piston valve pockets cut so I have .090" everywhere.

i've been getting away with 0.060 intake and 0.080 exhaust face-to-face, and then dremeling the perimeter of the pocket by hand until i think i've done enough.

brand new pistons and bores, though

tony is right too. if you're running high enough to float a valve, static clearances go out the window


i'm old enough to remember when patriotism meant not trying to overthrow the government.
Mike Baker #836923 01/16/21 12:25 pm
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I've wondered about that, too. Beehive springs and 6mm valve stems- From what I've heard, it's not unknown to see some weird harmonics come into play. The spring pressure has been upped a bit this time.
Some get by with .060, and I have read that others won't go less than .090". Since I had trouble at .060, I have no choice than to fall in with the later group.
And like you, Kevin, all shiny new. You going to race with us this year?

Mike Baker #836928 01/16/21 1:12 pm
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waiting for money to assemble the motor. everything is slow. cant predict anything. 2021 is just 2020 with unfinished business. but nothing else gets wirked on until that is done.

if youre running 6mm and beehives i wouldnt think you would have any float problems at any rpm below where the rings flutter.


i'm old enough to remember when patriotism meant not trying to overthrow the government.
Mike Baker #836990 01/16/21 11:59 pm
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knuckle head
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Here's info on ring grooves and flutter
http://blog.wiseco.com/ring-grooves


79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"

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