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Discussion Starter · #1 ·
When the head is resting on pushrod tubes, without compressing the seals, how much gap should I have between the top of the gasket and the head?
I reckon the gap on mine, with no gasket is about 0.2".
In another thread, it was noted that my head had been skimmed.
To put it another way, what is the normal thickness of the cylinder head flat?
I`m thinking that a lot of meat has been ground off, which explains why I thought the head bolts are too long.
There`s two remedies for this gap; fit two thick gaskets or get shorter tubes.
Unless anyone knows a part number for short push-rod tubes, the 2 gasket method is favourite.:confused:
 

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Caulky , with the head gasket in place and the head just resting on the push rod tube seals you want .040 - .060 . any more and you can warp the head , any less and it's more bound to leak .

Cheers , Woody

ps , there's different size prt seals to adjust this gap
 

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Woody had it right although more means leaks and less means head warpage, but I think you know what Woody meant.
If you are worried about the fit being too tight, try removing the rubber washer and/or O-ring or both. If this gives you sufficient clearance, use a high-grade engine silicon gasket sealant in their place. As an added bonus, if everything was clean and dry during installation, you won't need to worry about the scourge of Triumphs - oil tube leaks.
 

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Discussion Starter · #4 ·
This seems a bit odd to me.
Have I got the wrong pushrod tubes?
A long time ago I tried to buy 71-2575 tubes, BUT I was advised to buy 70-9349 for the late 650`s. I`m not too sure this is right.
Anyone know if these are different lengths?
If mine were 0.150" shorter, they would be OK.
And a standard gasket (0.048") would leave a gap of about .052".
Mine look like this:

And the gap is like this:

That is a `thick` gasket 0.070" and a loose fitting 3.2mm drill.(0.125")
Without any gasket, a 6.5mm drill fits (0.255")...over 1/4 "
 

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Hello,

Can you tell me where to get thicker than normal copper head gaskets?

Thank you in advance,

Ivan from Michigan


This seems a bit odd to me.
Have I got the wrong pushrod tubes?
A long time ago I tried to buy 71-2575 tubes, BUT I was advised to buy 70-9349 for the late 650`s. I`m not too sure this is right.
Anyone know if these are different lengths?
If mine were 0.150" shorter, they would be OK.
And a standard gasket (0.048") would leave a gap of about .052".
Mine look like this:

And the gap is like this:

That is a `thick` gasket 0.070" and a loose fitting 3.2mm drill.(0.125")
Without any gasket, a 6.5mm drill fits (0.255")...over 1/4 "
 

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am now confused...i was assuming that head warpage happened because gaskets were too thick...so they when stopped compressing...the total length of pushrod tubes with gaskets are now too long and stop the had from coming down...so head warps. Am I way confused?
 

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am now confused...i was assuming that head warpage happened because gaskets were too thick...so they when stopped compressing...the total length of pushrod tubes with gaskets are now too long and stop the had from coming down...so head warps. Am I way confused?
You are correct in your thinking, thirdbike has it backwards. Too large a gap will cause the seals to squeeze out and can also warp the head (raised at the center).
 

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am now confused...i was assuming that head warpage happened because gaskets were too thick...so they when stopped compressing...the total length of pushrod tubes with gaskets are now too long and stop the had from coming down...so head warps. Am I way confused?
Somebody's confused,and I don't think its you.
0.030"-0.040" PRT o-ring crush is recommended for 350/500 and650/750 twins.
More than that can damage the head.0.020"-0.030" works for me.Shop around for different thickness o-rings.

They allow 0.060" max. crush on a Trident,where o-rings don't seat on the head and the barrel is aluminium (more expansion).
 

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Somebody's confused,and I don't think its you.
0.030"-0.040" PRT o-ring crush is recommended for 350/500 and650/750 twins.
More than that can damage the head.0.020"-0.030" works for me.Shop around for different thickness o-rings.

They allow 0.060" max. crush on a Trident,where o-rings don't seat on the head and the barrel is aluminium (more expansion).
Over the three years I've been lurking on Triumph forums, I've seen many numbers offered up as being "right". It is quite amazing that for such an important measurement to be shrouded in misinformation and ambiguity. Like Pete, .030" works for me, and personally I would not entertain more than .040".

I have seen in a certain triumph service bulletin .060", but this spacing is just going to steeply increase the likelihood a premature head gasket failure. Settings above .040" are most likely the cause for all the bowed heads we read about. RR
 

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I'm sure you guys know this, but if you skim the head you have to shorten the pushrods by the same amount. Otherwise you will have excessive valve lift, possible coil bind, etc. Of course, the pushrod tubes would probably have to be shortened as well. Since you apparently have replaced them, they may simply be too long to work with the other parts. Shortening them on a lathe should be easy.
 

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I'm sure you guys know this, but if you skim the head you have to shorten the pushrods by the same amount. Otherwise you will have excessive valve lift, possible coil bind, etc. Of course, the pushrod tubes would probably have to be shortened as well. Since you apparently have replaced them, they may simply be too long to work with the other parts. Shortening them on a lathe should be easy.
Not so.

I have used heads with 25-35 thou taken from them without such other modifications. There is plenty of adjustment in the valve train to accommodate small variations in head thickness.

When heads are shaved to great extents, it is often necessary to use a thicker gasket to allow the usual seal sizes to be used. RR
 

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Not so.

I have used heads with 25-35 thou taken from them without such other modifications. There is plenty of adjustment in the valve train to accommodate small variations in head thickness.
RR
There is plenty of adjustment to accomodate large variations.I set one engine up with no head gasket,valve stems about 0.100" longer,and still had adjustment.I used thinner o-rings to get about 0.020" PRT o-ring crush.

Please don't anyone turn down the flanges of their pushrod tubes.You can face off the flange of the cam-follower blocks,if you need more room for standard PRT o-rings.

Technically,moving the rocker shaft closer to the cam-follower (without shortening the pushrod an equal amount) does effect total valve-lift. 0.050" change in rocker shaft height can increase valve-lift about 0.0005",if the pushrod length was perfect to begin with.

That hardly makes valve spring coil-bind an issue,when the standard spring is 0.150" or more away from coil-bind.
 

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I have used heads with 25-35 thou taken from them without such other modifications. There is plenty of adjustment in the valve train to accommodate small variations in head thickness.
Doh! :Not again That is probably right, if you are using a stock cam. I was speaking from my experience with Nortons anyway. I'll go back to lurking now (slinks off).
 

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...and if you happen to be in the US, like myself, there is a wholesale company in California called JRC Engineering (www.jrceng.com) which imports various parts including the thick gaskets from Tri-Cor England. Simply go to JRC's website and click on "Find A Dealer" tab and find a dealer near you -OR- call Bill at JRC directly at (951) 940-5411 and he will help you find your local distributor too.

I made two phone calls and I have a .080" gasket already being shipped to me!

Thanks for the help, Caulky and RetroRod!

Ivan from MI


I have sent a PM to Ivan, but for anyone else who is interested I got my thick head gasket from TMS Nottingham.
Part number 70-4547/80
http://www.tms-motorcycles.co.uk/store/products/list.asp?cat_id=115

*Also there`s a .120" thick gasket available from Tri-corengland
http://www.tri-corengland.com/cgi-b..._70-4674.html#a70_2d4547_2f80#a70_2d4547_2f80
 

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Doh! :Not again That is probably right, if you are using a stock cam. I was speaking from my experience with Nortons anyway. I'll go back to lurking now (slinks off).
Don't feel too bad Coroja, we've all been there done that. :D RR
 
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