Heat insulating washer

What should the thickness of the heat insulating washer that goes between the head and inlet manifold be?
I'm running a 2 into 1 manifold with a with what I think is an insulator between the manifold and carb but it's just 1.6mm thick.
I'm having a bit of a problem with the throttle sticking when the bike gets hot, and I'm thinking it might be due to the heat as it's all fine when it's cold. I've not got any kinks in the cable, it's a clear run from twistgrip to carb, the twistgrip is all free, the cable is new and lubed, and the carb has less than 600 miles on it.

Heat insulating washers are not needed with the 2 to 1 manifold due to the fact that the rubber adaptor is there between the manifold and the carb.
However, surfaces must be smooth and true along with good fresh gaskets. Air leaks is a real enemy here.

pvisseriii said:

Heat insulating washers are not needed with the 2 to 1 manifold due to the fact that the rubber adaptor is there between the manifold and the carb.
However, surfaces must be smooth and true along with good fresh gaskets. Air leaks is a real enemy here.

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Sorry I should have mentioned it's a Mk1 Amal and flange mounted so I'm thinking I need the insulator!

My old original heat insulators were about 1/8" thick. The new ones I got (Andover) were about 1/16" thick like yours. I re-used the old 1/8" ones.

Maybe get a second insulator and stick the two together with some sealant if you can't find something thicker?

Russ

willy mac said:

pvisseriii said:

Heat insulating washers are not needed with the 2 to 1 manifold due to the fact that the rubber adaptor is there between the manifold and the carb.
However, surfaces must be smooth and true along with good fresh gaskets. Air leaks is a real enemy here.

Click to expand...

Sorry I should have mentioned it's a Mk1 Amal and flange mounted so I'm thinking I need the insulator!

Click to expand...

I would put just one in between the adaptor and the manifold. The proper gaskets would seal better at the head.

Because the heat insulators do not squish, using them across the double face of the manifold might leave gaps unless they are absolutely perfectly matched in thickness across their span.

I hope you see where I am going with this.

batrider said:

My old original heat insulators were about 1/8" thick. The new ones I got (Andover) were about 1/16" thick like yours. I re-used the old 1/8" ones.

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Did you replace the insulating washers as part of a rebuild or for another reason?

willy mac said:

Sorry I should have mentioned it's a Mk1 Amal and flange mounted so I'm thinking I need the insulator!

Click to expand...

This is just one more opinion, but I think you should not put an insulating gasket between the carb and the manifold. The carb is machined for an o-ring between it and the manifold. It's the only junction on the inlet trac that doesn't leak. It's probably best to leave it as it was designed. You do need insulating gaskets though because you aren't using the rubber adapter for spigot style carbs. Why not put the insulators between the manifold and the head like the stock arrangement? The only difference in your case is that the manifold is one piece. Two 1/16" or one 1/8". Maybe someone can recommend a good sealant, but you really need to make sure you don't overtighten the fasteners and warp the carb body.

willy mac said:

batrider said:

My old original heat insulators were about 1/8" thick. The new ones I got (Andover) were about 1/16" thick like yours. I re-used the old 1/8" ones.

Click to expand...

Did you replace the insulating washers as part of a rebuild or for another reason?

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I had the head off for a valve job and was replacing all the rest of the gaskets.

Ugh I gave up on the o-ring seal d/t tightening up enough so nuts don't back off tends to bow the flange, but admit I ham fisted, so got stable sealing and a bit more heat shield with a rubbery type composite gasket I cut out. I use the 1/8" thick hardened impregnated paper type next to head. Heated carb and slide should open up clearances for less stick. I've had cold carbs stick with Norton life changing damage. Carbs can get too hot to touch after a run on shut down period but have not had them stick in that state. Only thing I cant think might cause carb to stick if very hot is its so tightened on its flanges it can't give there so bore distorts instead. Might just try stretching the spring out a bit more for more sure return force.

Only thing I cant think might cause carb to stick if very hot is its so tightened on its flanges it can't give there so bore distorts instead. Might just try stretching the spring out a bit more for more sure return force.

Thought about doing the stretchy spring thing when I rebuild the carb, I don't think I've over tightened any of the fasteners, I've ordered a couple of washers from RGM so I'll maybe try a couple together with a bit of High Temp Sealant and see how we go with that.

rpatton said:

willy mac said:

Sorry I should have mentioned it's a Mk1 Amal and flange mounted so I'm thinking I need the insulator!

Click to expand...

This is just one more opinion, but I think you should not put an insulating gasket between the carb and the manifold. The carb is machined for an o-ring between it and the manifold. It's the only junction on the inlet trac that doesn't leak. It's probably best to leave it as it was designed. You do need insulating gaskets though because you aren't using the rubber adapter for spigot style carbs. Why not put the insulators between the manifold and the head like the stock arrangement? The only difference in your case is that the manifold is one piece. Two 1/16" or one 1/8". Maybe someone can recommend a good sealant, but you really need to make sure you don't overtighten the fasteners and warp the carb body.

Click to expand...

My manifold is only secured by the 2 outboard bolts so trying to fix the washers between the head and manifold is a bit hit and miss, hence the fitting between the carb and manifold. To date I've not had any problems with air leaks, so my current set up works well except for what I think might be heat transfer. We'll see how a few stacked together with high temp sealant in between works.