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Carb insulators and sealants

Submitted by steve_constable on Fri, 18/12/2015
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Commando

Hi

I am fitting new 930 carbs to my 72 Interpol/interstate.

i can see that the carbs seal nicely onto the manifold with the embedded o-ring. I have bought new RGM Tufnol insulating washers to go between the head and the carb manifold. (Previously there was only a thin paper washer).

The Tufnol washer is hard and my question is, does this need any sealant or does it need paper washers either side to make a good airtight seal?

i can't find the answer to this in Technical or in any of my manuals so some experienced advise would be much appreciated.

thanks

Steve

Submitted by karl_nixon on Fri, 18/12/2015

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I put very very thin smear of Blue Hylomar on. I don't think it really needs it if all is flat as it should but I figure as Hylomar does not set hard if any was to find its way into the inlet tracked and enter the combustion chamber (tiny bits I mean) it would simply be bounced around until it was blown out of the exhaust.

Submitted by keith_glassborow on Sat, 19/12/2015

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As per Karl's advice. I've gone back to Hylomar after many years stuck on Silicone. I also just replaced the thin 1.7mm carb to head spacers with 5mm thick ones using Hylomar and its never idled as well (when hot) in 17 years. That's despite or in spite of new carbs, new bodies and brass slides etc. Amazing stuff; Hylomar!

Submitted by james_fanning on Sun, 20/12/2015

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Have always fitted the thick Tufnol washers dry on my Mk3 and Mk 1A 850's over the past 30 years plus without sealing problems.

Submitted by Anonymous (not verified) on Sun, 20/12/2015

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It's always reassuring to know that there is no air being drawn in via the joints. An alternative strategy is to use Hylomar on one side to keep the washers in place and a high melting point grease, e.g. of the lithium type, on the other face so that the carbs. can be removed easily if or when required.

It's a pity that they had to reformulate Hylomar when some solvent legislation came in a while ago. It doesn't seem to handle as nicely as it used to but it still does the job of course.

Submitted by les_howard on Sun, 20/12/2015

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I prefer Wellseal every time. I apply it thinly with a small cheap artists brush to both surfaces...leave it to dry for at least 1/4 hour and bolt up. You will be able to put your finger in and use a small piece of petrol soaked rag to wipe away any surplus inside the manifold if it has squeezed out. Having suggested Wellseal instead of Hylomar (which I'm not keen on anymore as it dries and skins over far too fast making a messy job) I would still usethin paper gaskets between the3surfaces.

Les

Submitted by david_comeau on Sun, 20/12/2015

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28 years of researching and running various commandos, I have noticed the books shows only hard phenolic spacers. Though I have seen 2 different thicknesses, I always have run them clean with no sealer or nonstandard paper gaskets (sic) since I had never found an original commando with any applied. Maybe I'm the exception but I have also NEVER had any evidence of the carburation to be affected from a lack of goo. I also only use the orings in the carb to seal to the manifolds. However I have found the early manifolds 68-71 (06-0509) to warp at the carb from over tightening (and warping the carb too)...especially if you add non standard thick paper spacers. Hence the need for later72+ up graded manifolds (with thicker flanges).

 


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