Cylinder Head

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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Cylinder Head

Postby Oggers » Tue Jun 16, 2020 7:46 pm

Well, to add to the litany of troubles with this bike, the cylinder head gasket looks like it has gone. Weep which looks like it is coming from the interface of the block and head at the rear. It needs doing. Apart from the gasket and the special tool - which I now have - anything else I should need - or do when I have the head off? Do we recommend a smear of Wellseal on both sides of the gasket?

To add to the misery, the dynamo seal went again big style. For the third time, I now have an oily right boot. This bike is rapidly heading for the classifieds!

Chaincase seems to keep some oil in though :beer:

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Re: Cylinder Head

Postby ajscomboman » Tue Jun 16, 2020 8:34 pm

If the base gaskets are the thick pink, blue or black ones then it's recommended not to use any sealant at all according to the manufacturers. If using paper gaskets then Wellseal.

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Re: Cylinder Head

Postby Oggers » Tue Jun 16, 2020 9:23 pm

To be clear for a 55 G9 - I assume there is a cylinder head gasket of some description and that by base gasket - you mean the one under the barrel? If so, is it worth replacing this also - assuming that does not leak?

AMOC parts seem to do a complete engine gasket set.

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Re: Cylinder Head

Postby Mick D » Wed Jun 17, 2020 6:34 am

Hi Oggers

I believe your engine has been recently 'rebuilt' :roll: :roll: Might be worth just re-torquing the head before stripping to replace the head gasket which will in itself require subsequent re-torquing.

There were also issues with the head gaskets being supplied in a thinner gauge not so long ago resulting in some head leaks - yours may be one of these, in which case ensure you get a full thickness replacement, (not sure of the thickness' but a search on here will bring up the references).

Regards Mick

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Re: Cylinder Head

Postby ajscomboman » Wed Jun 17, 2020 7:42 am

As far as I'm aware the gasket set contains paper base gaskets should you choose to go that far. I guess that in the first instance I'd go with Mick and see if they go down again and seal. If not then should you lift the heads it maybe obvious where the leak is, if not then I'd lift the barrels.

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Re: Cylinder Head

Postby Oggers » Wed Jun 17, 2020 8:02 am

Gents - thanks for the replies. I have already torqued the head down slightly. I didn't want to overdo it as I couldn't get the torque wrench on - 22 ftlb springs to mind, and I could not get to the front nearside nut....but yes the nuts will go further and yes, I may just torque then down further and see what happens. Didn't appear to make much difference when torqued down a little more though.......

It "looks" like the head gasket as the top of the barrel is wet with oil, but I'll remove the tank for a clearer picture and revert.

...amd if anyone wants the blessed thing for slighly less than what I paid for it, I may be interested!

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Re: Cylinder Head

Postby ajscomboman » Wed Jun 17, 2020 8:32 am

As the top of the barrel is wet then it's naturally a very good indicator. Personally I think you've just been plain unlucky, 500 engines can and are very often quite dry. They can be made very dry around the cases but never ever around the dynamo seal. As your has gone again you've really got to dig a bit deeper and seriously look at the breathing. Blowing that quick is not normal. Head gaskets is a very easy fix. If you use copper gaskets with the o-rings you'd only have to torque it down once as they never seem to move once done. Well none of mine ever have, touch wood, and no leaks. Club now stock the correct thickness and the o-rings.

PM me a picture and a price.

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Re: Cylinder Head

Postby Oggers » Wed Jun 17, 2020 12:01 pm

PMs sent chaps......

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