Head gasket

Information relating to the Matchless G12 or AJS Model 31 650cc twin
Posts: 400
Joined: Tue Oct 24, 2017 11:05 am
Location: DEVON UK

Re: Head gasket

Postby MalcW » Tue Feb 18, 2020 11:34 am

Groily wrote:That's reassuring to read Malc.
Neill quotes 18 for the earlier 500s, but 'tis because of the 22 in the later info for same size fasteners that I go 20 on mine.
22 is what I've done the 650 to (with copper hitherto).
After the normal re-torques and valve adjustments, hopefully all will be well for a good long time at that on composites.

I think it's the re-torquing and valve adjustment that's the critical bit, especially with the composite gaskets.


Posts: 1335
Joined: Thu Jul 04, 2002 12:00 am

Re: Head gasket

Postby Groily » Tue Feb 18, 2020 12:57 pm

Quite agree Malc. I have follow quite a strict routine for checking tightness and valve clearances:

*On final assembly
*One full heat cycle - up to running temp and then leave to go stone cold (without going anywhere)
*After 50-ish miles
*After 500-ish miles

Maybe overkill and it gets boring taking seats and tanks off . . . but seems to have been worth it over the years - and there's often a bit to do at each stage.
The 650 on copper has been the only one that leaked anything, and that was only a weep from an exhaust rocker oil feed.
If it would stop raining I'd get the 50-mile check done!

Posts: 491
Joined: Mon Jan 01, 1990 12:00 am

Re: Head gasket

Postby raffles » Tue Feb 18, 2020 7:18 pm

Lazy Iknow and every one will be up in arms BUT yes I do 28ft lbs 0n the 5/16" studs and have never in
the twenty years i have had the bike pulled down the heads after initial assembly. The engine has been
rebuilt three times.Standard when I got it, so just ran it for 18 months untill I could hear the bottom end
rattle. first rebuild after 400 miles the company that did the regrind did not as asked clean the sludge traps
journals were polished and 27,000 miles put on 3rd rebuild to stop oil leaks "O"ring conversion on oil filter
tunnel plus reface crankcases and rebore.That was two years ago and Ihave never touched the heads since
Wrong? but it works for me .Oh and those who know me will say he does the miles and dont hang about

Posts: 253
Joined: Sat Jan 14, 2017 11:48 am

Re: Head gasket

Postby bob121 » Fri Mar 06, 2020 5:52 pm

I would say I'm guilty of over tightening the head nuts.
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