G11 topgasket problem

Information relating to the Matchless G11 or AJS Model 30 600cc twin
Locked
lajuritz
Posts: 1
Joined: Sat Jun 02, 2012 10:03 am
Location: NORWAY

G11 topgasket problem

Post by lajuritz »

Hey.
I have a Matchless G11 that have a huge problem. head gasket blowing all
the time. We are talking about only a few mil then it stops.
Is this a known problem, and in that case, do you have any advice to come
up with to solve the problem.
thank you.
Greeting
Lasse Juritzen.
Norway
Groily
Member
Posts: 2151
Joined: Thu Jul 04, 2002 1:00 am
Location: NORMANDIE FRANCE

G11 topgasket problem

Post by Groily »

Just a thought Lasse but it might be a good idea to measure the depth of the rebate in the heads against the height of the spigot on the cylinder barrels, and then the thickness of the gaskets you are using. If the metal bits touch before the gaskets are compressed . . . it's a problem I have met more than once . . . . Some gaskets aren't much more than a mm thick, but if I remember right they ought to be about 1.7mm to 1.8mm, say 65 to 70 thousandths of an inch when new.
If there is a problem, it's easy enough to take a bit off the spigots on the cylinders - which is what I have done on 2 of my engines. No problems afterwards.

This assumes clean flat mating surfaces, decent non-stretch studs and nuts, and using about the right torque setting, say 20/22ft lbs or thereabouts.
Another thing you can do is mill flat the load bearing areas under the cylinder head fasteners. An end mill down the holes will do it - a long one on the deep holes.

Then, it's best to check the tightness of the heads very carefully. First, I start the engine and let it warm up to a reasonable operating temperature. Then stop it, leave to go completely cold. Back off the nuts a half turn, then retorque. Then do maybe 50 miles and do the same again, then repeat after about 500 miles. Sounds over the top, but it's surprising how there can sometimes be some big variations in the torque after the first few miles of settling down. When happy with everything, check valve clearances. Things should then hold together for a good long time without any more problems.

Good luck.
wilko
Posts: 2337
Joined: Wed Oct 12, 2005 10:45 pm
Location: victoria AUSTRALIA

G11 topgasket problem

Post by wilko »

Are you using the cotton reel spacers under the nuts? Make sure you're not running out of thread on the studs before the nuts tighten. Happened to me. Also UNF nuts were used and binding up on the threads before it was actually squashing the headgaskets.
Locked