oil leaks

Information relating to the Matchless G12 or AJS Model 31 650cc twin
Member
Posts: 23
Joined: Sat Nov 24, 2012 7:08 pm
Location: DORSET UK

oil leaks

Postby mollymole » Mon Jan 13, 2014 5:08 pm

I am having a problem with an oil leak between cylinder base and barrel,in spite of several attempts and the last being with a thicker base gasket.Could it be exasperated by the fact that the 59 crankcases are not fitted with a pressure release valve.The later type cylinder heads I am using have oil metering jets fitted would it help reduce the start up pressure if these were removed.Iam resonably sure the oil is not leaking from between the case faces,but is there an easy why of confirming this??
mole

Member
Posts: 1700
Joined: Mon Oct 05, 2009 1:00 am
Location: ESSEX UK

Re: oil leaks

Postby 1608 » Mon Jan 13, 2014 6:31 pm

If memory serves me right there are also oil restrictors in the channel btn the crankcases too, so removing the restrictors in the heads will not help. I fitted the restrictors in my 1960 heads because having been discontinued they were re-introduced in 1962 ( according to the manual ) so I believe they were of more benefit. I think they prevent over-oiling of the rocker area. My theory is that base gaskets don't ( shouldn't ) leak, especially the thicker ones now supplied. With the torque involved in pulling the heads down and the head gaskets not leaking, why should the base gasket leak. Mine don't any way! I personally think its more likely that the c/case joint leaks in the area of the oil gallery which is rather thin. With respect, I think a lot of people are wishful thinking in that the base gasket is leaking rather than the c/case joint. I can't think of a way of determining whether the c/case joint is leaking, as the barrels need removing etc. You could remove barrels, block the oilways on the top of the c/cases and force oil into the oil gallery and see if there is any seepage at the joint. My view anyway.

I have to say, it is very important that the c/case tops are perfectly flat and the head bolt threaded holes in the c/cases are not proud, 50 yrs of over-tightening the head bolts.

Member
Posts: 59
Joined: Mon Jan 01, 1990 1:00 am
Location: DENMARK

Re: oil leaks

Postby ajsph » Mon Jan 13, 2014 7:19 pm

Block the three holes with your fingers, press oil in the last one with help from an oil can, , and you will see if the cank case leak from the oil gallery.
Poul

Member
Posts: 1700
Joined: Mon Oct 05, 2009 1:00 am
Location: ESSEX UK

Re: oil leaks

Postby 1608 » Mon Jan 13, 2014 9:52 pm

But, may only leak when engine or oil is hot, or warmed up at least.

Member
Posts: 23
Joined: Sat Nov 24, 2012 7:08 pm
Location: DORSET UK

Re: oil leaks

Postby mollymole » Tue Jan 14, 2014 11:30 am

You are probably right about the wishful thinking,but would like to be sure before splitting the cases. Incidentally the studs and nuts are new and the faces clean and I followed the recommendation regarding torque .I can't see how you can reasonably check the oil gallery without replicating the pump pressure. Maybe as it is not serious I will let the fault develope.The appearance of the garage floor has change significantly since the renewed interest in British bikes.
Were any of the restrictor jets fitted to the engines without release valves?

Member
User avatar
Posts: 1272
Joined: Sun Jan 01, 1995 1:00 am
Location: WREXHAM UK

Re: oil leaks

Postby Malleon » Tue Jan 14, 2014 10:45 pm

Were any of the restrictor jets fitted to the engines without release valves?

Yes!

Member
Posts: 497
Joined: Mon Jan 01, 1990 1:00 am
Location: WEST SUSSEX UK

Re: oil leaks

Postby g80csp11 » Tue Jan 14, 2014 11:24 pm

I have to say that I've struggled with getting my G11 oil tight , as I think many twin owners do . last rebuild over Christmas I used the smallest amount of 'Ducati Spare Parts Threebond Liquid Gasket' between the crankcase halves and under the base gasket with wellseal on top and the std head gasket.
I have to say 'oil tight' for the first time in several year .
My mate has done the same on 2 other G11 rebuilds with the same results

It's much thinner than normal instant gasket , and made for crankcase joints on modern Jap bikes + Italian
Only time will tell if its oil tight for the longer term , but highly recommended
only need the smallest amount applied with small brush

any of the threebond products for motorcycles are the same . mine was about £14 a tube

Return to G12 / AJS Model 31

Who is online

Users browsing this forum: No registered users and 1 guest