Crankcase nightmare

vectra · Post by **vectra** » Thu Aug 06, 2009 3:48 pm

I have know learnt that I have a 1960 G9 engine with a mismatched crankcase.
Drive side Alternator, Timing side Dynamo, Dynamo crank. Fitted with dynamo and magneto. Duplex frame.
Primary chain case dynamo type(not compatible with alternator crankcase).
I don’t know how to check if the cylinders and heads are from the original alternator unit.
If I can determine exactly what I have I will decide what route to take.
I can purchase a 1961 alternator crankcase complete with the crank. This would be more in line with the original machine.
On the other hand I could throw caution to the wind and fit a 1956 G11 engine which is available.

Eric · Post by **Eric** » Thu Aug 06, 2009 8:08 pm

How have you determined that the drive side is for an alternator whilst the timing side is for a dynamo?

There is no difference in the cylinders and heads between both types.

Its seems that you have almost everything for a deluxe model G9 that would have been fitted with a dynamo & magneto, you seem to have the impression that a dynamo model was not made but it was as the de-luxe variation.

The drive side crankcase should have the engine number stamped near the throat for the cylinder what does it say? It maybe possible for the dating officer to validate the bike from this number.

I didn't think the G9 (500cc) bike was produced by the factory in 1961 as most information seems to suggest 1960 is the last year it was made.

The 1960 G9 engine was considered by many to be the very best of all 500cc twins, so why consider fitting the earlier engine?.Edited by - Eric on 06 Aug 2009 7:13:56 PM

Don Madden · Post by **Don Madden** » Thu Aug 06, 2009 10:16 pm

Brian is right, there are obvious differences in alternator & dyno drive side cases & they do not interchange as the mountings for the two chaincases is very different.

I would go for the 1961 alternator as they are more reliable than the Lucas dyno. Of course, if you don't ride at night, that doesn't matter.

I have seen 7 fin G11 barrels & pistons used with 1960 G9 bottom end & heads successfully. It seems strange & the combustion chamber is the wrong shape but compression is about the same.

Cheers, Don.

vectra · Post by **vectra** » Fri Aug 07, 2009 6:45 pm

Thanks for the input.
Another problem I have. I am told that numerous oilway changes were made in the late 50's and early 60's, if this is correct should I be wary of obtaining different heads?. If this is correct what should I look for?.
Brian

Don Madden · Post by **Don Madden** » Sat Aug 08, 2009 3:25 am

They did make numerous changes but the most significant was that 1956-59 did not have an oil pressure relief valve & it took until 1960 to admit it was a mistake. The changes do not make top end oiling incompatable.
Cheers, Don.

Duncan · Post by **Duncan** » Sat Aug 08, 2009 10:50 am

There were also changes to the number of metering plugs in the cylinder head, in my experience with all plugs installed there is no shortage of oil to the top end, my guess is that they may have omitted them in certain years to increase the oil return/drain supply to the camshafts/cam followers, not something that should be a problem in normal operation.

If you do not have one already get a copy of “Matchless & AJS Restoration” by Roy Bacon (ISBN 1-85579-041-6) for guidance on the year by year changed there is also addition information on this site: https://www.jampot.com/article_read.asp?id=20

wilko · Post by **wilko** » Sun Aug 09, 2009 3:33 am

It amazes me that they considered the dynamo model " Deluxe".

Eric · Post by **Eric** » Sun Aug 09, 2009 12:52 pm

It was because many keen motorcyclists did not like the idea of having what they considered to be an unreliable coil ignition system as fitted to the standard alternator bike.

You did also get chrome tank panels and a brake light as part of the de-luxe specification.

However it seemed almost all dealers ordered at least the tank panels as optional extras so the bikes looked very similar at casual glance.