G9 with G11 Barrels

Information relating to the Matchless G9 or AJS Model 20 500cc twin
Posts: 2
Joined: Thu Nov 27, 2008 4:05 pm
Location: WEST SUSSEX UK

G9 with G11 Barrels

Postby KenB » Mon Oct 03, 2011 5:30 pm

I have a 1956 G9 which I bought a couple of years ago. The engine and frame numbers match the log book and confirms the engine as a G9. However, there are 7 fins on the barrels. My understanding is that the G9 should have 6 fins whilst the G11 has 7. If this is true, I would like at some stage to revert the engine back to a 500cc G9. Looking at the parts list for 1956 the crankshafts for the G9 and G11 have different numbers, presumably because of balancing. My questions to you noted experts are:-

Would a G9 crankshaft perform okay with G11 pistons? Which I am guessing is my situation.

Is there a way of telling whether the crankshaft is for a G9 or G11 without splitting the crankcase?

If there is a mismatch would there be any long term reliability issues?

Hope someone can help.

Member
Posts: 2882
Joined: Mon Jan 01, 1990 12:00 am
Location: USA

G9 with G11 Barrels

Postby Don Madden » Mon Oct 03, 2011 11:49 pm

As you suspect, the crankshafts are the same except for balance. I think the only difference you find will be where the engine vibrates the most. The internal parts are the same, rods, bearings & other parts. The pre-1956 cases , barrels, heads, etc will not fit. You can even put in a generator G12 crankshaft with the 7 fin barrels if you use the 1958 only 650cc pistons, (providing you can find any) & rods. Cheers, Don.

Edited by - Don Madden on 03 Oct 2011 11:49:56 PM

Posts: 2338
Joined: Wed Oct 12, 2005 9:45 pm
Location: victoria AUSTRALIA

G9 with G11 Barrels

Postby wilko » Tue Oct 04, 2011 12:00 am

I would guess the 500 barrels would be harder to find considering most would have opted for the larger capacity by then?

Member
Posts: 137
Joined: Fri Dec 31, 2010 10:02 am
Location: STH AUSTRALIA AUSTRALIA

G9 with G11 Barrels

Postby Trefor » Tue Oct 04, 2011 12:00 am

Just an idea-could you sleeve the barrels down to accommodate the 500 pistons if the stroke is the same?

Member
User avatar
Posts: 924
Joined: Tue Sep 09, 2003 12:00 am
Location: LONDON UK

G9 with G11 Barrels

Postby Samuel » Tue Oct 04, 2011 9:36 am

Why bother - the 600 is considered sweeter
Sam

Posts: 2
Joined: Thu Nov 27, 2008 4:05 pm
Location: WEST SUSSEX UK

G9 with G11 Barrels

Postby KenB » Thu Oct 20, 2011 5:52 pm

Thanks for replies. My main concern is that I have a mismatch of crankshaft and pistons which could cause problems. Obviously the factory thought that a mismatch was not a good idea because they went to the trouble of producing separate crankshafts for the G9 and the G11. If it is a case of just more vibes I can put up with that, but if it is going to cause an engine failure then I am concerned about pushing the engine too far.

Posts: 467
Joined: Tue Jan 11, 2011 12:25 pm
Location: WORCESTERSHIRE UK

G9 with G11 Barrels

Postby dogwheel » Thu Oct 20, 2011 6:40 pm

Ken, what is your bike like to ride?
If it's a sweet motor, wouldn't it be best left as it is?

Member
Posts: 50
Joined: Fri Jan 04, 2019 6:05 am
Location: Sth.Aus.

Re: G9 with G11 Barrels

Postby matg80s » Tue Feb 19, 2019 5:27 am

...
Last edited by matg80s on Sun Apr 07, 2019 9:37 am, edited 1 time in total.

Member
User avatar
Posts: 1896
Joined: Mon Jan 01, 1990 12:00 am
Location: LANCASHIRE UK

Re: G9 with G11 Barrels

Postby dave16mct » Tue Feb 19, 2019 10:01 am

G11 barrells won't fit in these crankcases. 56 on crankcases had a wider throat to accomodate the 600 barrells, 500 barrells then had a thick spigot to fit in the wider throat. The 500 barrells you need have oil grooves on the outside.
Dave.

Member
Posts: 50
Joined: Fri Jan 04, 2019 6:05 am
Location: Sth.Aus.

Re: G9 with G11 Barrels

Postby matg80s » Tue Feb 19, 2019 11:49 am

...
Last edited by matg80s on Sun Apr 07, 2019 9:38 am, edited 1 time in total.

Next

Return to G9 / AJS Model 20

Who is online

Users browsing this forum: No registered users and 8 guests