AJS & Matchless Owners Club

I am currently having my engine looked at on my 1956 G11 600 twin.
I have a loud mechanical knocking under engine load which gets worse as the engine warms up. After taking lots of advice it is thought that the big ends are worn, but I won't know until it is apart.
It has been suggested that this is common problem with Matchless due to poor oiling of the engine, principally due to the capacity of the pump on models of this year.

I have read many articles, and it has been suggested to me that a double capacity pump can be fitted, as it is on later models.

What models were fitted with the larger pump?
What part number is the larger pump?
Are they a straight swap?

Do I need to replace the timing cover, with a larger one to accommodate the pump?
What models have the larger cover?
Is it a straight swap?
What is the part number for the larger cover?

Hi Martin,
yes it is possible to improve your pumps and oiling devices.
Yes is necessary to change the timing cover.
He is a part of a mail that Ray Spencer (ray@multiplan.fsnet.co.uk) TEl 01282 839 512
You can see his adverts in JAMPOT :

"The maximum cost to completely refurbish the pump unit for your bike would be £220.00. This would include the following:-

1. Fit new gears, bushes and machine side plates on both pumps.
2. Fit anti wet sump device to delivery pump and leak test.
3. New bleed valve in back plate.
4. New pressure relief valve type 2,3,4
5. File ports on delivery pump
6. Gaskets, post and packing in UK only.

Delivery is usually about 6 weeks.

It may be that the scavenge pump is not sufficiently worn to require overhaul, therefore the cost would be less. If you send me the pumps and backplate I could do a wear check and then give you a firm price for the work "

Kind regards..

Yes, it sounds like the big ends are loose. The pumps are quite adequate, other than leaking past the spindles causing wet sumping. The problem is the rod fixings, which stretch oval, lossing oil pressure. Forget the pump size upgrade & spend the money improving the rod cap fixing. The studs can be replaced by allen head cap screws & nuts. Cheers, Don.

Big ends don't last forever. When were they last re-ground and how many miles have they done, do you know. It might just be acceptable wear and nowt t' do with the pump.

You can have your crankshaft metal sprayed by T & L Engineering to go to standard. About 50 £ per journal.

Thanks for your replies.
I don't get wet sumping, which would suggest that the pump is ok.
Could be just worn out big ends.
I have no idea how many miles it has done in it's life, and whether they have been re ground.
All will be come clearer when the engine is apart.
Just waiting for my local classic engine workshop.

Put an oil pressure gauge on it and see how much it drops to when hot.The noise could be primary drive issue.

Hi Martin,
for pumps, high capacity (64 g/h) were listed 28521 for feed pum, 28522 return pump, 28520 complète pump assembly since 1962 or 1963. Prévious pump assembly was listed 18037 (for at that time 7£,9s 7p !) gears width was 1/4 for feed, 7/16 for return. Timing cover for Hi Cap is 29610. Hi cap front et back plates remained as previouly : 15576 and 15573. Body became 28483 and 28482. Cartying plate (with release valve) became 30513 in 1964. New gears are available, but not front & back plates wich need generaly to be bronze bushed, because hole became egg shaped. Yes, pumps were working before these improvements. But if AMC performed it, it must had a good reason !

The factory refused to admit their unique rod design was a problem. The used an extended hours test on a 500cc engine as proof the bottom end was robust but the problems started with the capacity being increased to 650cc. They hoped the increased flow would offset the leakage from loose big end.

All the above is my opinion, of course, but I have rebuilt at least 100 of the twins & as a design engineer, am in the habit of doing a failure ananysis as part of the repair process. Nearly all had oval big end eyes.

Cheers, Don.

In other words, save your money on the pumps and buy some fancy new rods!