AJS & Matchless Owners Club

Note that the Burman & AMC gearboxes use a different spacer behind the engine sprocket. The models with AMC 'box have a wider spacer to align the chain run better. If changing from one type to 'tother do check the alignment with a straight edge. Don.

Thanks Don.
I'll check when I put the engine back in.

I took your advice and have ordered the 22T engine sprocket together with all new bearings and bushes. New big end also.
I'm still struggling to find a +0.040" Piston, as I've decided against the JP Piston from Australia. I'm not happy with the one I have in my '55, so don't want to have the same issue in 2000 miles. I want a NOS Hepolite, Robbins or Wellworthy or NOS Matchless, or something. PML have not got back to me about machining or using a compression plate. So, I'm still on the hunt!

Marty,

Just a thought:

It appears (to me at least) that your 56 G80CS has been "updated" with a later AMC gearbox and clutch. Could the previous owner have fitted a 1960s type head also? The 1960 head is different from 56 and requires a different piston.

Bjørn

bjorn wrote:Marty,

Just a thought:

It appears (to me at least) that your 56 G80CS has been "updated" with a later AMC gearbox and clutch. Could the previous owner have fitted a 1960s type head also? The 1960 head is different from 56 and requires a different piston.

Bjørn

Bjorn,
Now you're opening a can of worms! hehehe. How would I tell the difference between heads?

Marty,

The 56 - 59 CS heads have interrupted finning in the spark plug area. The 60 onwards motor have continuous cooling fins. See the photo below.

There are a number of other differences as well, the 60 onwards heads are 5mm higher, have different valve diameters and valve lengths. Combustion chambers are different and later type pistons cannot be used in 56 - 59 heads.

There has been some discussion on the forum earlier regarding plug position on the 56 - 59 heads. The 56 heads I have seen have the plug mounted on the side, later models (from 57?) had a central plug firing through a slot. See photos.

Bjørn

While I am at it.......

Photos below of 56 CS and 60 CS pistons. Also combustion chamber of 60 type cyl head.

Bjørn

Bjorn,

Thanks so much! This makes it easy to see. Definitely I have a '56 head then according to your description.
Photo of your '56 piston also gives me the confidence to purchase one I have found online. My piston seems to have a considerably higher crown than yours, but by the looks, yours may be a Robbins with more of a Domed look to it.

Maybe there's a slight difference in compression ratio.

Cheers.

Here are a couple of pics of my '56 piston. I can't see any marks on it to know what brand it is. Seems to look similar to Hepolite pics online with the high crown. I couldn't be certain though.