AJS & Matchless Owners Club

Hi - can anyone tell me the measurement, in mm, from the centre of the spindle to the centre of the nose(?) on a g80s ('54) rocker arm (inlet on tappet side) and also for the same rocker arm on a 250 or 350 light weight ie G2 or G5 (which are shorter). I think I have found the latter but need to confirm with a measurement.

Alternatively is there any other way of telling the two apart - ie any markings?

NB: The picture above is just to illustrate the measurement required it is not the rocker in question ( I presume the one is the picture is an older pre-war design with a squared off interface).

Thanks on advance

Stephen

I don't have a heavyweight rocker to hand but this is the lightweight rocker.
It would seem to be 1.1/8" (28.575mm) which from memory, is about 1/8" less than the heavyweight item.

Perfect Pharisee - thanks so much for posting this picture with a clear measure. That will help me in my search no end. This next bit is cheeky I know - the one in your photo isn't for sale is it?

Here's a 1947 NOS H/W arm. (6/2d !!). Exactly 1" (25.40mm) vs the L/W 1 1/8"

Hi

That's strange - elsewhere it has been stated that the LW arm is the shorter of the two. What's the definitive answer please? (Just trying to understand the rational behind the 'upgrade').

Regards Mick

no need to measure to tell the difference between L/W and H/W rockers. The L/W rocker have a Flat end near the pushrod nipple and H/W rockers are curved all the way to the tip of the pushrod end.

Dunno, Mick.
Stephen doesn't say (nor in his Profile) the year of th'engine My pic is of a 1947. P'raps they vary according to year?
I've just measured a matching NOS arm which goes on t'other end of the rocker shaft and at the same point it's 1.5" exactly. If the measurement on the 'input' (i.e. the pushrod) arm is less than at the same measurement points of the 'output' arm (at the valve stem) there will be a greater throw at the valve side than the pushrod side.
(Obvipussly you can 't fit an arm wit a greater dim on the valve side as it wouldn't match the fixed distance (1.5") between the shaft centreline and valve stem. One with a lesser measurement can be fitted at the input side because the pushrod isn't fixed and will move laterally (aka flop about) to accommodate the difference.
(I hope you're keeping up with my complicated simple explanation? )

So AJSComboman - its as simple as these two photos?

Hi

Even more confused by the above posts now

These are my 'unmolested' heavyweight rockers:
Regards Mick

Ok... I've been down the garage and hoiked out an old heavyweight rocker. This one from a '55 M18S.
As you can see, the dimension you're interested in is 1.1/4".