AJS & Matchless Owners Club

Hi All , just trying to check where the oil is coming from. I have removed the head and this is what I discovered, also want to check the head and piston are correct the bike is a 62 250csr the head has 43 re 62 stamped on it and the piston ha bhb 042848 and g62 stamped on it. Any help would be great!

For the piston the following table ( http://archives.jampot.dk/technical/Pis ... models.pdf ) gives the piston as a standard size, 7.8 compression ratio, 250 piston.

Welcome to the Forums, Graham.
I know little about Lightweight models but if there's oil from the zorst it must be passing through the cylinder so there's this thread in the L/W G5 section which may be of use to give you some clues as to what may be causing the issue. The topic started a year ago but was concluded in a post just yesterday.
Have a look at the story in the link here:

viewtopic.php?f=16&t=28018

I can't help either, I had a 1966 14CSR and the piston was very different, very domed and I think something daft like 9.5 or 10:1.

I'd look at the thread that Spriddler has indicated. I found that copper gaskets, after several rounds of use, annealing and re-using, got thin enough that there was insufficient "pinch" between head and barrel.

Johnny B

Hi guys
Thank you for your reply’s and advice, I have replaced head gasket (copper) and now have really good compression around 120-130 . When I was checking compression there seemed a lot of pressure on the down stroke and when I ran the bike briefly with rocker cover off it did seem to spurt out oil as if under pressure rather than a gentle plus? Could I also have a breather problem? As I do get a lot of oil going into the crank when sitting for a day or so. I know the pump should scavenge the oil back to the tank but wondering if the down stroke is possibly sending oil in crank area some how. Any thoughts would be great as more of a 2stroke kid of the 70’s

There should be an oil adjustment valve in the head . You turn it in so the oil to the rockers is reduced to a level you are happy with . From your description it sounds like to much oil is getting through it certainly shouldn't be spurting out .

I would like to check if anyone knows the correct way to set the rockers which can be set in various positions. The tappet that sits on the top of valve and the one that sits on push rod are movable on the shaft, so I just need to check the way to set them up ?
Any help would be great!

I would like to check if anyone knows the correct way to set the rockers which can be set in various positions. The tappet that sits on the top of valve and the one that sits on push rod are movable on the shaft, so I just need to check the way to set them up ?
Any help would be great!

Webby900 wrote: ↑Tue Aug 23, 2022 5:51 pm I would like to check if anyone knows the correct way to set the rockers which can be set in various positions. The tappet that sits on the top of valve and the one that sits on push rod are movable on the shaft, so I just need to check the way to set them up ?
Any help would be great!

I think it's self-evident when you assemble them in the rocker box as the splines on the axles and rocker arms give quite coarse adjustment.
In short, fit the rocker at the valve end to the axle and when that rocker is just touching the valve stem fit the rocker at the pushrod end so that it's as near as dammit horizontal. I'm pretty sure you'll find that if you fit the pushrod end rocker incorrectly on the axle it'll be well up above the horizontal or way too far below the horizontal.
This is what you want to end up with........

BTW - you'll find that if you intend fitting new felt lubricating inserts they are an absolute bu**er to get into place so I gave up and left them out and no harm has ensued. (I later discovered that leaving them out as a last resort is also endorsed by the well-respected engine builder Ken de Groome).

Not sure if this will be of any help, but on my first assembly of my model 8 head I did a clearly muppet move and completely missed the 5th head bolt (042196). As the thread referred to above, this bolt has quite a job to do by sealing the head gasket and ensuring no compression or oil is lost. My mistake was obvious to me by the slight hissing and failure of oil to reach the rocker box. So off came the top end again and did a bit of swearing then, reassembled including the fifth.
I found that once the cylinder sleeve nuts were tightened, followed by the fifth bolt, I then rechecked the sleeve nuts (which need a bit more), and then re-nipped the fifth bolt and all was roses. Hopefully, this may be of some help.