AJS & Matchless Owners Club

At a guess I would say it's a blanking plug.

Colin

Yep, 042044 is the blanking plug on the end of the oil pump. It's held in place with bolt 042046 and washer 042151.
O-ring 042177 needs to be in good condition as it provides a seal against the oil pump pressure.

Here's a picture:

Thank you for this advice, as you know I've been exploring no oil feed to the jets above the rockers.
I've replaced the missing 5th bolt in the head, but still no oil after 5 minutes fast idle.
I have scavenging from the little hole in the tank and ironically there seems oil up at the top from somewhere !
All rocker box holes are clear , barrel oil hole clear, I've bought a new oil pump pin so that's my next place to look and now maybe the little O ring.

Whenever you can upload a picture would be nice when you can, thank you

Pic now added.

Thank you

well ,
we've removed the oil tank and cleaned it out - removed the plunger and inspected it and carefully replaced a brand new plunger.

run the bike - probably better scavenging I reckon , but still no oil to the rocker jets!!! - but daftly plenty splashing around up there. loads splashing around.

next step is to remove the rockers and check them for wear in their bushes in the rocker box - I figure if the bushes are worn , then what oil that is up there will bleed out from the worn bushes and not leave any pressure to come out of the jets!!

Reference your picture of the plunger and O ring you kindly added.

When I was inside that area replacing the guide pin , I looked at the plunger.
I removed the little bolt and tried to remove the blanking plug , but could not get hold of it.
I assume the only way to remove is with the gearbox out and oil pump out and push the plug out from the inside !
However, there were no leaks around the O ring area and when I put an oil can there the oilway was clear .

That's correct - the blanking plug is pushed out from the plunger side. However, it's unlikely to be stuck so it may be possible to remove it by taking the retaining bolt out and prising it along with a small screwdriver down the bolt hole. Or even a blast of compressed air into an oilway - it's on the pressure side of the pump, so that should shift it.
Worth a try?

Thought: if you squirt an oil can into the rocker cover oilway, does any oil come out of the jets?

good morning ,
I tried blowing an air line in there(once the bolt was removed) and air came out "somewhere inside" so the oil way was clear.

I tried putting an oil can on the bolt hole and squirting oil in there and again oil came out somewhere inside BUT crucially not the jets

when running for 5 minutes or so maybe 10 - there is so much oil splashing and spraying around up the top end around pushrod cups and rocker spindles that it's difficult to establish whether it's coming from the bottom UP and hitting everything - or out of the spindles.

but nothing actually out of the jets

thank you

If the blanking plug is not leaking do you really need to remove it? are those jets definitely clear?