Insipid oil return

[AndrewM]

I have been recommissioning my 1946 AJS Model 16 over the past few months and it is ready to register for road use again:



However one final concern I have is that the oil return flow seems a bit insipid. The oil is returning, but I was somehow expecting something a little more generous, instead I just seem to get a slow dribble. Is this amount of oil return at high idle acceptable? It does't seem to increase significantly with a few more revs, and if I put my finger over the oil outlet I don't feel any pressure pushing back.



Is this a concern or am I being overly paranoid? So far the bike hasn't been registered so I haven't been able to take it out for a long ride, but I'm a bit concerned about whether enough oil is circulating for me to do this confidently.

[ajscomboman]

Normal for a plunger pump. Give it a blip and then you should witness a surge then it will return to a trickle.

[AndrewM]

Normal for a plunger pump. Give it a blip and then you should witness a surge then it will return to a trickle.

I'm not seeing any noticeable increase in flow as I raise the revs, but I will try running the bike for 5-10 minutes first to make sure the oil is fully circulating before I try that again.

[SPRIDDLER]

Normal for a plunger pump. Give it a blip and then you should witness a surge then it will return to a trickle.

I'm not seeing any noticeable increase in flow as I raise the revs, but I will try running the bike for 5-10 minutes first to make sure the oil is fully circulating before I try that again.

The return side of the pump has greater scavenging capacity than the delivery side so once the c/case has been 'emptied' the flow will be spasmodic, often just spurts. The reciprocating plunger type pump doesn't give the continuous flow that you get from a rotating impellor type of pump.
See the excellent animation of the plunger pump here:
https://www.jampot.com/article_print.asp?id=519

[AndrewM]

I'm resuscitating this thread as I still have some concerns about oil flow on my 16M. After the replies above I switched from the 20/50 oil the previous owner had used to straight Castrol 50, and the oil return to the oil tank assumed the correct appearance, coming through in blobs and bubbles. So happy with overall oil flow.

However, when taking off the rocker cover to verify that oil was getting into the rocker box, it looked completely dry, barely a trace of oil on the top of the pushrods or inside the rocker box. Certainly not the sort of residue I would expect if 50 weight oil had been getting splashed around.

I tried taking the rocker cover off and going for a ten minute ride, expecting to see a trace of oil on the pushrods or splashed around inside the rocker box after the ride, but nothing.

Since then I have taken the oil line off the front of the engine, about half a cup of oil drained out, and detached the oil line from the rocker box. I can blow compressed air down the oil line with no problems, and can similarly blow compressed air from the connection point on the rocker box, and two jets of air will blow out above the rocker arms just above each pushrod. So all seems good at the top end and the oil line to the engine is clear. I tried running the engine for 5 minutes to see if any oil came out the top of the oil line, which I had draining into a cup. Not a drop came through.

So am I being unrealistic in my expectations of how much oil should be circulating at the top end of the engine, or am I just not waiting long enough for the oil to rise up the line? Or is there potentially a problem or blockage at the oil pump end, and if so how do I test for it?

[SPRIDDLER]

You said in your opening post that you have recommissioned the bike. Was it new to you or were you riding it before the recommissioning?

I have taken the oil line off the front of the engine, about half a cup of oil drained out,

.
So it would seem that some oil is is exiting from the pump into the rocker feed pipe so one can assume that the oil feed hole in the gasket at the pump front plate is fitted correctly.

As you will note from the animation to which I linked in my earlier reply only a very small amount of oil is fed to the rocker box. The animation also shows how the throw of the pump plunger has to be such that the drilling in the plunger aligns (just once in every revolution) with the outlet gallery in the pump body.
On the basis that between Sept '45 and Aug '48 the plunger was changed and the plunger guide pin increased from 3/16" diameter to 1/4" diameter (and the timing side axle was changed to a two-start), if the 3/16" guide pin has been fitted to a plunger requiring the later two piece 1/4" guide pin the reduced throw of the plunger may be insufficient to correctly align the drilling in the plunger with the gallery outlet to produce a full flow to the rocker pipe outlet. After nearly 80 years who knows what parts may have been replaced?
However, this all depends upon a caveat of how well you know the engine's history and whether you are expecting too much flow to the rocker box.
I'd also detach the rocker feed pipe at the pump front plate and run the engine just to confirm in my mind that at least some oil is leaving the pump.

Oil pump rocker feed c.jpg

[AndrewM]

Hi Spriddler, Yes, bike is new to me, imported into Australia from the UK, sold me via Kettering Classics, but had been unused or lightly used for some time prior to my purchase and had some significant carburettor and timing issues, which I sorted out.

Prior to my post I had taken off the forward end cap of the oil pump to check that the pump was not gummed up, and it seemed fine, had fresh clean oil in it and as I said, about half a cup of fresh oil drained out. I also verified that the gasket was in the correct orientation and that the hole in the gasket lined up with the hole in the cover. So I suspected blockage in the oil pipe or rocker box, but this does not now appear to be the case.

After I posted but before seeing your reply, I put everything back together, but not before injecting about 1/4 cup of oil into the rocker box oil ways via the connector on the rocker box to make sure everything was sufficiently well oiled for the time being.

I then disconnected the oil pipe at the lower end, started the engine hoping to see a trickle of oil coming out, but got nothing after about a minute of running, which I thought should have been long enough.

It seems to me that there must be a blockage in the oilway in the crankcase feeding the rocker box oil pipe, or the rocker feed hole in the plunger is blocked. Oil is circulating through the engine at acceptable volume, so the pump is working to some extent, but it concerns me that some oil circuits are not getting oil.

I may do a sanity check tomorrow and take the pump endcover off, remove the gasket and put the cover back on, just in case the gasket is moving and blocking the hole each time I reassemble it. Doesn't matter if it leaks for a moment, it should only take a few minutes to test whether the flow is affected

[SPRIDDLER]

I then disconnected the oil pipe at the lower end, started the engine hoping to see a trickle of oil coming out, but got nothing after about a minute of running, which I thought should have been long enough.

Hmm, yes, a minute should be enough to check.

It seems to me that there must be a blockage in the oilway in the crankcase feeding the rocker box oil pipe, or the rocker feed hole in the plunger is blocked.

It seems unlikely but as a last resort you could remove the plunger to check that the drilling is clear, and at the same time check for the correct size for the guide pin. I only say 'as a last resort' as it's a fiddle to remove the pump's rear plate and the tiny BA screws are ripe for stripping the thread in the c/case unless you are very careful when refitting them.

I may do a sanity check tomorrow and take the pump end cover off, remove the gasket and put the cover back on, just in case the gasket is moving and blocking the hole each time I reassemble it.

There was a recent post mentioning that the rocker outlet hole in the new gasket had been misaligned and had to be enlarged/recut. I'll see if I can find the post and give you a link to it.

EDIT: Here's the thread about the oil pump gasket...........

viewtopic.php?t=29784&hilit=oil+pump+gasket

[g80csp11]

remove the pipe feeding head at the pump plate and start engine if you dont see oil from here when running its not the head , also that the pump pin is correct and not excessively worn as pump travel is controlled by pin in groove

[56G80S]

Joining in here, what is meant is that with the front, rocker feed, plate off you will clearly see the plunger moving back and forth. Others will correct me if wrong but the plunger would normally almost reach the end of the bore in the casting. If not, there's something wrong.

Hope my pump ends aren't mixed up!

Johnny B

EDIT and of course, the plunger spinning round and round.