I don't trust the oil pump on the dommie, probably due to me putting a clear hose on the head feed then seeing how little oil actually went up there and how little made it back to the tank too. Hence I have a new pump from the club spares scheme ( If you want the old one to refurb, PM me)
The feed pipe spigot on the old one is 4mm - about the depth of the rubber seal. The feed pipe spigot on the new one is 9mm. The depth of the hole in the timing side cover is 11.4mm.I can see logic in extending the spigot to be longer then the seal is deep, but it does mean there is now a bit of a constriction as the oil flows from the pump into timing cover drillings. Should I just reassemble as it is, or should I think about taking a couple of mm off that longer spigot?
The bike is a 1955 build Dommie 99 ( one of the 1st 600s) and I am not sure if the spigot length changed as the twins evolved from that early engine.
Interesting, not something I have seen. If it was mine ,I would check that the extension does not obstruct the oil flow into the cross drilling, and shorten enough to clear. Perhaps the extension is to make it less likely that the seal will fall off un-noticed or get dislodged while the cover is being replaced? Someone will know more.
When the Commando arrived in the late 60s the gasket for its timing cover was far thicker than the thin paper one used on the Dominators. This made the gap between the oil pump and cover greater and so a thicker rubber button was used to make up the gap. But I don't think the spigot was made any longer to support the thicker button. However, the mk 3 Commando had a very different button which was more like a tap washer. I believe this had a substantial shim to support it and so may have had a longer spigot. On some Commando models the shim was not fitted to the pump.
Thanks, I think I'll shorten the spigot so its the same as the original, I have a paper gasket and the new seal is the same as the one that came out.
FYI a picture for comparison
Have you tried to find out if the lone spigot will even allow the timing case to fit? There cannot be any reason for that spigot to be longer than the thickness of the rubber seal, after the seal has been compressed. But also, if is too long, will it be too big to enter the hole? Interesting post - I was looking at the rocker flow last weekend and mine is also very slow, unless I put by finger over the exit hole inside the oil tank. Now I'm worried - there's no rocker wear that I can feel - but have I accidentally blocked something recently? I took the banjo off one side and expected oil to splash everywhere but it didn't do so.
The spigot is shorter than the hole in the cover is deep so it will go in, but I didn't measure radii so don't know if the extra length blocks the lateral drilling heading off towards the crank. However as you say, there is no need for the extra length beyond the end of the seal so it'll shorten it unless someone pipes up about any benefits from that length.
I believe that a lot of people are worrying unnecessarily about the amount (or lack of) oil going upstairs. The top end really doesn't need a lot of oil going there - it is OHV not OHC!
If you can see oil at the edges of the rocker-rocker spindle (where the shims/thackeray washers are) when it is running, then that is enough. Most people only ever look (if at all) when the engine is idling, or just above idle, when the oil pump is running at its slowest. As revs go up, flow will increase as well.
More oil up top = more oil to get down again. Too much oil = smoky exhaust as it gets sucked down the inlet guides.
There is every chance that the bike has been running for over 60 years with the 'compromised' oil supply as the designers intended, and if it isn't broke, why bother trying to fix it?
David, I thought the long spigot was for a Mk3 commando 850 with pressure valve. I have a number of pumps that have minor differences. You never know what fits what these days without a trial fit, do you.
Another option open to you is to switch the spigot from one pump to the other. All you need to do is lever off the spigot with two thin screw drivers and make sure they are reassembled the correct way round.
(Advise recently given to me by local NOC member - it worked for me)
If I remember right you need to remove the spigot to do a proper re-furb of the pump.
The oil pump spigot is available separately from Andover as NM15515. Sticks out about 5mm one way, 4mm the other.
I have one in my hand right now.
The spigot diameters are very slightly different of either side on the feed bush, it only presses in one way.
Considering the flow to the head, John Hudson measured this and it is not a lot compared to what is fed to the rest of the engine.