90 Sport oil pump problems, 'wet sumping'?

[grundlegrabber]

I have a 1969 90 Sport that I seem to be having some trouble with. It is a near-perfect original bike with only 315 miles on it. Last time I ran it (last fall), it was hard to get started and smoked like hell once I finally got it to go. The smoke eventually dissipated as it warmed up.
    Today I got it out and trying to fire it up, it wouldn't start and then on about the third kick it sort of locked up and blew oil out of the head gasket! Pulled the spark plug and kicked it through several times, then tried starting it again. Eventually got it fired up and would barely run, as it was blowing so much oil out of the muffler that it coated my yard. Took the bike on a short ride, about 3 miles, and it was perfectly fine and ran great.
    So what I am thinking here is that the oil pump is leaking down, causing the crankcase to fill with oil. Similar to the "wet sumping" that tends to occur on old British bikes sometimes. Anybody else experience this problem? Are these oil pumps problematic? I assume I am going to have to replace the oil pump to resolve this issue, as well as the head gasket due to what happened when it blew the oil out. Are there any NOS pumps left for this bike? Or does someone have a better idea?
    Little background info on the bike, I've had it about 4 years now. I think this problem has been going on to some extent since I bought the bike. It smoked like hell when I got it, but the guy who sold it to me was running premix in the tank along with the oil injection. The muffler has always seemed to have heavy oil deposits in it and it drips slightly out of the muffler-to-headpipe junction when it sits. I do shut the petcock off and run the bike until it dies every time before I store it. The smoke always clears out after running the bike for 5 minutes, and it always runs great after that.

[rocketman]

Hi Rob. Are you keeping an eye on the trans oil level? It could be leaking past the seal. Just a thought. Mark.

[grundlegrabber]

Mark,
Trans oil level seems to be staying full, I checked it yesterday and oil still runs out when the check bolt is removed. I have not added any trans oil. It stops smoking after running for 5 min. From past experience I remember that when crank seals are bad, it usually doesn't stop smoking, correct? Unless for some reason the seal only leaks when it sits. Good idea though. Not sure if I can tell what color the oil is that is leaking inside the motor without taking it all apart (the injector oil I'm running is blue).

[rocketman]

I guess you could temporarily disable the injection system and run it on premix to narrow it down. Mark.

[disc_valve]

Hi, GG.

I had a similar sort of problem with my 100TMX motor a while back. In my case it was a self-filling transmission - 2-stroke oil was seeping into the gearbox via the pump drive shaft whilst the bike was parked up unused. It was definitely 2-stroke oil, as the gearbox got overfilled and the excess I drained out was bright red! I suppose it is possible for the oil to somehow seep through the pump and into the engine via the oil output line. There is a ball check valve in one pump port (sometimes in both) which should stop this, but its worth checking to see if the ball(s) are still there.

The balls and springs are loose in the banjo union bolts, and are easy to lose on dismantling and tricky to fit on reassembly, so it's best to pull the oil lines off the pump and take the pump to the bench to check. Once on the bench, unscrew both oil unions and (carefully) see what's inside. The pump inlet umion will have the spring nearest the pump followed by the ball. The outlet union has the ball nearest the pump, followed by the spring. Not that the springs have different parts numbers, so take care not to swap them over.

Also, you can prove it's pump oil getting into your motor by disconnecting or crimping the oil lines next time you park up. If the "wet-sumping" doesn't happen then you know it's oil from the tank, not the gearbox.

Hope that helps,

Graham

[grundlegrabber]

So just an update on this issue. Ran the bike for awhile 3 weeks ago. When I put it away I crimped off the oil supply line with some hose pincher pliers. Took it out today, removed the pliers of course, and it fired right up with no excessive smoke. So it seems like the oil pump is the problem and I will be needing a new one. Thanks for the replies everyone.