[Greybeard]

Now that the 37 Ariel 500 and the 49 Matchless 500 are sorted, I shoved the Lion onto the operating table and made a start.
I didnt find anything too drastic so far but noted the following.
1. Both end plates of the oil pump, especially the feed side, had the expected circular wear marks from the pump gears. I refaced both on a surface plate to remove the marks. Im not sure that it will fully cure the Lions prodigious tendency to wet-sump, though in fairness it can sometimes be standing several weeks between runs so Im perhaps expecting too much. Its probably no worse than my AMC twins (both fitted with taps). I may consider fitting a tap in the oil feed or draining the tank at the end of the day, I'll see how things develop. Im fully aware of the potential pitfalls and have measures to avoid them so no further dire warnings are required 
2. The 3/8th ball bearing in the pressure release valve had a fairly rough surface in places. Im not sure how much of an effect that would have on wet-sumping but would not help the oil pressure. Ive ordered a replacement, well, 10 actually from Simply Bearings. The rate the Lion is getting through them I reckon I'll have enough for the next 1000 years or so 
3. Finally, I did find a lump of silicon gasket material that a PO had used on the valve chest in the oil drain for the pump's return feed. Whether it was sufficient to impede the sump draining time will tell. Silicon sealant is something that has no place in a motorcycle engine. My AJS 650 that I bought years ago had its gauze filter (which someone had fitted in the return pipe rather than the feed) was choked with the damn stuff.

As a matter of interest, I took the Ariel out for its first run yesterday. Whilst I expected the difference in power of the two engines to be noticeable - the Ariel is an OHV 500, the general difference in feel of the bikes was huge. Whilst both bikes have the same forks, BAP gearbox , identical tyres and rigid rear end, they felt totally different, the Ariel feeling much more modern and spritely. The Sunbeam felt much older, bulkier and more stately, not worse, just a completely different, perhaps more serene experience.

Steve

[Thomas]

Hm, the breather... wouldn't expect that because it is at the top part of the crankcase. So much oil can't fly up. But you can easily test that by taping some tissue paper to its end. Then you'll quickly see if oil comes out.

[Greybeard]

Yes, the tank was full before the ride and yes, it was returning to the tank when I first started the engine. Obviously not monitored during the ride! After the ride - about 60 or 70 miles, the tank was very nearly empty. There was no evidence of blue smoke or obvious oil leaks. Suggests to me that oil was being pumped into the engine, filling the sump then escaping un-noticed by perhaps the breather.
Once I begin stripping it down I may come across the cause of the problem.

Steve

[Thomas]

I am a bit confused and recommend starting again from the scratch. I understand the following:

1.    There is oil missing in the tank after a ride.
2.    There is no sign of any leak.
3.    There is no oil burning visible.
4.    Excess oil can be found in the sump.
5.    The oil is pumped back into the tank while riding.

Right?

If 4. is valid, then one should check the ball valve. However, one should then expect smoke coming out of the exhaust due to wet sumping. Did you check if 1. is true? Was the tank really full before riding?

BTW: I do not expect a pipe leak because one would see it.

Cheers, Thomas

[Greybeard]

I'll make sure to check for airleaks when I make a start, John, but I think the return maybe built into the crankcase as there are no external feeds from the crank to the pump, just the return to the oil tank direct from the timing chest (and the feed pipe of course)

Steve

[singleminded]

Start by looking at the return pipe between crankcase and pump, if there is an air leak there it will cause problems

[Greybeard]

Thanks, John. It all looks like a simple arrangement - I wonder what has gone wrong. Only one way to find out I suppose.

Steve

[singleminded]

From what i can see of the part numbers the oil pump gears all seem to be much the numbers. some years including yours have either an A or B suffix to them.
The picture is of a 1929-1934 scavenge side of the pump.
The driven gears for feed and return are on the same shaft, the feed gear is part of the shaft and the return is keyed on. the other 2 gears are free to rotate. the difference between feed and return is that the return gears are wider.
You get the idea from the picture.

John

[Greybeard]

I dont mind bits falling out as theyll always go back together - its when broken bits fall out that my heart sinks 

Steve

[Thomas]

I would bravely go to it and open everything. I was also afraid that something would fall apart and I wouldn't be able to put it back together. But that never came true. It was important for me to take lots of photos at every step. That works well.

[Greybeard]

Thanks, Thomas, I had seen that. It was the internals of the oil pump in particular that interested me. I see you had no need to suspect yours was faulty so had no reason to dismantle it.
I shall have to steel myself and delve into it 

Steve

[Thomas]

Hi Steve, sometimes you can even find information in the club website.    No SV and actually no details about the pump but the same year. It might give you at least some hints.
Cheers, Thomas

https://www.marston-sunbeam.org/technicalNotes/model9EngineRebuild.html

[Greybeard]

Good afternoon, folks. I'm seeking a little advance information before I start giving the old Lion a 'coat of looking at'. The last run I had out on it, it ran fine though I did note that the oil tank was almost empty by the time I got home  There was no sign of any excess oil being dumped on the bike and a mate following me reported no blue smoke that might indicate it was burning the oil. The bike has always tended to wet sump when standing for a while and I'm now beginning to suspect that there is something amiss with the pump itself as it hasn't been scavenging - it had been previously as I always check for an oil return before each run.
None of the books I have show details of the oil pump on the '37 SVs. I'm assuming that it's a geared type pump contained within the timing chect. Does anyone have any drawings/cutaways etc of what might be lying in wait for me when I get the bike onto the operating table?
Any suggestions gratefully received in the meantime.
Regards. Steve