Forum

[simon]

And a shiver went through the Middle East. They really were a Royal Oilfield!

[Roy]

Hi Norm. You are correct that it can only pump back what is pumped in but according to the manual it is designed that it can pump back twice the capacity of the input pump to obviate oil collecting in the sump. For this reason you will often find air bubbles coming out of the oil return jet and the flow even sometimes slows down depending how much oil is in the sump and the angle at which the bike is standing perhaps on a side stand.If the engine has been standing with the piston at the bottom of the stroke and it wet sumps then the scavenger pump really pumps overtime to clear the surplus oil back to the tank.

[WDCO42]

Hello Dave,
As said Norm, the scavenge pump has effectively just to take care of the oil that comes from the big end and the back of the cylinder, and has around a third more pumping effect than the feed one, and fills only the front oil tank. The rest of the scavenge (cylinder head)goes by the timing case via its gears to the rear oil tank. The level between the two tanks is via a (very) small canal under the "real crankcase".
On a previous post, I read very interesting things about some non vented Bullet's oil filler caps, that if fully tightened, wouldn't vent the oil tank, and cause (extra) leaks to the engine. On the G, it vents the front oil tank, the one where your crankcase oil goes to... (the rear one has its own venting system), maybe something as stupid as a fully tightened cap could be the cause of your leaks...
Hope it will help you
Claude

[WDCO42]

Hi Roy, the feed oil pump is 6.35mm, and the scavenge one is a bit more than 9mm. So the manual is very hoptimistic about the pumps ratios... The sole 1 to 2 ratio I saw was on the J2 model.
Claude

[DM]

Fired her up last night after sorting the mag, carb and valve timing, now have a hell of a lot of oil pushing past the NEW piston and rings into the pot, how it still ticked over I don't know.
Anyway, too much oil in the crank case, very little return to the tank via head and a hell of a lot of oil getting past the piston....all leading to an overhaul of the pump assembly.

[WDCO42]

Hello Dave,
Wow, you have a quite recalcitrant engine !!! Two questions : have you put off your new piston's rings ? if they are fitted the wrong way, they can suck the oil to the chamber. The other (forgive me) : the scavenge pump is the one on the front. Are you sure you haven't inverted the pistons ?
I'd look too at the breather, maybe the pipe is blocked somewhere.
Hope it will help you
Claude

[Norm]

Dave how long did you run it for, if it has a sump full of oil it can take a bit to clear and it can smoke for 10 mins before it can burn it all out. Try leaving the piston on TDC to see if that stops it wet sumping. Pull the pumps apart, very simple job and just make sure the pumps are the right way around, PO could have put them in the wrong way around,this is the problem when you have no history on these things. The big piston one goes to the front of the motor, this is the scavenge pump. Also check for wear in the housing behind the pump

[DM]

Norm & Claude,
Thanks for the info.
Firstly, I have now fixed the mag firing problem and the engine fired up again (with oil still in the pot) and continued to run and smoke like a bast'.
Yes piston rings are positioned correctly, must admit I did doubt myself for a time there. I pulled the pump apart last night to find that the components were fitted correctly but the return feed is week, I will lap the discs in and blow all air / oilways through before reassembly.
I noticed that there was no oil return to the tank and according to Hitchcocks a build up of crankcase oil can blow past the piston rings ????? never seen that before, however working on that assumption I am being clinical with clearing all oilways as best I can with an assembled engine.
Is it possible for the return feed ball bearing and spring to become stuck closed??

[WDCO42]

Hello Dave, you'll have to open a bottle of champaign when she will run correctly! For your last question, about the feed ball bearing on the return, I don't think it is the problem : if this ball is stuck, all the oil will go to the head, go down the timing case, and then to the rear oil tank. This circuit isn't intended to cope with such amount of oil, but is quite independant with the scavenge one that causes your troubles. On the later one, the oil drops to the bottom of the crankcase, and goes to the front tank via the front plug and filter and the scavenge pump. Your problem is on this circuit. Have you checked the gauze of the plug is clean ?T the recess in the bottom of the crankcase isn't it blocked (it's where all the small bits and dirts will arive)? Have too a special look at your breathing system, it can cause such troubles.
Hope it will help you
Claude

[DM]

Catch up:
Piston and rings replaced.
Valves and guides replaced.
oil pump cleaned out and discs bedded in.
Mag re-built.
Starts 2nd kick (with fresh oil)

Problems still existing:
Oil still getting into the combustion chamber (re-bore??)
Engine oil evacuating out the end of the crank (drive side) you can actually hear air escaping prior to oil oozing out and filling the primary case, and I mean filling to a point the oil tank practically empties out (crank seals??)

Possible next move:
As this was going to be a minor project and due to time and space running out before I get my other bike and another frame back, I am willing to pass her on to another to finish off (1947 350G - matching frame / engine No's - two previous owners)
So if anyone's interested just get in touch, failing that she will be mothballed until I get space and time.
Dave 07787 562 016. Glos.