Lubrication problems

[TommoT]

Hi to all!

Yesterday my newly restored G80 -56 (w. -53 engine) was fired up for the first time. After a few minutes of warming up the engine sounded strained and mechanically unsound so I shut it down immidiately. I did see some bobbles and frothing in the oil tank so some circulation must have taken place.

I stripped the engine down leaving only the
bottom end alone. My aim was to establish the engine's exact condition. These were my findings:

1.
The oil feed to the rocker box was obstructed by a gasket!
2.
Plenty of oil was found in the oil pump itself. Oil litterally ran out of the pump after removing the end cover. No oil had accumulated in the sump.
3.
The cylinder bore was very dry. Apparently there is no damage to the bore or piston, but it must have been very close to a regular seizure!
4.
The oil tank has a venting pipe at the back of the tank. Oil seems to be seeping out here in small quantities. The cap has a small diameter hole, with some kind of valve or venting system. This is blocked .

Conclusion:
Lubrication of the cylinder bore seems to be the ess than satisfactory. Somewhere between the oil pump and the cylinder bore, something goes wrong. The oil tank seems to have breathing problems.

Questions:
How does oil get from the pump to cylinder bore? Are there holes to be aligned between the crankcase and the cylinder? How do I reestablish proper venting of the oil tank (its the flat
pannier type year 1956)?

[Kieran Enright.]

Dear Tom,

I have not owned a G.80 yet (I'm still putting the money together to buy one), so what I suggest is based on a lot of experience with other Brits (mostly BSA's), but it may help.

I believe the G.80 oil pump is a double plunger type, with one plunger for feed and one for scavenge. The fact that you saw frothing and bubbles in the oil tank, and the sump was oil free, suggests that the scavenge side is working ok, but does not prove that the feed side is working. If the pump is fitted with one-way valves, are they free to move and fitted the right way round?
I would expect the cylinder wall to be lubricated by oil which has passed through the big end bearing flowing onto the surface of the flywheels and being flung off as they rotate, so the cylinder wall is lubricated by a combination of splash and oil mist. If the wall was dry, that suggests that the big end may also have been starved of oil.
A common return route for oil fed to the rocker box is down the push rod tubes, where it lubricates the cams and followers, so it would be worth checking these as well. Hope this does not sound too gloomy, but the speed with which you stopped the engine may well have prevented any major damage. Hope you get more detailed advice from somebody who really knows this motor.

Best regards,

Kes Enright

[TommoT]

Thank you for your comments. I am getting a picture now of what has happened, but I'm still a bit puzzled by my findings. The rocker arms, valves and cam followers seem oiled, but this could ofcourse be left overs from the oil I used when assembling the engine. The oil flow in a G80 engine is much as you describe, in theory, but it only has one plunger. I have not been able to spot any oil channels to the cylinder wall so the flywheel spray seems like the only answer!

Thanks again for taking time to reply

Safe riding
Tom

[Peter Wright]

Lubrication can indeed be a tricky business. A roller bigend will survive with very little oil, witness the early total loss systems, but a dry cylinder will soon lead to disaster. When the more knowledgeable return from the Jampot Rally you will no doubt have your problem solved but here are a few thoughts.
The early engines had a cylinder feed to the rear wall of the cylinder which came up via a spring loaded ball valve betwreen the pushrods to a groove around the cylinder base flange. This was deleted for 1956 so obviously wasn't deemed necessary anway.
You probably need a 1/4" plus of oil in the sump before the return pump will start to pick it up. This can result in quite a worrying delay on first start up. What I do is spin the engine on the kickstart until oil starts to return. I also loosen the unions at the pump and rocker box to confirm it is getting upstairs. This can take a very long and tiring time on the kickstart as the delivery is small. Because of this I also prime the timing gear by pouring oil down the pushrod tubes.
It is surprising the effect an even slightly worn pump guide pin will have on the delivery, and therefore return. Assuming all your oilways were clear this would be my first port of call.
Kieran is right in saying that the cylinder is largely lubricated by oil flung from the bigend (the only mechanism after the cylinder wall feed was discontinued) so if this isn't receiving enough you are in trouble. A remote possibility is that the timing side bush has turned and covered the oil hole for the bigend supply.
Hope this is of some help. Let us know what the outcome is; it all adds to the general fund of knowledge and experience.
Peter

[TommoT]

Thanks for all comments!

Having wiped clean both the piston and the cylinder bore I discovered that there has been metal to metal contact between the two parts. A track almost ½" wide on the piston shows sign of melting whereas the bore seems less hurt. What worries me is that the flywheels are also very dry, so I will take the bottom end apart and check if all bearings are ok! Phew! This is getting scary, but lots of lessons learned!

Safe riding
Tom

[Kieran Enright.]

Dear Tom,

another idea has just come to mind for when you put it back together. A friend of mine had a Gold Star which was in a very high state of tune, and after he rebuilt it, he rigged it up with an electric motor driving the engine through a chain and sprocket. I think he used a car windscreen wiper motor and drove it by the sprocket on the drive side crankshaft, but you could probably turn it fast enough to prove the lubrication system with some sort of crank handle bolted onto the clutch. My friend wanted to run the Goldie at a fast tickover for an hour or two with no load on it, just to run it in very gently, but he also wanted to check the lube system, so he left the cylinder head off, and diverted the feed to the rockers into a tin can so he could check that was getting through. He certainly proved that oil was reaching the big end and the cylinder bore. What he hadn't realised was that the compressed gas in the combustion chamber gets down the back of the piston ring grooves and presses the rings out against the wall to form a gas tight seal. But, with no cylinder head fitted, there was no compression and the rings were just floating. He found that he had to keep stopping the engine after a minute or so and wipe the excess oil off the top of the piston crown, or the engine started spraying it all over the garage roof. Fingers crossed that it turns out well for you, anyway.

Best regards,

Kes

[TommoT]

Hi,
and thanks for your comments. Engine is now completely in bits. Oil seems to have found its way to the bottom end. Both the timing side bush and the ball bearings were ok. With a syringe and all crankpin exit holes, but one, blocked, I was able to press oil through to the big end. So it seems that only the cylinder and rocker box was running without oil! Strange, could this be a simple matter of priming all oilways with oil? Maybe fill up the crankcase bottom for the scavenge side to have something to work with? When reassembled I'm surely going to turn this engine over until oil is verified in every corner of the engine!

Safe riding!
Tom