Lightweight scavenging problem

hammy · Post by **hammy** » Mon Jul 16, 2007 10:45 pm

I completed the rebuilding of my G2 engine around 2 years ago. The engine started Ok and oil was noted to return to the oil tank. The engine was started about once a week for a number of weeks and all appeared OK. The bike was never taken on the road.

Domesticity forced a pause in progress to the bike.
Recently, after a return to proceedings, the oil level in the tank was noted to have fallen, so after topping up with a small quantity, the engine was restarted and no oil was seen returning.
The oil filter was removed but still no returning oil.
A small quantity of oil was poured into the filter gallery, effectively priming the pump? and oil was then seen returning to the tank with the engine running.
After a few days, on restarting the engine, again no returning oil.

Has anyone has similar problems or got any good ideas?

Thanks

Paul Hamilton

bag-o-nails · Post by **bag-o-nails** » Tue Jul 17, 2007 12:55 pm

Hi Paul
i am sure alan will know the answer to this one
but in the mean time have you looked in tech Articles there is some good stuff on oil pump plungers wet sumping etc
come on biscuit where are you!

Biscuit · Post by **Biscuit** » Tue Jul 17, 2007 1:41 pm

Bearing in mind that the delivery capacity of the pump is quite small, are you running the engine long enough for the oil to circulate?

hammy · Post by **hammy** » Tue Jul 24, 2007 10:45 pm

quote:
Hi Paul
i am sure alan will know the answer to this one
but in the mean time have you looked in tech Articles there is some good stuff on oil pump plungers wet sumping etc
come on biscuit where are you!

Thanks for the tips.
I have rebuilt the pump with a new plunger, obtained from jampot spares, along with new front and rear 'O' rings. Not certain yet of effectiveness so fingers crossed.

Biscuit · Post by **Biscuit** » Wed Jul 25, 2007 12:16 am

Has the oil returned at some point with the new pump plunger?

If not, did you check that the pump was oscillating and rotating?

Sorry if I'm teaching Grandmother etc, but it is SO important the guide pin is seated properly and not trapping the plunger.

Samuel · Post by **Samuel** » Wed Jul 25, 2007 12:31 pm

If the oil pump is broadly similar to the one in the heavyweight then I had a similar problem - the plunger pin was not correctly locating in the pump groove so although it was rotating no oscilation took place. A new pin from Russells solved the problem.

hammy · Post by **hammy** » Fri Jul 27, 2007 8:58 pm

The new pump is rotating and oscillating.
Oil is returning to the tank, but so far just before each time I have started the engine I have added about 2cc of oil to the oil filter gallery (using a syringe via the oil return drilling connecting the tank to gallery). I have yet to try starting without this addition priming.
I have also left out the filter felt element. I did buy a new one from jampot spares but found it to be around 1" shorter that that previously fitted, which also came from Jampot spares. Both types are of the cylindrical plain felt variety, so I need to sort out what this problem is.
The original filter I found in the engine prior to rebuilding was a cylindrical strainer type. I assume this type offers less resistance to the flow of oil than a felt element. Could this be part of reason why oil was at least previously reluctant to return?
The plot thickens.

Biscuit · Post by **Biscuit** » Sat Jul 28, 2007 12:44 am

Paul, between the inside of the oil tank is a small hole going through into the crankcase. I saw a reference to this when I was working on a friends M8. The reference stressed the importance of ensuring this hole was clear.

Unfortunately I can't find the reference, and can barely remember the location of the hole, I think, but I'm not sure that it was above and to the right of the return hole, and it went in to the case at an angle.

What I'm thinking here is that as the engine cools down, a temporary vacuum is formed in the crankcase that could draw the oil out of the filter chamber, this hole may be there to prevent this occurence.

Must stress this is all guess work, we really need someone who knows the engine well.

hammy · Post by **hammy** » Mon Jul 30, 2007 10:57 pm

Biscuit, I have noticed this remark regarding the small drilling. It is indeed situated above and to the left of the return drilling. The angle of this hole is such that you cannot easily poke a wire or similar straight into it (at the point of manufacture it must have been drilled from the inside of the crankcase half).I shall find myself a piece of Bowden cable and try and curl it round into the drilling to have a go at making sure it is clear.
I did however have success with returning oil. I started the engine without first adding oil to the filter gallery and within a minute or two had oil returning to the tank. I may add there was no filter in the gallery. It appears the older engines are fitted with a short felt filter element. I had previously used a long element and appropriate spring. This may have been a significant mistake, the longer filter perhaps requiring a greater pressure to ensure oil passes through it? Anyway Jim at Jampot spares thinks a short type is correct but I will need a longer spring if I am to use this and I am not sure of the correct length. Jim has only the type appropriate for the long flter.

Biscuit · Post by **Biscuit** » Tue Jul 31, 2007 12:44 am

I was hoping to reassure you by relating how long the return took to appear on the G3 (I know the engine is different, but the pump's the same)

After a week non-use it took 5 seconds to dribble into the tank.

I have just put the engine together after a complete strip down, new filter fitted, and the oil was returning in just over 4 minutes, probably most of that time was spent filling the filter chamber.