A strange occurrence! Oil pump . . .

[hardy]

Hi brains trust,

A while back I drained the oil tank to clean out and fix leaking oil filter bolt seals. While the tank was empty I removed, re sealed and reset oil pump stroke. Anyways...

Last night I filled the oil tank with two stroke oil(red) and removed bleed plug. I left the plug out overnight with a tub underneath to catch the overflow.When I came out in the morning a found the pump to be full and leaking gearbox oil! strange!

From memory I don't think there was a lip seal on the oil pump shaft.  Before I go pull the whole thing apart again, has someone got some thoughts or pics of input shaft on oil pump?

ryan...

[disc_valve]

Hi,

I am guessing that your bike is a 90cc or 100cc model (you didn't say). There is a check valve (loose ball and spring) in the pump inlet port that prevents oil seeping into the pump when the engine is stopped - the valve opens readily when the pump sucks. Gearbox oil could possibly seep intro the pump gear chamber past via the pump drive shaft, which I guess is likely to be what you are seeing. There is no oil seal on this shaft - it just relies on the fit of the shaft in the bronze bush in  the transmission case. In normal running, there will be oil in this gear case but the pump case is sealed so the oil can't leak out. If, however, you remove the bleed screw, there's a neat hole for oil to escape.

It is best to manually fill the gear case with transmission oil from a pressure oil can and then replace the "bleed" screw. (It's not really a bleed screw, more an oil level screw). Disconnect the oil tank line at the pump end, let that drain to remove oil bubbles and refit it to the pump.

You will then need to bleed system by running the motor at a fast idle with the pump lever held wide open and watch the oil in the transparent section of the output line. You should see any air bubbles working their way along the line. Once the transparent section is free  of air bubbles, continue bleeding for about another minute to ensure that the last bubble has reached the end of the delivery line, then shut down and the job's done. The engine will probably smoke like a good 'un for the firs mile or so on the next test ride until the excess oil has been cleared from the crankcase.

Hope that helps,

Graham

[hardy]

Thanks for the reply graham,

The bike is a 1968 gtr350. I'm guessing the oil pump still seals on the bronze bush and input shaft?

[BRT-GTR]

Hi Ryan, / Graham
                              I was half way through a reply when Graham posted but will post anyway. It may help others.
            Based on a quick assessment of a spare 350 pump, you remember correctly, there isn't a lip seal on the input shaft. It has a spiral groove that pulls oil from the primary drive case (and gearbox) into the worm drive chamber on the oil pump to lube the worm and the worm wheel. This chamber is separate and sealed from the rest of the pump, so would receive no lubrication without this arrangement. I assume the bleed screw you removed is the one with the fibre washer on the worm wheel cover. This would allow gearbox oil to slowly leak out.

Never really thought about the function of the bleed screw, not mentioned in the 350 manual. Is it covered in one of the other model manuals ?. I would agree with Graham about priming the worm drive case with oil.  I’ve learned something new here.

    There is no separate provision on the pump to bleed the oil injection side. The manual suggests removing the oil tank line from the pump union and letting it run until air is removed. To bleed the pump itself, reconnect the tube, manually turn the pump control lever to max and run the engine at idle for about a minute. You can usually see any air bubbles being pushed through the outlet tubes towards the check valves. If you have drained the two outlet oil injection tubes, prime them also from an oil can with 2stroke oil.

Hope this helps, Brian

[Colin]

Hi Brian,

Now that bleeding oil into the worm drive sounds like a good idea and one which I had never thought of, in fact I'm going to do it today.
In the past I have just run two strokes on premix until they have pulled the oil from the tank through the hoses themselves , but never say never   .
I have not run the GTR yet so who knows  .

Colin.

[hardy]

Hi guys,

Thanks for the replys. Makes more sense now, what I thought was the bleed screw for two stroke oil is actually the air bleed for the oil pump case.

I wonder if you didn't bleed the air out of the pump case if it would get an airlock and not fully fill with gearbox oil?

Ryan

[disc_valve]

Hi, again,

I made a wrong assumption that it was a 90 pump, but the 350 pump is the same type of pump, it just has an extra shaft inside to send the oil alternately to the left and right outlet ports. As you say, Brian my comments apply just as well to the 350 pump. The only difference in the 350 system is that the it has check valves incorporated into the union bolts attaching the oil lines to the crankcase. If you have trouble bleeding either of the outlet lines, it could be that one of the check valves is blocked.

Graham

[slawsonb]

I guess I am struggling to understand the need to bleed the gear case inlet to the pump. The pump drive shaft has a worm machined into it that will positively feed oil to the pump. If during assembly the shaft and bushing are properly lubed with gear oil (10W30) then that should be adequate for the first short period while the worm is taking up oil from the gear case. Is the concern providing lubrication to the pump internals or bleeding air?
I have to admit that until now I was not aware of the bleed screw and the need to use it. (Mysteries continue to be revealed. )I have done several rebuilds and tear downs in the past that removed the crank case cover (2161-9000) and the pump and have never experienced any adverse effects. Have I just been lucky?
...bert

[BRT-GTR]

Hi Guys,
            Bert, like you I have previously rebuilt 350 engines, without appreciating the need to fill the oil pump gearbox with 30 grade oil. Providing the pump is not replaced with an absolutely dry gearbox, I am sure the shaft spiral would soon pull oil in from the primary transmission and keep things lubed. I never experienced any problems in the past.

 However, if you have a look at the service manuals, on site, for the 175 twins and there are two of them, the Clymer after market manual does identify the need to fill the pump gearbox with oil as part of the pre-delivery inspection. See P69, 175dt section, Item 5. Graham is right again, as usual !!, it is an oil level screw not a bleed screw.The 350 manual does not mention this at all. I have noticed the manuals for models before the 350 are far more comprehensive and explanatory. I suspect BS did a quick job on the 350 manual knowing that production would cease in the not too distant future.

  We live and learn, Brian

[slawsonb]

Thanks for the usual well thought and researched reply, Brian. I was certainly not questioning our Sage Graham's advice. The idea of "oil level screw" which I failed to comprehend in my first read makes this clearer.
Hardy (Ryan), you certainly started a great thread. I just keep learning more and more from this site. Awesome!
...bert

[disc_valve]

Hi, Brian,

I've had a look in my Bridgestone "library" (a pile of boxes in the wardrobe in the spare room), and I have only found one reference to topping up oil pump gearboxes on the 90. It's in Service Letter BSG-0037, concerning Pre-Delivery Inspection on the BS90 O/I. It recommends removing the level screw and checking/topping up the oil level before starting a new engine. As it is in a Rockford Service Letter rather than a BS Factory document, maybe US Dealers reported a few cases of damage to the oil pumps on new bikes due to a lack of oil from the factory??

I tend agree that there should be enough oil around on a rebuilt engine if the pump hasn't been touched, but as they say "better safe than sorry". I always add a squirt or two through the level screw after refitting a 100 or 350 pump.


In the case of the BS175. early models relied on the owner keeping the oil pump gearbox topped up manually. There was no other oil feed into the pump gear case, which is why the factory made a point of topping it up in  the manual.. On later 175s, Bridgestone modified the crankcase, disc valve cover and pump gear case to provide an oil splash feed directly from the transmission. At the same time, they deleted the previous level screw hole from  the pump gear case, so there is scope for creating problems if you mix and match an early crankcase set with a later pump casing!

Presumably, Bridgestone found problems in service with the early Dual Twin set up where a leak or a failed left crank seal could drain the oil out and leave the gears running dry.

Graham

[BRT-GTR]

Hi Graham,
               Thanks once again for the full explanation of the pump oiling systems, I will certainly be priming the pump gearbox on future 350 rebuilds, now that I know about it.
 The bikes may have been shipped in a dry condition (for safety reasons) from Japan and would need  'Pre-Delivery commissioning' , rather than 'inspection'. I don't know whether they would have been test run at the factory, can any former dealers / mechanics comment on this?

 Don't ever lose that 'library' we rely on it, should be in a fire proof safe not a wardrobe.    Regards, Brian