Stripdown and setting of 350 oil pumps

[disc_valve]

I posted this reply to a members query a couple of years back, and I'd forgotten where it was when another member asked me about it. If I  couldn't find it easily, I'm sure no-one else would, so I've re-posted it in a new topic. For those who read the old reply, there's no new information added.

Graham


SETTING THE PLUNGER STROKE ON BS350 OIL PUMPS

   If 2-stroke oil consumption seems to be excessive even after correctly adjusting the oil pump cable, the plunger stroke setting may have been disturbed. The pump has to be removed from the engine and partially stripped to check and adjust this.

   Remove the two screws holding the oil pump cable bracket to the transmission casing, and unhook the oil pump cable from the pump control lever. Make a note of which oil line is attached to which port on the pump, and then pull off the oil inlet line and the one accessible oil outlet line from the pump unions. (Remember you will have to clamp or plug the end of the inlet line to avoid draining the oil tank contents). Unscrew the two oil pump fitting screws and remove the pump from the engine, pulling off the second outlet line from the back of the pump after the pump comes free. Be prepared for a small amount of oil to be spilt as the pump is lifted away. The oil unions can be unbolted and removed if required, but leaving the union bolts undisturbed avoids the risk of damaging the threads in the pump body or creating unwanted air leaks on reassembly.

   Remove the three 4mm screws holding the two halves of the pump together and split the pump casing, being careful not to damage the thin paper gasket. Remove the spring from the end of the large pump plunger gear and place it to one side to avoid loss or damage. Rotate the pump plunger gear by hand, and you should feel it lift slightly once per revolution under the action of a cam on its rear face - this provides the pumping action. At the opposite end of the pump, there is a small grub screw and locknut in the centre of the pump end plate. Loosen the locknut and turn the grub screw in gradually while rotating the plunger gear, until you reach the point where the gear just fails to lift as it rotates. From this position, turn the screw back out by 3/4 of a turn and re-tighten the locknut. This will give the correct minimum plunger stroke of 0.45mm.

   NOTE:- The locknut tightens against the pump end plate, and the end plate itself screws into the pump body on a left-hand thread. If you are not careful when tightening the locknut you may inadvertently loosen the end plate which will then unscrew itself as you are riding, drastically increasing the plunger stroke and oil delivery rate - the exact opposite of what you were trying to achieve. Hold the pump end plate with pliers and just nip the locknut with a spanner - it only needs to be tight enough to hold the grub screw setting.


   This is as far as you need to go ant to set up the plunger stroke, but if you wish to complete a full pump stripdown and flush out the pump oilways, proceed as follows. Lift out the large plunger gear to reveal the cam pushrod and the small distributor gear. The pushrod simply lifts out. There is what looks like a 5mm cross-head screw in the pump body beside one of the outlet ports – this is the retaining pin for the distributor shaft. Unscrew and remove the retaining pin and lift out the small distributor gear and shaft. Finally, unscrew the pump end plate (left-hand thread, remember) and release the pump control lever and its return spring.



   Before reassembly, ensure that all internal pump components are scrupulously clean and primed with fresh 2 T oil. Assembly is simply the reverse of the stripdown, but be careful not to overtighten any of the screws or bolts that thread into the pump body. The oil pump body is cast in a soft zinc alloy and threads are easily stripped. Also, when replacing the cam pushrod and the distributor gear, be careful not to damage the small oil seals in the pump body.

   Begin reassembly by refitting the control lever and the pump end plate if they have been removed. Ensure that the lever moves freely through its full range and returns to the throttle closed position when released. Replace the cam pushrod and the small distributor gear into their respective holes in the pump body and then refit and tighten the distributor shaft retaining pin.

   Now you need to ensure that the large plunger gear and small distributor gear are refitted in correct mesh with each other. Examine the cam form on the bottom face of the plunger gear, and identify its steeper end. Align the small dot mark on the face of the small distributor gear with the centre of the plunger gear hole. Without moving the distributor gear, refit the plunger gear with the steep end of its cam form positioned exactly over the centre of the distributor gear. Gently push the two gears into mesh

   Confirm that the two gears are properly in mesh, by rotating the plunger gear one turn and re-positioning the steep end of the cam form exactly over the centre of the distributor gear. The dot mark on the small distributor gear should now point exactly away from the centre of the plunger gear (there is a 2:1 ratio between the two gears). Finally, replace the spring in the end of the plunger gear, refit the pump end casing with its paper gasket and tighten the three casing screws.

   Prime both oil outlet lines with a pressure can and reconnect one oil outlet line to the outlet port at the back of the oil pump. Refit the pump to the engine and firmly tighten the two retaining screws. Reconnect the remaining outlet line to the front of the pump, and then reconnect the oil inlet line after first checking that oil flows freely from it under gravity. Refit the oil pump cable bracket and hook the cable onto the pump control lever. Turn the throttle grip and check that the cable and control lever both move freely and return when the throttle is closed. Finally, remove the 5mm cross-head screw on the drive end of the pump gear casing, put a few squirts of clean engine oil through the screw hole to lubricate the pump gears on start-up and replace the screw.

   Start the engine and warm it up at idle speed for a couple of minutes. Then with the engine still idling, raise the pump control lever by hand to the "full throttle" position and look for signs of oil and air bubbles moving in the outlet lines. If no pumping action is apparent, stop the engine immediately and investigate the cause. In the absence of any obvious external fault, remove the pump again and double check that you have assembled the internal gears in correct mesh as described above. If you can see pumping action in the outlet lines, continue to bleed the system by holding the pump control lever fully open with the engine running at a fast idle until both outlet lines are free of air bubbles.

   Once the system has been bled, take the machine for a short test run. After the initial run, inspect the oil pump for any obvious oil leaks and the oil outlet lines for air bubbles. Any air pockets remaining after the pump has been re assembled and bled should have cleared after a few miles of normal running. If air bubbles continue to appear in the outlet lines, it is likely that you have an air leak somewhere in the system. A minor leak may not be enough to allow oil to escape, but it can allow air to be drawn in when the pump is operating. The oil union bolts should be firmly tightened - but take care not to overdo it and strip the threads in the pump body. If this doesn't cure the problem, carefully examine all the oil “banjo” unions, sealing washers and fitting bolts for cracks or other damage, and replace any that are suspect. The oil lines also need to be free from visible splits and be a good fit on the banjo union spigots. A careful smear of silicone gasket goo on the spigot can help to seal the joint - but make sure none gets into the oil lines or you may clog the oilways and wreck your engine. It may also be a good idea to wire the oil lines tightly onto the banjo unions at both pump and oil tank.

   A properly set up BS350 should do around 350 miles on a litre of 2 stroke oil in normal use. If oil consumption is still excessive after carefully setting the pump plunger stroke and adjusting the oil pump cable, then the plunger adjustment screw may be turned in slightly to reduce the oil delivery rate. Note, however that this is a last resort and you must first be certain that there are no other ignition or carburation faults making the engine run off-song, as this may result in larger than normal throttle openings and hence increased oil consumption. If you do reset the plunger adjustment screw, never move it by more than a quarter-turn from the factory setting described above, or you will risk drastically reducing the oil supply on a closed throttle - a recipe for possible engine damage on the over-run - and be prepared to revert to the factory setting immediately if the engine shows any signs of distress.
 

[slawsonb]

Just wanted to thank you (probably again) for creating this comprehensive instruction, Graham.
...bert

[coxy]

Good stuff Graham. I will get the wife to print this one off.
Question. Have you ever repaired a stripped thred for the intake line union bolt in the oil pump cheers

[disc_valve]

I put a helicoil insert in  a 175 pump many years ago as an experiment, although I never used that pump.

I'm not sure it's an ideal solution, though. Lots of metallic swarf kicking around from the thread cutting, and you'd need to be very careful to start with a bare pump body (no internals) and make absolutely sure to clean it out thoroughly afterwards. It would also need careful jigging up to make sure the repaired thread is absolutely square to the union mating face, otherwise you'll have problems sealing the joint.

Has anyone else out there tried it successfully?

Graham

 

[ziggy stardust]

Yes I did it on a Kawasaki triple pump, stripped it down first though before any drilling and tapping. After cleaning away the swarf I found it difficult to assemble so I put the outer casing on a hot radiator for a while to expand and then it all went together nicely.

Z

[slawsonb]

What's a "hot radiator"?...lol
...bert (desert boy)

[ziggy stardust]

Don't suppose you have any need for wellies either Bert?

Z

[slawsonb]

Well, when it does rain, the horse corrals can get a little mucky, so I do own a pair of wellies for those infrequent occasions.
...bert

[ziggy stardust]

We've started to rebuild the Ark here, now that is a restoration. Sorry to have digressed.

Z

[srpackrat49]

I,ll tell ya watt   here in Oregun    we have a saying   ya don,t have to shovel rain ....  but in dec. we got over 2.50 in. of rain in one day... i think it was like 47 in. for the month.....

[slawsonb]

Wow, we won't be needing an Ark here in AZ (unless we've all been really bad...;-), but I'm sure it will be cake compared to some of the trials of BS restoration!
...bert