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Stripped oil pump

nkt267

Well Known and Active Forum Website User
VOC Member
I think I already know what most of the answers to this are:eek:
I fitted a new oil pump to a Comet,the old sleeve came out in 2 pieces and had been split for a long time by the look of it. I lapped the plunger in so that it ran smoothly and assembled the engine, it turned ok on the kick start..
It took a lot longer than I expected to get the oil to prime through the new oil filter to the quill (on the kickstart only) and once primed I started the engine and cracked open the quill screw to check for a good flow, also had good return.
I ran the bike for a bout 5 mins on 2 occassions and all seemed ok.
I got it ready for a test run yesterday and could not get any oil return.Removed the plunger tonight and guess what--It's stripped:mad:
Any other ideas apart from maybe I should have lapped it in a bit more?
How much lapping in before it is worn out? John
PS pump is single start and seemed good when inspected.
 

passenger0_0

Well Known and Active Forum Website User
VOC Member
Oil Pump

Sorry to hear about this problem - it's always dissapointing when new parts go bad for no apparent reason. Were you using a bronze worm? Just a thought, if the plunger is still free to oscillate within the sleeve then check the depth of the guide screw that engages into the plunger cam. If for whatever reason this screw goes in too far either the thread or the end of the screw will foul the plunger - causing overloading of the drive worm. Look for evidence marks on either part. Good luck in sorting it out - cheers David.
 

ogrilp400

Well Known and Active Forum Website User
VOC Member
You point out that the oil flow was working so that points out that the pump was functioning correctly. You then say that you removed the plunger and it was stripped. Hmmm, perplexing. By saying "you removed the plunger" It sounds like the plunger slid out easily, no sign of anything stressing it enough to strip it. David points to the scroll screw but surely if that had bound up then it would be next to impossible to remove. But again you have not mentioned that the scroll screw has been distressed. If something had got into the works to stop the plunger oscillating, then I would expect the scroll screw to shear off. If something got into the works to stop the plunger rotating (which is a likely cause of the teeth stripping) then the plunger would have been locked in the sleeve and impossible to remove.
 

timetraveller

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VOC Member
Things to check and which are often not mentioned in the world of Vincents as we like to think that people who make parts actually know what they are doing. Are you sure that both the worm and the plunger are single start? The worm is self explanatory in that if you look at either end you will see that the thread only has one start. Was the plunger single start? If it is then the teeth should be parallel with the axis of the plunger. Several years ago one spares producer made a whole bunch of supposedly double start plungers with the teeth parallel to the axis. For a double start they should be angled relative to the axis of the plunger. Was the run out of the teeth on the plunger shallow? The reason for this question is that a batch were made where a cutter with too large a diameter was used which resulted in the end of the teeth where they get shallower and run up into the outer diameter of the plunger having too shallow a gradient. This meant that as the plunger moved up-wards the clearance between the worm and the teeth reduced until it became an interference fit and everything wore out very quickly. All these faults resulted in pumps which wore out in hundreds of miles, not minutes, so they are unlikely to be the source of your troubles but worth checking before you put it back together. There should be very little clearance between the plunger and sleeve so it should not be necessary to wear the components out by too much lapping in before using. Too much clearance here is why so many Vincents sump now when they didn't 50+ years ago. Can you remove the worm without dismantling the engine? If so, then when reassembling everything and after you have put in the locating screw which fits into the scroll in the plunger and which makes is reciprocate, rotate the plunger by using a long bolt or stud and without the worm in place. It should rotate easily. Is the plunger hard, i.e. hard as opposed to soft metal. For it to wear out in minutes suggests that either it was locked solid or is made of putty.

Good luck.
 

nkt267

Well Known and Active Forum Website User
VOC Member
Running a file across the plunger is the only method I have of checking hardness, not very accurate, but it seems ok.I have compared the plunger with an original one and it looks identical.There are no signs of over heating on the undamaged sections. I still have to get the worm out, and check where the metal off the plunger has gone to, to see if that is at fault.I suppose it could be posible that putting a new pump in with an old worm may have caused a meshing problem. I won't really have a better idea till I completely strip the engine. I am posting a photo for all to see..John
http://www.vincentownersclub.co.uk/photos/showphoto.php/photo/6091
 
Last edited:

Howard

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VOC Member
Is it a quirk of the photo (or a quirk of my eyesight) or is the wear (cutout) deeper on the right of the photo?

Hard to believe so much wear happened in 10 minutes with plenty of oil in the area, but the wear shows it was turning and reciprocating, so it should have been pumping.

H
 

timetraveller

Well Known and Active Forum Website User
VOC Member
I'm guessing but from the look of the plunger I would guess something has got into the outlet from the pump and stopped it being able to pump oil. The Vincent oil pump is not designed to work against pressure but I have no personal experience of how quickly things go wrong when pressure builds up. A thought. Is it possible that what was returning into the oil tank was oil already in the sump etc and that oil never was being pumped out of the pump after your refit? The oil coming out of the big end quill would have to have been in the oil filter chamber. If the plunger is hard to file then it is probably too hard to wear out in 10 minutes.
 

Howard

Well Known and Active Forum Website User
VOC Member
I'm guessing but from the look of the plunger I would guess something has got into the outlet from the pump and stopped it being able to pump oil. The Vincent oil pump is not designed to work against pressure but I have no personal experience of how quickly things go wrong when pressure builds up. A thought. Is it possible that what was returning into the oil tank was oil already in the sump etc and that oil never was being pumped out of the pump after your refit? The oil coming out of the big end quill would have to have been in the oil filter chamber. If the plunger is hard to file then it is probably too hard to wear out in 10 minutes.

If the pump wasn't pumping, would the plunger be the first part to wear out? I had a blocked oilway some time ago, and that resulted in the 1812 overture from the timing gear (followers mainly) long before the pump showed any sign of wear.

H

H
 

nkt267

Well Known and Active Forum Website User
VOC Member
I hope that when i get the engine apart something will shout at me as to the cause of the problem. I had a message suggesting the nut E80 may have come loose, something may be out of line somewhere as the worm appears to have cut midway through the width of each plunger tooth.has a chip come off the worm? the strip down may reveal all . More of a problem if nothing is obvious as I have just ordered a new pump..John
 
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