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Stripped oil pump

nkt267

Well Known and Active 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

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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

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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

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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
 
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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

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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

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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

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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
 

Howard

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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 . ..John

John

That's not the case. Look at the edges of the cut made by the worm, the angle is the same as the cam slot for the pawl (but opposite). The plunger must have been turning to wear out every tooth, and it must have been reciprocating to form that wear pattern.

Trev

If the worm was loose on the crankshaft surely it would spin on the crank and not wear the plunger.


I think Timetraveller is on the right track when he says "If the plunger is hard to file then it is probably too hard to wear out in 10 minutes." 10 minutes at a fast tickover (I guess) is say 12,000 revs between 12 teeth on the plunger, that's 1000 rubs per tooth. With or without lube, that's not a lot for hardened gear teeth, and quite frankly, the plunger isn't taking a lot of power.

I'd try rubbing the file on the teeth (I assume you may have tested the bearing surface that's easiest to check - I would have), I've seen gears with very thin case hardening, once through the hardened skin they wear very quickly. If the teeth are hard, I haven't a clue what's wrong, I'm just not sure anyone's offered the right solution so far.

H
 

clevtrev

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VOC Member
John



Trev

If the worm was loose on the crankshaft surely it would spin on the crank and not wear the plunger.


True, but there is no sign of any pick-up on the body diameters, so I can think of no other reason, other than some sort of debris in the gear flute, that would cause the mismatch that must have taken place.
 

John Appleton

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I think none of these. The wear on the new plunger is indicative of "tooth on tooth" contact, caused by new plunger-old worm fitting. On a worn worm, the pressure face of the teeth gradually recede causing the gap between the teeth to get greater. On a worn plunger the driven face of the teeth recedes causing the gap to get wider. Result-excess backlash but clearance for the crest of the worm tooth to miss the next tooth in line on the plunger.
Fit a new plunger with an old worm, and you still get excess backlash as above, although not as much, but you loose the clearance between worm and the next plunger tooth in line. Result- worm tooth sits partially on TOP of plunger tooth and gives the classic results we see in the photos, ie. the metal has not been worn- it has been moved , giving the smooth appearance we see here.
John
 

Howard

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VOC Member
John



Trev

If the worm was loose on the crankshaft surely it would spin on the crank and not wear the plunger.


True, but there is no sign of any pick-up on the body diameters, so I can think of no other reason, other than some sort of debris in the gear flute, that would cause the mismatch that must have taken place.


Trev. I know what you mean. It just looks worn out to me, no real sign of anything wrong (or broken), just worn out.

John. No offence meant, but I assume you were careful to remove all the grinding paste after lapping in. Sorry, that's the only other thing I can think of.

H
 

nkt267

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VOC Member
No offence taken Howard, talking about good practice is always good and may jog someone's memory at a later date. I read all posts even if they don't apply to a Comet,I can always learn something new and I often need to:D
I class myself as a reasonable amateur.
Anyway-- back to the chase-- I have the crankases apart and thank god no catastrophes. In my second post in this thread I wondered if the old worm and the new pump combination was the cause . John Appleton had the same idea,I wish I had the idea before I assembled the engine:eek:
The worm is an original and must be made of better material than the plunger as apart from the now obvious wear it is fairly undamaged,no chips or cracks.
I cannot at the moment see much swarf in the area but a thorough inspection and clean will be carried out before the new pump AND worm are fitted. So-- no one to blame but myself. John

One day I'll learn to spell proper like
 

Howard

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VOC Member
I think none of these. The wear on the new plunger is indicative of "tooth on tooth" contact, caused by new plunger-old worm fitting. On a worn worm, the pressure face of the teeth gradually recede causing the gap between the teeth to get greater. On a worn plunger the driven face of the teeth recedes causing the gap to get wider. Result-excess backlash but clearance for the crest of the worm tooth to miss the next tooth in line on the plunger.
Fit a new plunger with an old worm, and you still get excess backlash as above, although not as much, but you loose the clearance between worm and the next plunger tooth in line. Result- worm tooth sits partially on TOP of plunger tooth and gives the classic results we see in the photos, ie. the metal has not been worn- it has been moved , giving the smooth appearance we see here.
John

John

I see your reasoning on this, apart from one thing I can't get clear in my mind.

Assuming parts wear evenly (and that itself may be wrong) surely the pitch of the old worm and the new plunger will be the same, it's just that the old teeth will be thinner causing more backlash.

ok, two things, why doesn't the wear stop when the new plunger teeth are as thick (thin) as the old plunger teeth?

H :confused::confused:

Later thought - is it anything to do with the plunger moving axially - I keep forgetting this isn't a straightforward worm and wheel.

H
 
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John Appleton

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Howard, the NUMBER of teeth is the same on a new and old worm. The effective pitch is NOT the same. What John will be seeing on the old worm is teeth much further apart , because they are thinner. Try to mesh this worm with a new plunger and you will get the "tooth on tooth" that I mentioned earlier. The fact that it is a reciprocating plunger is irrelevant and can be ignored. I hope this much simplified explanation clarifies my earlier post, but if not , keep the questions coming.
The other thing to bear in mind is, the damage visible on Johns new plunger is Not caused by wear , but by the new teeth being rolled out of the way of the worm. Obviously this rolling will all happen within very few revs, and is what I was referring to when I said the metal had been moved and not worn.
John
 
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Howard

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VOC Member
Howard, the NUMBER of teeth is the same on a new and old worm. The effective pitch is NOT the same. What John will be seeing on the old worm is teeth much further apart , because they are thinner. Try to mesh this worm with a new plunger and you will get the "tooth on tooth" that I mentioned earlier. The fact that it is a reciprocating plunger is irrelevant and can be ignored. I hope this much simplified explanation clarifies my earlier post, but if not , keep the questions coming.
The other thing to bear in mind is, the damage visible on Johns new plunger is Not caused by wear , but by the new teeth being rolled out of the way of the worm. Obviously this rolling will all happen within very few revs, and is what I was referring to when I said the metal had been moved and not worn.
John

Nope. Not with you yet. Not saying you're wrong, just not sure of your reasoning.

If the number of teeth is the same, and the wear is the same, the pitch will stay the same. NB My understanding of pitch is the distance between the equivalent point on adjacent teeth, I'm not sure what you're referring to as "effective pitch". The wear on the teeth will affect the backlash, but not the pitch (assuming it's even).

H
 

clevtrev

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VOC Member
Nope. Not with you yet. Not saying you're wrong, just not sure of your reasoning.

If the number of teeth is the same, and the wear is the same, the pitch will stay the same. NB My understanding of pitch is the distance between the equivalent point on adjacent teeth, I'm not sure what you're referring to as "effective pitch". The wear on the teeth will affect the backlash, but not the pitch (assuming it's even).

H
I agree with that, the thrust wear face will show a constant pitch.
For the worm to roll over on top of the pump, the outside diameter has to be reduced. I have seen worms almost to a point at the crest, ditto the pump, and still working.
 
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