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Stripped oil pump

nkt267

Well Known and Active Forum Website User
VOC Member
That was my first thought Trev.If it has I just hope that the mainshaft is not damaged..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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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
 

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

Well Known and Active Forum Website User
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

Well Known and Active Forum Website User
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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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
 
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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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