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
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
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
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, 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
I agree with that, the thrust wear face will show a constant pitch.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