Mk3 Oil Non Return Valve

dobba99 said:
At 100 PSI the plunger is subject to approx 15Lbs of force, and that force is spread evenly over the surface of the plunger. 15 Lbs is not able to 'hydroform' the plunger. <..> Hydro forming is done with pressures in the thousands of psi.
Click to expand...
You are abolutely right. However, hydro forming occurs by (internal) pressure, not axial pressure as you suggested. The hoop stresses occurring here are very small, in the order of 8 MPa for the actual dimensions, so we need at least 100x higher pressure to achieve hydro forming.
For this reason, Masseyracer's brass plunger should work just fine.

Upon drilling through the plunger's crown, spring and plunger popped out. What I found was that a sludge mud pit had formed below the plunger, creating suction at the plunger. Because of the anaerobic nature of a mud pit, a considerable partial vacuum can develop, acting at the internal and external surface of the plunger holding it firmly in place. Anyone walking with Wellies in deep mud has experienced this effect! Because the small vent bore was blocked, no pressure equalization was possible, but this happened when drilling through the crown! Once bore and plunger were cleaned of sludge, the plunger slid freely and showed no tendency to stick in the lower position.

To avoid this happening again, it's advisable to clean plunger and corresponding bore in the timing cover at certain intervals.

- Knut
 
mdt-son said:
You are abolutely right. However, hydro forming occurs by (internal) pressure, not axial pressure as you suggested. The hoop stresses occurring here are very small, in the order of 8 MPa for the actual dimensions, so we need at least 100x higher pressure to achieve hydro forming.
For this reason, Masseyracer's brass plunger should work just fine.

Upon drilling through the plunger's crown, spring and plunger popped out. What I found was that a sludge mud pit had formed below the plunger, creating suction at the plunger. Because of the anaerobic nature of a mud pit, a considerable partial vacuum can develop, acting at the internal and external surface of the plunger holding it firmly in place. Anyone walking with Wellies in deep mud has experienced this effect! Because the small vent bore was blocked, no pressure equalization was possible, but this happened when drilling through the crown! Once bore and plunger were cleaned of sludge, the plunger slid freely and showed no tendency to stick in the lower position.

To avoid this happening again, it's advisable to clean plunger and corresponding bore in the timing cover at certain intervals.

- Knut
Click to expand...
I never mentioned 'axial' pressure, and if we are getting picky about it i could say the 'internal oil pressure developed by the oil pump' That makes it an 'internal' pressure. Also where are the hoop stresses? the oil at pressure only sees the face of the plunger, not the void that contains the spring.
In other words your 'hydroforming' theory was bollocks.
 
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dobba99 said:
I never mentioned 'axial' pressure, and if we are getting picky about it i could say the 'internal oil pressure developed by the oil pump' That makes it an 'internal' pressure. Also where are the hoop stresses? the oil at pressure only sees the face of the plunger, not the void that contains the spring.
Click to expand...
By axial pressure I mean axial to the plunger, which is what you confirm just now. Oil seeps past the plunger, and there will be a cavity of oil behind it (less pressure initially). Then, by Newton's 3rd law, the pressure in the cavity will be equal to the pressure hitting the crown, especially when the drain clogs up. As there will now be internal pressure in the cavity (and assuming the outer skirt is sealed for dynamic pressure), there will be hoop and radial stress in the plunger, admittedly and as stated, of low magnitude,

- Knut
 
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Fast Eddie said:
If not, why not ?
Click to expand...
In theory the gear pump creates inifinate pressure when the outlet is blocked so the plunger could not stick shut against the pump outlet. In practice it just produces a high pressure due to the internal clearances and links between feed and scavenge. I had a C15 where the pump outlet was blocked, I had clear oil feed pipe showing what was going on. The oil initially was pulled into the pump, then stopped dead before then large air bubbles came out going the wrong way. The only way to fix this after taking the engine apart and changing the ball and spring three times was to remove them completely.
 
mdt-son said:
By axial pressure I mean axial to the plunger, which is what you confirm just now. Oil seeps past the plunger, and there will be a cavity of oil behind it (less pressure initially). Then, by Newton's 3rd law, the pressure in the cavity will be equal to the pressure hitting the crown, especially when the drain clogs up. As there will now be internal pressure in the cavity (and assuming the outer skirt is sealed for dynamic pressure), there will be hoop and radial stress in the plunger, admittedly and as stated, of low magnitude,

- Knut
Click to expand...
If the bleed/drain hole is blocked, the whole of the plunger is surrounded by oil at pressure so no hoop stresses and no radial stresses, so again your theory is bollocks
 
I've often wondered if a ball bearing would be better suited than the piston, as it would tend to centre itself on the seal, and be far less likely to get stuck open. ( This is what AMR use when modifying the case).
 
cliffa said:
I've often wondered if a ball bearing would be better suited than the piston, as it would tend to centre itself on the seal, and be far less likely to get stuck open. ( This is what AMR use when modifying the case).
Click to expand...
Probably not a good idea to consider replacing the plunger with a ball in the Mk3 cover, there would be a danger that it could blank off the port that feeds the crank as that is where most of the oil is going. If the ball was restrained from doing that (with something like a cage) then yes it is feasible.
 
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cliffa said:
I've often wondered if a ball bearing would be better suited than the piston, as it would tend to centre itself on the seal, and be far less likely to get stuck open. ( This is what AMR use when modifying the case).
Click to expand...
Probably, the piston does seem like over engineering to me. Besides the AMR mod that's how the Trident anti-drain valve is done and also some BSAs although done differently, also use a ball.
 
@dobba99 made a good point about the ball potentially blocking the outlet, but I wonder how AMR do it. I've never really seen any close up pictures of their setup. I wonder flow of oil keeps the ball central in there, like a ping pong ball on an airline pipe. (Bernoulli Effect)?
 
I actually found an article the Motorcycle classics did about the AMR mod, and blowing up one of the pictures you can see that the ball bearing is pretty small in comparison to the piston...

Mk3 Oil Non Return Valve


This is the article if anyone is interested https://www.motorcycleclassics.com/...ping-issues-on-norton-commandos-zm0z21jazbut/
 
I installed an earlier cover with the AMR mods. No worries about a sticking valve! Not worth going to all that trouble trying to repair a factory bodge.
 
I never had a problem with sticking but have had the conical seal split twice. May have been old stock but present one has been good for years now. It's the source of my advocacy for an oil pressure gauge. Bike will wet sump but only during winter storage.
 

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