MKIII Timing Cover - Anti-drain back spring/plunger

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lbridges

lbridges

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I'm still working, albeit slowly, to bring my MKIII back to life.

As a part of that process I removed the timing cover. There was no spring or plunger for the anti-drain back system - parts 41 and 42 on this page . Don't know if it never had it or if a PO removed it.

Ordered new from Old Britts.

Was there ever a reason to NOT have this in the system? I'm asking should I leave as is, or wait for the parts and install per the manual?
 
This gizmo lowers max oil pressure so only reason I can think of beside an over sight is oil pump so worn out it couldn't make full pressure but that'd take a guage to know for sure. Finding stuff like that tends to make me pensive in flashes when riding away from home. But if not blown up by now, then easy to bring back to snuff or just forget about it as Norton stopped installing oil guages real fast once reports flooded in on No Oil pressure seen at hwy speeds. Its a non issue with or w/o the oil pressure relief valve apparently. Theres a hand full of usless stuff in Commandos, some forever a mystery like the paper washers in the forks no one knows what they do.
 
hobot said:
This gizmo lowers max oil pressure so only reason I can think of beside an over sight is oil pump so worn out it couldn't make full pressure
Click to expand...

The "gizmo" does not lower maximum oil pressure.

It is an anti-drain valve!
 
There is an oil pressure relief valve (whose effectiveness is unknown) but as LAB suggests, the parts I'm missing are the anti-drain back gizmo.

I assume the only issue would be wet-sumping. Anything I should look at specifically since it wasn't there?
 
According to some of our members the MkIII anti-drain valve is often found stuck in the open position, in which case it is completely ineffective and would perhaps be one reason why somebody would decide not to bother with it?
 
Just as important as missing items 41 and 42 on this page is checking the condition and replacing (if indicated) item 26; the rubber doughnut seal on the pump.

If I recall correctly, item 26 is a bit different from earlier Commandos as it was thicker. There may also be a steel shim behind the item 26. Other knowledgeable persons on this list can clear this up.

I would wait and replace item 41 and 42 as every little bit helps to reduce drain back into the crancase. The "gizmo" is performance benign and does not reduce max oil pressure. The worst that could happen is that it periodically hangs open when you shut the engine off and you get drain back sooner rather than much later.

I am not sure how the factory intended for this thing to properly function. You can clearly see that when the engine is off and oil pressure and flow ceases, the plunger should slide towards the oil pump and cover the side drilling in the timing cover. What I am not sure of is whether they intended for the plunger to also form some sort of seal against the oil pump rubber seal (doughnut). That is why I suggest you make sure that the rubber doughnut is proper for your specific engine, that it is shimmed properly and it is still compliant (rubbery). I read somewhere where you can check the adequacy of the oil pump seal fit by offering the timing cover to the engine and measuring the stand off or gap before nipping up with bolts.

My opinion on why this factory fix was not so effective is that even if the plunger was 100% effective it would only seal against crankshaft drain back but the oil pump would remain under gravity pressure from the tank. I am certain that there is some leakage through the pump and out past the pump shaft, into the timing chest.

It would be fun and interesting if someone had the time and a cut away timing cover to test and see exactly where the oil is leaking with a plunger anti drain back valve and and an elevated oil tank.

I know I would sleep better at night knowing the answer. :)
 
Dances with Shrapnel said:
Just as important as missing items 41 and 42 on this page is checking the condition and replacing (if indicated) item 26; the rubber doughnut seal on the pump.

If I recall correctly, item 26 is a bit different from earlier Commandos as it was thicker. There may also be a steel shim behind the item 26. Other knowledgeable persons on this list can clear this up.

I would wait and replace item 41 and 42 as every little bit helps to reduce drain back into the crancase. The "gizmo" is performance benign and does not reduce max oil pressure. The worst that could happen is that it periodically hangs open when you shut the engine off and you get drain back sooner rather than much later.

I am not sure how the factory intended for this thing to properly function. You can clearly see that when the engine is off and oil pressure and flow ceases, the plunger should slide towards the oil pump and cover the side drilling in the timing cover. What I am not sure of is whether they intended for the plunger to also form some sort of seal against the oil pump rubber seal (doughnut). That is why I suggest you make sure that the rubber doughnut is proper for your specific engine, that it is shimmed properly and it is still compliant (rubbery). I read somewhere where you can check the adequacy of the oil pump seal fit by offering the timing cover to the engine and measuring the stand off or gap before nipping up with bolts.

My opinion on why this factory fix was not so effective is that even if the plunger was 100% effective it would only seal against crankshaft drain back but the oil pump would remain under gravity pressure from the tank. I am certain that there is some leakage through the pump and out past the pump shaft, into the timing chest.

It would be fun and interesting if someone had the time and a cut away timing cover to test and see exactly where the oil is leaking with a plunger anti drain back valve and and an elevated oil tank.

I know I would sleep better at night knowing the answer. :)
Click to expand...


I thought #26 looked like it should be replaced at the same time as 41 and 42, it's on the same Old Britts order I placed last nite. And yes, I see a steel shim behind the rubber part. I don't know if it comes with the rubber #26, or if it can be reused. I will wait on Ella to ship and I can see the parts before going further.

EDIT: There was no steel shim, the metal plate (for lack of a proper term) the rubber seal sits against looked like a shim until I pulled off the seal, then it was apparent that the metal was part of the housing. Corrected for any future readers.

I would sleep better at nite if I thought I had found all the "mods" one of the two POs did to the bike. Some were quite entertaining, like no electrical no connectors in the headlamp shell (which on a MKIII is a lot of wires) all had been cut, then hand-twisted together, insulated with a brown packing tape - like for shipping a box.
 
When I took my cover off the first time i also thought mine was missing. The when cleaning it I blew some air threw it and the plunger and spring popped out. I was stuck and really looked like there was nothing there so blow some air threw it first!
 
Check carefully to ensure that the plunger is not stuck back in the housing, as several posters have mentioned. The bore is 3/4" deep and there is enough room to press a second plunger in there which will prevent any oil feed to the crankshaft.

I once met an owner who had done this. He managed about six miles thanks to one or other teflon oil additive before it seized.

The plunger is quite a close fit in the bore and has only a light spring. With thick oil, despite the bleed hole behind, it can easily stick open. I polished mine until it was a very easy sliding fit and it works well these days.
 
Thanks for the warning guys, I probably wouldn't have thought of it.

I can see holes going in and out of the timing cover housing cavity where the plunger would fit, so in my case I believe it is really and truly missing.
 
lbridges said:
I can see holes going in and out of the timing cover housing cavity where the plunger would fit, so in my case I believe it is really and truly missing.
Click to expand...

Not necessarily. In the fully retracted position (oil pressure up and flowing, the plnger would be fully nested and the oil galleries would be wide open.

Try rapping the timing cover a couple of times on some soft wood to see if something dislodges. If I can dig out my Mk3 timing cover after dinner I can take a reference measurement. Maybe someone on the list has one handy now to do the same.

The bottom line is if you put another one in and another one is already there (inadvertently double up) you probably would not be able to push it back far enough to uncover the oil passage to the crankshaft. So that would be a fall back test for you.
 
I did measure my cutaway cover and posted above that the bore is 3/4" deep (roughly measured with the vernier). It's easy enough to check if there is a plunger there. If it's really gummed in then it will probably need an airline or warming up to let it drop out.

It could be of course that the previous owner found it to much of a fiddle to put back (or didn't even realise that he'd lost it).
 
Dances with Shrapnel said:
Not necessarily. In the fully retracted position (oil pressure up and flowing, the plnger would be fully nested and the oil galleries would be wide open.

Try rapping the timing cover a couple of times on some soft wood to see if something dislodges. If I can dig out my Mk3 timing cover after dinner I can take a reference measurement. Maybe someone on the list has one handy now to do the same.

The bottom line is if you put another one in and another one is already there (inadvertently double up) you probably would not be able to push it back far enough to uncover the oil passage to the crankshaft. So that would be a fall back test for you.
Click to expand...

79x100 said:
I did measure my cutaway cover and posted above that the bore is 3/4" deep (roughly measured with the vernier). It's easy enough to check if there is a plunger there. If it's really gummed in then it will probably need an airline or warming up to let it drop out.

It could be of course that the previous owner found it to much of a fiddle to put back (or didn't even realise that he'd lost it).
Click to expand...

Thanks again - I have many entries on the wall of shame for doing stupid things - so it's near impossible for me to receive too many cautions.

I went back and checked again (measure twice, cut once)...I have about 3/4". Blew out the tiny vent hole next to the plunger bore just in case something was lodged in there that caused the PO to delete the plunger & spring. Now I wait for parts.

Well while I'm waiting, any ideas on how the check the bore - to make sure that isn't why the part was left out?
 
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