New Commando owner with bad sumping problem

[Tom P]

Hello all,
I've recently picked up a 72 Combat 750, She runs well and handles better than any 50 year old bike should. However I noticed that it would wet sump the entire tank over night. So today I took the timing cover off and checked the oil pump, I flattened the body on both sides of the pump using a DMT lapping plate to minimise slop between the gears and the side plates as per the manual. The pump seemed in very good condition with no perceivable slop in the shaft after assembly, However on reassembly it seems that all the oil in the tank dumped in to the sump in minutes.
It has a Mk3 timing cover (with the chain inspection hole) and has had the engine rebuilt by Norman White who modified the scavenge to rear pick up and reposition the breather to the back of the timing cover.
My question is what could cause that level of wet sumping? what are the paths that the oil can take to get to the sump?
Cheers
Tom

 

[L.A.B.]

Hello Tom,

However on reassembly it seems that all the oil in the tank dumped in to the sump in minutes.

My question is what could cause that level of wet sumping? what are the paths that the oil can take to get to the sump?

That's far higher than would be expected from a severely worn oil pump which suggests the main leakage isn't passing through either the pump feed gears (into the timing cover gallery) or through the pump shaft clearance (to the scavenge side and then to the sump) and with a Mk3 timing cover then it shouldn't leak through the OPRV (as it might with a pre-Mk3 timing cover) because the Mk3 cover OPRV return drilling is, or should be blanked off, however, the drilling in the timing side crankcase would normally still be open as far as the timing cover joint where it should be sealed by the timing cover gasket and blank joint face of the Mk3 timing cover.
This is the OPRV crankcase return oilway drilling to the pump feed inlet that needs to be plugged temporarily with a timing cover screw (the oilway is threaded) to prevent the contents of the oil tank from draining whenever the timing cover is removed so it's possible the oilway is somehow 'open' with the timing cover fitted.

 

[grandpaul]

A very worn crank nose and/or incorrect seal will leak badly...

 

[L.A.B.]

A very worn crank nose and/or incorrect seal will leak badly...

The contents of the oil tank would have to leak through the pump first to reach the crank seal and that's not going to happen "in minutes" unless there was something badly wrong with the pump but that's just been serviced.

Also, as it's a Mk3 timing cover then I assume it has the Mk3 anti-drain valve (plunger, spring, Mk3 pump feed bush and rubber seal).

 

[CanukNortonNut]

You say you have a 72 but changed to a 75 mkIII timing cover. Are you using the MkIII oil seal on the oil pump for your new timing cover? They are different. Just checking?

 

[Torontonian]

You say you have a 72 but changed to a 75 mkIII timing cover. Are you using the MkIII oil seal on the oil pump for your new timing cover? They are different. Just checking?

Yes , just checking this situation myself. Seeing as another one fit the MK 111 timing cover , I would pull it for inspection.
It's very possible it dumps oil by using the wrong oil pump seal. Or the thinner/ thicker than required T.C. gasket.

 

[Nortoniggy]

Even if the oil pump rubber was missing altogether the oil still has to pass through the pump as Lab says, so that isn't going to be the cause.

 

[cyclegeezer]

Is it possible the oil pump to case gasket is missing or damaged? Or that the pump is loose on its mounts?

 

[L.A.B.]

Is it possible the oil pump to case gasket is missing or damaged?

That still wouldn't account for "all the oil in the tank dumped into the sump in minutes" (assuming that is a reasonably accurate description from Tom P?).

Or that the pump is loose on its mounts?

As the pump has just been serviced then it seems unlikely that tightening the pump down would have been overlooked or that the pump gasket is damaged.

Also (assuming the pump seal is fitted) the pump would be held tight against the crankcase by the timing cover.

 

[Tom P]

Thanks for all the input, i'll take her apart again this evening and have another look, from what I have gathered the oil must be getting through/past the pump, so I will have a close look there as well as checking that the OPRV crankcase return oilway drilling is blocked by the gasket

 

[kommando]

Thanks for all the input, i'll take her apart again this evening and have another look, from what I have gathered the oil must be getting through/past the pump, so I will have a close look there as well as checking that the OPRV crankcase return oilway drilling is blocked by the gasket

Better to just block it off with a grub screw.

 

[jseng1]

You need to trouble shoot it with as many parts in place as possible. Remove the timing cover and observe where the oil is leaking. Then run a hose to the end of the crank and see how much oil is passing through. Use clear vinal oil line and fill it to the level of a full oil tank. Get the picture? You might have to get creative but to actually find the problem you need to pin point it - otherwise you'll be chasing down a bunch of rabbit holes. Let us know what you find and how you went about setting up the test etc.

 

[L.A.B.]

Remove the timing cover and observe where the oil is leaking. Then run a hose to the end of the crank and see how much oil is passing through. Use clear vinal oil line and fill it to the level of a full oil tank. Get the picture?

Assuming the Mk3 oil pump seal is fitted (not the O-ring in kommando's picture) then the only way oil can reach the crank is past the oil pump feed gears into the timing cover crankshaft feed gallery.
Also, assuming the Mk3 cover has the standard Mk3 anti-drain valve fitted then the amount of oil passing into the timing cover gallery even with a worn pump should be practically nothing so the rate of passing through the crankshaft seems irrelevant.

 

[jseng1]

Assuming the Mk3 oil pump seal is fitted (not the O-ring in kommando's picture) then the only way oil can reach the crank is past the oil pump feed gears into the timing cover crankshaft feed gallery.
Also, assuming the Mk3 cover has the standard Mk3 anti-drain valve fitted then the amount of oil passing into the timing cover gallery even with a worn pump should be practically nothing so the rate of passing through the crankshaft seems irrelevant.

The oil is draining in no time. Something is wrong. My suggestion is to first check if its running through the oil pump and how quickly. Then see how fast its running through the crank between the journals and the crank pin holes. Neither the oil pump nor the crank journals will stop the oil from moving. When you've got the timing cover off - then you might as well attach a clear hose to the oil feed tube and another to the end of the crank. Tape the open ends to the frame and fill them to the same level. Then time them. This isn't about determining what is relevant or irrelevant - its simply an experiment to find out what's going on and where all that oil is leaking through. I myself would like to know and compare the two. It would also be good to compare and time the crankshaft oil leakage with the crank at BDC and at TDC. I've heard that the parking with the motor at TDC will slow down wet sumping (you can do this easily with the kickstart). Is it true or not? I'd like to know for sure because its what I do and I hope I'm not wasting my time with it.

If the oil leaks through the gear teeth of the oil pump faster than it gets through the crank - then lapping and tightening up the oil pump is a waste of time. Lets see some test results. I hope you can enlighten us Tom P.

 

[L.A.B.]

The oil is draining in no time. Something is wrong. My suggestion is to first check if its running through the oil pump and how quickly. Then see how fast its running through the crank between the journals and the crank pin holes. When you've got the timing cover off - then you might as well attach a clear hose to the oil feed tube and another to the end of the crank. Tape the open ends to the frame and fill them to the same level. Then time them. This isn't about determining what is relevant or irrelevant - its simply an experiment to find out what's going on and where all that oil is leaking through.

The pump has recently been lapped and the Mk3 anti-drain valve (if fitted?) would reduce the drainage through even a worn pump to almost nothing as I mentioned so can't be anything to do with the rate of drainage through the crank, therefore, the "experiment" seems rather pointless in my opinion. Also, which "oil feed tube" do you mean?

I myself would like to know and compare the two. It would also be good to compare and time the crankshaft oil leakage with the crank at BDC and at TDC. I've heard that the parking with the motor at TDC will slow down wet sumping (you can do this easily with the kickstart). Is it true or not?

That obviously doesn't apply when the rate of drainage in this instance can apparently be measured in minutes, not days or weeks so for the reasons previously mentioned (lapped pump, Mk3 anti-drain valve) the rate of drainage would seem far too high for the oil to be passing through the pump in the normal way, consequently, the rate of drainage through the crank is irrelevant as the flow through the pump and anti-drain valve would be the limiting factor which indicates the leak is most likely to be elsewhere and not oil draining through the pump.

If the oil leaks through the gear teeth of the oil pump faster than it gets through the crank - then lapping and tightening up the oil pump is a waste of time.

Then so is measuring the flow through the crankshaft as that should always be higher than leakage past the static pump feed gears even without the Mk3 cover anti-drain valve in place.

 

[storm42]

What would happen if the pressure release valve was stuck open a bit?

 

[Tom P]

Well, progress has been made. I removed the oil pump and noticed that the cast iron endplate was very slightly proud of the sealing face so it was not allowing the pump to seal on the gasket. So far it looks good, but I will be interested to see how much oil has sumped by tomorrow morning.
Thanks for all your ideas and help
Tom

 

[RoadScholar]

Although I applaud your efforts and your willingness to jump you'd get a D- at best. I'll admit to making more dramatic mistakes. Mistake #1 was taking my dad's lawn mower engine apart to see what made it tick. I put it back together and had no parts left over, but I forgot to refill the oil sump. My dad got home early the next day and started to cut the grass, he got just about half done when the engine seized. It took me almost 4 months to pay off the new engine and my tools got impounded during that time. Since then I think I'm up to mistake #3000+ and figure I might just live long enough to make at least 500 more, at least one of which is bound to be a duzy...

What you discovered would account for the high leak rate, but if you used the Mk3 pump to timing cover seal you should have had some difficulty fastening the timing cover; there isn't much clearance there. I would also think operational oil pressure would be lower, how much I can't say. You may want to consider installing an oil pressure gauge?

Just in general. Lapping the oil pump surfaces isn't a bad idea; a lot of members reference this procedure. However, I hear very little about members measuring the distance between the gears and the pump casting; too much clearance here negates lapping the surfaces. Additionally no one references the gear lash or the condition of the gear meshing surfaces, all of which have influence on oil pressure. I know how expensive OE pumps are and what SRM gets for theirs, but when I consider what it costs to properly overhaul an engine a new pump is chump change. I also install an oil pressure gauge which may or may not be spot on, but which is always relative.

Best.

 

[Fast Eddie]

Just in general. Lapping the oil pump surfaces isn't a bad idea; a lot of members reference this procedure. However, I hear very little about members measuring the distance between the gears and the pump casting; too much clearance here negates lapping the surfaces. Additionally no one references the gear lash or the condition of the gear meshing surfaces, all of which have influence on oil pressure. I know how expensive OE pumps are and what SRM gets for theirs, but when I consider what it costs to properly overhaul an engine a new pump is chump change. I also install an oil pressure gauge which may or may not be spot on, but which is always relative.

Best.

+ 1

 

[MexicoMike]

Well, progress has been made. I removed the oil pump and noticed that the cast iron endplate was very slightly proud of the sealing face so it was not allowing the pump to seal on the gasket. So far it looks good, but I will be interested to see how much oil has sumped by tomorrow morning.
Thanks for all your ideas and help
Tom

Sounds like it was a simple oversight - not tightening the endplate cover bolts! Who hasn't done something similar? I know a professional mechanic on a famous drag-racing team who once left a shop towel in the engine during a "refresh" between rounds with unhappy consequences! Surprisingly, he still had a job afterwards! (The advantage of having several championship seasons to offset that one "Aw, ship!" event)