how badly does one need that pressure relief valve

i am wondering how badly do our engines need that pressure relief valve?

i understand WHAT it does but if it would stop working and thus ,in case of too high pressure , the surplus of oil will go up to the rockers what is the benefit of dumping it in the timing cover , or more to the point what danger is there not to do so

I have been looking at 3 different types of timing covers - early domi with onlly one bolt where ,on commandos there is the valve
later domi ,much like commando but for magnetos (so incl early commandos )
Commandos

all 3 have same funtion , and although the boss suporting the spindle on wich the itermediate gear fits is different (for reasons not relevant here , second sprocket for mag ) i see no reason as for why the valve is needed . I agree it is a good idea but that is it
Anyone nows more about this ?

I want to fit an early timing cover on my commando engine so any know how is appreciated

positive hard drive pumps [ gear driven] need some protection from excessive resistance, otherwise the pump could fail, a sheared key in the deliverly side would result in a engine failure. If your engine was worn to a point where the oil pressure could not exceed the delivery out let,then alls well. BUT if the escape resistance is greater than the out pressure.....well something is going to give...remember a gear pump will keep pumping intill it bursts..or the drive fails.
I would consider plugging up the dump..very unwise.

I commonly plug the oil dump port into the timing cover and drill the passage leading to the oil intake passage as is done on the MK3 and early model covers. The oil pressure relief is needed on a cold start or the oil pump shaft will break. Jim

Jim
Is it your experience the oil pump shaft breaks?

I have seen the crank oil seal invert on over pressure.

Dave, I installed a MK3 cover on an earlier engine that did not have the passage drilled in the crankcase so there was nowhere for the relief oil to go. I was wanting to take advantage of the anti-wetsump valve. I did not realize what I had done until a few days later when it broke the oil pump shaft and caused a real mess. I have heard of the seals inverting but I have not experianced that. I think it is the rubber coated seal that has the ability to invert but I have not tried it and don't use them. Jim

dynodave said:

Jim
Is it your experience the oil pump shaft breaks?

I have seen the crank oil seal invert on over pressure.

Click to expand...

Hi Jim
The few MKIII covers I have all have a relief blow off passage that dumps in the timing chest. They are to the right and above the (plugged) OPV feed drilling.
Had one (whole MKIII bottom end) at the rally and we could have tested the cover on the oil pump test rig. Maybe yours had a seized OPV. I've seen them on my rig and it sends the pressure to the roof.....then I shut it down....
I set my rigs OPV to kick in about 55psi.

Dave, After thinking about this -You are correct, the MK3 cover has a port in it and I had plugged it and drilled a new port so oil would return to the inlet side of the pump like the mid year engines did. This was on my N15 a long time ago. What I didn't realize was there was no hole in the crankcase from the oil pump inlet to the gasket surface on this motor. To correct it I drilled the passage in the RH crankcase from the hole in the gasket through to the oil pump inlet passage in the case. Jim

lynxnsu said:

i understand WHAT it does but if it would stop working and thus ,in case of too high pressure , the surplus of oil will go up to the rockers what is the benefit of dumping it in the timing cover , or more to the point what danger is there not to do so

Click to expand...

Too high oil pressure can also blow the crankshaft oil seal lip inside-out.

A local guy had a Commando that actually did have a drilling for OPV feed back to the pump inlet....YET the drilling did not breach all the way INTO the inlet and was therefore non functional. Scratched our head on that one for a while. :mrgreen:

Yes- that was how my case was. It was an early Commando case I picked up and used to build a hot rod motor for my N15. It was drilled for a tach drive. The oil relief hole was drilled and tapped for a bolt but was not drilled the last 1/2 inch to the inlet passage. Jim

Thank a lot for the info
I will post later how i am going to solve it ( or try to )
but thanks for the tech info and letting me take advantage of your mistakes...normally i make my own but this is easier and cheaper

I dont know enough to say how much we need them but for me the question is How do you know if it is working?

I was just reinstalling one and wondering :?:

Can you test it :?:

Caferider said:

I dont know enough to say how much we need them but for me the question is How do you know if it is working?

I was just reinstalling one and wondering

Can you test it

Click to expand...

Fit a temporary oil pressure test gauge.