Wot, no oil pressure release / relief valve? Square 4 Mk1

[allan.walker]

Whilst trying to solve a wet-sumping problem, I have found a different oil-related 'discrepancy.'

This is a picture of the r/h end of the front crankshaft, with the cap removed. The engine has a Mk1 bottom end with a Mk2 top end fitted by the previous owner. He has made many other modifications and I think that I have just discovered one more...

Another member (thanks, Gui) provided me with a picture of where the oil pressure relief valve is (should be?) located on a Mk1 Square Four. It is clear that mine does not have one!
The oil pump is a Morgo without a built-in oprv, so it looks like there isn't one anywhere on the engine.

I'm waiting for some fittings to arrive so that I can connect an oil pressure gauge so I can see what is happening, but in the meantime, would anyone have any comments on this puzzling situation? Could it be that the previous owner fitted a front crankshaft from a Mk2? Is there any way to retro-fit an oprv, without having to strip the engine?

Allan.

[Paul_Linden]

I think you are correct Allan, in that the previous owner fitted a mk2 crank at the front.
In theory it is possible to convert it to a mk1 by drilling and tapping, but doing it with the crank in situ is going to put swarf in the oilways. Don’t do that, take the crank out if this is the way you choose to go.
It might be easier to add an OPRV to the oil pump, or, adapt a Mk2 pump (which has the oprv) to fit. Either way talk to Morgo about it.

[allan.walker]

Thanks for confirming my suspicions, Paul.
A good suggestion regarding contacting Morgo. I'd rather avoid a complete stripdown if there is an alternative.

[Gui.dorey]

The question that’s puzzling me, though, is how did it work for the previous owner? He had a MKI bottom end, but replaced the front crank for a MKII thus eliminating the PRV - how did he deal with the pressure relief?

[allan.walker]

Well, I can only guess that he didn't deal with it!

I haven't experienced any symptoms which suggest that the oil pressure is too high. The wet-sumping problem was not oil pressure related....

There is no oil pressure gauge fitted, so how would anyone know what the pressure was? I've bought one to put on the bike, and I'm waiting for a couple of connectors to come in the post.

I shall contact Morgo, as Paul suggested. In the meantime, I am tempted to fit the gauge and see what it shows (once I've had chance to rebuild the primary drive, of course.) The bike has done 1000 miles since being built, so perhaps another brief run to observe what happens with the oil pressure may be safe enough......

[nevhunter]

Damage is likely without a pressure relief valve, IF it gets high enough somethings gotta give. You might have been lucky so far, but maybe a gasket or drive key or even a piece of a casting. Nev

[camstevens]

Hi
Does oil come out of the crank centre when you kick it over? Just wondering if there has been a capillary or orafice drilled into the crank as a crude relief?

Cam

[allan.walker]

Hello Cam,
I haven't tried that, because the primary drive is apart at the moment, but I've tried to poke a piece of wire into the hole which can be seen in the centre of the crank. The wire only goes in about 1/4" and then stops, so it looks like the hole doesn't go through to the oilways.
I will try your suggestion, though. The chap who built the engine has done some very clever things, so who knows?

[allan.walker]

Damage is likely without a pressure relief valve, IF it gets high enough somethings gotta give. You might have been lucky so far, but maybe a gasket or drive key or even a piece of a casting. Nev

Yes, I am concerned about that. I've never heard of an engine without an OPRV fitted as standard. It must be there for a good reason.

[Paul_Linden]

A quarter inch deep hole at the end of the crankshaft might be where the previous owner started to drill it out, intending to fit an OPRV. Why didn’t he complete the job? I bet there is a broken drill bit stuck at the bottom of the hole.