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

Singles, twins and fours.
allan.walker
Holder of a Nylon Anorak
Holder of a Nylon Anorak
Posts: 162
Joined: Fri Sep 28, 2018 8:35 am
Contact:

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

Postby allan.walker » Wed Jun 16, 2021 10:16 am

Whilst trying to solve a wet-sumping problem, I have found a different oil-related 'discrepancy.'
IMG_4024.JPG


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! :o
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.

User avatar
Paul_Linden
Holder of a Waxed Cotton Anorak
Holder of a Waxed Cotton Anorak
Posts: 593
Joined: Sat Oct 15, 2011 10:08 pm
Location: Exeter, UK
Contact:

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

Postby Paul_Linden » Wed Jun 16, 2021 5:03 pm

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.
Square 4 mk1, Square 4 mk2, Colt, BSA C12.

allan.walker
Holder of a Nylon Anorak
Holder of a Nylon Anorak
Posts: 162
Joined: Fri Sep 28, 2018 8:35 am
Contact:

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

Postby allan.walker » Wed Jun 16, 2021 5:15 pm

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
Holder of a Nylon Anorak
Holder of a Nylon Anorak
Posts: 299
Joined: Tue Sep 05, 2017 7:42 pm
Contact:

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

Postby Gui.dorey » Wed Jun 16, 2021 5:18 pm

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?
1951 Ariel Square Four MKI
1954 Ariel NH Red Hunter
1929 BSA Sloper
1946 BSA B31 (project)
1954 BSA C11G
1960 Harley Sportster XLH
1951 Harley WL 45

allan.walker
Holder of a Nylon Anorak
Holder of a Nylon Anorak
Posts: 162
Joined: Fri Sep 28, 2018 8:35 am
Contact:

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

Postby allan.walker » Wed Jun 16, 2021 6:16 pm

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
Holder of a Golden Anorak
Holder of a Golden Anorak
Posts: 4338
Joined: Tue May 10, 2011 9:42 am
Location: Victoria.. Australia.
Contact:

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

Postby nevhunter » Thu Jun 17, 2021 2:24 am

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
Holder of a Nylon Anorak
Holder of a Nylon Anorak
Posts: 190
Joined: Mon Nov 21, 2016 5:01 pm
Location: Kew, London
Contact:

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

Postby camstevens » Thu Jun 17, 2021 7:36 am

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
Holder of a Nylon Anorak
Holder of a Nylon Anorak
Posts: 162
Joined: Fri Sep 28, 2018 8:35 am
Contact:

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

Postby allan.walker » Thu Jun 17, 2021 8:26 am

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
Holder of a Nylon Anorak
Holder of a Nylon Anorak
Posts: 162
Joined: Fri Sep 28, 2018 8:35 am
Contact:

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

Postby allan.walker » Thu Jun 17, 2021 8:29 am

nevhunter wrote: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.

User avatar
Paul_Linden
Holder of a Waxed Cotton Anorak
Holder of a Waxed Cotton Anorak
Posts: 593
Joined: Sat Oct 15, 2011 10:08 pm
Location: Exeter, UK
Contact:

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

Postby Paul_Linden » Thu Jun 17, 2021 12:10 pm

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. :o
Square 4 mk1, Square 4 mk2, Colt, BSA C12.


Return to “Four stroke”

Who is online

Users browsing this forum: No registered users and 9 guests