Sq4 coupling gear oil seal

[Gui.dorey]

Hi everyone,

I finally took the Sq4 out of the corner of the shop, and started dismantling the engine. As a recap, my con rod on Nr 3 broke early this year, I believe due to a faulty pressure relief valve. But final analysis is still pending until the engine is apart.

I can’t remember what is the proper way to remove the oil seal on the rear coupling gear. Is there a non destructive method, or just pull it out and replace with a new one?

Cheers,
Gui

[allan.walker]

Hello Gui.
I couldn't see a way to remove it without damaging it, so I 'dug' it out and fitted a new one.
Of course, that doesn't mean that there isn't a non-destructive method! Someone with better knowledge should be along soon....

btw, it's good to know that you are going boldly where you have gone before. Good luck. I've just finished rebuilding (again) my Mk1/2 hybrid and done the first run/cool/re-torque session. If it's dry tomorrow, I'll put a few miles on it. Fingers crossed!

btw2. I have bought new OPRV's from the usual supplier, who also sell the separate parts. One order comprised only the ball, spring and split pin (bodies on back-order.) When the body arrived, the split pin previously supplied didn't fit the hole in the body...

Having read on this forum that there have been 'issues' with OPRV's, I ordered another full one, as a spare, from the same supplier. It arrived as a kit of parts (not assembled, as the website showed.) Guess what, the split pin did fit the body on this one, but the spring was 1/4" longer than the previously-supplied one and was a different diameter......
When I came to fit one of the OPRV's into the end of the crank, the thread was really tight and it would not screw-in more than half-way without undue force. I removed it and tried the other OPRV and that screwed-in nicely.

Three examples of p-pqc on the same part!

I'm looking forward to reading how you get on.
Cheers,
Allan.

[Gui.dorey]

I managed to get the seal out intact. I removed the spring first and the seal then came out. I shall post pics of what I find on a separate thread - I survived an engine blow up on a Sq4

[Gui.dorey]

Allan,
Make sure you test your OPRV to see if it is really working. Mine was new with new spring and valve and it wasn’t sealing properly. It is well worth it setting up a test rig as suggested by Paul Jameson just to be absolutely sure.
Cheers Gui

[allan.walker]

Yes indeed, Gui.
I took a shortcut to testing the OPRV (i.e. didn't make a 'rig' to test it with air pressure.)

I fitted it (well, the one that would actually fit...) in the end of the crankshaft and kicked the engine over lots of times with the plugs out. To begin with, I left off the screw-on end cap on the front crank so I could see what was happening. Later, I fitted the end cap.

It was clear to see the OPRV letting oil out as the pressure rose and it was easy to verify the pressure on the Morgo oil pressure gauge. Interestingly, the gauge registered a higher reading after I had replaced the crankshaft end cap. My theory on this is that the Morgo oil pump is supplying so much volume that the amount of oil being vented through the OPRV is greater than the drain hole into the crankcase (behind the end cap) can cope with.
I think that the cavity behind the end cap is being pressurised by the vented oil, thereby restricting the amount of oil which the OPRV can vent.

I found that it was easy to register 100 psi just by using the kickstarter, even though the OPRV was venting copious amounts of oil, so my next step was to remove the OPRV and dismantle it and fit the shorter of the two springs which the usual supplier had sent me. Once the OPRV was refitted, I could only manage 80 psi by using the kickstart. Perhaps I was getting tired, but it seems to me that the shorter spring allowed the OPRV to vent at a lower pressure.
( Please bear in mind that the engine has reground cranks with new b/e shells and t/s bushes, so clearances-wise, things would be at a minimum.)

Reasoning that warm oil (20/50) would be thinner and allow easier flow and thereby reduce pressure, I fitted the plugs and started the bike. It started and ran nicely on the second kick. The oil return to the tank was as it should be and at a fast tickover the pressure gauge showed about 90 psi - higher than 'spec,' but as the oil warmed and thinned, the gauge showed 50 psi at fast tickover.
Raising the rpm slightly brought an increase in pressure to about 65 psi.

I stopped the engine and let everything cool down overnight and then re-torqued the head. Starting the engine again brought similar results, so I am going to take the bike on a gentle jaunt tomorrow (weather permitting) and see how things go.

[Gui.dorey]

Sounds good, but watch that pressure gauge.
Mine was just as you described, but once open the OPRV wouldn’t seal again, and I expect the problem got worse with as the oil got hot. Mine took about 5 mi to come up to temperature, so if at around that distance your gauge shows a pressure close to 0 at idle, easy it back home and check that valve again.

[allan.walker]

Sound advice!
Thanks Gui.