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

[allan.walker]

I've finally had time to plumb-in the oil pressure gauge.
I thought I'd better check the connections were sound before attempting to start the engine, so I kicked it over half a dozen times.
With each kick, the pressure rose and on kick no.6 the needle was bouncing off the end stop...it was registering over 100 psi at kickstart speed.

As previously mentioned, the bike has covered about 1000 mikes since being built before I discovered the lack of an oprv, so, knowing what I know now about the pressure being developed, should I carry on with my plan of starting it and seeing what happens to the pressure reading as the engine warms up and the oil thins????

[Gui.dorey]

Allan,

Not claiming to know if I’m right, but it still seems to me the first thing to suffer or break would be the pump. The pressure builds up in the feed circuit and I wouldn’t think the plain bearings or big ends would suffer due to high pressure. The weak link has to be the pump’s internals. Could be totally wrong of course and missing something. So perhaps you can contact Morgo and ask the what the highest pressure rating is that the pump can take. I would guess the whole system can take it and it might just cause a problem on the long run, after many miles of running without a OPRV.

On mine, I get an indicated pressure on my tank gauge after a cold start of 100 psi or more. Anyway, the needle hits the stop and stays there for a while until the engine is truly warmed up. Then it starts creeping down and after a while it actually shows 0 psi at idle. Of course I don’t trust the guage as I don’t know how old it is, if it’s a cheap replica or original, or how it is calibrated. So I’ve always just used it as an indication that I have pressure and as a guide for operating temp - until the needle starts moving down, I take it easy and don’t pull high revs. Am I really reaching 100 psi or more? I’ve no idea, but if I am, then nothing gets damaged. The point is the difference in pressure between a hot and cold engine. Going by my gauge is a bit extreme, but from what others report I would say the pressure warm is at least half of when it’s cold. As the engine warms up (which shouldn’t take long), the pressure drops quickly, as the hot oil flows much easier. Without the OPRV it will take much longer of course, but once the oil is truly warm, it will drop. So even if you are getting, say 150psi after starting, it will probably drop to 75psi after warming up, which won’t damage anything if you are just testing. I am not recommending in any way to run the bike like this on the long run ( the OPVR was there for a reason), but for a test at idle and a heat cycle to see what happens, I would probably be brave enough to do it. After getting the max pressure rating from Morgo I’m running 20w 50 btw - with thicker oil, the pressure should be higher obviously.

Perhaps some more experienced Sq4 owner’s or more knowledgeable minds can either confirm my theory or completely bash it. I would like to know either way and learn some more here.

Gui

[john.whiting]

Any breakage will happen in the first few minutes after starting ,when the oil is thickest......I suspect the pressure may be rising to 1000psi or more if the motor is revved ......There must be some way of including a relief valve in the morgo pump.

[allan.walker]

Hi Gui,
Thanks for detailing your experience. I am inclined to run the engine and see what actually happens. My gauge is a new one from Morgo, so I'm assuming that it's at least as accurate as any....I am running 20/50 oil as well. Perhaps a 15/50 synthetic may be worth a try if pressures during the 'tset' are too high.......
I have a Commando on which I fitted a gauge a couple of years ago. From cold, it registers about 60 psi (which seems correct and suggests that the oprv is working properly) and when warm and riding the bike, it shows about 10 psi per 1000 rpm.

Your suggestion to contact Morgo regarding the safe pressure of their pump sounds sensible so I'll do that.

John,
Yes, that's my thinking, too. Given that the engine has done 1000 miles without an oprv, I am thinking that a cautious test run may be ok.

I've been in touch with Morgo about the possible modification of the Mk1 type pump, to include an oprv. Their reply was that the Mk1 and Mk2 pumps are very different designs and it can't be done. However, I did have a thought about this. If I could make an aluminium plate, say 10 mm thick, shaped like the gasket face of the oil pump and replicating the oil passages, perhaps a drilling could be made in the edge of this, in line with one of the feed passages. This drilling could be tapped to enable the fitting of a standard Mk1 front crankshaft oprv.
Then, the oprv would operate and dump the excess oil directly into the timing case (like it does in a Mk2.)

A 'longer' drive nut would need to be made to drive the pump and there is also the question of clearance beneath the timing cover. Perhaps there would be sufficient space if I were to use a (more bulbous) Mk2 timing cover......

All a bit involved, but it seems like less work than stripping the engine and machining the front crank.

Oh - one more snag, Drags have no oprv bodies so I've got one on back order.

[allan.walker]

Well, I tried running the engine after fitting the oil pressure gauge. The needle went hard against the stop (over 110 psi, but how much over???) No surprise, really.
I had to give-up waiting for the oil to thin and see if the pressure reduced because of the knock from the drive side, which I had hoped was the shock absorber moving on the crankshaft splines.

My knocking primary may have been spline wear on the rear crank, but having removed the shock absorber and tried the JB Weld fix, the noise continued and grew louder.

So, when the engine was running during my oil pressure investigation, I carried-out a quick check by removing each plug cap in turn. (A tip I read recently on this forum.)
When I got to the l/h front cylinder, when I replaced the plug cap it sounded like I'd hit the crankcase with a hammer. I repeated this several times with the same result.
Conclusion: big-end gone on l/h front crank.

At least the strip-down will enable me to fit the missing OPRV ( as mentioned in my other thread.)

[Paul_Linden]

Well you’ve got to the bottom of things, and at least this didn’t happen while you were out on the bike.

[Bob.Murphy]

Conclusion: big-end gone on l/h front crank.

You're not having your troubles to seek with this motor, are you !

I'd be surprised if the big-end has gone with all that oil pressure. I had the opposite problem to you when I built my Square four back in 1968/'69. I had a MkII motor with the gear pump and MkI cranks with the OPR Valve in the front crank . . Too many OPRVs. The spring in the crank was far too weak and the oil pressure was fine (52 psi) when cold but dropped to nearly zero on the road - I ran a big end (No. 1 if I recall correctly) .

I found that the big-end was quiet if I kept the power on, but as soon as I went into over-run it knocked. Why would yours knock when you put the plug cap back on but not when the other cylinders are providing the power ?

I wonder where the woodruff keys in the coupling gears are when No. 4 cylinder is on the power stroke ?????

I'll be watching this with interest (though, unfortunately, I no longer have a Square Four - just the wishes for another one).

Bob.

[Simon.Gardiner]

The classic diagnostic test for worn big-ends is a rattle that disappears/reduces under load - I can vouch for it's accuracy on 4-cyl. water-cooled engines. However, I'm sure Sod's Law fully applies to all engine issues...

SG

[allan.walker]

Conclusion: big-end gone on l/h front crank.

I found that the big-end was quiet if I kept the power on, but as soon as I went into over-run it knocked. Why would yours knock when you put the plug cap back on but not when the other cylinders are providing the power ?

Hello Bob,
I can only assume that, when the plug is not firing, the goodness-knows-how-high oil pressure in the worn big end is keeping the working surfaces apart. As soon as the plug fires, there is an instantaneous increase in downward force and therefore 'knock.'

I, too, wondered about the relative positions of the keyways in the connecting gears and if this has a bearing (sorry!) on where the noise is emanating from. However, the fact that the knock has grown much worse and is constant, together with the plug cap test, leads me to believe it is the big-end.

Why this should have occurred, I couldn't say. All will be revealed, I suppose, when I pull it all apart.

oh, just a thought. You wouldn't still have your 'extra' OPRV would you? Drags are on back order.........

[allan.walker]

... and at least this didn’t happen while you were out on the bike.

Yes Paul. No problems with getting the bike recovered. It's strange how things work out. Recently an idiot drove straight into the back of me when I was on my brand new T120, stationary in a queue of cars. The bike looks like it's a write-off (in the hands of insurance assessors.) The upside(?) is that it happened 100yds from my home....

It helps to be a glass half-full person, I suppose.

Every silver lining has a cloud around it.