Sq4 MkI - what now?!?

[Gui.dorey]

The rods were the original ones and not club rods. The big ends were actually ok and not worn at all and I fitted new std journals which were perfectly all right. It could be indeed fatigue, although I’m not entirely convinced. From what I could see from underneath the no 3 big end looked scoured, typical from a seizure due to lack of lubrication. But only time will tell when I open it up for a thorough investigation.

I still suspect something was wrong with the lubrication system. It is not normal to find that amount of oil in the cases. There was over one litre in there! And the Morgo hat just been overhauled and there was always a steady flow back into the tank. So the return seemed to be doing its job. My question is why was so much oil going into the crankcases, and maybe not going to the big ends where it should have been? I can’t think of a reason, but maybe one of you chaps has an idea…

Also strange was my oil pressure. Ever since the rebuild the gauge would show over 100psi on start up, and gradually decrease as the engine warmed up. But when fully at temperature, it showed 0 psi and stayed there even at speed. I put it down to a faulty gauge, which is probably not even original, but in retrospect perhaps the gauge was working and my oil pressure was indeed nil. Why would this happen, I also don’t know. Again any thoughts are highly welcome!

I did most of the checks everyone suggested and never really found anything wrong. But somewhere there was a problem.

I suppose taking the engine apart will be my project for next winter. I just don’t have the courage to do it now during riding season. I prefer to enjoy riding my 350 NH and the other bikes. I still have a very nagging oil leak on the red hunter from the timing case through the mag, but that’s for another thread

[paul.jameson]

Take the timing side end cap off the front crank, remove the oil pressure relief valve and test that to see what pressure it blows off at. If need be I can PM you my design of a simple test rig for this purpose. If the oil pressure relief valve wasn't working, oil pressure would drop to zero as the oil warms up and all oil would flow straight into the sump, rather than to the big ends.

[simon.holyfield]

Take the timing side end cap off the front crank, remove the oil pressure relief valve and test that to see what pressure it blows off at. If need be I can PM you my design of a simple test rig for this purpose. If the oil pressure relief valve wasn't working, oil pressure would drop to zero as the oil warms up and all oil would flow straight into the sump, rather than to the big ends.

Could this be one of those incidents, as I've experienced twice, where the relief valve split pin gets caught up in the spring and allows the ball to lift?

[Bob.Murphy]

Ah, Paul beat me to it.

I ran a big end on my square when the relief valve spring I put in initially was too light for the purpose (No. 1 cylinder).

The motor was a 'bitsa', a Mk II with Mk I cranks, I therefore had the gear pump with its relief valve as well as the valve in the front crank.

An embarrassing lesson, fortunately it didn't do much damage.

Bob.

[simon.holyfield]

Take the timing side end cap off the front crank, remove the oil pressure relief valve and test that to see what pressure it blows off at. If need be I can PM you my design of a simple test rig for this purpose. If the oil pressure relief valve wasn't working, oil pressure would drop to zero as the oil warms up and all oil would flow straight into the sump, rather than to the big ends.

It wouldn't leave all the oil in the sump though, would it?

[Bob.Murphy]

If the rod started to break-up bits of it could block the scavenge pipe (the bits would have to get past the sump filter of course).

With no oil pressure and therefore no restrictions to the flow and a Morgo pump . . Could the supply-side overwhelm the scavenge-side ??

You have a powerful high-pressure on the supply-side but only atmospheric pressure on the scavenge-side Hmmmm .

Bob.

[Richard Kal]

A friend had the same problem with an A10 recently; oil level dropped in the oil tank and increased in the sump.
The problem was in the scavenge circuit.
Very low (insufficient) oil flow returning to the tank; not much return flow visible out of the pipe in the oil tank.
The problem was the riser tube in the oil tank was nearly completely blocked with hylomar, bits of rubber, etc.
Richard

[nevhunter]

If the bearing is scored it must be oil starvation or grunge or not enough clearance or cap reversed. The oil pressure readings are ominous.There must be something wrong with the oil circuit. Prove the system with compressed air during assembly. Feed from timing side mains is in need of verifying. Nev

[Gui.dorey]

Hi Paul Jameson, go ahead and send me a description of your testing rig. Do you mean if the pressure relief valve opens too soon, that the oil will flow straight to the cases and not to the big ends? I have a new valve assembly wit a new ball and spring from Drags. Would that also explain the filling up of the cases with oil, because the Morgo pumps more in than it scavanges?

And to answer Simes question, I did make sure the spring wasn’t caught in the pin after reading your blog. I’ve had the front plug off a few times and never had that problem on mine.

As to the return being plugged with debris, we can rule that out as I checked it when I had the Morgo overhauled. I even shaved a few mm off the end of the scavange pipe to make sure it wasn’t fouling on the sump plate. There were also no cracks or anything on that pipe.

[paul.jameson]

The test rig is a piece of 7/8" brass rod about 2" long with a hole down the middle. At one end the hole is widened out using a centre drill and tapped to take the pressure relief valve. At the other end I have soldered in a valve stem recovered from an old inner tube (with the valve removed during soldering, of course). The hole down the middle is the tapping drill diameter for the pressure relief valve for most of its length to maximise internal volume.
To use, I simply screw the pressure relief valve in the end and apply air to the tyre valve using the inflator on my compressor. You easily get a good idea of when the valve opens and also if it tends to have a constant leak. One of the old valves I had did seem to have a constant leak - it whistled at all pressures, most unlike the other valves I had and nothing cured that. I tried a new ball, a new spring, re-seating the ball, etc but nothing worked so I binned that valve.