Sq4 MkI- new life

[Gui.dorey]

The bright side, if one can called it that, is that I just got so far as to bolt the case together and assembling the coupling gears… I’m currently still waiting for the barrel to come back from the shop. There is a picture of the current state a few posts back.

Paul, I just checked and, yes I can detect some movement on the rear crank. But not on the front one. I was able to slip a .003 feeler gauge between the crank and plain bearing. A .004 one wouldn’t go in.

As to Allan’s question I might have an explanation. The return is higher than the feed, but once the engine stops, all the oil on the top end and everywhere else drips into the sump. On restart, the pump scavanges it back up, but it takes a while. Add to this a greater amount than normal flowing into the sump and it will take much longer for the sump to be scavanged dry. Since I didn’t empty the sump before every ride, and due to all the problems, my rides were always relatively short, being not much more than test rides, I would imagine the sump just kept filling more and more. Perhaps a longer ride would eventually give the Morgo enough time to empty the sump, but I never got there. When I finally went for a longer ride the conrod broke. This was about after 50kms.

[simon.holyfield]

I'd buy that explanation regarding the return pump.

On the clearance, I'd worry about measuring diameter tolerances using feeler guages in something the size of a piston, let alone a main bearing. The stiffness of the gauge going into a curved slot of small radius means the slot needs to be much wider than the thickness of the gauge, so your radial clearance must be greater than 0.003".

[Gui.dorey]

I'd buy that explanation regarding the return pump.

On the clearance, I'd worry about measuring diameter tolerances using feeler guages in something the size of a piston, let alone a main bearing. The stiffness of the gauge going into a curved slot of small radius means the slot needs to be much wider than the thickness of the gauge, so your radial clearance must be greater than 0.003".

I know, but thanks for pointing it out. It was just to show that there is a big clearance in there. I’ll have to take it all apart again, and get a new set of bearings, I’m afraid.

[paul.jameson]

At that stage of assembly then, its no contest. Undo the nuts, whip the timing side bits off, then the coupling gears, remove the cranks and measure with bore gauges and micrometer. But I suspect the answer is a foregone conclusion. In measuring, it is certainly worthwhile seeing if you have any taper, either on the crank or in the bush. Not easy to do, especially with my cheap bore gauges, but a worthwhile exercise. An interview with Val Page, recorded by Jim Lee, refers to the large deflection in a Square Four crankshaft so given half a chance, the bush will wear more towards the inside. Your video only shows the oil coming out of the outside, which is also where the feeler gauge went in.

[Gui.dorey]

Hi chaps,

Reviving this thread to report on what I found and progress. It took me a while to get to it as I’ve haven’t had much time this year to work on my bike.

Anyway, as suspected the clearance between the plain bearings and the crankshafts were way beyond the maximum allowed. I had almost 0.5mm on the rear one! The front was better, but still above the max of 0.1mm (0.004”).

After getting new ones from Drags, I used the lathe to bore them out to give me just about 0.03mm clearance. I actually got a wonderful surface finish on the babbit which even surprised me.

After pressing them into the case, all the clearance was gone as they somewhat tightened, so out came the reamer. I reamed each one carefully until the required clearance was achieved, and in the end I have 0.03mm (0.0012”) on the front and 0.075mm (0,003”) on the rear. I was happy with the result as a hobby mechanic and with my available tools and measuring equipment.

So now the bottom end is assembled and back in the frame. Took me two days to set up the valve timing which can twist anyone’s brain into mush, but also got that done. Also installed an oil filter, which I didn’t have before. Had to fabricate the bracket for it myself, and routing those thick hoses was a nightmare. There’s no space down there between gearbox, frame and engine!

So… coming along slowly.
Cheers
Gui

[nevhunter]

The sort of clearance you have will make audible noise moreso as the engine oil thins. About .001" is good for Babbit surfaces on that journal size. Extra clearance allows the Shaft to hammer and reduced the life of the bearing and may also not provide enough oil to the big end (s) .Nev

[paul.jameson]

Keep up the good work Gui. Although, as Nev says, the clearance on the rear crank is a bit on the high side, I would run with it as it is within Ariel's tolerances. You are not towing the family around in a double adult sidecar through a congested city in hot weather on a daily basis so it should last for quite a while. For peace of mind you might want to fit an oil pressure gauge or warning light though.

[Gui.dorey]

Well, the Sq4 roared back to life today. Unfortunately my joy was short lived as it seems all my efforts haven’t led anywhere.

I filled the oil tank with a run in oil 20w50. She started after a few kicks and settled quickly into a nice idle. I had one of the rocker box covers off to verify that oil was reaching the rockers, which it was. It was also coming back to the oil tank in a steady flow. The gauge showed an oil pressure of 80 psi, and so I waited for everything to get to temperature.

After some minutes the pressure started dropping slowly, but to my dismay once the engine was fully warmed up the gauge was showing 0 psi. It goes up of course if I rev the engine, but at idle it drops to 0. Also, the steady stream of oil into the tank continued, instead of reducing itself to bubbles and oil. So exactly the same symptoms I had before the engine blew.

Some videos here of the whole thing. I’m going for a beer now.

Cheers
Gui

[nevhunter]

Put a dial gauge on the shaft and lever it up and down and even sideways and determine what clearance you actually have. Nev

[allan.walker]

Hello Gui,
From the videos, the pressure increases to 'reasonable' levels as you rev the engine. I wonder what engine speed corresponds to the better readings. I have often read (not specifically about Square Fours, mind,) that an oil pressure equating to 10 psi per thousand rpm when running is considered to be acceptable.
I would be tempted to run the engine on the stand in top gear and see what the oil pressure looks like. At least, by trying this, you're avoiding the possibility of a problem on the road.
This still doesn't answer the problem of a zero reading at tickover, of course.

Best of luck,
Allan.