SQ4 - after the service

 A few little teething troubles appeared after the recent service, most notable of which was the oil pressure. Normally the oil pressure sits at 75 psi when cold and rolling at main road speeds, dropping to 25 psi idling after 15 miles or so.

Today, it was going up to 75, but intermittently dropping to 40 or so - very odd. I bled the Morgo again:

When that appeared to be happy - there were no bubbles I turned my attention to the relief valve.

See that bit of debris half way along the spring? I cleaned that out, and after a suggestion from Richard in the AOMCC, I changed the ball and reseated it.

I then rode to Cromer and back, clocking up about 13 miles - until it warmed up, it sat solidly at 75 psi and was still showing 50 psi when I got home. Back to normal.

It’s a bit snatchy at low speed. Initially I thought this was carburetion (not that I have changed anything), then perhaps transmission snatch, but all is normal there.

I’m going to retard the timing a bit.

SQ4 - back to the road

 A couple of days ago, the Square Four came off the bench to be replaced by the FH in order for me to torque down the cylinder head at 270 miles. The Square rolled easily onto the floor as it's great weight dictates with little left to do than fill the oil  and fuel tanks. 

It had been off the road for something like 4 weeks for a service and one evening I ladled in a gallon of fuel drained from the FH tank. It wasn't until I went to start the engine that I realised the fuel was pouring out of the fuel tap. It had dried out. Choosing the easy solution I soaked it in fuel overnight to see if I could get the cork to swell up again: 

This worked a bit but not well enough. The next day found me replacing the cork with a new one and also replacing the two o-rings in the reserve plunger that I made some years ago. 

Finally getting the engine started revealed another problem - no oil pressure. I ran it for 10 to 15 seconds or so with no success and shut the engine down. I realised that I would have to bleed the feed to the Morgo oil pump. I don't believe I have drained the tank before - the last time I changed the oil I didn't wash the tank out so the oil lines from tank to engine would never have been drained since I built the engine all those years ago. 

Bleeding the pump is very easy as it has a built-in hole for the purpose:

I was pleased to find the timing chest very clean and the sprockets and chain in excellent condition with the tensioner working properly. A few minutes with a screwdriver had oil seeping from the bleed hole and the whole thing sealed up again. 

Restarting the engine found the oil pressure leap up to 50 psi immediately. There is a little niggle here however in that normally the oil pressure will rise to 75 psi on startup from cold, but we do have different oil this time. I'm using Motul 20W-50 in place of the old green tin Duckhams lookalike that I used to buy from Halfords. 

Secondly the engine is not running very cleanly, misfiring a little. There may be some investigation to do.

Dealing with teething trouble...

So this week, I've been out and about for another short ride, but first I refitted the Morgo pump. I did about 8 miles as usual, out of town and up to 40 mph. The lubrication job I did on the speedo seems to have stopped it sticking at full range.

The Morgo obviously provides more oil flow than the plunger pump, and I finished the journey with about 10 psi on the oil pressure gauge.

I also finished the journey with a completely flat rear tyre, which looks like it might be a valve failure. I wobbled along the road, complaining about the tramlines the council left when they resurfaced, only to keep my wobble, rapidly turning into a squirm from the rear end, when I ran out of tramlines. I recovered the puncture with a handy can of tyre weld I had in the pannier.

Of course, the low oil pressure problem is not sufficiently improved with the Morgo to use the bike in anger. Lifting the rocker covers with the engine running (rather dangerous - they are very hot) you can see little jets of oil coming from the rocker oil holes. I've fitted three new old stock rocker shafts to deal with the wear I found in the shafts last year - one was already fitted due to a damaged thread:

A thought occurred to me, corroborated by AOMCC forum members - retarded ignition causes overheating. Checking accurately revealed that the ignition was indeed retarded: I moved the distributor about 10 degrees, equating to about 20 degrees at the crankshaft, to get it right (thanks MikeN!).

So we will have to see what happens. Just waiting for a new inner tube...

Oil again

So, I have changed the oil.

A week or so ago, I was getting 55 psi on cold start dropping to near zero when very hot, using cheapo 20W/50 for running in. 

I worked through the clearances I measured when I built the engine, to determine the flowing areas of each of the bearings, to understand where my engine was in relation to factory minimum conditions - When I rebuilt the engine I replaced all the bearings in the bottom end, but only changed one of the rocker shafts, because they are easy to change and Drags only had one in stock. What I found was that I can improve pressures by changing the other three, especially if I can return the rockers to minimum clearance as well.

However, obsessive tinkering is something I have always been afflicted with. I wanted to change the oil, since I knew the viscosity at 100 C for both 20W/50 and monograde 50, which are more or less the same; viscosity at 40 C is almost double for monograde 50 over 20W/50, and I know my oil sits in the tank at about 73 C, so I expected a significant rise from changing to monograde 50.

Today, I started out cold with 55 psi and the relief valve operating, so I know I will never see more than 55 psi with the plunger pump. After a 4 mile run around town, its dropped to 25 psi hot (idling), and the relief valve is not operating, which is as I would expect.

So, situation much improved, but more testing required.

More on Oil

So today, we have something like 6 degrees Celsius outside. I've just completed about 3 miles around town and I have measured the oil temperature using a meat thermometer (not the one that was stuck in the Christmas turkey last week), and we have 73 degrees Celsius.

Please don't stick it in the Turkey

If you use one of these though, you will need to stop the engine first. The RF interference driven by the HT cables is phenomenal and stops the thermometer working at all. I guess the thermocouple wires pick up the RF.

Now, looking at the oil data sheets, we can see that the kinematic viscosities are similar at 100 degrees Celsius. Plotted they look like this:

This gives us a clue, but we can't get too excited because there are only two data points per grade. The temperature/viscosity relationship is not linear. Look at this, plotted on a logarithmic scale:

This gives us a better picture. Notice that the viscosity of the SAE 50 is about 20 cst at 100 degrees C, which agrees with the data in  the first chart, but that at 75 degrees C the viscosity is about 40 cst. That should give us about a bit more oil pressure for the same temperature than the 20/50W we are using now.

Oil & Oil Pressure

So this is one of those posts that we use to collect thoughts.

Amelia has done about 25 miles, and has had her head torqued down and the oil pressure relief valve spring replaced. She is running in on Tetrosyl 20w/50 multigrade oil, to API SE spec. When cold, the oil pressure gauge shows about 55-60 psi at idle speeds; after a 6 mile run around town, at speeds up to 25 mph or so, the oil pressure drops to almost zero at idle.

Darcy's Law tells us that flow through an orifice is proportional to the area of the orifice, the pressure drop across the orifice and the viscosity of the fluid.

The viscosity of the 20w/50 will be something like 18 centistokes at 100°C, rising to something like 135 cst at 40°C. After the run, the oil was visibly very free flowing and hot.

The relief valve may be controlling the pressure at idle - it may prevent the pressure exceeding 55-60 psi, but if this is the case it will have no effect at higher temperatures unless it is stuck open which seems unlikely given that the pressure displayed on the gauge falls gradually as the temperature rises.

Additionally, the effect is repeatable - the cold idle oil pressure is always 55-60 psi, and it always drops to near zero when it is hot, so I do not think we are seeing mechanical changes in the relief valve or the engine clearances - yet.

The Morgo is a gear pump which requires clearances between its gears to operate, and these clearances will allow more fluid to slip ineffectively around the gears when the viscosity is low. Are we right to fit gear pumps when the engine runs so hot?

And then there is the gauge. Ariel indicate that these engines should run at about 40-45 psi on SAE 50, so my gauge readings are not unreasonable, but we don't really know how accurate the gauge is or even if its accuracy is linear.

But one thing is clear - when the oil is hot (and we don't yet know how hot it really is) the loss in viscosity is such that the pump can push its full flow capacity (which itself may be compromised by low viscosity) around the engine without creating any pressure in the system.

And pressure is needed to prevent the bearing surfaces coming into contact with each other.

Another Four Miles

Well, I have had the timing cover off and the pump is solid, so I have stripped the relief valve to reseat it. Oil pressure after a four mile run today is much the same, as we await the new spring.

Still, she's running a treat and she looks lovely!

So to get my head around engineering behind the oil pressure regulator I need to confirm what size the ball seat is, i.e. the diameter of the oilway in the offside end of the front crank. The ball is 3/16", so the seat must be maybe 5/32"? I'm trying to understand what the spring rate would need to be for a given back pressure in the system.

For example, a 5/32" seat would give an area of 0.019 sq in. exposed to pressure, so a 1 lb spring would give me about 50 psi. My existing spring is not that heavy (its the original one, new one on the way) and, surprise surprise, does not achieve 50 psi on the gauge - thats assuming the valve is ever opened!

I plan to have a look and see if the regulator valve is used next time I run the engine, and I will have to find a way of calibrating the pressure gauge..

Latest trip

Well, a bit more news today, and a four mile trip around town. 

The fuel filter has gone back in the spares box to be replaced by a plain pipe and a gauze strainer in the carburettor banjo - all air locks now banished to the spares box along with the fuel filter. Apart from a very fast tickover, all seems well in the fuel department.

I've been looking at more loose ends. I had meant to look at the chain oiler screw in the primary case for a while, since the thread in the primary chain case was refusing to allow the oiler screw to pass through it. I measured it, found it was 2 BA and cleaned it out only to realise that the screw I had was just an old carburetter mixture screw and was way too short. This is what it is supposed to look like:

Thanks to Steve Clarke for this picture.

The clutch has seen some adjustment and a much better cleanup job on the splines. It's dragging a little, but a vast improvement over what I had. Changes whilst riding are noiseless - engaging first at a standstill is still noisy but much less so. By the time I had got back it seemed to have loosened up and needed adjusting again.

The electrics are all behaving themselves; the handling is also fine but as I have discovered before I need to keep an eye on the tyre pressures - 28 in the front and 24 in the rear seems to be about right, and the consensus of opinion canvassed on the splendid AOMCC forum.

I've re-torqued the head, as regular blog readers will know. Cold, the oil pressure is about 35 psi - but this dropped to about 10 psi with the engine hot, so do we think the relief valve could be due for a new spring? AOMCC wisdom suggests that the Morgo pump may have loosened off (thanks Mark) so we will have to have a look at that before the next trip. I will get a new spring for the relief valve as well. It's getting properly hot now, but the engine is quiet and I have no exhaust or oil leaks.

Looking forward to the next trip!

Mighty Morgo

Today I fitted the Morgo oil pump made by Autovalues Engineering from Bradford.

The Morgo is a gear type pump, and is very nicely manufactured, well packed and is provided with a comprehensive set of instructions. While there are several Morgo rotary pumps for other Ariels & Triumphs, the fitting kits and instructions are bespoke to the model you are fitting. Very nice quality, well thought out.

The pump comes with a fitting kit, consisting of the left hand drive nut, a set of shims, a gasket, two tab washers and two mounting bolts

This is the drive side of the pump, showing the Oldham coupling used to drive the pump from the camshaft.

And here is the drive nut for the pump. Those slots are closely toleranced to prevent rattles and wear

Here it is in place. I've got it fitted with the original studs at the moment, since I don't like the idea of wearing threads in the soft crankcase to remove a service item but in practice you have to engage the pump coupling before bolting up - it is close fitting in its slots, as it needs to be, and this makes the bolts supplied with the pump the only practical way of fitting it.

I need to prime the pump - so I will refit it with the bolts supplied with the pump.

Time for a list.

I'm getting confused, there seems to be a lot of stuff going on, lots of bits laying about, lots of work faces.

Whenever life gets like this, I like to make a list to get my head around where I am.

So the engine is more or less apart:

• the crankcases are dismantled & roughly cleaned - the oil pick up pipe is still in, the bushes & bearings are still on. The dynamo strap is off and needs replating; the timing side bushes are still in tolerance but are flaking, so will have to be replaced. Either Bernard Ashpole or Colin Reed Apsley will do this for me. The roller bearings look good but will be replaced anyway. The camshaft bush is in tolerance but will be replaced; then there is the question of whether I polish the crankcases. I kind of like the contrast between the polished timing cover and the faded grey cases.
• then there is the question of modifications - the Morgo gear pump, the camshaft spraybar, the valve stem seals, and the oil filter.
• I'm thinking that the additional flow from the Morgo pump will let me flow more oil to the rocker box and down onto the camshaft, rendering the spraybar superfluous. The valve stem oil seals will help avoid that extra oil going down the valve guides. The pump will also keep the oil to those far-off journals flowing at sufficient pressure
• The oil filter is a must to avoid the sludge traps filling up;
• The oil cooler seems inappropriate since club wisdom suggest that the oil will not get warm enough anyway, and the cooler will not be used. The more onerous issue seems to be to get the engine heat into the oil in the first place.
• the camshaft shows a small amount of wear on the peaks; the journal for the crankcase bush is wearing unevenly and is on the low side of acceptability. We'll probably get this reground and make a bush to suit.
• the front crankshaft has been cleaned and a preliminary clean performed on the oil ways. The big ends refuse to be shifted - I am waiting for a thin wall socket to get them apart. The timing side journal is within tolerance and is in good shape. No.1 big end rocks a lot more than No.4; No.1 little end bush is out of position - it's protruding beyond the rod eye and the oil hole is misaligned.

• the rear crankshaft is waiting attention; the timing side journal is within tolerance and is in good shape.