FH - more shims & trimming nuts

 Following Thursday’s abortive first attempt, I pulled the cases apart again for a look at the big end nuts and to fit another shim to the drive side main bearing.

Roger Gwynn, all round guru, Ariel Hero and founder of Draganfly Motorcycles (without whom us Arielisti would be lost at sea) told me on the AOMCC Forum that the big end nut/crankcase clearance is close in these engines but you don't need to remove much material to avoid a clash. Roger recommended grinding some material from the cases.

What I've done today is make a 1 mm chamfer on the offending edges of the two timing side nuts, so now I know what clearance I need to provide. If I can provide that clearance without modifying components I will be a happy bunny.

Club member Mick suggested that the fact that no bolt thread protruded beyond the nut wasn’t satisfactory, since the locking part of the nut was probably bearing on a reduced (tapered) part of the thread:

I've ordered a new set of nuts, still self locking but to a slightly shallower pattern (still big end nuts, not something nasty) and I'll use these with larger but thinner washers I think. That will guarantee the self locking bit of the nut is on the full diameter of the bolt thread. I’ll probably have to make the washers myself on the lathe.

Meanwhile, adding a 0.1 mm shim to the 0.25 mm shim already there has given me 0.07 mm end float, or about 0.0027”.

That will do nicely.

FH - Assembling the bottom end

 With the crankshaft together and the few internal components of the crankcase assembled, it's time to put them together. First step is to thinly coat the mating faces with Threebond 1215:

With the cases bolted together, we can measure the end float again. This time we have 0.18 mm - last time we had 0.34 mm, and I added one 0.25 mm shim under the bearing. Something has changed, or I have made an error because 0.34 - 0.25 = 0.09, not 0.19...

That's 0.0075" - we are aiming at 0.005". I'll see what shims I have in stock.

The next challenge comes when we check crankshaft rotation - it doesn't. There are two clashes one on the rear of the case, one on the front; the rear is a scrape that allows the crankshaft to move, but the clash at the front is more serious and prevents movement altogether. You can see the witness marks in the picture - this is probably the big end nuts fouling the crankcase:

That's coming apart again.

FH - Engine bottom end

 While the painted parts are away, I've got the engine on the bench. Way back when, I established the state of the bores, mains and big ends and what I want to do now is to trial fit the new large bearing crank into the original cases.

A little while in the kitchen at home saw the main bearings fitted:

It's then no more than an hour's work to assemble the crankshaft and the timing gear; the good news is that the timing gear bushes already in this case are in very good condition with very little play. Shame I already bought a new set.

It was clear that the crankshaft was a bit tight. The setup with the DTI reveals no end float and the crankshaft was mildly stiff to turn, but then it does have a large plain bush at one end:

Investigation revealed that the drive side bearing wasn't fitted fully home against the crankshaft web. With that fixed, we have 0.34 mm end float:

That's about 0.013"; we want a maximum of 0.005", according to BSA Service Sheet 208 - Waller is silent on the subject. Since 0.005" is 0.13 mm, we need to shim 0.21 mm; I've bought 0.25 mm shims which should give us 0.09 mm end float, or 0.003".

More later when bits arrive.

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.

End Float

So now we have the crankshafts, rods and cases assembled:


Ain't she pretty?

Next stop, setting end float. Not a difficult job, but you'll need a supply of shims and the right kit to measure the end float.

The Square Four is designed such that the timing side bushes form the datum against which the end float is measured. Many current machines are also built such that the timing side bush is responsible for taking any end load (there shouldn't be much) from the crankshafts into the cases, since most folk fit main roller bearings without the original lip.

The load is taken into the bronze face shown here. This is the rear crankshaft:

The front one is similar:

Excuse the picture quality. Blackberry camera - 'nuff said.

There is a large, thick washer fitted of the end of the crank to take the thrust into the bush:

The shims shown in this picture fit between the large washer and the end of the crankshaft, and hence the gap between the crankshaft and the face of the timing side bush. This is the 'end float' and should be in the limits 0.002" - 0.004". Draganfly stock the shims.

This is how you set up to measure it:

Here, the dial test indicator is set up on a magnetic base fixed to one of the engine plates, which I have temporarily fitted to the crankcase for the purpose. You can move the crankshaft by hand, to & fro, and the DTI will show you how much it moved. You add shims until you have the movement to spec. If it doesn't move... you probably have the bush nipped up between the crank and the washer. Add all your shims! Take them away until you have the right clearance.