FH Dry Build - Barrel and Head

After completing the primary case installation, I moved on to the head and barrel. This was pretty straightforward, and I retained the head and barrel in place with a couple of bolts each, though the threads will need cleaning up when I rebuild the engine.

The main purpose of this step is to establish fixing points for the exhaust, carburetter and head steadies. The head steadies fit to two of the downward facing rocker box studs and its clear that the existing ones are fretted quite badly and will need replacing.

Secondly, the kit of parts I bought all those years ago included a brand new Amal Concentric Mk1 928 carburetter so it will be interesting to see how that performs - it will be a new experience for me. The FH was intended to have two bolts holding the carburetter in place, but unfortunately the large tickler fitted to the 928 prevents one of the bolts going in - it will need a couple of studs making up or I could use the 5/16" CEI x 1 1/16" stud specified by Ariel for the iron head singles under part number 0183. 

Removing the barrel

Next stop, remove the cylinder block. Nuts are stuck fast, so we need a dose of Plus-Gas:

This is the 3/8" flange barrel used by Ariel throughout Huntmaster production, and by BSA until the 1/2" barrel flange appeared for the 1955 A10 Road Rocket. Poking around waiting for the Plus-Gas to do its job, take a look down the pushrod tunnels:

That's a leaf, possibly hawthorn... How did that get in there?

Nuts undone, we need to break the red Hermetite sealing the base gasket. This won't take much force and I'm not overly worried about the pistons anyway, so we'll do it like this. Two bolts in head bolt holes, either side of one piston; a suitable bar between them (if this had been remotely reluctant to move I would have made a stiff bar out of a bit of angle or something) and a lump of wood on top of a piston.

A quick tweak on the crankshaft has the block pop up - but it's not all plain sailing. The timing side piston sticks at the bottom of the bore, in the rusty unworn section and takes a bit of persistence to remove it. When it comes off, we find these rather worn cam followers:

A look at the flywheel reveals this is the earlier, smaller, built up crank used until 1958 - perhaps not surprising in that this engine is marked 'LF' and is clearly a 1955 design. The crank has no radial bolts in the flywheel like the later 'large bearing' cranks.

Ariel adopted the large bearing crank in 1958, when BSA rationalised it across all A10 models; the large bearing crank initially appeared in the 1955 Road Rocket.

Here are a couple of general views. The engine has been fairly damp inside for a while:

We'll have a closer look at the camshaft later. I've seen worse.

However... have a look at this video - it's as though someone forgot to put the shells in!

Measuring the bores

Before we get into the rest of the strip down, lets have a preliminary look at the bores. From up here they look really clean - there are no ridges at the top of the stroke:

There's a bit of a clonk when you turn the engine over.

Right now I am hoping that is in the timing chest, maybe a loose dynamo chain. Offside piston crown has been scratched by some exuberant decoker in the past:

Nearside piston crown is much the same:

Onto the bores - I measured them each in two positions, at the top and at mid stroke with a comparator and a Moore & Wright 2" - 3" micrometer. Both measurements were in the fore & aft direction which should be worse than the transverse direction:

Here are the results of my preliminary measurement:

• Offside cylinder, top of piston stroke, fore & aft: 2.818"
• Nearside cylinder, top of piston stroke, fore & aft: 2.815"
• Offside cylinder, middle of piston stroke, fore & aft: 2.826"
• Nearside cylinder, middle of piston stroke, fore & aft: 2.822"

Nominal standard bore is 2.755", so these are a 60 thou overbore which would have been 2.815". We'll measure the bottom of the stroke when we get the cylinder block off - we can measure the pistons as well and decide what we are going to do. Sixty thou is the maximum oversize so essentially if these are too far gone we will be resleeving this barrel... These Ariel barrels are not the same shape as the much more common BSA A10 barrels on which this engine design is based, and we are unlikely to find a better one.

I'm told these dished pistons are not available either, so we will be looking at flat topped pistons and an increase in compression ratio...

Looking at what we've got...

With the engine on the bench we can have a good look at what we have.

First issue: one of the primary case bolts is broken in the crankcase. We probably won't be using these cases (I have the original crankcases elsewhere, these are not them!) I may not worry about this - but I will probably remove the bolt just for the fun of it. What's worse is the state of those splines:

Nothing untoward here - that hole is for a blanking plug (thanks to Simon Gardiner, AOMCC, for that bit of information)

The sump plate, filter and studs are all missing:

Looks like it has most of it's original screws:

Long magneto bolt:

Unfortunately it appears we have a broken fin on the front of the cylinder head. This may have been caused in a shunt since this is where the head steady bolts on I think.

Bird's eye view of the rocker box:

General views of the engine:

Servicing begins

Well, its been a beautiful day here in North Norfolk, the sun is shining, it's quiet but I have spent most of the day in the office. A lunchtime walk revealed the tide out and an empty beach, just to underline how lucky we are to live here.

I had a couple of hours spare in the evening to repair some floorboards and make a start on servicing the Square Four. I had a number of jobs to look at before the summer season, so stripping had to start.

Its always a bit of a fiddle to get the oil pressure gauge line undone, and as usual I used only the tools I carry on the bike. This revealed that you need two 3/16" BSW open spanners, so I added another to the tool kit. Once the tank was off, I planned to remove the plugs, carburetter and distributor in order to re-torque the head and cylinder bolts.

The spark plug spanner I made last year is intended to replicate the one in the spare parts list, and it works well in getting to the number two plug which is now confined by the new bi-starter parts:

The plugs themselves, one to four from left to right are a little sooty; we will keep an eye on that, but there is no evidence of any oiling. The oil comes from the weeping head gasket!

Once I had the carburetter off, I was able to tackle the head bolts with the usual variety of spanners including my new baby torque wrench, using the torques Ariel specified.

I was able to get a half turn on most of the bolts, which I expected.

I planned on removing the distributor to turn it through 180 degrees, to put the condenser 'bulge' near to the oil tank and give myself enough clearance for a carburetter insulator. Having done this, and attempted to re-time the engine I realised that the position of the distributor did not now allow it sufficient movement to adjust the timing. Furthermore, there was no way I could add a carburetter insulator without new manifold studs - so back to square one.

However on putting the distributor back in I realised it was not turning freely - so off it came again. I found that the shaft was so stiff I could barely turn it by hand. It freed off, with WD40 and some light oil, but how was it intended to be lubricated? I could see the 3/32" hole in the body, and the milled flat down into the drive housing, but there was nothing to introduce oil to the shaft. Was I missing something? I think that there was a modification in this area for the Mk2?

Actually the modification Ariel recommended was to allow oil to drain out of the distributor but Paul Ptak, on the AOMCC Forum came to the rescue. He said:

Pull the rotor arm off and drip some light oil into the shaft? The machine screw under the rotor arm is drilled though and I believe the shaft is cross drilled to allow the oil to get from inside the shaft on to the bushings.

Why didn't I think of that? I've done it hundreds of times on distributors on various cars... I must be losing the plot. Thanks Paul!

So that was almost it for the evening. I didn't fancy rebuilding the distributor (good thing - I was obviously tired) but I did try the new-first-paint tank in place:

And I also stared to look at various missing clips. Having bits in stock, especially fasteners, is a wonderful thing. These are from Draganfly:

 Here's one I made earlier:

Obviously needs a hole and some paint but we will replace the one holding the brake cable to the mudguard with this.

Cylinder Head Assembly

So, I have most of the parts to replace the head, apart from the high temperature sealant recommended by Bruce Longman. Over the past couple of days I have fitted the new head studs:

The thread into the head on later engines is 3/8" BSW, and there is a parallel section on the stud which has to engage with a counterbore in the head. You can see these here:

As the head had been skimmed, much of the counterbore had been machined away. To deal with this, I recut all the head stud threads and remachined the counterbore. Hours later, I have all the head studs in place. After I'd done all this work I ran the 5/16" CEI die down the eight studs in the block, just to make sure there would be no trouble when the head went on.

Next up was the polishing. It's fairly clear from the state of the casting that the fin edges, the 'V' along the top of the exhaust ports, and possibly the sides of the rocker box were polished - maybe also the carburetter flange. Personally I'm not sure that Ariel would have done this, since the rocker box sides would be quite difficult to polish without resorting to small buffs and hand work - there is no access for a polishing wheel, so this would have been time consuming & expensive. I've polished the fins for now; I also like the contrast between the polished rocker covers and the unpolished rocker boxes.

Final thing is the assembly of the rockers themselves. These are all back in, with a couple of replacement shafts (thread damage). One of these went in and out several times - and turned out to be too large on the OD, and with the two grooves for the 'U' washer in the wrong place. The best of the old ones went back in and the replacement will go back to the supplier.

So, now I am waiting for the high temperature sealant and the head can go on!

Reciprocating Engine

At last we have a reciprocating engine again.

 

Yesterday, pistons prepped with tinplate/tiewrap compressors, block ready with new gasket stuck in place with Threebond.

It took 6 hours over two days to get to this point. I'd get the block over all the compression rings, and it would persistently get stuck on number 1. After five attempts, which included checking ring radial thickness again, I realized that the 2nd ring on No. 1 had no shiny filed surface on the end - it was straight out of the box and had not been gapped at all.

That's what comes from working sporadically over several weeks. You need military precision on your record keeping, and to meticulously check & recheck what you did yesterday...

Here we have it all bolted down, with Threebond oozing out & Clay Jones shiny stainless steel nuts holding it all together.

 

Magic.

Rings...

So the block is now ready to go on - it's time to gap the rings and fit them to the pistons.

I bought my rings from FW Thornton after asking both them and JP in Australia to quote. I had asked Drags as well, but the GPM rings they supply require the ring grooves to be machined to depth - and wisdom from the AOMCC forum suggests this is not easy.

So, having a modicum of engineering knowledge and some measuring tools, I read up on rings & piston design courtesy of Mr. P Irving's writings and set about sourcing the rings from basic dimensions. Duncan Rowley (who is a very helpful chap) at Thornton's came up with this set of rings from my dimensions:

We have our rectangular top rings:

And our Napier pattern second rings (this one is upside down):

And the oil control rings:

Speaking of which, don't forget to clean out these holes:

These are there to clear the oil which the oil control rings scrape off and return it to the sump.