Wednesday, 31 October 2018

Timing chest

These are the weapons we'll use to attack the timing cover. The original screws are all intact and most of them are in pretty good shape. I'd ground my largest impact driver bit to fit in the screwhead recesses without causing damage:

Half an hour later. Beats me why people insist in putting gasket sealer in screw holes.

A general view. No obvious horrors so far:

This is the early Mazak pump. Take a close look at the upper mounting bolt - there appears to be some little gremlin sitting on to of the pump. I wonder what that is?

The dynamo drive:

I thought this chain was supposed to be endless?

Before I start cleaning this up, let's have a look at the magneto & the auto advance unit. In this video, I have not attempted to remove the auto advance from the magneto. That movement is all in the AA unit and the magneto spindle:

Oh dear...

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!

Monday, 29 October 2018

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 worn 60 thou overbore. 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...

Saturday, 27 October 2018

Starting the Engine Strip

Inspection starts with a look at the rocker box. Both covers are present, one has it's captive nut, one is missing...

Here's an ugly looking stud and some cornflakes gaskets for general amusement!

All is well at the inlet. The cover stud is seized to the nut and has come out with it:

Removing the exhaust side stud with two 5/16" BSC nuts locked together:

Removing the inspection cover studs, we find one elegant Ariel stud with BSC threads at both ends, one 1/4" for the nut and one 5/16" for the rocker box. The other one, which has no nut is bent and is 5/16" both ends, one BSW, one BSC. Obviously a replacement but a shame, because the thread in the rocker box has been recut BSW. I'll be making a special on the lathe.

A stripped stud retaining (or not) the rocker box at the rear. Steve Carter, an AOMCC member who rides thousands of miles each year on his Huntmasters, uses a bolt here to avoid the worry of losing that nut down the pushrod tunnel:

General view of the head mating surface. All the springs look good at first glance:

Here's the underside of the rocker box:

More cylinder head general views:

Quick shot of the underside of the head. Looks OK, bolts were very tight but came out with some effort:

Bores and pistons. After I took this shot I gave them a quick clean up - the bores are unmarked and have no ridges; pistons have no undersize showing.

These are the dished pistons. Simon Gardiner (AOMCC) tells me that dished are the 6.5:1 standard pistons; if they had been flat-topped, they would be the the export/sports 7.25:1 pistons.

Friday, 26 October 2018

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:

Avoiding injury...

Planning the FH rebuild I could see i was going to have a problem with lifting the engine onto the bench and having no wish to impose any pain on my long-suffering wife by enlisting her help, or injure my back  by not enlisting her help, I decided that a hoist was in order. I bought this 1000 kg chain hoist from eBay and fastened it to a heavy piece of pipe in my roof beams. The hoist will do a 2.5 metre lift:

After finishing the chair repairs you see in the picture above, I lifted the engine onto the bench to start work using the hoist, which made short work of the lift and saved my back. I lifted it using the top gearbox stud which put the centre of gravity more or less in the right place for a level lift:

Some while back I bought an engine stand and described it in this blog post:

It's quite flexible. I decided to use one of the lower front engine mounts and one of the rear engine mounts; I made sure the stand was aligned with the engine centre line to keep it balanced. Using the hoist, it was easy to get the engine upright once the stand was in place:

Here it is, ready for some inspection & a bit of dismantling:

Saturday, 20 October 2018

Oil, socks and misfires...

Some of you may know that I have been troubled by misfires just recently to the effect that the good old Solex has been stripped more times in the last month than in the 70 or so years since it was manufactured, and the distributor is not far behind.

Link in the oil line modification I did a while ago, and the calorific nature of the engine's energy-conversion activities and a pattern might start to emerge, especially when a lot of those misfire-ridden journeys occurred when we were blessed with warmer weather.

Lo and behold, one day I was working through the ignition system and removed the HT leads, to check them over and apply some heat-shrink numbers to the cables. It was then that I found the oil, sitting in the five little pots on top of the distributor cap and manfully attempting to insulate the distributor from the HT leads, and succeeding some of the time.

Since I cleaned all this out, I have not suffered a misfire (but the weather has turned colder, so no pre-natal poultry accountancy services required just yet).

Ariel knew about this problem, providing a rubber sock to protect the distributor connections from oil and water:

Distributor sock 5239-49

As you can see, its a curved tubular cover which envelopes the whole distributor cap and leads in one conical tube. Here's one, fitted to  'barn find' machine.

And another - though this one looks like heatshrink to me:

No, this is not the Sorting Hat from the Harry Potter movies. It's a shroud I've attempted to make from a very large piece of heat shrink:

It looks marginally better in this picture:

Here are some close-ups. It goes right up under the tank, passing over the tank mounts:

I'd really like an original one, but for now this is doing the job sufficiently well to prove the case for the cause of the misfire.