FH - ignition timing

 Edging ever closer towards first start, I diverted myself from wiring activities to time the ignition.

Regular readers will know the rocker box isn't fitted yet, and I can tell you that it's much easier to set the engine in position for ignition timing without pressure from the valve springs trying to restrain you.

As I've fitted 7.25:1 pistons to this machine, I am timing it to Cyclone specification - 3/8" BTDC at maximum advance in place of the 11/32" for the home market models. Here it is on the ubiquitous Wagamama chopstick, of which I have hundreds:

The timing is set with the timing side piston at 3/8" BTDC on the compression stroke.

With the engine in the right position, I fitted my little clamp to hold the ATD at full advance. The ATD is screwed most of the way on, but is not yet on the magneto shaft taper:

With a green Rizla in the points, I can rotate the magneto until the paper just loosens in the points. It's useful to have a 4 BA spanner available to just hold the magneto shaft on that central bolt while you gingerly tighten up the ATD nut from the other side. With the petrol tank off, it's easy to reach the magneto from the timing side of the bike.

Next, fully tighten the ATD nut. You can then back the engine off and come back up to 3/8" BTDC; if the Rizla is just coming loose in the points (with the ATD still clamped to full advance), you are good to go.

FH - followers, pistons and barrels

 With the little QR50 out of the way and the FH back on the bench, we can get on with the build. The barrel has been painted for a while, the bottom end is in the bike, there's no primary or timing side and no pistons. Off we go:

First step is to fit a circlip to each piston; the gudgeon pins come out with some mild warming and are refitted just as easily. As you can see, I've put a large rag under the pistons as I don't want a circlip in the crankcase at this stage, and the pins go back in and the circlips go on without any drama.

Next, we can refit the reground cam followers. I've ground the radius back into these such that they now have no wear grooves. The retaining screws and pins (with the missing ball) have been refitted:

Next, we fit the ring compressors - these are just strips of tin held in place with ty-wraps. These were cut for the SQ4 and are not really long enough for these larger pistons. You'll see the wood - these are to prevent the pistons rocking about when the barrel goes on.

Before the wood strips go in, we squirt oil all over both small ends. 

The wood strips are wide enough to completely stabilise the pistons while we put the barrel on, but first we use Threebond 1215 to apply the base gasket to the barrel, to keep it out the way. This wasn't ideal as I was forever wiping gasket goo off my gloves -  it would have been better to have the gasket, goo down, on the crankcase and apply the goo to the upper side after the barrel was over the rings.

After a lot of fiddling, swearing and anguish the barrel went down. The compression rings were not too bad but the three piece oil control rings, with their thin 'rails' were a pain to get in as they popped out of the compressors before they were caught by the barrel.

They went in eventually, and we can retain the barrels with four nuts.

FH Barrel

 While waiting for the kickstart rubber, I've degreased the FH barrel in the cleaning tank and given it  good scrub and scrape. Removing the rings from the new + 0.060" IMD pistons and testing them for fit reveals a nice 0.004" clearance in both barrels, per the IMD recommendation.

Therefore, it's time for a coat of engine paint. This is the same stuff I used on the W/NG which seems to have survived OK:

FH - Plastiguage and the big ends

 Next step is to check the big end clearances. I've measured the journals, but I wanted to get some evidence of the clearance that I had ended up with after fitting new -0.030" shells. There isn't much detail on what the acceptable clearance is  before you must regrind, other than the data describing the sizes you regrind to and the recommendation that there should be minimal clearance after regrinding.

Waller indicates 0.003"- 0.004" for the big end shells used on 1948-1955 Square Fours (Fifth edition page 37); Phil Irving quotes 0.001-0.0015" clearance per inch of diameter (Tuning for Speed 3rd Edition), which equates to 0.00165 - 0.0025" for my 1.65" big end. Mr. Irving, otherwise known as 'Slide Rule' using those delightful pseudonyms beloved of motoring writers in the '40's, also notes that the clearance can be much larger as long as oil pressure is maintained.

So, let's introduce Plastiguage. This is a paste, extruded into rods a bit like Plasticene. You trap a bit in the bearing and squash it, so that the known Plastiguage rod diameter is squashed to take up the clearance of the bearing - you then use the card provided to determine the clearance from the width of the squashed Plastiguage. Plastiguage comes in different sizes to measure different clearance ranges.

So, you cut a length to suite the bearing like this, and then you make up the bearing. You make sure the bearing is clean first.

When you open the bearing again you can see the squashed Plastiguage and you can compare it to the card. This suggests something like 0.002 - 0.0025" clearance for the drive side. I'm happy with that.

This is the timing side, and it's about the same:

All good there then. Next job is to make sure the oil flows into the big ends. I'll inject it into the timing side oilway:

And it comes out the drive side big end!

During this process, I removed (with a little heat) one of the gudgeon pins from the new IMD 7.25:1 pistons I got from the AOMCC so I could check the fit in the connecting rod little end bearings. This proved to be perfect once I had cleared a small burr from one side of both bearings; not sure how that came to be there.

Happy days.

W/NG - An unexpected event

A few weeks ago I was cracking on home on the W/NG, doing 55-60 up the North Walsham by-pass (the old Midland & Great Northern alignment to Honing) when she suddenly cut out. After finishing the ignition checks I kicked it over to find apparently no compression. I popped the exhaust valve cap off for a look, found nothing and a few minutes later she started OK and carried me home apparently fine.

Stuck valve perhaps? She was pretty hot...

At home, I put the endoscope down the bore for a look and it was clear there had been a partial seizure at some point. Thinking about it, there had been a squeak from the rear tyre and a little shimmy at the back end, and I'd had the clutch in very quickly.

Pulling the head off you  could see the scuff in the bore very clearly:

The rings were OK, apart from the fact that the second ring was tight in it's groove. Hardly surprising really:

Rightly or wrongly, I polished this out. Doubtless someone will tell me I should have replaced the piston.

I built this tool to hold the barrel while I honed it - it's just a couple of bits of plywood:

You can mount it in the vice either way, but this is the most convenient for honing. I mounted it vertically to grind the cylinder head to barrel joint.

I used a cylinder hone to clean up the bore. Hopefully these honing marks will retain a bit more oil...

I also replaced the inlet valve guide which was very loose - the new one had an interference fit in the head but was a smaller bore size - too small for my valve stem. I bored it on the lathe to change the diameter from 5/16" to 3/8", but writing this post I've realised I probably have an exhaust valve in the inlet position... 

Anyhow, it's all gone back together and is running beautifully, apart from a pesky leak from the decompressor. I've reverted to fibre rocker box gaskets (I can't get the aluminium ones to seal) but I've still got a weep from the decompressor, which has a very worn stem. 

It'll take a bit of work to fix that as I want to re-engineer the sealing arrangement, but that will have to wait. It's been OK for the last 70 years. 

QR50 - engine top end

One of the things that was apparent from the beginning that the piston needed replacement, as there was a large crack in the skirt. I measured up the bore and determined that the bike was still on the standard bore, and bought a new piston assembly from ebay - new rings, circlips, piston and pin:

Fitting wire circlips is always a bit traumatic. I did lose this one, found it again, and fitted it successfully the second time:

I resprayed the barrel with B&Q barbeque paint, as I used on the exhaust. We'll see how that turns out!

The original head had a lot of fins missing. This one came from eBay:

W/NG - Barrel & Piston

The piston that came out of the W/NG surprised a few people. It looked like it had been wire wound at some point in it's life. It was flat-topped and had an oil control ring, both features that differ from standard.

Here's a new +0.040" Ariel piston - new old stock, still in it's original wrapping, from AOMCC singles spares. You'll see it has a raised crown and three compression rings.

The old piston was not in a happy place when it came out. The top ring was in at least three pieces - at least, I found three pieces. Not enough to make a whole ring...

The small end was also in a pretty bad way and in fact the rod eye turned out to be oval. The bush had no oil slot cut in it either.

I had the barrel rebored and honed to suit the new piston by L.A. Whitmore of Briston, Norfolk - an excellent little company which unfortunately is no more. The rebore took out most of the wear.

Much later, after I had finished the bottom end I cleaned up the barrel using my bench-mounted and my flexible wire wheels. There is actually a fin repair here as well - that must have been done in Italy.

I followed this with two coats of engine enamel from Paints R Us which appears to be excellent. We'll see when it has been in service for a bit.

For my next trick, ladies and gentlemen, I will replace the barrel studs after cleaning them on the wheel. I've put them in with Loctite 243 medium strength thread locker.

I need to check the rings. They are all showing a 0.012" gap - rather large, but well with Ariel's 0.030" limit and they are very difficult to measure as they are cut at an oblique angle and consequently any sideways movement opens the gap.

Next, I'll check the fit of the gudgeon pin in the small end. It slides in easily with no rattle; as I would hope. Alpha Bearings reamed this to Ariel specification and made a bush to suit the small end eye.

Five minutes with the Rothenburger has the piston warm enough to receive the pin and a few seconds later it is on. Next job is to fit the circlip - but cover the crankcase mouth before you try. The circlip is bound to ping off somewhere and the last place you want it is in the crankcase.

Don't try this delicate operation without gloves if the piston is still warm, and make 100% sure the circlip is seated correctly:

I don't have a piston ring compressor - I maybe should have bought one but ever since building BMC A series engines when I was much, much younger I have used this approach - a strip of tin and a ty-wrap. Works a treat if you get the tension on the ty-wrap just right for the barrel to push the tin down and off the rings, and it's dead cheap for when you need four of them.

See? all fitted with no drama, though since writing this I remembered I had intended to fit the engine plate covers before the barrel went on - access is a bit more restricted now.

That's Morris SAE50 in the bore. Next job is to time the ignition, finish fitting the magdyno and the chain cover and start preparing the cylinder head.

W/NG - time for some serious engine attention

As some of you may know, the W/NG hasn't been too happy recently - it's been consuming spark plugs at an alarming rate and has caused several unscheduled stops by the roadside - particularly annoying, because I'm lucky enough to live by the sea and a bike is the best choice of transport in the summer - you will never find another parking spot for your truck again if you choose to move it.

So, the W/NG is the go-to machine for local use, until it decides it isn't going to play nice any more. Next up is the SQ4... which has a flat battery and knackered points (my fault - embarrassing story), so now I know what a garage full of dead Ariels looks like:

So I've pulled the W/NG apart.

The rocker boxes come off easily. There is some head damage around one of the bolt holes, which I will probably leave well alone:

The piston is an oily mess and the top ring is in three pieces:

The small end is cratered but is dimensionally OK. I've not measured the pin or the piston yet, but the bore is 2.871 in the middle of the stroke (fore and aft direction) which is getting on for 40 thou over factory standard. There is no ridge at the top, so we will have to see what the piston dimensions are.

The valve guides are awful. I've not measured the valves yet, and I have no way to accurately measure the guides but the exhaust valve rocks maybe 1-2 mm at full open, the inlet maybe half that. The inlet guide is loose.

Then there is the big end. I can feel up and down play of maybe 0.5 mm; side to side rock is maybe 3 mm at the small end.

All in all, a good afternoon's work. A lot nicer than the morning, which was spent pulling one of these apart: