FH - reassembly

 Having checked the pistons, looked at the big ends, camshaft and followers I was ready to put the barrel back in place.

First step is to Wellseal the barrel flange and stick a new gasket in place. I decided it will be easier to have the gasket on the barrel with well seal both sides before introducing the barrel to the crankcase.

Attempting to refit the barrel over the pistons revealed something interesting and that I had not spotted before - there is no lead-in chamfer on the bottom of these barrels making it very difficult to get the rings into the barrels. I used a half round file to make a chamfer of maybe 1 mm, much smaller than is commonly found on cylinders but it made all the difference.

The cylinder head went back on with Wellseal on both sides of the head gasket. I put the bolts in with Copperease and tightened them down as tightly as I could with a 12 in ratchet drive.

I've fitted and removed the rocker box several times now, and I know the optimum way to do it. Fit the gaskets to the head and apply your chosen sealant to both sides, then fit the rocker box from the front right direction remembering to trap the two exhaust push rods either side of the web in the middle of the inlet side.

I hope no one sees this as an act of wanton vandalism but I have removed one of the vestigial fins from below the rocker box, because they are an absolute pain. When they are in position, you have to put these two nuts on before the rockerbox sits down on its gaskets, because the shape of the casting means that you can't get the half nut on with rocker box fully down. One of these things was missing when I got the bike and I have just removed the other one.

I must remember to clean up that area next time the head is off.

With a bit more spannering, the head steadies are in place and the oil lines are connected. We will end this blog post here as this concludes the work on the replacement of the cylinder head.

FH - oil from the drive side cylinder

 I might have mentioned a few times that the Huntmaster has been burning oil from the drive side cylinder, manifested as an oily exhaust pipe, and oily spark plug, and smoke when pulling away. It's always done this ever since rebuild. I had been hoping that this was just really bedding in but after 550 odd miles I think I have to admit there's something wrong. Since it's back in the workshop for its 500 mile service the rocker box has to come off anyway to retorque the head and we can do some investigation.

I had hoped that the rocker box drain might be blocked and excess oil being sucked down the exhaust valve guide but a poke down the drilling with a bicycle spoke reveals the hole is completely open - as I had expected since I cleared the hole out during rebuild.

Removing the head revealed this - a bit of an oily mess on the drive side (that's on the right of the picture) and a fairly normal looking though dark combustion chamber on the timing side.

And then this! That bare piston crown is the drive side, the one that is smoking. There is barely any carbon deposit there at all compared to the other side which looks quite normal to me. It should be noted that the mixture is quite rich at the moment as the mileage is not really high enough to do any proper plug chops.

This is the timing side exhaust valve.

And the drive side exhaust valve, looking a lot hotter.

Here is the upper side of the head gasket - that is the side that touches the head itself. The area within the red ring shows I think a leak from the cylinder into the head bolt drilling and possibly into the drive side exhaust valve drain. Perhaps this explains both the smoke and the oil coming from the cylinder head joint and dripping onto the primary drive case.

It pays to be careful when removing the cylinder. I released all the nuts and made sure that I collected them all with their washers and put them aside. Next we used the leather mallet to loosen the cylinder joint which was quite straightforward - not forgetting that the forward magneto pickup has to come out to remove the cylinder. 

It's wise to lift the cylinder with the pistons in their uppermost position so that you can lift the skirts above the crankcase mouth to get a couple of pieces of wood into the joint to support the weight of the cylinder. You can then introduce a suitable cloth into the gap to prevent any broken bits of ring or circlip falling into the crankcase. 

Once you have lifted off the cylinder the wooden battens can support the pistons.

Removing the cylinder very carefully reveals two pistons in very good shape - to be expected since they have only done 550 miles. The purpose of this exercise of course is to check that the rings are sound and indeed they are so we can take some comfort in the knowledge that the results of the compression test we did months ago are supported by rings which appear to be in very good condition.

Investigating the head gasket sealing area and the bolt holes reveals a couple of interesting points. Well, one main point really and that is that most of the cylinder head bolts open into a gap between the fins, a few fins below the head joint and secondly that one of the front middle two bolts doesn't pull down properly as the thread appears to be very tight. This is in the area where we suspect the leak to have been.

We will leave this for now as I have a day on the railway tomorrow and some other bits to do. I've made a post on the FH Facebook group to make sure that I've selected the right tap to clean these threads out!

FH - more tinkering?

 Another little ride out today - twenty miles around the local countryside:

Starting easily, it's running a lot less busily with it's raised gearing.

The brakes are feeling much better now - there's quite a lot of travel but they are certainly biting.

The steering head bearings are very loose - there's a lot of juddering on braking. There might be an oil leak from the cylinder head area - there's a drip on the front of the top of the primary case, coming from the barrel, and there's some oil at the back of the barrel.

It seems to be quite smoky on the drive side - I'll keep an eye on this.

Everything else seems to be working well though I think I can hear the ignition hardening up again so perhaps those points are closing up.

All in all though - lovely!

FH - cam followers

After a 60 mile round trip on the Square Four which left me worrying about its coupling gears I decided to have another look at the cam followers in the Huntmaster. I had refinished the wearing surfaces to true them up but I knew that one of the followers had worn through the case hardening. I decided to stop messing about and get some replacement followers.

These are available as an exchange part from Draganfly Motorcycles and they came very quickly, in a couple of days. Refitting is very simple and I replaced the barrel with a layer of Wellseal on the gasket.

Before I did this however I wanted to make sure that the cams were going to be properly lubricated on startup so I used my oil can to make sure the channel under the camshaft was full of oil as you can see in the picture below.

With the barrel fitted, I could oil the followers from above:

I threw the pushrods in to start understanding how difficult they would be to fit. I once spent ages chasing a valve timing problem on the Square Four only to find that I had the pushrods in the wrong followers!

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:

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. 

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. 

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.