Yes, the FH is still on the bench after I have been faffing about with the Square Four. The issue is that when I put the rocker box back on I squashed one of the studs for the head steady into its nut and damaged the thread - so the rocker box had to come off again. I decided to buy some new half nuts and reduced hex nuts to tidy up their appearance and I just got round to putting it all back together.
Of course it still takes two goes because as usual I have forgotten that you have to start the nuts for the head steady and the two reduced hex nuts at the rear due to curves in the cylinder head which prevent you getting a nut on...
I've been fiddling about with the ignition timing this week as there had been some significant hesitation coming off-idle and some poor performance at low speed - what we used to call 'kangaroo petrol'.
I retarded the timing a bit and realised the bike had stopped kicking back on startup, and the slow running was better, and it would fly along like a bat out of hell - but coming off idle still wasn't as smooth as I'd like.
In the end, after fiddling with the idle mixture and getting nowhere, I stripped the carburettor.
I didn't find much. Some debris in the float chamber, the flange fixing to the head looser than it should have been, and one of the float chamber screws was loose. I blew out all the jets and ports with carb cleaner and found everything clear.
Putting it back together, I added this little tee to the idle mixture screw to make it easier to adjust (it's a bent bit of brazing rod, soft soldered to the brass screw), and used some Threebond on the flange.
A few little teething troubles appeared after the recent service, most notable of which was the oil pressure. Normally the oil pressure sits at 75 psi when cold and rolling at main road speeds, dropping to 25 psi idling after 15 miles or so.
Today, it was going up to 75, but intermittently dropping to 40 or so - very odd. I bled the Morgo again:
When that appeared to be happy - there were no bubbles I turned my attention to the relief valve.
See that bit of debris half way along the spring? I cleaned that out, and after a suggestion from Richard in the AOMCC, I changed the ball and reseated it.
I then rode to Cromer and back, clocking up about 13 miles - until it warmed up, it sat solidly at 75 psi and was still showing 50 psi when I got home. Back to normal.
It’s a bit snatchy at low speed. Initially I thought this was carburetion (not that I have changed anything), then perhaps transmission snatch, but all is normal there.
It's been a while, or it feels like it. It's actually almost a week since I did anything to the FH - I've done a couple of railway turns and the weather has been a bit wet.
The head bolts are torqued to 32 lbs ft or so. I tightened them down using a 1/2" square ratchet (as per the manual, as tight as I could get them), then checked them with a torque wrench set to 32 lbs.ft. - so they may be tighter than that. The 32 lbs.ft seems to be bandied around a lot in connection with iron-head A10s.
This is the drive side cylinder - 140 psi or so. this was showing 75 psi on the last test, and is the cylinder that weeps oil.
This is the timing side cylinder, which showed 95 psi in the last test.
Now, obviously these numbers are a lot higher than we saw before, but don't be fooled, this is partly because I had the throttle open during the test - it was closed previously. The big win here is not the high numbers, but the fact that the two cylinders are no longer 20 psi, or around 25% different.
I bought a couple of sets of rocker box gaskets on eBay - they are identical to BSA A10 rocker box gaskets, though the tappet cover gaskets are different. I fitted these with Wellseal last time, and destroyed them lifting the rocker box. This time, I'm going to use Threebond 1215 on one side with grease on the other.
After returning to the road following the split oil line incident, the FH has now clocked up 270 miles and it's high time to retighten the cylinder head. There are a couple of issues - it's still leaking on the drive side, and it puffs a bit of smoke from that side as well. Perhaps the return oil way is leaking oil both into the cylinder and out of the joint, onto the fins. We know from this post that there is a compression problem, and the behaviour demonstrated during the compression test supports the head gasket leak theory.
Removing the tank reveal this nasty fretting damage to the rocker oil feed pipe. Given that this pipe and it's banjos are in the way when the rocker box comes off I think I might cut the pipe here and fit a bridging rubber piece so that I can remove the banjos easily with the rocker box next time.
With the rocker box off I could get the spanners back on to the head nuts. I got quite a bit of movement on the central ones so I'm quite optimistic there will be an improvement in the compression figures for the drive side cylinder. We shall see when it's back together.
Not surprisingly perhaps but I discovered that you can't do a compression test with valves that won't open and the bike on the bench, because you can't fill the cylinders and you can't get enough purchase on the kickstart to give it a proper kick.
Never mind. While I'm under the tank I thought I'd have a look at these broken grease nipples for the steering head - this is the first time that I've successfully used an easy-out for anything!
I fitted a new one from stock, but I've only got one unfortunately...
A couple of days ago, the Square Four came off the bench to be replaced by the FH in order for me to torque down the cylinder head at 270 miles. The Square rolled easily onto the floor as it's great weight dictates with little left to do than fill the oil and fuel tanks.
It had been off the road for something like 4 weeks for a service and one evening I ladled in a gallon of fuel drained from the FH tank. It wasn't until I went to start the engine that I realised the fuel was pouring out of the fuel tap. It had dried out. Choosing the easy solution I soaked it in fuel overnight to see if I could get the cork to swell up again:
This worked a bit but not well enough. The next day found me replacing the cork with a new one and also replacing the two o-rings in the reserve plunger that I made some years ago.
Finally getting the engine started revealed another problem - no oil pressure. I ran it for 10 to 15 seconds or so with no success and shut the engine down. I realised that I would have to bleed the feed to the Morgo oil pump. I don't believe I have drained the tank before - the last time I changed the oil I didn't wash the tank out so the oil lines from tank to engine would never have been drained since I built the engine all those years ago.
Bleeding the pump is very easy as it has a built-in hole for the purpose:
I was pleased to find the timing chest very clean and the sprockets and chain in excellent condition with the tensioner working properly. A few minutes with a screwdriver had oil seeping from the bleed hole and the whole thing sealed up again.
Restarting the engine found the oil pressure leap up to 50 psi immediately. There is a little niggle here however in that normally the oil pressure will rise to 75 psi on startup from cold, but we do have different oil this time. I'm using Motul 20W-50 in place of the old green tin Duckhams lookalike that I used to buy from Halfords.
Secondly the engine is not running very cleanly, misfiring a little. There may be some investigation to do.
The following page provide descriptions of the threads in common use; the drill sizes, pitches and hex sizes associated with them, and a few interesting tit bits of information...
I've taken the opportunity to remove the petrol tank because it's time I did the valve clearances and had a look at a persistent oil leak that has been going on for years. I thought it was fixed; I changed my mind and decided it was a head gasket problem - but then careful observation of the rocker box oil line revealed some seepage. It's obviously been quite bad in the past at some point, before I fixed it last time, because there's oil on the steering damper plates under the steering head. There must have been quite a jet to get it out there.
Some years ago I did repair a leak here but it appears I didn't do it very well:
When I took this apart it was clear that they was some oxidization within the joint which had prevented the solder wicking down inside the fitting. I cleaned that up with wet and dry and tinned the pipe with some solder, using plenty of flux to sweat the joint into place. It resists that twisting now.
The next job is to do the tappets and pulling off the rocker covers reveals some lovely clean valve gear.
These are all supposed to be set to 0.001" with the engine cold. I used the famous 'Rule of Nine' to set them up.
Valve clearances all proved to be very close to where they should be - I adjusted a couple of them but most of them were ok. I moved on to the spark plugs - cleaning them, checking their gaps but again they were all ok.
This one is from cylinder number 4, but it's fairly typical of all the others. You might think it's a little dark on the centre electrode and indeed we might consider adjusting the mixture a little. We could put another washer under the float valve to lean out the mixture across the whole rev range.
I took the opportunity to change the thumb nuts holding the HT cables to the plugs for some larger ones that I made some years ago.
With the rocker cover off I took the opportunity to snug down the head bolts and nuts. This is quite straightforward except for the pair that are buried in the fins - these two at the back are particularly difficult and you have to take the carburettor off to get at them. The one on the timing side of the bike is almost impossible because the casting has not been cleaned up sufficiently for you to be able to get at the nut.
Next time that I take the head off, there will have to be some grinding in there.
Reassembly was quite straightforward, apart from getting the oil tank back in. I've now 'adjusted' the area above the engine plate and below the frame rail with my favourite (small) hammer. It goes straight in now, but you have to remember to take the oil supply/return manifold off the engine first. You can't get the oil tank bottom bracket past the oil lines with the lines in place.
These wet black rings are the fibre washers that seal the ends of the rocker shafts. They get very hot and are subject to oil seepage from the rocker box.
I need some new ones.
They are not a standard fibre washer - they have a large outer diameter of about 3/4 inch but the hole in the centre is for 5/16 inch - unfortunately they are out of stock at Draganfly:
So here are the bits we need. At the top of the picture there is a 20 mm punch which I have turned from bit of handlebar on the mini lathe. Below that is the special washer and the nut that fastens the rocker shaft in place; top left is the punch used to make the central hole. The new washer is to the left - it's the grey one.
The sump plate looked a bit mangled when I took it out after the oil was drained.
After degreasing I cleaned it up using some clock cleaner which is an ammoniated fluid used for stripping the corrosion from brass and copper. It works very well on the gauze.
When I got it clean, I manoeuvred the washer that stiffens the hole for the oil pickup pipe out of it's wire prison. I managed to get it back into place and squeeze it tight to retain the gauze.
With that done I could think about refitting the sump plate. I destroyed the gasket completely when I removed it so I needed to make a new one.
With a sump plate it's easy to cut a piece of gasket paper to the right shape and to mark the holes.
Punching the holes is the easiest way to make them tidy and I used the corner of the sump plate to complete the ring of gasket around the holes.
I cut the centre out with a craft knife - it will be big enough to use for something else.
When I drained the sump, there was around a cup full of oil coming out and of course the gauze was damaged. The pickup pipe was the cause of both of these problems in that it was out of position - too high and off centre. It's just a copper pipe retained with a bracket inside the crankcase so it's quite easy to bend it into the right place.
With some Threebond 1215 the sump plate is back on and the plug fitted.
This week, we are mostly decorating in Cromer! The FH now has 205 miles on the clock, and is still smoking a tiny bit and leaking a bit of oil, possibly from the head gasket.
Here it is, collecting caulk from Screwfix and CO2 from Argos...
I've checked the points today and am pleased to record that they haven't closed up.
I also checked the QD hub nuts after an unusual sound began from the back - they had loosened off a lot.
There's no picture, but yesterday I rode a couple of miles along the main road at 1/4 throttle, killing the engine and coasting to a halt. The timing side plug was brown on the centre electrode, black on the outer. I won't be making any carburetion changes for the moment!
I snatched a few minutes in the workshop today to look at the cylinder head leak and the oily exhaust on the Huntmaster. It passes a little bit of smoke from both cylinders but nothing persistent and only when pulling away. To start the investigation and to try to eliminate the valves and valve guides and further home on the problem I thought I would do a compression test.
I started with the drive side, which is the side that is showing oil in the exhaust pipe. This revealed a figure of something like 65 psi with the cylinder dry. Perfect compression at 7.25 to 1 should be giving us something a little over 90 psi.
This didn't improve after several kicks.
The timing side shows us something like 95 psi. The exhaust on this side is dry.
I ran a bit of oil around the top of the drive side piston in an attempt to improve the sealing and to reveal either a head gasket problem or perhaps a valve problem.
This wet test brought the compression up to 75 psi - still a bit down on where we should be. The rings have only done around 145 miles but given that the timing side is working well there is obviously a problem here, and combined with the oil leak around the top of the cylinder we are looking at a head gasket leak.
Looking at the plugs I wasn't surprised to find that they were both dark and wet. The last journey the bike had made finished with a few minutes riding at very slow speed through town - on the pilot jet. We will lean this out next time.
Riding back from the railway yesterday along the main road revealed that the bike will maintain 45 miles an hour at just under a quarter throttle - so until we are properly run-in we are not going to be able to do anything other than look at the carburettor slide cut away at the very most. We can adjust the pilot air again but we won't be able to examine the mixture from the main jet.
Just a little trip out this morning to pick up a part for the boiler from the Cromer plumbing centre. The bike is running very nicely and I managed to start it without the centre stand.
It's feeling a little bit squirmy so I decided to check the tyre pressures - the rear was a little bit down so we'll see what happens.
I also put some tape and some marks to the throttle to help me set up the carburetion in the future.
This is the more traditional version of the Amal carburettor tuning chart showing us which elements of the carburettor affects tuning at various throttle openings:
Here is a more modern version, showing us a bit more detail and the overlap between the effect of the different elements:
Aside from practical adjustments like needle positions and the setting of the pilot jet, there are a few things we can change:
The main jet - available in a myriad of different sizes.
The slide cut away - various sizes are available both larger and smaller.
The needle. Most four strokes used the same needle, but there is a 'lean running' needle (part number 104) which is longer and thicker and clearly allows the engine to run with less fuel at higher RPM.
As the engine gets closer to being run in will be able to do some plug chops to determine the mixture at various throttle openings. At the moment, with only 138 miles on the clock what we can do is quite limited but I think we can look at perhaps the first half of the throttle opening range.
With the Square Four on the bench, the Huntmaster fixed and a trip for a job in Cromer in the offing it's time for a little bike ride.
In preparation, I topped up the oil a couple of days ago as I had had the return system apart and expected the filter to be empty. I turned the engine over on the kickstarter with the plugs out in order to prove circulation before I used it again.
After I'd finished my decorating job, I came back to the bike to find a little puddle under the rear chain case. I guessed there might be too much oil in the oil tank and so it proved:
I filled the big syringe twice getting this back to an acceptable level. It's been off the road for a couple of weeks and obviously wet sumps!
At the same time I adjusted the front brake and the head race bearings.
It's high time Square Four had an oil and filter change, so with the oil return line repair complete on the Huntmaster the Square Four is back on the bench after a 10-minute run to warm the engine oil up.
As usual it's an absolute pig to get the oil tank out but it's very easy to drain the tank and the sump - I have a new sump plate (well, it was new 10 years ago) with a drain bolt and magnet in the middle of it. I had something like 300 ml of oil out of the sump - I'm not sure whether that's unusual or not.
I was surprised to find the sump strainer damaged - I think I'll get a new one from Draganfly.
With the oil tank out I can degrease the area around the top of the box where the filler is - it's always quite mucky around here because it's very difficult to top the box up without getting grease everywhere.
The oil tank is also a very tight fit - it's always a struggle to get it out. I'm wondering if it's fouling the the frame tube, perhaps stuck between the frame tube and the gearbox plates.
I had the tank in the parts washer for 15 minutes washing the outside and the inside and was pleased to find very little sludge and no debris in the tank at all. There's obviously been some further washing of the engine through the detergent oil that I'm currently using as the cases appear very clean and the goo in the bottom of the tank and on the sump of drain plug is just like the dark grey substance you would get from the crankshaft sludge traps.
You can see one of the cams in this picture - the wear ridge is quite clear. I have a new camshaft ready to go in when I decide that I'm bored enough to rebuild the engine!
I filled in my maintenance spreadsheet but for the record the mileage is 4089 miles.
This is the engine to oil filter pipe on leak test. No holes there!
However, this one is the oil filter to oil tank line:
So there's a nice leak there. The next step is to rework the oil line arrangement to the filter which I will do using a slightly different route between filter and tank since I think a contributing factor to this failure has been that the oil line has exceeded its minimum bend radius.
It's a fasteners that I've been making for the Model A are all turned from mild steel - there is no stainless on the bike at all. The plan is to use some gun blue or chemical blacking to reproduce the iron oxide finish from the original fasteners, called 'coslettising'. As an experiment I have used this product on the Huntmaster's oil filter bolt:
Since I made it some years ago I have modified it to provide greater engagement of the thread. After turning I degreased it and suspended it in the cold blue for about 5 minutes followed by a rub over with linseed oil.
