FH - carburetter

 If any of you recall this post from last year, you'll know that the Huntmaster kit arrived with an Amal 928 Concentric carburetter:

Now that we are getting around to fitting the cylinder head, we'll need to sort out the jetting for this carburetter. A plea to the AOMCC forum revealed that revered Huntmaster rider Steve that his FH is fitted with a 626 Concentric with a 200 main jet and a 3 1/2 slide with the needle clip in the middle position.

The difference between a 928 and a 626 is the body size - the 900 series is the larger. The 600 Series comes in 22mm, 24mm, 26mm and 27mm bore sizes and the 900 Series in 28mm, 30mm, and 32mm bore sizes. Presumably a 626 has a 26 mm throat and a 928 has a 28 mm throat; for the record, 28 mm is just over 1 3/32".

As you'll know from this post, this FH is built to Cyclone spec, more or less equivalent to a Road Rocket. Later Road Rockets use a 1 1/8" Monobloc; earlier ones use a 1 1/16" Monobloc with a 340 main jet, so this 928 should be there or thereabouts but jetting it might be fun. We learned from the forum that Concentrics run about 10% richer than Monoblocs, so we should fit 10% smaller jets and a slide one size smaller.

Standard fitting for the 1958 FH is a 376/12 Monobloc, which is 1 1/16" throat diameter. Jetting is as follows:

• Size: 1 1/16"
• Main Jet: 240
• Pilot Jet: 25
• Needle Jet: 106
• Needle Position: 3
• Slide: 3 1/2
• The carb parts list indicates it uses ferrule 6/132A, which means it doesn't have cable adjusters.

Standard fitting for the 1958 Road Rocket is a 376/36 Monobloc, which is 1 1/8" throat diameter. Jetting is as follows:

• Size: 1 1/8"
• Main Jet: 290
• Pilot Jet: 35
• Needle Jet: 106
• Needle Position: 3
• Slide: 3 1/2

The kit 928 R300 is set up like this:

• Size: 28 mm or 1 3/32"
• Main Jet: 210
• Pilot Jet: None, drilling only; apparently 0.0016 but I understand these can be drilled out and a jet fitted
• Needle Jet: 106
• Needle Position: 3
• Slide: 3 1/2
• It hasn't got any cable adjusters.

Apparently you can fit a pilot jet in the threaded port shown here, on the right & under the bell mouth:

Watch this space!

Workshop - Switzer Bike Lift

First published 12th March 2023

Legend has it that the bike lift is, or at least becomes (with advancing years) one of the most useful tools in the workshop. Some while back I spent a few hours faffing about with drawings, replanning the workshop in an attempt to fit one in. 

Thoughts turned to this again recently and looking around I discovered this Switzer lift, marketed by KMS, which is shorter and less wide than most. 

I posted a question on the AOMCC FB page and got a host of encouragement from the members, including one who had exactly the same lift and was happy to take some measurements that were not available on the KMS website. Using these measurements, I modelled the space the lift would take up on the garage floor with some timber and paint pots, and lived with it for a week. 

And I'm glad I did! The model didn't get in the way unduly and I took the plunge. Actually, when the lift is in place, particularly in the raised position, it seems to liberate space - it effectively gives you another bench and more foot room than having the bike on the floor. 

The bike is so much easier to get to now. That ramp lifts off, and I've laid it on the floor under the lift and there is a removable panel to allow you to drop the back wheel.

At the front, there's a bump bar and a wheel clamp.

The lift arrived in a plywood box - 10 m thick, poor quality ply but I'll use it for something.

The ram is going to spend most of it's life extended - I've coated it with ACF50 to try and inhibit corrosion. The lifting pedal you see here is removable.

At the front end, there are two jacks that stabilise the lift and a stout bar that holds the lift in two positions should the hydraulics leak down.

I'm really pleased with it.

Almost a year later, after the lift had been in constant use I added a new wheel clamp:

It's much more rigid than the original one.

FH - Lucas HF1441 horn

While waiting for bits for the QR50, I took the opportunity to refinish the horn for the Huntmaster. It tests OK in that it pulls a current and deflects the diaphragm, so some adjustment will have it working.

Lucas catalogues are very useful. This is catalogue 716A, section F - six pages of horns and horn pushes. The application page tells you which part number you should have:

In the case of my 1958 Huntmaster, it's a HF1441 model horn, part number 70048. The spares list tells us a bit about it:

It's black, and looks like this:

So, I had the correct horn (bought from eBay I think - it was missing from the kit) and all I needed to do was strip it and give it a coat of paint.

First up was the various bits of bracket:

It’s good to clean the points in these horns, but this nut is usually very tight and it retains the diaphragm to around the moving point. I had it soaking in Plus-Gas for a few days but I couldn't shift it:

Since the horn worked I gave up and cleaned the old paint off with emery tape. 

I painted it with the usual U-Pol etch primer and gloss black. I know the tone disc is supposed to be black, as is the nut, but it looks nice like this: 

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.

QR50 - a bit of a service

 After three years in the field, the little beast is back. The boys are complaining the bike has no power after ten minutes running and with busy lives, my son and daughter in law have no time to check it out - so it’s back to Grandad’s workshop.

The Square Four is now off the bench to test the kickstart against the clutch, and then close up the clutch, refit the exhaust and test ride it. All went well with that, so the QR can go on the bench:

The first thing to attend to, and rather alarming, is the fact that the fork top threaded inserts are both loose. Now, these had a ring machined into them which allowed them to sit in the top of the fork leg, which I welded into the fork leg. Now, there is no evidence that the ring was anything other than an interference fit around the insert - indeed, there is no evidence that the insert was anything other than an interference fit in the fork leg.

Now, the inserts are retained in the fork leg by two strong plug welds on each side of the leg:

Next job, the tank. The wrap hasn't survived very well on the tank - the shape is small and complicated. I've pulled it off and treated it with some special plastic primer:

The primer is actually clear - ignore the grey bit, that was an experiment with the ordinary PlastiKote primer to test adhesion: it doesn't work very well, but the special stuff is excellent. This RS Paints Honda Helios Red doesn't come off:

The lack of power appears to be down to the choke - the choke cable goes into the carburetter through a plastic nut which has broken, allowing the choke cable to come out. When it comes out, it appears to operate the choke such that the mixture is rich all the time, even with the choke knob pushed in. That will certainly lead to a lack of power.

The part of the nut that was broken retains the boot, which in turn retains an elbow and the cable.

I turned a new part up from brass and pressed it into the old nut, which I had bored to suit. It starts very well:

As you can see at the end of the video, it dies if you fully open the throttle - the kids were complaining that it didn't have much power. The float height is bang on:

It appears after a lot of searching and cross checking Honda part numbers that a Keihin PA26 carburetter with a #78 main jet is correct for all years of QR50 production. This is the main jet out of mine, which is marked PA 28D but still has the 12.2 mm throat of the correct carburettor:

A #58 is not a #78! It looks like it gets very weak at full throttle, something born out by the colour of the plug. I've made a new carburettor spacer while I wait for the new jet:

A few days later, the new jet arrives as expected - but it's the wrong size. Some of these little carbs use a jet with an M7 x 0.75 mm thread, and these are available; unfortunately mine uses an M6 x 0.75 mm thread and these are not available. So what I did was measure the diameter of the new #78 jet using a range of small drills - I found that a 0.8 mm would not go in, but a 0.75 mm would; the #58 would accept a 0.55 mm, but not a 0.6 mm. I concluded these Keihin jets are identified by their diameter.

One option would be to put the new jet in the lathe and reduce the diameter, and I probably would have gone down this path had I possessed a M6 x 0.75 mm die (it's a fine pitch) but I didn't fancy buying a die or setting up for single point threading, so I did something that ideally you should never do and drilled the old #58 jet out to 0.75 mm, which might leave it a bit lean.

It doesn't run out of breath at high rpm any more:

It's got a new set of tank decals too:

Gearbox Done

 After spending the winter rebuilding the gearbox and the clutch, I'm pleased to be finishing the job as the weather warms up.

First job, before finally closing up the gearbox is to fit the kickstart stop rubber that has been waiting on the bench for literally years. I needed to remove the metal part of the stop and reduce the 1/2" OD to about 7/16" to get the rubber to go over it. I mangled one in the process of realising that, which delayed the job by a week:

Next, when the kickstart is on and the gearchange mechanism is timed, I need to fill the gearbox. This is easier said than done as on a SQ4, the filler is hidden behind the oil pipes. Surgeon's forceps are useful to get it out:

Since the Morris K400EP grease is quite fluid, the easiest way to get the grease in is to use a syringe. This is a 250 ml syringe and you need 750 ml. It's got a flexible hose and a rigid copper pipe on the end to get the grease through the filler and into the top of the gearbox. You can fill the syringe by sucking the grease out of the tin:

Next time i do this, I'll do it warmer weather. This was hard work:

In a departure from usual practice, I've measured the oil going into the primary case - 150 ml of engine oil, to determine how much I can get in without it leaking.

I'll road test it, then see if 150 ml is too much or not enough.

Running the engine on the rear stand shows I can select all gears completely silently. It's never been as good as this: