FH - a little more progress, and a big step...

 Well there's been a little bit more progress today. First off, I've finished the second of the finned exhaust clamp bolts:

Secondly I've been talking to people in the club about tyre sizes and whether I can get my desired tyre (Avon RoadRiders) in the size that I want. Having a look at the distance between the tyre and the chain guard reveals around 3/8" to 1/2" but also that this tyre, an Avon SM Mk11, is actually a 325-19. The front tyre, a Dunlop TT100 by the way is a 90/90-19 or 3.60-19. They are both from the 1980's.

I am hoping to buy Avon RoadRider tyres but unfortunately they are not available in the right sizes for this bike. The options appear to be to use a 100/90-19 for the rear (Avon's recommended replacement for a 350-19) and a 325-19 (original size) or a 90/90-19 for the front.

The next bit of progress is very small - it's just a P clip for the front brake cable. I've attempted to adjust both brakes but right now the front tyre is in the wheel clamp.

Lastly and very quietly and secretly I have hooked up the temporary fuel tank to the carburettor and started the bike. Unfortunately it will only start using Easy start, but at least it starts and runs. There may be some problem with the fuel supply or with the float bowl. It runs and returns oil and it runs nice and quietly so now I know that I have the HT needs the right way round, and the oil system is working properly, and the valve timing is correct and the ignition timing is more or less correct though it does spit back through the carburettor.

I think we'll have to wait 'til Monday to have another chance at it, but sleeping on it and looking at some of my pictures suggests that the float bowl gasket is missing. This will give you an air leak in the pilot fuelling circuit...

FH - exhaust clamps

You might remember that I brought some exhaust clamp screws from Draganfly that were the wrong size - my fault not theirs. One of the jobs I have on the list is to make some new ones and that's what we're going to do today.

The clamps are 5/16" CEI and have this 45 degree feature on the plain side:

I bought some 0.445" 303 stainless steel hex bar to make some new screws. The picture below shows the first one, prior to parting off:

I put the prototype screw in place to determine how long the hexagon needed to be in order to get access for the spanner, marking it with a Sharpie:

Here's the finished screw, parted off, faced off and provided with a tidy chamfer:

Lovely. Fitted with a dose of Copaslip.

I just need to make another one!

FH - inching closer...

 The day seems to have disappeared again without too much workshop time but at least I've got a little bit done. 

The choke cable is now terminated to the right length, with a new nipple at the carburettor end. I didn't have the flat nipple that goes into the lever unfortunately and I didn't fancy making one on the lathe but I did have a little tiny one that goes in the choke slide.

There's not much to see here but at least we have a throttle slide and a choke slide that move independently of each other and don't have any slack in the cables.

The next little job is to make a couple of 5/16 CEI bolts to retain the finned exhaust clamps. Here I'm reducing some 0.445" stainless hex bar to the appropriate diameter for the bolts I need.

They're going to have a chamfer feature where they mate with the clamp - here is the chamfer on the clamp itself. When I have cut the thread on the bolt I will work out what the height of the bolt head above the clamp face needs to be:

That's all for a bit. I've got a 10-hour turn on the railway tomorrow which won't finish until after 11:00 at night, and then my grandchildren are coming for the weekend. Hopefully we will get the speedometer in the post either tomorrow or Saturday, so they'll be plenty to play with next week. I'll order the V-Reg2b voltage regulator as well, so we can convert the RB108.

FH Dry Build - Exhausts

Well, it turned out that five years in a damp loft by the seaside wasn't the best thing for the old siamese pipes the bike kit arrived with, so as the pipes they supplied for the SQ4 were so nice I bought a new set from Feked. Feked make nice stuff which they pack very securely and deliver promptly. A good outfit:

...and they fit, too. The silencer construction is a perforated tube with glass wool around it, juts like the Burgess original on my W/NG. Should sound throaty! 

Nice deep socket fits the cylinder head stub:

Bracket is in the right place:

Two things here - the pipe bend is a little tight but will spring down to the right position with a little force, and the silencer end of the pipe needs about 2" trimming off it:

I'm not sure this bend is in the right place, but it does clear all the bits it needs to:

Someone else's bike, much the same:

Looks pretty good.

Model A - Exhaust

Well, that's a job off the list. Thanks to fellow Ariel enthusiast Mark, I have this splendid genuine Ariel tailpipe for the Model A, delivered to me at Holt Station on the North Norfolk Railway. The trouble people will go to to help a fellow motorcyclist leaves me speechless sometimes:

This is a terrible picture but the Model A is sheeted up behind the SQ4 and the W/NG while I am doing the FH dry build:

This might be better:

It looks marvellous.

Thanks Mark.

QR50 - Exhaust & Silencer

Updated: first published November 2020

There's been a lot of sheet metal work on this bike - the magneto cover, the faux swinging arm and the silencer which was completely missing. It's one of those pressed sheet metal affairs quite widely used in the 70s and 80s on bikes when it can be hidden and some (think the last BSA and Triumph unit singles) where it cannot.

Here's one from eBay:

It's got an integral exhaust pipe, the only part of it I had left, and a separate tail pipe which looks like this and mounts in the and of the silencer. see how long it is?

It appears in the parts book like this. I haven't got those perforated guards either:

Now, these come up on eBay from time to time but at over £100 a go I was never going to buy a new one, or even a second hand one but I have a welder, a bandsaw, a brain and a calculator and making one couldn't be too hard could it? Of course, because it was entirely missing I had little idea of scale so I took this library picture and scaled off it:

You can get some idea of the thickness from the diameter of the tailpipe. I made a cardboard template for the sides, with an allowance for the curved edges:

I started to make a model from the template, to mock it up and work out how to form some of the details, like the spherical corners:

Try as I might, I couldn't see what Honda had built into their silencer but I did know that the exhaust gas went in at the front end and that the tailpipe was long enough reach to the front, so the gases must be led around various chambers inside. The formed ridges obvious from the outside of the original silencers seemed to confirm this, so I used my template to work out a series of chambers and modelled them mathematically. I found the calculations online at https://www.glue-it.com/wp/knowledge/exhaust-silencer-design/ and built a simple spreadsheet to calculate what a silencer would do at various engine speeds.

Here's the equation for one of the silencer/pipe combinations:

The resonant frequency fn for the chamber is calculated as :

Where C is the speed of sound and Lc is the length of the chamber. I plotted the results of the calculations:

From a rough sketch, I built a cardboard mockup. I started with the inner shell, and built the divisions into it:

The tailpipe needs a large tube to receive it:

The silencer is supported by the exhaust pipe and the bracket at the front. The pipe will be welded into the shell and have a brace inside:

The complete internal layout:

Here's the model with the outer shell added, fitted to the bike to determine the shape and hole positions for the bracket:

Now that the model has proven the fit of the silencer, we can use it to start on the build 'in the metal'. What I have done here is use the template again to transfer the shape onto the two sheets that will form the inner and outer shells. I've used spray paint to transfer the shape:

I've used the model to mark out a piece of thicker sheet for the bracket:

Using a couple of short lengths of scaffold pole, I have started rolling the edges of the inner shell. Here, it is held onto the bracket with magnets:

Using the same technique as that used on the cardboard model, I have split the hemispherical corners ready for bedning:

I closed them up around the same scaffold pole, so the radii are correct:

Welded and painted:

When all the corners are done, we can cut the dividers using the bandsaw, linisher and some cone drills. They are set up temporarily with welding magnets:

There will be a fourth piece which will be used to reinforce the exhaust pipe as it enters the silancer:

The tubing is just cheap 19 mm ERW steel tube. In a former life it was a curtain pole.

The tail pipe needs a mounting tube welded in the shell. This needs to fit tightly around the tailpipe, so I will roll it up from sheet:

The original tailpipe features a frustrum at one end. I've used the model to transfer the shape to a bit of sheet, which we can roll up using a hammer and a small mandrel:

Here are the pieces of the tailpipe and it's mounting tube:

Tacking up the tailpipe:

We need to assemble the silencer to locate the tailpipe in the right place, prior to tacking in the mounting tube:

With that done, we can have a look at the tube arrangement inside prior to welding it up. 

The location of the incoming exhaust pipe and its bracing plate are key to the internal tubing location, so we will have to put some time into that. I had considered making a die and hot forming the tube, but a few experiments showed that the bend needed would be too tight to successfully form by that method, so I decided to mitre & weld the bend instead:

Here's the tube in position. I used this set up to mark the position of the brace inside the shell with a Sharpie.

Knowing the position of the brace I could tack in the internal tubes into the dividers:

You see the position of the brace in this shot. The tube from the front chamber to the rear is tacked in all three dividers in this shot, and I am setting up the tube between the two middle chambers:

This shows all the tubes tacked in. The empty holes in the dividers are for the tail pipe.

Next step is to get ready to weld the bracket on. The bracket will have five plug welds and four fillets' the Dykem marking blue is to mark the radii prior to linishing and welding the double sheet.

The whole silencer assembly is fitted (yet again) to determine the final position of the incoming pipe and it's brace. Whilst the internal assembly is tacked together, it is held in the shell with magnets at this stage.

Here's the incoming pipe, trimmed a little and with the brace in plate. I've introdcued another small plate to provide some flexibility around the position of the pipe as it passes through the shell:

Here's the assembly tacked together and in place in the shell - it's not in the right place - something must have slipped during clamping...

With that last element in, we can replace the baffle and tube assembly and put the two shells together. I should have allowed considerably more (spare) material since for some reason there is a gap at the bottom. I'll make a 1/2" wide strip to go all the way around the seam.

I've now tacked the shells to the baffles and to each other:

These two images are from eBay - someone is selling laser cut heat shields for these exhausts but unfortunately they are in aluminium. I will have to make my own as I want them in steel - they won't last five minutes in ally, before they are bent out of shape.

Here we go. I cut the shape from a bit of 0.9 mm cold rolled sheet using aviation snips and started to raise the edges on a dolly:

I worked the edge up gradually:

Until I had the shape I wanted. I trimmed out parts of this raised edge to let the pipe pass underneath:

I also reduced the height a little using the linisher, and cut some holes with a cone drill:

The heat shield is held to the pipe with a couple of M5 screws. These go into weld nuts I fitted: