Saturday, 2 February 2019

Dry Build - Repairing the Chain Guard

Moving on, we can start on the repair of the front section of the chain guard. This is a bit mangled:



Someone has modified it (with a tin opener) so that it can be removed without taking off the gearbox sprocket.


I don't understand this though:


This is what it is supposed to look like. These pictures are from the excellent members of the AOMCC:




You can see in this last picture, the position of the chain oiler. This is the bit that has been cut out of my mangled example, so we will need to re-create it. Mick D sent me these dimensions:


Mick says this is a 1" hole. I have the grommet from Drags:


Here's a view of the chainguard in situ - that's the chain oil pipe you can see there:


So, on to sorting it all out. Some heat and a hammer has this area flat again:


Heat and hammer again, but this activity only serves to reveal that we will have to cut this lot out:


Five minutes with a pair of aviation snips has cleaned this up. We can now find a bit of sheet to let in:


This bit will need cutting out:


Sanding off the paint allows us to measure the material thickness with the micrometer. It's 0.043", about 18 SWG or about 1 mm thick.


Now, we'll need a pattern to cut a bit of 18 SWG sheet. We can do that with a bit of paper and a pencil - we'll just draw around the other, good side to get the curve around the swinging arm, and we can use the geometry of the main shaft hole to construct the missing curve there.


The chain guard fits around the horizontal frame gusset, which is accommodated in two slots above the 'swinging arm curve'. Luckily, there is enough  metal from these slots to show us where they are.

In the end, we have this little sketch.


Now, we glue that to a sheet of 18 SWG and cut it out with snips and a file. It doesn't want to be too precise, as it needs to be 'fitted' to the job. Then, I put a 2 mm flange on the end of the repair section, around the main shaft hole to match the flange on the original part. That will make the face much more rigid.

In the next picture, the chainguard has a chunk of oak, 1" thick, stuck inside it so we can secure it in the vice. I've trued the lower edge of the cut out area with my hammer, and straightened the cut edge with a file. You'll notice the top edge is still quite bent - I will address that next. I've also messed up the flange at the bottom there, it needs to come in a bit more.


See the little blue and red crescents in the picture? For those that were wondering, they are magnets holding the repair section in place. Here's another magnet, showing the position of the grommet hole:


Ready for welding:



Butt welding with TIG in 18 swg. Set at 25 A with 5 l/min argon:


There are a few points where I need to fill holes I'd blown in it, but generally not too bad. Back side shows good penetration.


Before we go any further, we will do a trial fit and take some more pictures, to understand where the guard is near the frame and other components.


Next, we are going to mark out and cut the hole for the chain oiler grommet. The oiler pipe goes vertically down the triangular gap in the middle of this picture - the grommet position is quite critical:


Using Mick D's dimensions, we can mark out the hole. I thought I might chain drill it and file to shape, so I have used the old-fashioned witness marks around the diameter:


I've made two more repair sections for the rearmost lower edges. We will weld these in later.


I found these step drills on eBay somewhere and they seemed to get a good write up. I decided to use the biggest one to drill the grommet hole:


They make a much better job of drilling holes in sheet metal than a conventional twist drill.

A couple more hours in the workshop sees it fully welded, dressed and protected with a layer of primer.



Lathe Repair

I love my little lathe, and it sees a lot of use as regular readers of these pages will know.

Recently I've been doing a bit of thread cutting and the change wheel cover has been on and off; the control box has been on and off too, because I needed to oil the lead screw bearings. During this process I managed to break one of the wires to the speed sensor - which was hardly surprising as it is quite vulnerable:


When I removed it, I broke another:


You can see how vulnerable they are. The conductors are tiny and they are soldered directly to the sensor board, with no protection or strain relief.

Making a note of which was which, I put some 0.1" pin headers on the board, and soldered the conductors to them. The idea of using the pin headers was that they would give me something to anchor the heat shrink I'd put around the cables - the cable, heat shrink, pin header arrangement is much stronger than the direct soldered conductors used originally.


The whole thing needs potting really, but it works OK.

Friday, 1 February 2019

Dry Build - Putting the Gearbox in

Now that I have the footrest spacer sorted out, I will put the Burman GB gearbox in. I've stripped out the engine & primary side again, leaving the oil tank & tool box in place.


Frame spreader comes into it's own again. Here's the gearbox going in:


Followed by the gearbox plates, remembering to get them the right way round. One has a hole for the clutch cable, the other has holes to accommodate the flats in the top two studs.


Engine back in:


This is where you really need the frame spreader. It makes it very easy to get this spacer in, though space to actually turn the spreader is quite limited:


Having got it all back together, the next job is to repair the chainguard. Of course, I should have removed the gearbox sprocket before I put the gearbox back in - there is no way this nut will come undone with the gearbox in the frame, no rear wheel, and no brakes.

Sunday, 27 January 2019

Dry Build - Footrests

One of the item's I'd tripped up on while putting the crankcases in was the footrest bar. I'd not found the spacer that serves to separate the gearbox plates - or rather I had, but I thought that someone had mixed them up as the spacer I had was too short.

Anyhow, planning to replace the missing engine & gearbox fasteners with stainless I thought I'd set about making the missing spacer, so I bought some 3/4" 303 stainless round bar.

Then, of course, I found the missing spacer bundled up with the footrests and another footrest bar...


Oh well, I thought, I'll use that stainless bar at some point, resolving to replate the original spacer - but when I went to assemble it I found it was rather mangled, so I've made a new one:


This is designed to fit quite tightly between the gearbox plates and frame tubes, just as the front engine plate assembly and crankcases fit between the frame tubes at the front. I had to spring the frame tubes apart to get those in, so I made this frame spreader out of an M10 turnbuckle make it easier to avoid damaging the paint when I come to assemble it for real. I didn't want to be prying freshly painted tubes apart with a screw driver or a crowbar:


As you can probably tell, the centre of the turnbuckle was shortened and welded up, while the screws had both hook and eye removed and 3/4" ply blocks glued into blind holes in the plywood block. Here it is in place under the front engine plates:


Spacer fits perfectly now:



Tuesday, 15 January 2019

Dry Build - Rear Brake Pedal & Bell Crank

Let's have a look at the brake pedal and crank arrangement next. Here's the crank in place - the rod is very rusty & I broke it trying to dismantle it...


The crank is held in place with a hex head screw (which I think is 5/16" CEI) and a large washer - both of which are missing. There's a clevis on the end of the brake cable.


I'd thought I might buy a new rod assembly from Acme, but having attacked the original with the wire wheel I see that much of it (rod aside) is in pretty good shape and would replate, so I have sat the broken bits in the vice with some Plus-Gas in them.


Drilling that broken rod out is going to be straightforward. Here's how I did it:


I decided to use the lathe to ensure that I drilled the broken std out on-centre. Since it was tricky to hold the banjo shaped swivel in the chuck, I made a simple collet out of a bit of aluminium round bar. The larger part of the swivel would sit behind the collet, which grips the parallel part.


I used the collet to hold the swivel in the 3 jaw chuck, and drilled the bit of broken rod out with progressively larger drills. I cleaned up the thread with a tap.


The rest of it cleaned up easily with the wire wheel. The bolt and washer used to retain the bell crank in the frame are missing - I understand ( thanks to Mick D on the AOMCC Forum) that the bolt is 5/16" CEI, about 3/8" long. The thread needs cleaning up:


I've turned up a new washer from a bit of 25 mm 303 round bar:


Moving on, the brake pedal is all good and the spindle fits nicely into it's hole in the frame.


No idea why it is plated though. The spring, although it fits and is working, is very pitted and will need replacement:


I've made a new brake rod from a piece of 1/4" round bar. The collet chuck and tailstock die holder are very useful for jobs like this:


Here we go, new and old:


All fitted up. Next step is a new brake pedal spring and then the brake light switch.