FH Crankshaft 3 Review

Confusing isn't it, all these crankshafts.

Number 3 is another small journal crankshaft I have acquired.

It's missing a few flywheel bolts, but at least someone has released one of the sludge trap plugs.

Now, before we go any further we need the reference dimensions for comparison with the results of the dimensional survey. Here's the data sheet again:

The timing side journal in this one looks fairly good and measures 1.355" in several positions, which would grind to -0.020"

The oil pump drive thread and the timing pinion journal will clean up I think.

The big ends vary a little - 1.418" on the timing side and 1.417 on the drive side, which is about -0.040"; Drags have shells down to -0.050", so these could be used one way or another.

The splines, drive side main and shock absorber thread will clean up ok.

FH Crankshaft 2 Review

A while back, I dismantled and measured up the small journal crank that came with the 1955 engine I have in my 1958 FH kit, now christened 'Crankshaft 1'. The post is here: https://ariel...small-journal-crankshaft.html.

As we discussed, the 1958 cases should be fitted with BSA's new large journal 'Rocket' crankshaft and in view of the wear on the 1955 crank, considerations of originality and the fact that a well known retailer had a standard large journal crank available at a very reasonable price led me to replace it.

Here it is; no flywheel, somewhat rusty...

Of the three crankshafts I have, this is the only large journal crank. We'll call it Crankshaft 2.

It's got nice looking splines and drive shock absorber thread:

Less nice - looks like the pump drive end has had an argument with Thor, King of Hammers and not come off too well. And why is that bearing stuck half way along the journal?

Other than that, no new horrors, but we need to understand what we are aiming at. This BSA service sheet gives us the dimensions we are aiming at; small journal cranks on the left, large journal on the right:

We need to get it up in the vice and clean it up.

First job is to get some oil on that bearing and pull it off. We need to decide if this crank is a pile of scrap and the ashes of burned currency or whether it will become the foundation of my new bike's engine.

Cleaning the surface rust of the big end journals reveals some smooth surfaces, with no score marks, but with small rust pits:

Both of these journals are 1.655" - 1.656" diameter, measures in several places - which equates to an unworn -0.030" grind; not the standard cranks I was hoping for but usable nonetheless. We'll need to polish them but for now we can tick that box.

Next is the dubious looking oil pump drive thread. It's 9/16" - 20 CEI, left hand - no chance of finding a die for that, unless I buy one and that in itself might be a problem. I could clean it up in the lathe, but that will be another challenge as the end has felt the hammer and the centre drill hole is deformed and probably wont fit the dead centre in the tailstock - so we'll need to buy a fixed steady if we are going to try that approach. Breaking out the thread files cleans the end up nicely enough that the old oil pump drive fits beautifully and reveals their is still enough thread for the lock nut.

Next stop, the timing side main bearing journal. Unfortunately, this measures 1.242" - which is about 120 thou undersize. I can make a bush to fit it, since it's in good shape but is it safe to use? If I use it I will have to recut the oil way, since that has virtually been ground away.

The thrust face is a bit untidy - there is a small ridge which will clean up.

Thinking about this, I've realised that the drive side journal is 1.18", with all the bending load that is subject to from the primary along with the cyclic loads from the power stroke. I guess a 1.242" timing side journal will always be OK.

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.

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.