Monday 26 May 2014

1921 Ner-a-Car Update 3

The arrival of the time of year normally associated with summer has meant that I have fewer free weekends, so work on the Ner-a-Car has slowed a little. But here is a summary of a few small jobs that I have been up to on it.

The last instalment ended with a seized engine bolted to my milling machine. No amount of pushing and pulling on the flywheel seemed likely to get it moving, so I decided to try something forceful but gentle: Hydraulic power.
I used the same technique as I have used on brake calipers in the past. Grease guns make really quite a lot of pressure, and grease is fairly thick, so easy to keep inside things.
I machined up a ring to block the transfer port, bolted a lump of aluminium over the exhaust port and made a widget with a thread for a grease nipple in the inside and an 18mm spark plug thread on the outside, inserted it in the cylinder, and started to pump. It worked a treat. The picture below shows the piston skirt just emerging. At this point it became clear that the inlet port would also need to be blocked.

The easiest way to do that turned out to be to make a really badly designed gasket with no hole out of a bit of aluminium sheet:

Unfortunately it turned out to be all for naught, (other than another usable cylinder) as the piston was badly cracked. 

The piston was also strangely clean. Perhaps someone forgot to use 2-stroke oil? 

The next thing to do was to do a survey of the sizes of the various pistons and bores to work out what the fit was like. Luckily I have a nice bore gauge which I found in a skip(!). 

It looks like the one good piston is a reasonable fit in the cylinder from what I keep thinking of as the "good engine" despite the faults that keep turning up. It might be a shade tight, but I believe that iron pistons in iron bores run lower clearances than I am used to, and I would assume that a 2-stroke piston sees a fair bit of cooling from the intake charge. 


If the engine is going to run then it needs a working carburettor. I have one but it had a a couple of missing screws, no cables, no cable adjusters, rusted-away springs and no handlebar controls. Other than that it seems perfect :-)
I cheated and bought the handlebar controls from eBay, the springs from Lee Springs and a couple of brake cables from Halfords. 
The brake cables had nearly the right nipples on one end, but not on the other, so I made some brass nipples and soldered them on. 

I made the adjusters from brass, drilled and threaded on the lathe, then made hexagonal by a routine that I have for the CNC mill. 

And here are the cables and new springs assembled into the throttle slides. Yes, there are two slides, a throttle slide and an "extra air" control. The bike has fixed ignition timing, but manual mixture control. 

The hardest part of making the missing screws was working out the thread. The bike has a lot of BSF and BA, but the carburettor was bought-in and could easily have been metric, or brass-thread, or proprietary.  So I made the screw on the end of a long bar and tried it in place before committing to a head. 

One head is square, and one is hexagonal. Luckily the CNC routine can do any number of facets. One of these days I will make some heptagonal nuts for fun. 

So, now the carb can be attached to the engine, and won't fall apart in the middle. 


With the inlet looking like it might plausibly work, it was time to look at the exhaust. I had no silencer at all, and the tube is a fairly specific size. Luckily I have a sheet metal rolling machine. It is rather useful, but not useful enough for me to keep it in my own workshop, it clutters the corner of my dad's workshop, 220 miles away. So, I scheduled a visit to see the folks. My dad also had some suitable imperial gauge steel, it was even authentically rusty. This picture is of it being rolled:

And after having the seam welded up. 

The silencer is made of a tube, two end-caps and a tie-rod through the middle. The end caps were probably originally pressed, but it's generally quicker and easier to spin things like this. 

This is the "silencer" with end caps fitted

The internal baffles:

And the complete thing with the mounting brackets. One original, one replica. 

The silencer is now festering in the molasses tank with the other rusty parts. 

Engine build-up.

With a piston chosen, and a carb and exhaust system ready to attach, it seemed like time to bolt the engine together, even if there was no spark from the magneto.

I haven't taken the crank apart on this engine (I had to take the crank apart on the seized engine to get the cylinder and piston off). So actually there wasn't much to do to bolt it all together. So it didn't take long to spot a bit of a problem. If you look you will see that the piston cylinder base and the crankcase top are not parallel. This seemed to me to be a sign of a bent con-rod, probably a result of the broken piston in this engine (or the cause).  So I did have to take the crank-case apart anyway. It's a very simple engine, and a roller bearing big-end, so not a huge job.

To test the rod I made a nicely-fitting test bar out of a length of ground steel bar and set the rod up on the T-slot table of the milling machine. With a set square it was plain to see that it isn't a subtle problem. 

Nothing that a bit of brute force and a long tube can't fix:

That's better:

 Halfords don't sell gasket sets for Ner-a-Cars, so I have been making them in the old-fashioned way, with a ball-pein hammer and the casting itself out of sheets of gasket paper.
This is the cylinder base gasket. First the cylinder base itself:

Then the outer profile and the transfer port. (I finished the transfer port with scissors)

A word on the technique here. It isn't like peining rivets, this is a very light action, trying to shear the paper between the edge of the casting and the hammer. 

I should have taken a photo of the assembled engine, shouldn't I? 

A lick of paint

My shed is too small to hold the Ner-a-Car, and spraying in the machine shop/garage seems like a terrible idea. Spraying outside is disrupted by the merest hint of a breeze, and rain stops play. What I needed was a spraying booth. Or, a gazebo. I bought one from eBay for £30. It was only after it had been posted that I noticed it was from somewhere less than 2 miles away. It was delivered while I was out, so got taken to the parcels office, 20 miles away. 

It was bigger than I thought, only just fitting in the garden. There was just room to walk round it. 

Being big did at least mean that it wasn't too cramped inside:

I think it looked more racy in the 2-tone primer. 

I am going to need a bigger garage, or some sort of multi-tier parking system. 


It is simply not worth the trouble of rewinding a magneto yourself, there are folk who will do it for less than £100, and have the right test gear, and do the job right. But I decided to have a go at it myself anyway. If I fail, I can always take it to a pro afterwards, after all. 

Firstly I stripped off the old secondary. An awful lot of layers of 40swg copper, looking a little discoloured, and with a hint of verdigris. 

And then the primary, 4 layers of 22SWG. The primary is the ball of wire top middle. A lot fewer turns than I had imagined, actually. 

Then a couple of fixtures to grip the core on my lathe for winding the windings. The right-hand side is a modified lathe centre with a screw thread for attaching special attachments, like the one I attached specially for this job. 

I have made a couple of guide wheels, and the next stage is to scour the internet for coil winders to see how they work. I reckon that the CNC lathe (which has an encoder on the spindle) ought to make a pretty decent coil-winder with the right software and attachments. 

I started this episode of the blog apologising for not having much to add. Having finished it, perhaps I have done more than I thought. 

No comments:

Post a Comment