Every motorcycle rider gets to the point where they want more power. For the Cyclemaster owner, this is usually as you are straining on the pedals up a steep hill, wondering if the engine in the back wheel is just a dead weight making your task harder. So what can be done?
First thing is make sure it’s running at its best, in standard condition. Critical things to check are ignition, fuelling and exhaust.
Getting the basics right.
1/ Ignition. The Wipac magneto needs to make a spark that jumps 5 to 6 mm in air when spun at around 1000 rpm with a drill. To get this you need clean points with a gap of around 0.016″, a good condenser, a flywheel woodruff key that is a tight fit (so peak magnetic flux happens at the right time) and an HT lead that is low resistance and not leaking to earth (often where it exits the case). For the timing, I find a little advance makes it rev out better but a little retard gives better low end torque, so you choose.
2/ Fueling. The first thing is to be sure there are no leaks. Often the Amal carburetor mounting breaks at one of the 4 segments where it clamps onto the steel inlet stub. I struggled with leaking here for months until a friend repaired it by making a new brass adapter that was threaded into the machined carburetor body. Not an easy mod but it works perfectly.
The next place where you need perfect sealing is the crankcase. The crankshaft, drive side, rubber seal must be in good condition AND correctly positioned. The seal runs on a small step on the crankshaft and it can miss this step if either the seal or crankshaft are incorrectly positioned. The seal may not be pressed in far enough or the crankshaft may be too far towards the disc valve side – NOTE: the datum position for the crankshaft is against the drive side bearing – away from the disc valve. The pressed metal cover over the disc valve can also come loose and leak (as mine did), so check it’s sealed.
Next you need the right mixture to give maximum power (called stoichiometric mixture). I find the standard jet and needle are fine on the Amal carb, with the needle in the middle position, as recommended in the manual. The main thing that causes incorrect fuelling with a clean carburetor is flooding, either due to poor sealing of the float needle or vibration. I strongly recommend the carburetor is flexibly mounted – see my earlier blog we have lift off – thanks to Bernoulli….
Finally, you need the correct fuel oil ratio. Remember adding more oil , weakens the air petrol ratio, and adding less richens it. I use Castrol semi synthetic at around 30 to 35:1, making the motor slightly rich which helps it run a little cooler, avoiding the risk of seizure, particularly on hotter days.
With everything set correctly, this is what my spark plug looks like. It’s perhaps a little weak but this was after a “fast” ride
3/ Exhaust. The exhaust ports and silencer must be clear of carbon build-up, or the motor will be well down on power. I regularly soak my silencer in a strong solution of caustic soda, even leaving it overnight. You can also drill a hole through the main baffle plate like I did to help the gases flow more easily.
So once you have the basics right, it’s time to think about more advanced options, if you still need more power. This is where I am at the moment, so none of the following modifications have been tried yet.
To get more power from an engine you need to burn more fuel in the most efficient way, in the shortest possible time – easy? Maybe…
To get more fuel into the engine you could fit a larger carburetor and open up the inlet tract. Another way, would be to open up the slot in the disc valve plate, so it’s open longer. I’m not sure of the standard timing but it could be open from just before bottom dead centre (BDC) to just after top dead centre (TDC). Opening just before BDC would perhaps allow the suction through the transfer ports, to draw in more fuel.
The next step is to get more fuel above the piston. This is done by removing metal to open up the transfer ports and even cutting slots in the piston skirt and barrel to make the transfer passage as large as possible. Another way, (that has been used on Cyclemasters I’m told) is to raise the cylinder by fitting a spacer between it and the crankcase. This has the advantage of also opening up the exhaust port for longer, so the gases escape more effectively. I’ve heard it said that the exhaust port is the limiting factor on a Cyclemaster engine but I don’t know if it’s true. I’ve calculated that a 1 mm spacer would open the transfer and exhaust ports for approximately 38% longer, so this could give a very significant power increase.
However, if you raise the cylinder you need to machine a similar amount from the the cylinder head to avoid reducing the compression ratio. If you remove more then the compression ratio increases and the downwards pressure on the piston increases, improving power output. I’d probably remove metal from the top of the cylinder, rather than the head, to maintain the same gap between the piston and the circular profile in the combustion chamber.
You then have to ignite the fuel, consistently at the optimum time and to do this you need electronic ignition. The good news is that there are cheap ignition kits available from China that can be made to fit, particularly if you have a friend with a machine shop, or have access to machines and can use them yourself. The kits are the internal rotor type, so you are faced with 4 challenges
- You need to make an adaptor to fit the new rotor onto the crankshaft taper,
- You need to drill and tap the primary chaincase casting to mount the stator,
- You need to make a dummy flywheel to add mass to the rotor
- You need to experiment with the rotor position to get the best ignition timing as there’s no manual you can follow.
Here’s a photo of an Chinese electronic ignition that a friend fitted to a Cyclaid. He made an iron flywheel and tells me it starts much easier and revs far better.
Lastly, an expansion chamber could be fitted to get better suction through the engine. The shape of the expansion chamber is critical to give maximum suction at the desired rpm and a lot of experimentation would probably be required to get the tube diameters and lengths right.
Now for the extreme..
If time, effort, cost and complexity wasn’t a problem, then you could try these modifications:
- Bore out the cylinder to take a bigger diameter piston. The cylinder wall is quite thick, so the standard bore of 36mm can probably be opened up to at least 38mm, giving a capacity increase of 12.5% to 36cc.
- Rebuild the crank with an offset crank pin, to increase the stroke from 32mm to 36mm. This increases the capacity by 14% to 41cc
- Build a twin cylinder Cyclemaster by connecting the crankshafts.
- Fit the Cyclemaster engine forward of the seal tube, with chain drive to a multi speed hub in the rear wheel (e.g. 14 speed Rohloff hub – circa £1,000!!)
I say extreme, but I know people who have done these modifications, to a Cyclemaster so they do work.
Problem then would be, how do you stop a fast Cyclemaster?
Maybe that will be subject of my next blog?