beware, this gets technical….

so switch off now, if this type of stuff bores you.

In this blog, I’ve listed some things I’ve learnt when re-building my Cyclemaster engine and some tips that may help you. They are based on my experience but if you don’t agree with something,  then feel free to just ignore it.

1/ Put the small crankcase casting on after the clutch casting

You can then support the crankshaft at the opposite end to take the reaction from pressing on the drive gear and the clutch housing. This also ensures the crankshaft is fully into the drive side housing and avoids the risk that it may be mis-aligned and put excess pressure of the disc valve.


However you must put a support between the crankshaft webs – see below

I measured the crankshaft web gap at 6.88mm, then found a spanner that measured 6.83mm thick – perfect. Just insert the spanner between the webs and you won’t damage the crank, if you have to tap the clutch casting on.

2/ Warm castings before fitting them.

This makes it easier to fit them where bearings are a press fit. I use a heat gun, gently, on low heat setting.

3/ Repair crankshaft taper and magneto fit

My crankshaft was damaged and the magneto wasn’t fitting correctly. This is the reason it sheared 2 woodruff keys. It also explains why the flywheel was loose when I got the engine and the Woodruff key was missing.


Look closely and you can see the crankshaft taper is swollen. This was repaired by gently filing the raised area down, then putting fine lapping compound on the shaft and spinning the flywheel without the key fitted. When the fit had improved, I finished it off by lapping the joint with chrome polish – Solvol Autosol in my case.

The flywheel still didn’t tighten onto the taper correctly and this was because the nut was also too tight, as some threads were swollen.


I used a gauge to measure the tpi (threads per inch) at 24 and my vernier to measure the thread OD (outside diameter) at 0.305″. The nearest thread I could find was 5/16″ x 24tpi UNF (Unified) so I bought a die to cut the thread so the nut would go fully onto the thread.

                       CUTTING THREAD WITH DIE                 FINISHED SHAFT

Hopefully that’s the end of my flywheel problems. Only downside is I’ll need a “Puller” to get it off now, as previously it just came off when the nut was loosened.

4/ Make your own gaskets.

It saves a little money and is quite a satisfying job to do.I’ve been collecting bits of brown paper for a while, so just select a piece that is the right thickness and rub it over the casting. It’s like tree bark rubbing but use a dirty finger rather than a crayon. Then I tap the holes very gently with a small spanner to cut them out.

Finally cut the profile, using curved nail scissors for the tricky bits if necessary. And this is the finished gasket.


5/ Do a little tuning when it’s in pieces

I can’t be certain this will help but improving gas flow can’t do any harm. I polished the transfer ports and removed sharp edges, as shown.


6. My tips for fitting clutch Hub

The Cyclemaster manual recommends you fully assemble the clutch plates, then fit the assembly to the output shaft (LH photo). However if you do it this way you cannot see if the Woodruff Key is correctly located. So I suggest you leave the cover plate off and fit it when the clutch is on the output shaft (RH photo) – see below:

Also I find it helps to hold the key in position with a small screwdriver down the back.

Finally check you can see the end of the key. 

DSC_0022 TEXT.jpg

If the key is not in position you will have no drive and the engine will need to be opened again.

7. Amal carburettor

The main jet in the carburettor is very small as the engine is small and does not need much petrol. This makes the jet very sensitive to dirt and it blocks very easy. My engine was running badly then would not start so I cleaned the jet.

Some people say the filter disc from the float chamber must be fitted a certain way or the fuel does not flow through it. I cannot see why the fuel would not flow both ways but I turned mine anyway.


and now it starts, runs and idles well – see video. I think it was dirt in the jet but I can’t be certain; turning the filter may have helped.

After running for 30 mins at low revs the spark plug looks like this. 


It’s dark brown which indicates perhaps a little rich but this is better than white as that indicates too lean, which can lead to piston seizure. So I’ll leave the fuel mixture as it is, until the engine has done more mileage.

But to do that, I’ll need to get it into the Raleigh, or “Sir Walter” as he’s called and that’s the next job.



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