9E Conversion to 225cc

[Tony T140]

Hello,

I was thinking of boring a spare 9E barrel to take a 1H piston for a 225cc conversion. I checked out the dimensions at the bottom of the barrel spigot, particularly iwo the inlet ports, and there doesn’t appear to be enough material for it to be rebored to at least the required 63mm.

Has anyone else successfully converted a 9E barrel and was it necessary to modify the inlet porting?

Thanks for your help.

Regards,

Tony

[John Wakefield]

I dont think its a very good idea, it will leave the cylinder wall thickness very thin and the extra 25cc wont have much effect. Many years ago I had a go cart with a 197cc 8E engine that had been bored to 225cc, the cylinder broke away at the base.
Much better to find a 31A (250 barrel with thin base flange which will bolt straight onto the 9E bottom end, alternatively you can fit a 32A 34A barrel if you fit the 1/4" longer conrod to the flywheel assy.

[teamferret]

I've ran a couple of bored out 9E barrels with no problems, they do vary and i seem to remember going through the many that my dad had at the time and choosing the chunkiest. As John says, there is not much difference in performance but at the time it suited me to go down that route

[Tony T140]

Thanks for the advice. I have already fitted a 31A barrel to my 1958 20TA, but I thought I might try a 1H conversion for my latest build as I have some 9E barrels lying around. It sounds as though the benefits are small so I'll have a look around for a 31A barrel.

Thanks again for the advice.

Tony

[John Wakefield]

Whilst on the subject of overbored Villiers singles. There was a conversion back in the 70's to increase the capacity of the 32A / 37A to around 260cc using the piston from a Starmaker. This involved boring the cylinder from 66mm to 68mm. The piston had to have two bronze bushes fitted to accommodate the smaller dia gudgeon pin of the 32A. Again little of no improvement and not worth the cost involved. I think the idea was that it put the bike in the 350cc class so pot hunters could get an over 250cc award in trials that gave that award.

[dave higgins]

Most 2 stroke engine tuners improve inlet porting characteristics & increase crank case compression to improve air speed, which creates a greater cyl volume of combustiable fuel, at the same time, creating enough gas flow through the exhaust to clear the cylinder, but at the same time, create enough back pressure in the cylinder to prevent early distarge of combustable fuel/air mix.
Get that right & then you can start the never ending task of chasing out the weak points of the rest of the motor!.

[IanCordes]

Whilst on the subject of overbored Villiers singles. There was a conversion back in the 70's to increase the capacity of the 32A / 37A to around 260cc using the piston from a Starmaker. This involved boring the cylinder from 66mm to 68mm. The piston had to have two bronze bushes fitted to accommodate the smaller dia gudgeon pin of the 32A. Again little of no improvement and not worth the cost involved. I think the idea was that it put the bike in the 350cc class so pot hunters could get an over 250cc award in trials that gave that award.

John.

You can do that by re-boring and fitting a regular Villiers + 0.080" piston these days. For every + 0.020" rebore of the 246cc barrel you gain 4cc, so + 0.080" = 262cc. That is what I have in my 20DC, which along with scrambles porting and a re-worked head, along with a massive raise in gearing, now goes quite well! .

I expect they experimented with Starmaker pistons back in the day because 32A-type were only available in a maximum + 0.060". Nowadays 0.100" pistons are available, giving 266cc.

Ian

[teamferret]

I ran stormer pistons when I was scrambling in the pre-60 class as they were bigger (and some my barrels were past the then oversize) and better quality, but they were shorter. I tried various ways to raise the inlet port to suit and it was always a quick bike but prone to seizing. my rials bike runs an oversized MZ piston at 71mm so is 280cc, but it feels a little harsh

Ian

[shelly]

You could try one of these new aluminium heads which are supposed to give more power