Ken Adams is the owner of "Sunday Girl VIII"  and offered to share some information with me regarding the Zenoah engine.  After reading through Ken's e-mail to me I though how useful the information was and how many people would benefit from his experience.   I have therefore decided, hopefully with Ken's blessing to put the information on my web site.

Ken has four Zenoah engines in various boats - purchased at various times over the last four years. For Ken they have been faultless except for two occasions - one was at Eastbourne on the 28/10/2001 when one of the gudgeon pin circlips let go for no apparent reason - wrecking the piston in the process!

The other was a couple of years ago when the plastic dog in the starter distorted.

One modification that Ken found very worthwhile, which he has done with three of his four Zenoah's is to replace the stock cylinder barrel with a Bruce Hanson "tweaked "version. Hanson do two upgrades - one is what they call an "Indy" version the other - which he has, is an "Indy Pro Race" version. This conversion raises the 2.1 BHP (Break Horse Power) of the "stock" engine up to a reliable 3.5 BHP. The conversion uses the original design barrel and consists of:

* Raising the compression ratio by machining some metal off the cylinder base flange (lowering the cylinder)

* Taking some metal off the top of the exhaust port to increase the exhaust timing from stock 165 degrees to about 174 degrees.

* Raising the top of the transfer port to compensate for lowering the cylinder.

* Lastly (Ken reckons that this makes the biggest difference), gas flowing the transfer passages to mate smoothly with the transfer cut outs in the crank case. On the stock engine there is a significant step here.

This lowering of the cylinder also increases the inlet timing slightly.

The modifications are individually all very subtle (no wild timing) but collectively they add up to a big BHP increase.

A single ring piston instead of the standard two ring one makes for a freer running motor.

Hanson also do another upgrade - a fully balanced and pinned crankshaft - but you are paying about $100 for an extra 0.2 BHP power increase - just not worth it in my book! The model helicopter boys use this conversion though, because they want a motor with as little vibration as possible.

One thing to beware of - You do see some conversions which have a steel liner in a square shaped aluminium barrel. I've found that these perform no better than the Hanson ones but add 50% to the weight of the engine!!

Zenoah Engine Links