ROUGH NOTES AND BRIEF DESCRIPTION OF THE PROJECT SO FAR

( These are very very rough notes on how I converted a Russian Dnepr and sidecar to run on LPG. Hopefully one day I'll have enough time to update these pages so they are more informative and helpful)

Several months ago I bought a LPG kit with out any real plan as to what I would do with it until last weekend (December 2005) when I had the brain wave of fitting it to my Russian Dnepr motorcycle. There are several problems with the idea that needed to be worked around before it would work successfully.

These are basically
1) Carrying the fuel.
2) No specific kit for the engine.
3) The engine is air cooled.

I'll explain how I overcame these three problems individually.

1) Carrying the fuel.
The first and easiest to answer is carrying the fuel. This is no real problem as I have a sidecar on the bike and the tank I have fits conveniently in the boot compartment. The tank I have is from a caravan for fuelling a cooker, so apart from being small it has the necessary filler attachments, 80% cutoff and the all important blowout valve. The only real difference with this tank is that it is a vapour take off rather liquid but this turns out to be a benefit rather than a hindrance as explained below.

2) No specific kit for the engine.
This is not so much of a problem as most LPG kits are generally universal apart from the venturi mixer that sits on the carb. These are usually like an inverted gas hob and made to fit the carb and air filter and are unsuitable for a Russian motorbike So I made my own ventrui mixer. You can see how I made it in the photos below. The calculations and planning this are minimal, if not non-exsistant, and are of the "If it looks right then it is probably not far off" design methodology.

3) The engine is air cooled.
This is not as serious as first thought, (forget all this it is not relevant any more) especially if you have no previous knowledge of LPG systems and how they work. The problem is that a normal vaporiser fitted to a car is warmed using the hot water circulating around the engine cooling system however there is no water system on the Dnepr as the engine is air cooled. This supply of hot water is needed because as the LPG vaporises it chills so without this heat the vaporiser will quickly freeze up and stop working so an alternative solution is needed. I considered wrapping a copper tube around the exhaust pipe and running water through it to the vaporiser to heat it like that. I even considered using an electrical heater to keep it warm until I worked out how much electrical power I needed and the idea was quickly abandoned. Eventually I took the fuel consumption of the engine and compared it to the medium sized propane powered space heater and was surprised to discover that they were very similar. So this left me thinking - A space heater can run all day without the unheated regulator freezing up so why not a LPG regulator for an engine. Admittedly the gas bottle of a space heater gets a bit frosty but at least it carrys on working. This leads to two sub problems. The first being that all LPG automotive fuel tanks have a liquid take off and the evaporation takes place in the regulator and the portable gas bottles used with space heaters that have a vapour take off and the vaporisation takes place in the gas bottle. This is conveniently easy for me to overcome because my LPG tank is from a caravan and was for supplying things like cookers and so has a vapour take off so I have no problem there. The second sub problem is that an automotive LPG regulator is designed to take a liquid supply and I'll be feeding it with a vapour supply. My answer to that is to simply ignore this difference and carry on with the conversion.
Seriously, its not that much of a problem. I made a better job of getting around this in the BMW conversion.

PICTURES

Fig. 1. 10mm steel tube that are going to be the mixer inlets.

Fig. 2.  10mm steel tube brazed into place

Fig. 3.

Fig. 4.  Showing orientation of cutoff to encourage gas flow from the mixer inlet

Fig. 5.

Fig. 6.

Fig. 7.

Fig. 8.  Location of vaporiser (shiny thing) under the seat.

Fig. 9. Close up of mixer in position and tube attached. Larger tube is engine breather, Smaller tube is LPG feed from vaporiser.

UPDATES

UPDATE  (April 2006)

I've probably done 2000 miles on LPG and all is well with the engine. I've not been thorough enough to make any accurate estimates of fuel economy but it costs about £6 or about 14L to do about 100 miles.

There is no noticeable performance difference between petrol and LPG.

The Dnepr is not equipped with an electric start so its the kick or a push to get it going. But kicking the engine over does not put enough demand onto the vaporiser for it to start working so the only way of getting it to start unaided is to get the engine spinning by bump starting it. I live on a hill so this is OK for setting off on a journey but not always convenient or possible any other time. However if I first 'prime' the vaporiser by poking my finger through the vent hole onto the diaphragm so it leaks a bit of propane into the carbs and then give a solid kick to it there is the slim possibility that it will start, but not always.

Changing from Petrol to LPG is a bit of a pain due to the float bowls taking a good time / distance to drain allowing the switch over. This is almost impossible to do in town traffic as a bit of momentum is needed to keep the engine spinning during the 'spluttery' changeover period. However it is no problem on the open road or where the bike is above about 30 mph. Similarly you have to wait for the float bowls to fill before running on petrol again and if you stall in traffic it can be a problem.

Normal every day riding is fine and trouble free.

When I'm on the motorway or riding hard for about an hour the tank does chill a lot and is often covered in ice. I've measured the temperature of the tank and seen it below -15°C however there is still enough vapour pressure to work the vaporiser.  On very long motorway journeys the chill is more and I loose top end power and have even resorted to running on petrol whilst the tank warms. (see the BMW conversion)

UPDATE (May 2006)

The Dnepr engine is no more. The gear to the cam shaft lost some teeth and the engine is now written off as un repairable. However I have a BMW R80 engine in bits in a box in the attic and I think this is an opportune moment to get it running and installed into the Dnepr frame. The BMW engine is electric start, YAY!.

(The amount of people I know who gently mock me about it being the LPG that caused the failure is tediously annoying.)

UPDATE (August 2006)

After much work with an angle grinder, welder, a selection of big hammers and plentiful cups of tea I've managed to fit a BMW R80 engine to the Dnepr. Not just the engine as is the common conversion but the whole power train - engine, gearbox, final drive transmission and rear wheel. There is a whole story of problems surrounding this conversion that I decline to tell here. Needles to say the engine is running on LPG.

UPDATE (September 2006)

Probably clocked up close to 1000 miles on the BMW-Dnepr and all is fine, the welded together bits have not become separated and the rebuilt engine is still running as it should. The LPG conversion is also operating as it should and I'm getting better MPG from it than the Dnepr, which is odd as the BMW engine is 150cc bigger, so apart from going a bit further for each fill the tank is chilling a bit less so the icing problem is hardly significant, even on long hauls on the motorway. The electric start is simply fantastic and makes starting on LPG easier. Most days it fires up after 8 to 10 revolutions of the engine and it starts almost immediately when the engine is warm.