Hitchcocks Forum

It crossed my mind, using ancient technology, that a petrol start diesel might be possible using a Bullet engine. Rather than fit a diesel lump, remove the distributor and fit an injector pump in its' place. Crankshaft ignition would need to be used and a small, auxilliary petrol tank - the main fuel tank being for diesel. Raise the compression to around 10:1 and keep the carb, but fit an injector into the decompressor hole, the spark plug being retained to start the engine on petrol. When warmed up, turn off the petrol and flick the injector pump control to 'run', the empty carb now just controlling air intake via the throttle slide. Am I missing something, or could it work? Paul.

Best add, the spark plug would be kept in action on the diesel running, as on some of the old engines I have in mind, to help fire the diesel at a relatively low compression ratio for this fuel. Paul.

Hi Paul. I always thought that old type diesel engines controlled the power output by controlling the fuel pump injection rate, leaving the air intake fully open at all times. This is why the diesel engine is so thermally efficient as the full compression (often around 15:1) is always being put to use, no matter what throttle is being used, whereas on a petrol engine the full compression only acts on a restricted amount of air unless flat out. Obviously the throttle could be arranged to control the fuel injector pump and the carb could be operated by handlebar choke type lever as it would only be used for starting.....The other thing is the crank strength. With standard 6.5:1 CR the big end does not have a reputation for a long life, with 10:1 or higher, I can see it failing in next to no time. Using only 10:1 CR will take away a bit of efficiency too. It would probably work though for a bit of fun.

I doubt the bottom end would take the load, unless you sleeved cylinder to make it much smaller; perhaps it would be easier to convert to TVO?

,i think your idea may fail spend £300 and fit a brand new diesel engine of the yanmar clone variety,fit & forget if you need any ideas go to dieselbike.net ,the petrol engine conversion was done years ago

sorry chaps but I have an inbuilt aversion to oil burning engines... In built through having my breathing gear screwed up by the shyte spewed out by London buses, taxis, trucks & diesel engined cars & vans...............My 2 drachma

I know a petrol to diesel conversion was done years ago, Grunda, there was a Bullet converted by the millitary with 4 valve head etc, what I envisage is different and could possibly even run on both fuel types independantly. It would certainly save messing around with engine plates, spacers and the like to fit another engine, if the original lump could be used. As I said above, I know it's old technology, International Harvester and Allis Chalmers were doing simillar long before my time, but with digital electronic ignitions and all of the much more advanced diesel injection equipment around these days, it might be worth another go.

hi BW give it a go let us know how you get on,advice for bryan move to the country for fresh air you,ll not get non down the smoke although i,ve been known to polute the countryside with my oil burning!!

Hi BULLET WHISPERER ---- I like this type of Research Engineering, good fun and a chance to put your training and experiences to a practical problem. Just a few thoughts of my own for now }-------Fisrt, are you looking for the plodding, slow revving type of diesel or a high-speed version ?? I would consider the former as high-speed types usually employ 2-stage injection etc. ans this might complicate matters initially. The Electra X bottom-end construction would seem to offer a reasonable chance ?? H-section, forged steel rod onto a roller big-end. The standard piston is not much use for our us, maybe a domed, long skirt item can be sourced ?? ---BUT---why have this dual-fuel hybrid when most diesels start-up ok anyway using the Cold-start, full-fuel position from the pump's fuel rack.?? Let's simplify things a bit and just go for a Diesel Conversion Kit instead ??--thus still in keeping with your original thinking.... Can the spark-plug hole be converted /adapted to take an injector ?? LES H is correct re}--- speed control via movement of the fuel rack in the injection pump, that's a straight forward throttle cable job! A soleniod-operated fuel cut-off valve within the fuel supply from the tank to the injection pump energised by the "ignition" switch...We already have a de-compressor facility to help initial cranking against the 15:1 CR. The induction path now becomes a straight forward open tract with just an air filter at the inlet. The electric start will now DEFINITELY be of benefit !!---Sump oil will have to be changed to a diesel type ---- I use that on my Goldwing anyway !! That 5-speed gearbox can now be put to some good use as well. Hmmm---very interesting !!!WARNING !!!!-------- CONTRAVERSIAL STATEMENT IMMANENT!!! >>>>>>>>>> At least it would LOOK like a proper motorcycle....Uh-Oh, hello Mr Grunda----- can I buy you a pint ???

alan are you saying my enfield doesn,t look like a motorcycle or the engine doesn,t look like a motorcycles ?because your right about the engine it was probably destined for a cement mixer or roadsaw or dumptruck but heres the point it cost £300 for a brand new engine complete with electrics it has a handy cooling fan to combat running hot in any climate and it does at least 160 to the gallon at 56mph although i agree it doesn,t look like a motorcycle engine its better ,ask our lads on sunday filling their petrol bikes up at scunthorpe while i was drying my jeans off at the side of the fan!!all i can say is you know it makes sense !!!still smoking g12 (speeds quoted are from gps readings not dodgy enfield speedo) happy days !