petrol conversions

[Martyn Perks]

Hi all, need your collective thoughts! Am thinking of fitting an ignition kit from just engines onto my OS70 CZ that is in my Hirobo heli. Main reason is to improve the fuel consumption and lower fuel costs, as it gulps it faster than i could pour it down the drain! Anyone any experience of this?

[Engine Doctor]

Dont waste your time and money as you wont get the same sort of power from the engine with petrol . You will also have to keep a high oil ratio as the engine will have plain bronze big and little end bearings that will sieze if you cut down to normal petroil mixes . Try some of Southern modelcraft fuel . Fully synthetic 20% nitro costs about £15 a gallon and unlike the stuff with fancy coloured oil etc .

Good luck

E.D

[TonyS]

ED,

That's interesting. Just watched Tony Nijhuis video of his new 70" span Spit. This is a 120 4 stroke converted to petrol because in his view it's cleaner, doesn't damage the coverings like Nitro based fuel and is much more economical to run.

Is this not correct?

T 

[Solly]

Hi, I cannot understand the "plain bearings and higher oil" argument. I've been running a Merco 61 on sparks for over 10 years now, using 2.5% synthetic two-stroke motorbike oil and it's as good as new. Believe me, it's done a LOT of running in that time.  

[gerald stansfield]

Martyn,

I have converted 3 of my engines to petrol, an O.S. 30, an A.S.P 52, and an A.S.P. 82. and they run 20% 2 stroke oil. It is cheaper,cleaner, and they sound brill.

Gerry.    

[Doug Ireland]

Posted by Solly on 16/10/2010 15:17:52:

Hi, I cannot understand the "plain bearings and higher oil" argument. I've been running a Merco 61 on sparks for over 10 years now, using 2.5% synthetic two-stroke motorbike oil and it's as good as new. Believe me, it's done a LOT of running in that time.  

 2.5% is a bit on the lean side (40:1) for my liking. I converted a SC52FS to petrol some time ago and it runs happily on 5% (20:1) oil. On the other hand, my MVVS 45 recommends 40:1 ratio for running in then down to 30:1 for normal operation. The Wizard of Oz wrote a good article on plain bearings/oil ratio a while back, good reading.

[Simon Chaddock]

Doug

I think you mean the other way round (30:1 running in, 40:1 normal) or at least that's what the MVVS web site recommends.

 

Just an aside really but petrol itself has some lubricating properties whereas methanol has virtually none so apart from the higher calorific value of petrol a significant element of the improved fuel economy comes from the use of a higher fuel to oil ratio.

[Doug Ireland]

I stand corrected, thanks Simon.

[Engine Doctor]

As said in earlier post petrol will not give same power etc as methanol and as the application was for a high reving engine in heli he would be wasting his time .Petrol engines are designed with needle roller bearings in both big and little end bearings and ballbearing mounted crank. They also have ringed piston to reduce friction ,all this designed to use tiny amounts of oil . Petrol conversion in a fourstroke for use in a plane is a diferent matter and should give  give bags of torque and as fourstrokes dont rev  like the two strokes the lube requirements  will prob be ok but should still be higher than the 30 to 40:1 that petrol engines are designed for .Dont confuse the ratio with a percentage as 40:1 is only 2.5% oil and glows run on 20% oil ,a big difference  ; most f/s engines are ringed and crank and most cams are ballraced . the only plain bearing on most is the con rod so for safe running you would probably need 10 to 15 % oil (approx 10 to 6.5 :1 ratio ) . Even the Saito  petrol F/s use a higher  oil content. Has anyone had a bad experience from a petrol conversion ? Lets hear from you .

Regards.

E.D

[David Turner 5]

I bought one of those Rexel units and fitted it to an Enya .60.

 

I compared various parameters, running the engine as a petrol sparkie, a methanol sparkie and as a glow (augmented by a glow-driver at low rpm).

 

When running on petroil (8% Aerosave), the engine ran poorly and it was impossible to satisfactorily set the carburation.

 

Things improved when I ran methanol and spark ignition.

 

 

BUT, by far the best performance was  methanol and an augmented glow. Better pick-up, transition and idle. Noticeably better.

 

Maybe I'm a duffer and did it wrong. Dunno. I[ve no doubt that someone will come along to relate how their Enya runs great with spark ignition.

 

 

I think that a proper metering carb would address most of the problems with the conversion, but I've yet to get around to trying one.

 

 

Meanwhile, out of interest, my Saito 1.80 ran in my Stampe for 32+ flying hours without a dead-stick. The engine has a pump fitted and a glow augmentation. I've had a few petrol engines, (mostly magneto-type industrial conversions, such as Zenoah, Ryobi, Kawasaki, Quadra) but have yet to match that level of reliability.

 

So, Rexel ignition unit for sale ... offers!

 

 

 

Saito's originally recommended 3.5% oil mix (IIRC), but after numerous reported bearing failures, have opted to increase the ratio to 5% (I think).

[Engine Doctor]

Hello David . I forgot to mention the carbs on conversions . As you point out any successful conversion need the proper carb to get the metering right , and as you cannot use ex haust pressure for petrol ,it has to be a pumped walbo type carb. A few years back a lot of large Supertiger conversions were about . An aftermarket needle roller con rod was available but no adapter for a proper carb  so they disappeared from the market. The reason I believe was that they were notoriously unreliable (deadsticks) even as a glow engine so converting to petrol just made matters worse. I know someone will say "they have  an XYZ engine they converted to petrol X years ago and it hasn't missd a beat but they are the lucky ones. To sum up if its designed for methanol then thats what it will run best on and vice versa for petrol.

 

[David Turner 5]

I did, years ago, run a McCullogh on spark ignition and methanol.

 

Now, that experiment worked pretty well.  There was little appreciable difference between the two fuels ... except that methanol is half the price of petrol. But, then, you do use more of it..

[GONZO]

To fit a Walbro carb on a Super Tiger 2300 (and possibly 3250) use this easily obtained ADAPTOR Used on Evolution/MVVS 26cc engines - get the gaskets, heat insulator and bolts etc at the same time (total cost about £20). Scrole to bottom of THIS page to see 2300 conversion using authors DIY adaptor and other mods. VIDEO of ST 3250 on sparks, gas and with a Walbro carb.

[David Turner 5]

Yeah. I reckon that those big Tigers would make great engines, when converted to petrol. And cheap, too. The big Irvines would be pretty good, as well.

 

 

Mind you, they are pretty good as glow engines ...

 

 

A big Tiger, running nitro, but using a Walbro Carb, might provide phenomenal power and reliability, at a very reasonable price. 8% oil will fit the bill, I should think. And, since it's the oil which is the expensive "bit" of the fuel, the overall cost needn't be too high.

 

I pay 60p per litre for methanol, but I can have it for 40 pence per litre if I buy in bulk.

 

 

Trouble is, I don't use enough fuel to be much bothered about the price.

[Martyn Perks]

 

Its not so much the cost really, I can live with that (just)  but I do get fed up of 8 minute flights which gets through 750ml fuel even with a header tank. I've had a couple of close calls with the motor running real low in flight and one day it will catch me out! I love flying this machine and the engine is 100% reliableso I am reluctant to mess too much. Also cheap fuel, I believe, is the cause of many peoples' problems with engines so I use a good quality Model Technics fuel with high synthetic oil content for many years and several Helis and planes.

 

Perhaps  I should buy a Raptor again to thrash around the skies?

[Engine Doctor]

Hello Gonzo. Some excellent pics of conversions of supertiger's especially the needle roller big end. The carb adaptors at £20 arent bad value : add  the cost of the con rod conversion ,an  ignition module and a suitable walbro carb and the cost soars .   I doubt though that these parts  would fit a os 70 cz which started this thread but nice conversion for big two strokes.

 

E.D