ORIGINAL: sam123
ORIGINAL: optech
I've not been following .21 size engine development but aren't they all ABC style construction nowadays? If so, they wont last long on Gasoline fuel. The ABC construction is pretty temperature specific when running. Gas burns hotter so I wouldn't expect the engine to last long. Look for a ringed type engine if you really want to do this.
Mike
Hmm, the engine I have is of ABC construction, like you mentioned. I guess this could cause some problems [:@]. Do you think I could avoid this by keeping it as cool as possible (using a cooling fan and avoiding full throttle), and use a higher oil content? If the engine does end up dieing, I will definately upgrade to a bigger, ringed engine.
Optech, is right. This is a point I 've forgotten to mention to you. Conversions work better for ringed engines. But then again, in the years before glow plug, the small engines at least were not ringed. And I have seen many plans and patents of old engines (like the Atom and 0.099 of Arden design) and I haven't noticed a ringed piston. Neither a ball bearing in the con-rod... And considering the materials available back then, I assume all these made it worst.
I think that by going conservative (i.e at least 14:1-15:1 gasoline-oil mix, rich settings, sufficient cooling) you will not have a problem.
After all, the worst that can happen for an ABC engine is to increase the clearance between piston and sleeve and lose power, or stall the engine. It has the characteristic that it cannot "stick together", because Brass sleeve expands more than the aluminium piston and so you are protected from sudden destruction. The best of course is to have the metals already stabilised, i.e. have the engine run-in with glow fuel and glow plug.
As for longevity of the engine is considered however, keep in mind that increased temperatures and less lubrication may cause the converted engine to wear before the glow version. How fast, I do not know. My experiment is still ongoing for the four stroke...
Try to convert a cheap engine as this is an experiment. You didn't tell us which engine you are thinking of converting.