by loucrane » Fri Jul 14, 2006 12:46 pm
Jim,
You should be able to run your engine on glow engine fuel, with 25% (preferably all) castor, and no or little (say, 5%) nitromethane. FAI fuel (80% methanol, 20% oil) likely needs added castor to bring total oil fraction to at least 25%.
Gear lubes are very different from the types used for high speed sliding contact as in piston on sleeve, shaft in bearing, crank and gudgeon pins in connecting rod. There may be vintage motorcycle shops around which carry heavy, single grade motor oils. And, yes, 70 Weight is the SAE 70 spec. 3 to 1 (petrol to SAE70) should work. For early attempts, perhaps a bit more than 25% oil? the spark engines were designed to run on the heavy motor oil and petrol, and in these proportions. Modern oils and pre-blended 2-cycle fuels for lawn mowers, etc., are more likely to cause early and severe damage to an O&R engine.
I hope you have an understandable wiring diagram for a typical spark setup. Key adjustments are spark plug and breaker point gaps. About 0.010" to 0.012" should be close. Make sure the breaker points are fully open when you check and set the gap.
I'd suggest that you set up for initial running on a test bench, and with the battery not installed, work through reaching and adjusting the controls.
All wiring should be cleanly connected for minimal losses. By the way, you will likely short (earth?) yourself across the high voltage wiring at some time in the near future. The voltage may be 9,000V or more, but at very negligible amperage. A surprising jolt, yes, but usually not damaging. Wouldn't recommend doing that if you rely on a pacemaker...
With a glow fuel, mixture settings are far more tolerant, as the methanol will burn under quite unfavorable conditions. If you do start with glow fuel, expect to need to close the mixture needle considerably when you switch to petrol/SAE70 fuel.
The lever just behind the propellor is the spark advance/retard control. Turning the lever in the same direction the prop turns 'retards' the spark, and against prop rotation 'advances' it. For first starts, be sure this lever is well 'retarded'.
You can check that the circuit is functioning correctly by removing the spark plug and laying it against the cylinder head. Switch the circuit on and rotate the propellor. At about top dead center, the spark should fire audibly, perhaps visibly. ...Every time. It may not fire at fully retarded lever position, so 'advance' from that end a bit, until it does.
Don't leave the circuit 'on' any longer than necessary. While the engine runs, the breaker points are opened and closed - of course. At rest, the breaker points are more likely 'closed' - which can drain your battery quickly, and overheat the coil.
When the engine starts, it will likely run roughly. Bring the spark lever up a bit, which should smooth things a bit. Particularly on glow fuel, the exhaust should be quite smoky (vapor, actually, of oil and some unburnt fuel.) Lean the engine a bit, but not so that the exhaust vapor is severely reduced. The oil that is in the exhaust gases shows that it has passed through the running parts and remains unburnt.
In a way, a spark engine can be tuned similarly as a diesel. The spark lever directly controls ignition point; a diesel's compression screw has the same effect. The mixture adjustment works the same in both cases. Unlike in the case of a diesel, a spark engine will run quite 'rich' safely. Ignition is from the spark, not compression in a very small combustion chamber. And, as often the case with model diesels, load, RPM and spark point can be coordinated for relatively low vibration. Also, over-advancing spark is not kind to the engine, nor to fingers at the next start (should you omit retarding it a bit.).
The sounds are different, of course - spark is usually quite a bit louder! If that is a problem in your area, I have no suggestions...