Posted: Tue Dec 11, 2007 12:37 amI've been using these and similar retrofit modules for at least 25 years. I've even moved them from one worn out engine to a newer one. Out of probably a dozen or more modules, none have failed. I had also planned on trying these modules on my Rotax engines.
Don's installation looks very nice and neat. However, because of a concern for heat affecting the modules, I planned on mounting mine externally. I've always mounted the modules externally and as far from heat sources as possible.
Now, if external heat from the engine impinging on the module was the only heat source, I would feel pretty good about predicting that they would hold up if mounted externally. Unfortunately, there's a second heat source at play that, in this installation, might very well cause modules to fail prematurely. Most of the installations I've made were on small engines that never ran much over 3600 rpm, and were 4 stroke types with a spark every rotation (so called wasted spark type), so the module is called upon to switch the load that fires the spark plug 3600 times per minute at full trottle load.
Now, on the 2 stroke Rotax operating at close to 6000 rpm, and again firing the spark plug every revolution, the module will be seeing almost twice the duty cycle of the units I've installed, and that may generate enough additional internal heat to destroy the module.
Perhaps, if there turns out to actually be a reliability issue using these modules, installing the modules so that they only have to disperse internally generated heat in a cooled environment would mitigate the problem. Personally, I had planned on mounting the module external to the engine. I also considered mounting it where it would be in some prop blast, mounted to an aluminum, finned heat sink using thermal heat sink compound, and thermally isolate the assembly from the engine - just to be on the safe side (the old belt and suspenders philosophy). If you are using these modules in Canada they may never give a problem, but here in the mid-Atlantic region of the States, 100+ weather has to be taken into consideration.
Chappy
Don's installation looks very nice and neat. However, because of a concern for heat affecting the modules, I planned on mounting mine externally. I've always mounted the modules externally and as far from heat sources as possible.
Now, if external heat from the engine impinging on the module was the only heat source, I would feel pretty good about predicting that they would hold up if mounted externally. Unfortunately, there's a second heat source at play that, in this installation, might very well cause modules to fail prematurely. Most of the installations I've made were on small engines that never ran much over 3600 rpm, and were 4 stroke types with a spark every rotation (so called wasted spark type), so the module is called upon to switch the load that fires the spark plug 3600 times per minute at full trottle load.
Now, on the 2 stroke Rotax operating at close to 6000 rpm, and again firing the spark plug every revolution, the module will be seeing almost twice the duty cycle of the units I've installed, and that may generate enough additional internal heat to destroy the module.
Perhaps, if there turns out to actually be a reliability issue using these modules, installing the modules so that they only have to disperse internally generated heat in a cooled environment would mitigate the problem. Personally, I had planned on mounting the module external to the engine. I also considered mounting it where it would be in some prop blast, mounted to an aluminum, finned heat sink using thermal heat sink compound, and thermally isolate the assembly from the engine - just to be on the safe side (the old belt and suspenders philosophy). If you are using these modules in Canada they may never give a problem, but here in the mid-Atlantic region of the States, 100+ weather has to be taken into consideration.
Chappy