Thunder Tiger PRO 1.20 Gas Conversion * Page Two*
In my quest to have the ultimate micro-gasser I made some additional changes. My first change was to get rid of the 1/4x32 sparkplug. There's nothing wrong with these little sparkplugs except they are expensive, and hard to find. I attempted to modify the original head to accept a 10mm sparkplug. This didn't workout too good. There wasn't enough metal thickness support a bigger sparkplug. That's when I decided to make a new head for the TT 1.20. Because I'm making it, I decided to go to a gasketless 14mm sparkplug. These are available anywhere for weedeaters. The new head is made of T-6 aluminum barstock, and was turned on a lathe. The cooling fins are now horizontal instead of vertical like the original.
Here you see a side by side comparison of the heads. I raised the compression ratio to 10:1 on the new head, because it's now a gasoline engine.
Here is a top view of the new head. The big 14mm sparkplug worked out great and fits the new head like a glove.
This is the engine setup with the new head. It's a very clean looking engine, and has that go-fast appearance.
The next item on my upgrade list is to replace the CH Ignition with a newer (more state of the art) Electronic Ignition. I selected an RCEXL Ignition. This is the one Dessert Aircraft uses on the DA-50 and Copperhead uses it on their Venom Series engines. It's much lighter than the CH, and it has very dependable electronics. It looks cleaner too.
As you can see, this is a very professional looking setup. It has an electronic spark advance built into it as well. The shielded sparkplug cap fits the new sparkplug perfectly.
Here is the completed engine ready to fire up for the first time (after all the changes). The ignition timing was moved up to +28 degrees since it has spark advance.
The new ingition is temporarily mounted until after the engine has been run and tested. Here is a photo of it running. The engine fired up very easy. It idles very smooth at 1890 RPM, and it throttles up fast to a peak RPM of 8730. The carb could use a little tuning, but I'm happy with the overall results! The new head does a great job keeping the engine cool, almost too cool.
It took me 3 1/2 hours to machine the head but it was very much worth the trouble. The engine runs FANTASTIC, and it actually weighs a little less!