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.  

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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.

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Here is a top view of the new head. The big 14mm sparkplug worked out great and fits the new head like a glove.

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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.

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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.

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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.

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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!     

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Copyright 2006 M. B. Fuess