MOKI 2.10 XL GASSER (Conversion)
***Excerpt from Just Engines***
The latest engine from the factory
Because of Moki's robust design and potent power output, it seems to me that this engine would make a fantastic GASSER! And that's precisely what I'm going to do here. Our GSW Webhost Sonny Coleman, has volunteered his MOKI 2.10 XL to the cause. This will be one of my favorite conversions. The Moki lends itself to be a gasser for many reasons; it's light weight, powerful, and very well made. It's also is higher compression than other glow engines. All that's needed to make the conversion is a good Walbro carb, a good electronic ignition, a 1/4-32 sparkplug, and a few adapters.
So here we go!
The first thing I like to do is to fabricate the carb adapter. I made this one out of T-6 aircraft aluminum and machined to fit perfectly into the crankcase where the original carb was mounted.The Walbro I selected for this conversion is a WT-529. It has a 13.7mm venturi which has about 5 times bigger CFM of the original Moki carb.
This engine was in a crash so Sonny decided to replace bearings. He ordered Stainless Steel High Performance Boca Bearings and I installed them.They are as smooth as glass!
I used a torch to heat up the bearing flange, and the old bearings just fell out. I use the crankshaft for my bearing alignment and setting tool. I heated up the flange and set the new bearing in place with the crankshaft. This ensures perfect bearing alignment.
Here is the completed engine. You'll notice the shielded sparkplug cap is for the 1/4-32 sparkplug. I didn't want to give up the glow plug option. The Pump line to carb is where the Walbro gets the vacuum/pressure to operate the fuel pump. The ignition sensor is basically a ring that rests on the bearing support and overhangs the prop hub. It can rotate as needed to set the timing, and held in place with a #6-32 setscrew. The prop hub has a very small 1/8" diameter magnet imbedded in it. I decided to use the largest Walbro I had available, which is a WT-683. The WT-529 would work OK too...
I made most all of the conversion components retro-fit, so I didn't have modify the Moki any more than absolutely necessary. I set the Ignition Timing at +26 to make starting a little easier. After it's been run I'll bump up the timing to +31 degrees.
This is a 34.4cc engine so the closest benchmark engine would be the Zenoah G38. So I'll use a G38 to compare to.
The Moki has a 1mm longer stroke than the G38. This should translate to good prop spinning torque, but only running it will tell the story. I'm only slightly confident regarding the Ignition Module though. It's a "no-name" module I had laying around. It requires 6.0 Volts to operate and it doesn't have spark advance. I'll give it a try. I do have a CH Ignition, but I'd have to change out the sparkplug wire to accomodate the tiny sparkplug. This is a real pain in the ass.
The 1/4-32 sparkplug didn't work out all that great as it fouled out way
too easy. To correct this problem, I modified the head to use a CM-6 Sparkplug. The CM-6
uses a 10x1.0mm thread. It's a lot cheaper too.
This was an excellent solution for the sparkplug fouling. The next item to work on is the ignition. While the one I'm using works OK, it doesn't have spark advance. I really prefer having spark advance...
The strange looking ignition is actually a CH which was adapted for bench testing. It can't be used in flight because of the RFI it emits.Since the ignition doesn't have spark advance I set the timing to a conservative +26 degrees to minimize kick-back while starting. I also tested the engine with an 18x10 APC and a Walbro WT-645. The audio track is with this combination and it spooled up to 7770 RPM, and having an idle of 1640. This is considerably stronger than a Zenoah G38. Even comparing the Moki to my MODIFIED G38, it still out runs it by a small amount. It's only 150 RPM's, but more is more. I have been experimenting with different carbs looking for the ideal setup for this Moki. Right now I'm testing a Delorto carb and it appears to be the best choice. It provides the best idle and smoothest throttle transition. I just wished it had a choke.
I had to make a pump adapter for the base of Delorto so the pump would operate. The photo shows the Tygon line connected to the adapter. This adapter works for Walbro's too.
To make this conversion the ultimate gas engine you really need a needle bearing rod. Air Hobbies offers a rod-re-working service whereby they install needle bearings in your rod and intall a hard sleeve on your crankshaft. This will make your Moki conversion perfect!
I might note here that Mark Model Engines already has a 1.80 gas version available.
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