Fuji-Imvac BT-50 EIS Rotate The Cylinder (jug)


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Sometime in your RC flying career you may want to replace an existing engine with a FUJI. This can be a problem since Fuji engines have their muffler & carb on opposite side as compared to other similar size engines. This presents you with the difficulty of having to move the throttle linkage and change your exhaust cut-out in your cowling. Another nice plus to this cylinder rotation is that the regulator diaphragm on the carb is out of the prop blast!

An easy alternative is to rotate your Fuji cylinder to match up to other engines. This could be considered as un-orthodox by Fuji and its distributor. But the fact is, you CAN switch it and it works perfectly.   

Rotating the cylinder on a FUJI BT-50 EIS isn't difficult. But you do have to be careful. IF your engine HAS NOT been run it's even easier. I will start with an engine that hasn't been run since this is the easiest job.

First, remove the sparkplug, and four bolts that hold the cylinder on. Then remove the pressure pulse line on the crankcase. Now, bump the cylinder on each side with a rubber mallet to break loose the paper gasket. Make sure you don't ruin the gasket.   Rotate the piston to near TOP DEAD CENTER. Gently lift up the cylinder up about 3/8" and rotate it 180 degrees. Set the cylinder back down and insert the four capscrews. After the capscrews are tight, rotate the crankshaft several times to be sure nothing is binding. Now, close off the old pressure Pulse nipple.

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The original fitting is press-fit into the crankcase so I soldered this fitting CLOSED. You can do most anything to close it off I just prefer soldering.       

Now look at the opposite side of the crankcase, you will see a cast lug just like the one (with the nipple) on the other side except this one is un-drilled. Drill the his lug to fit your new nipple. BE CAREFUL not to hit your crankchaft!

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I used a piece of 5/32" brass tubing for my new fitting. I also used a small amount of JB Weld to be sure I have a good seal. Thouroughly CLEAN the inside of the engine to be sure there's no debris left from drilling.

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Connect up your pulse line from the carb and YOU'RE DONE! Was that SIMPLE, or WHAT?

OK "if" your engine HAS BEEN run and you want to rotate the cylinder, you have TWO OPTIONS. One, you can put new piston rings in it OR you can rotate the PISTON 180 degrees. The reason for this is, your rings are probably already seated. IF you don't change the rings OR rotate the piston you will likely have little or no compression until the rings re-seat, and they my never re-seat. So new rings OR rotate the piston is manditory.

You may wonder about the PERFORMANCE...

My engine was brand-new and I can tell you this: The benchmark prop for a Fuji 50 is a 20x10 Carbon Fiber spinning it at 7400 RPM. MY engine spun a 20x12 APC prop at 7400 RPM... you be the judge.

Now the down-side: More than likely, you will VOID your warranty.  However if you take reasonable care of your engine it's not very likely you will ever need your warranty anyway. In my 37 years of RC Modeling, I have never needed to warranty an engine. However, you will have to decide this for yourself.

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If you are careful and take your time you can EASILY change the cylinder orientation of your FUJI engine without any adverse effects. But again, this is completely up to YOU and your mechanical ability. I make absolutely no claims, and I do not accept responcibility regarding modification to your Fuji engine.


Fort Worth Texas

Copyright 2007 M. B. Fuess