I just received a new Fuji-Robin 25cc 2 stroke gas engine (for free). This is a Japanese built utility engine used for trimmers and brush cutters. I was really pleased until I got the casing off and discovered that the power takeoff is on the opposite side compared to the flywheel. If I make a prop adapter for the flywheel side, the rotation direction will be opposite for a normal prop. If I use the power takeoff side, the engine would have to be mounted with the flywheel toward the firewall.

Any suggestions? I would really rather use standard props than pushers. Is there any reason why the engine shouldn't be mounted with the flywheel toward the firewall? Alternatively, how well would the engine run backwards - I realize I would have to play with the timing.

Thanks

Ross

If it is a piston ported it'll run either direction. The timing will be the same. Honest, Mark Rose

The intake and exhaust timing will be the same, but the spark timing would be off if you run it backwards. But if you adjust the spark timing it will run the same,backwards. Mark

Put the blower housing,starter back on temporarily and looking at it from the flywheel side,pull the cord and see if it turns counterclockwise. If so your good to go with a prop on the flywheel side. I have one converted but havn't run it yet. not sure about that white plastic carb yet.

The pull cord is on the flywheel side and the rotation is clockwise. As I mentioned, the work shaft is on the opposite side of the engine and this would work with a prop hub attached (correct rotation). The problem would be that the flywheel would be at the back of the engine. It has a walboro carb.

Ross

Well not exact numbers, you would have to move the flywheel about 60 deg cw or the coil 60 deg ccw.

The pull cord is on the flywheel side and the rotation is clockwise. As I mentioned, the work shaft is on the opposite side of the engine and this would work with a prop hub attached (correct rotation). The problem would be that the flywheel would be at the back of the engine. It has a walboro carb.

Mark
Other than changing the spark timing do you think that would be any other issues with running in reverse? I don't know too much about engine design!

Any thoughts on a prop for this thing and what RPM I might expect? It won't be a major powerhouse but I have a project in mind for it. Any engine hop-ups recommended?

Ross

Every G23 ever made has the flywheel or mag rotor on the firewall side...No problem, other than a mount.....

you could probably bolt an alum plate to the crankcase and use spacers between it and the firewall, depends how the case is made i guess. main reason i use electronic ignition is to get rid of that big flywheel out front but i've never had a problem with the way the g23 is set up, it actually more sense.

Be careful when changing rotation on these engines. You may find that when running the engine that the Prop adapter and prop will come unscrewed from the engine. This puts you and anyone near you in a very bad situation. :^(
Cvan
P.S.
There were some insedences of this type of happening, listed under one of the other headings on this site.

I was wondering about reverse rotation as well, got an oddball project in mind of bolting two weedies together back to back of the the three bolt round backplate of the McCulloch 25cc engines, as of yet its still undecided on the crankshaft coupling, could just be on ground flat the other slotted with a sleeve over everything.
Then I use a two cylinder spark box and after making sure both are at TDC use the timing from the front engine to spark both, OTOH maybe both would balance better if one was TDC and the other BDC. Yhe rear engine gets spark on BDC, OR...split the spark wire into a "Y". And unless I buy the CH kit I'm going to use an old 9volt powered hand taser for the high voltage rquirement, its small and lite and see if my electronics will come up with a hall switch or something, would be a project just to see if its possible to make an inline weedie conversion

It's been done..there was one with two 3.2 Sachs and one with two Q35s..
There are some larger ones, also an inline 3 made from 4.2 Sachs/Precision Eagles...Flown by Chip Hyde at Madera, went about 180 mph on all three, about 150 when one of the three came loose...Dennis Crooks had a P38 that went 195 mph using two 8.8 inlines made from Husky parts..The engines were coupled together by grinding a hex on each shaft a plugging them into a hex socket...The Q 35s had a different coupler and made a heavy engine..Dick Sizer from Minnesota coupled two Go Kart engines together, weighed about 18 lbs, made lots of noise but never ran well...Bill VanLeeuwen made a really nice 250cc inline, ran well, awesome sound, but was not competitive with the 289cc Herbrandson oppposed twins..
There's a website in Canada that advertises an engine called a Merlin, two 3.2 Sachs engines, about $2500.00..I had an inline twin made from two G62 engines, hex coupler, got looser each time it ran..Made it back into two singles....3W made a good inline also....
Most inlines are kinda heavy for their power output.....
The hex coupler seems to be the best way, it needs to be a very tight fit to stay together....

I have been building and fabricating a concrete batch plant for over 7 years now, been installing a ton of waterpumps, 460v three phase stuff, there is some interesting couplings that are small like 1/4" or so in the Graingers catalogue, mostly I have been setting up the standard lovejoys of motors up to 40hp, myself I was interested in the idea because of it being something different, some planes like for instance the P-51 scream for inlines, if I had a goal it would be to recreate a Merlin V-12 for a 30% plane, or just to have a scale running benchtop model, 4cycle and all.

I remember still that unique RollsRoyce Merlin sound from the Reno Air Races, did you know about the Pond Racer back in '94? A modern day approach to a P-38, very new then.
I was there went it failed in flight, watched it go down , sadly the pilot died.