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Author Topic: Determining crank rotation?  (Read 210 times)

Offline Mark Mc

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Determining crank rotation?
« on: April 02, 2022, 05:18:27 PM »
At the Catoosa swap meet today I bought one of Bob Reeves' engines. I'd been wanting a Saito 30 for a while, and one of the engines on the table happened to be a FA-30S.  One of the club members said that he thinks Bob put a reverse crank in the engine.  Is there an easy way to determine which direction crank and gears are in this engine without taking it apart?

Mark

Offline Dennis Toth

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Re: Determining crank rotation?
« Reply #1 on: April 02, 2022, 07:42:20 PM »
If you remove the valve head covers and watch the valves as you turn the prop over you can see if on the compression stroke that the intake valve is closed. Try the normal direction and then the clockwise rotation. Another way is to have it hooked up to a fuel tank and choke it as you pull it through and see if it pulls fuel up.

If it is reverse rotation, Zinger makes wood pusher props that would work.

Best,    DennisT

Online Robert Zambelli

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Re: Determining crank rotation?
« Reply #2 on: April 16, 2022, 11:26:05 AM »
Hi, Gents Ė great question about the SAITO crankshaft.
Iíve been using these engines for over twenty-five years and as far as I know, there is no such thing as a reverse rotation crankshaft for the SAITOs.
If you look the mechanics of these engines, youíll see that the direction of rotation is determined by the relationship between the piston position and direction and the camshaft, the latter rotating at half crankshaft speed. Intake, compression, power, exhaust.
The SAITO incorporates a spur gear on the crankshaft and a twice-size spur gear on the camshaft. By using a special tool to lock the camshaft in position and setting the crankshaft at TDC, the two gears are brought into proper timing mesh when assembled. The cam lobes are machined onto the shaft and therefore not adjustable relative to one another.
There is a way, although not very safe to get the SAITO to run backwards, making marginal power. Letís say you are running muffler pressure and a uniflow tank. You flip the prop and the engine fires backward. The engine will actually draw fuel from the uniflow vent, through the muffler and into the engine via the exhaust port. The mixture will combust and the hot gases will exit through the carburetor. And yes, it can start a fire Ė Iíve seen it.
It should be noted that the OS four-stroke engines also have a gear-driven camshaft. The only difference is that itís driven by crossed helical gears instead of spur gears. Instead of needing a special tool, you simply align a small mark on the exhaust lobe with one of the screw holes in the cam housing.
Want your four-stroke to run backwards? Fear not, it can be done, but only with the ENYA engines! The ENYAs have two separate cams, each with its own drive gear. The intake cam must be rotated 70 degrees clockwise and the exhaust cam rotated 70 degrees anti-clockwise. The engine is now timed to run clockwise, looking from the front.
Have yourself some fun with four-stroke engines. Buy one that suits your needs (I prefer the smaller ones), set it up to your liking and just fly it. My SAITO 30 powered Little Cherokee has over 1000 flights and Iíve done one valve adjustment (when new) and thatís it. Never even changed the plug. Canít even remember the last time I adjusted the needle valve.

Offline Tim Wescott

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Re: Determining crank rotation?
« Reply #3 on: April 16, 2022, 11:46:25 AM »
Hi, Gents Ė great question about the SAITO crankshaft.
Iíve been using these engines for over twenty-five years and as far as I know, there is no such thing as a reverse rotation crankshaft for the SAITOs.

One could, in theory, manufacture a reverse-rotation camshaft, however.

There is a way, although not very safe to get the SAITO to run backwards, making marginal power. Letís say you are running muffler pressure and a uniflow tank. You flip the prop and the engine fires backward. The engine will actually draw fuel from the uniflow vent, through the muffler and into the engine via the exhaust port. The mixture will combust and the hot gases will exit through the carburetor. And yes, it can start a fire Ė Iíve seen it.

In theory you could swap the carburetor and the exhaust stack and get the same effect, without the excitement of waiting for your engine to catch on fire.  Depending on how Saito decided to time the engine, it may even work OK (I haven't tried it, nor do I know anyone who has, so don't go building a plane on the strength of this).  For it to work the same as regular, you'd need equal-sized intake and exhaust valves, they'd have to be timed in mirror symmetry around TDC, and you'd need to be able to run exhaust out the intake without it overheating.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Mark Mc

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Re: Determining crank rotation?
« Reply #4 on: April 17, 2022, 03:56:39 PM »
Thanks for the replies, guys.  I"ll play with it and see what I get.  I know that they can run backwards, because that happened to me with my older Saito .40 one day when it kicked back on start.

Markl

Online Robert Zambelli

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Re: Determining crank rotation?
« Reply #5 on: April 17, 2022, 04:43:18 PM »
For your information, guys, here is the factory diagram for forward and reverse running of the ENYA 46 and 53.



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