Thedrew

Background: I have a Saito 72 that was on a piper cub about 5 years ago. I wrecked it on its maiden voyage, the impact pinched the intake manifold shut, plane was totaled. I took a long break from this expensive hobby. I've recently bought a Great Planes Escapade ARF and installed this motor onto it, after tearing it apart and replacing the manifold of course. Finally started her up this morning.

I know that the mixure is set very rich, I backed everything off just to make sure I didn't start her up lean. It started right up... @ half throttle. Removing the glow ignitor cause the engine to die, dropping the throttle below half also caused the engine to die. What concerned me is the seemingly low RPMs at half throttle (my tach is out of batteries so i was just going to try to get the idle needle set) and the intense vibration. As you see in the video, the vibrations seemed to stop when i gave it a little more gas but resumed after taking it away.

I think my timing is off by one tooth, im confident its not more than that. The prop is balanced, the spinner i didnt check, only assumed it was good. All screws are as tight as they need to be.

Can anyone confirm this is a timing and not a mixture issue? If the timing is slightly off, what are the odds that i caused permanent damage to the motor? I started it 3 times, no more than 1 minute each run.

Thank you in advance for any insight and/or advise.

-The Drew

[youtube]http://youtu.be/KW2pIjQSMoY[/youtube]

wcmorrison

My Feedback: (2)

If you have not opened up the engine it is unlikely that it is out of timing.  If the mixture is very rich, it may take a glow plug driver to keep the glow plug lit.  Before I would go tearing the engine down, I would replace the glow plug with an OS Type F plug.  Read the notes at the top of the engine thread about Saito's and go to http://saitoengines.info for further information.

daveopam

My Feedback: (9)

I can't tell much from the vid. But I would definatly put an OS "F" plug in it. the timing is easy to check. Pull the plug and both valve covers. With the engine at TDC on the exhaust stroke, both valves should be slightly open. I say pull the plug so the engine turns easy, plus you can put a toothpick into the plug hole to find TDC. The other thing to check, is the O ring on the intake tube. If you are not very carefull putting the intake yube in the O ring may not seat correctly. If you get an air leak up there it will never run right. I like to swing the carb to the side while seating the O ring and when the tube is far enough in the head. Then swing the carb down over the back plate and put your screws in.

David

blw

My Feedback: (3)

Drew,

I'm assuming the engine must be well broken in if it's off of another plane. I love my old 72 and it is one of my favorites.

You most likely have the old style plastic backplate. You could be having to set either/both needle valves rich to compensate for the manifold leaking air. This will have you chasing your tail. The backplate flexes over time, and that allows air to enter the engine intermittently at the head where the manifold fits. This is a well documented problem.

Since this will cause all kinds of headaches, you should order a new backplate. The Saito 82 metal one fits, but I don't think any are in the U.S. and have been on backorder for a year or longer.

Use small washers under the screws that hold the new backplate. Use some sort of thread locker as mine would back the screws out in less than 5 minutes of running. I used a little epoxy.

When you are reassembling this, you need to use some automotive rtv under the shiny manifold washer. Application isn't really critical. If you haven't used rtv before, you can get a tube at any parts house. It goes on gooey and dries like firm rubber. Use something like a toothpick or very small blade to lay a bead around the black viton o ring at the cylinder head. Magnification helps as you do this. Dab a ring of rtv over and around the o ring. You are looking to put down a bead that almost looks like another o ring on top of the viton one. Then, gently insert the manifold and shiny o ring over that. Tighten the screws and let it dry overnight. This is an important step in fixing the 72 problem.

Replacing your vent line from the tank to the muffler tap is important. If the inside diameter is collapsing under pressure due to age you are in for a treat trying to track that down. Lines begin to go bad more often that most people think.

This may be your problem but there could be something else, I couldn't tell much from the video. Either way, this is fix that the 72 needs eventually.

Good luck as the 72 is a fantastic engine.

daveopam

My Feedback: (9)

As a temporary fix for a flexing back plate. You can run a zip tie around the cylinder head and the intake tube just above the carb. This will hold the tube tight to the head. Also make sure your throttle linkage is adjusted right. I saw one that would flex the back plate every time he killed it.

david

JollyPopper

My Feedback: (6)

I just picked up a .72 Saotp yesterday and the first thing I noticed was the plastic back plate. That kind of surprised me on a Saito, but it started and seemed to run well. I didn't put a tach on it, but I guess I'll have to check it out for air leaks. Would a small bead of RTV do any good around the back plate?

JollyPopper

My Feedback: (6)

Saotp? What the hell is that? Talk about a typo!!!!!!!!!!!

blw

My Feedback: (3)

Backplates on 4 strokes don't have to be air tight. It is a big thing on a 2 stroke.

1QwkSport2.5r

I would think a 4-stroke glow engine would run without a backplate even....

jaka

Hi!
First of all it looks as if you engine mount is to flimsy!

blw

My Feedback: (3)

Huh?

You can't see it.