Salty25

My Feedback: (9)

I've had this engine for about four years now. It has served me well over the years.

I put it in a WM Aeropet a couple of months ago and have been having problems with it every since. It is mounted inverted but it was inverted on the last plane I flew it on so I didn't think that would be an issue.

First I can't seem to get the prop nut tight enough. No matter what I do the prop keeps spinning on me and breaking the spinners. Yes I am using the double nuts that came with the engine. Using an APC 13X6 which I have used before, have also used a 13X8.

Today when I took it out to the field I ran into some other issue. I started it up and it was running fine. The spinner didn't fly off within 10 seconds like it had been doing. So, I thought maybe I got it tight enough this time.

While running up the engine I heard this loud, "Plat" as the engine died. Another guy at the field heard and asked what that was. Well, I wasn't sure so I tried to start it again. Still had compression and things seemed ok.

However, my started couldn't turn it over. It would get stuck on the compression stroke. I tried it on my Saito 180 and it turned it over and started it just fine. Of course I thought the starter battery may be low so I tried the other guys starter and got the same result.

So I took off the glow plug, it turned over smoothly. Took off the rocker covers, both rockers move and have clearance and the valves did move also. Put the plug back on and tried again. It spun over with the starter until I hooked up the glow driver, then it stuck on the compression stroke again.

I tried another glow plug and got the same result. Brought it home and took the engine back plate off to be sure it wasn't flooded or something. Everything looked good from what I can tell.

Any ideas or suggestions?

rcdude7

My Feedback: (264)

My guess is that the engine may have been running slightly lean and detonation was causing the prop nut set to loosen.

If the engine sticks at some point, don't force it, there may be some internal failure and the inards will have to be inspected to see what is causing this problem. Without inspecting the engine it is hard to guess what went wrong.

Are you comfortable taking your engine apart? If not, you can send it to horizon.

w8ye

My Feedback: (16)

Saito 72's have a problem with the intake manifold leaking where it goes into the head.

The fix requires a new back plate and new O rings from Horizon to seal the intake manifold at the head.

The symptom is that you can never get the mixture adjusted correct and the engine stay that way during a flight. It will drive you nuts.

Salty25

My Feedback: (9)

That is what so strange to me about the whole thing. I could turn the engine over by hand, the compression felt normal. However, the starter would not turn it pass the compression point.

If I take the head off do I need some special type of device/tool to put it back on? I've taken OS and Magnum engines apart before but never a Saito.

What would I be looking for besides something that is obviously broken?

Thanks for the input.

BobbyGee

My Feedback: (3)

On a SAITO there's no cylinder head - the whole cylinder comes off.

Here's an article that helped me get through my breakdown of a 72. I'd never done it before either. It was a big help.

http://www.flyrc.com/articles/4stroke_howto.shtml

If something's broken it will be pretty obvious. It might be a valve lifting rod, too. take a look there.

BobbyG

Salty25

My Feedback: (9)

Well, I took it all apart. I did see a little carbon build up but nothing broken, or bent from what I saw. Is it possible the timing gear jumped or something? I don't really see how it could; the gears seemed to be in good condition.

Well, I'll have to pick up a gasket set before I put it back together.

I'll have to read that article when I go to put this back together, not sure about lining up the timing marks. The old Chevy 350 was easy, two marks pointed at each other. LOL

Salty25

My Feedback: (9)

With the starter not being able to turn it over I was thinking of something that would case increased pressure. i.e. valve stuck closed.

Salty25

My Feedback: (9)

I put a new back plate and O ring seal on it about two years ago. It was running fine when I had it on my Paramount. I put it on the Aeropet and it started all the weird stuff. From one to the other only took a few days to build and mount.

Same fuel, same glow plug, same prop; just different plane.

Salty25

My Feedback: (9)

Both planes flew with inverted engines.

Blazer1

My Feedback: (1)

The problem is with the mounting location of the tank in the Aeropet.

blw

My Feedback: (3)

Salty,

The best bet is to do what W8YE suggested. I've been thru that and it really made my hurt for a while. Get some small washers to go under the backplate screws. Use locktite of some kind on the screws when you put the backplate back on. My screws would work themselves loose and back out in only a few minutes of run time. Get some RTV, and make a bead around the top of the manifold, where the manifold goes into the cylinder. Do this under the metal clamp washer, so you get a good squish and seal when you tighten things up.

I love my .72 with these mods to it. I love the sound of a .72 with some throttle put to it.

BobbyGee

My Feedback: (3)

Timing's easy - piston at Top Dead Center and the timing mark on the cam gear pointed straight down.

BobbyG

Salty25

My Feedback: (9)

Called Horizon today about the gasket for the engine. They don't have a listing for the gasket, not even in the engine gasket set. Can I go back together without a gasket or will it leak? Worse than a Saito normally leaks.

w8ye

My Feedback: (16)

You were talking to the Janitor?

http://www.horizonhobby.com/Products...rodID=SAI7232A

BobbyGee

My Feedback: (3)

?????!!!!! [:-]

I got the same gasket set and some other spares from Horizon about a month and a half ago. They had everything I needed and delivery was lightning quick.

Talk to someone else. It's part no. SAI7232A

BobbyG

Salty25

My Feedback: (9)

I asked for 7232, as it was listed in the manual. The first rep didn't see a listing for it and she put me in touch with a tech guy. Of course, he never came on and I was work so I had to get going.

I'm not sure what to expect when I put this thing back together. I broke it down and didn't find anything wrong, so why should it start working now all of a sudden?

Maybe it is the tank position as someone thought. I'll try it on the test stand and see what happens before putting it back on the Aeropet.

I don't think it was running lean, I've been flying this engine for some time now. I had problems when I got my first Saito with running it lean and learned to keep it good and wet.

blw

My Feedback: (3)

What you will find new is the faulty backplate to manifold seal has been fixed, if you do it like we are suggesting. This is the source for slight and intermittent leaks, and the lean runs.

Everything that you describe is an engine that is running lean and backfiring. That is what is loosening your prop nuts and messing up your spinners.

Salty25

My Feedback: (9)

OK, I should have the gasket set in by Wed at the latest. I'll put it all back together and let you know how it works.

daveopam

My Feedback: (9)

Salty, I bumped this up because I wanted to remind you to tell us what you found out.

David

Salty25

My Feedback: (9)

Oh, I won't forget. The parts are supposed to be at LHS tomorrow. I can't make it down until next Mon, unless the shipment comes in early and I can get there in the afternoon. I hate how work gets in the way of fun. [>:]

Salty25

My Feedback: (9)

Told ya I wouldn't forget.

Anyway, I picked up the gasket set a few days ago. I finally got the time today to put it back together and try it out. I reset the high end needle and started it up. That puppy fired right away; like it wanted to sing.

So I ran it for a bit on the stand. I couldn't find the crate I normally chain my engine stand to so I just grabbed the coffee table. Ssshhhh, don't tell the wife. No, she would kill me; it is an old one I use in the garage.

After running for a bit I put it back on the plane and ran it some more. Darn things run great now.

But I do think I know what the issue was. While at the hobby shop I figured I should pick up some more glow plugs. Well, looking at the plugs I realized I put the wrong plug in the Saito. Maybe I'm wrong on this but it sure runs great now.

blw

My Feedback: (3)

You really had me rooting for you there....a real man just grabbing the table when he needs it!!!

Salty25

My Feedback: (9)

I may be crazy... but I'm not stupid.

MJD

My Feedback: (1)

Next time polish the top up and keep the story going..

My Saito .72 definitely behaves differently on different plugs - I ran a few others but always come back to an OS-F, and seem to get the smoothest and best behaviour on that. Some stunk, some were okay but just not quite.

MJD

blw

My Feedback: (3)

Mine seem to run slightly smoother with Saito SS plugs. I can't say for sure.