In 27 years of flying I've never run into an issue such as severe and perplexing as this and thought that I would see if any of you out there have any suggestions. I have a Saito 1.80 in a Great Planes Super Stearman and have been experiencing a multitude of issues with it. The engine was originally in a Sig Cap 231 EX and experienced a lot of the same issues many of which are contrary to the experiences with Saitos that I find from others (including the same engine in the same airframes). Just to answer a few questions ahead of time: all of the props are balanced, I use 15% nitro 2-stroke fuel and it has been broken in on a stand. Even though the engine is out of warranty it only has about 4 gallons of fuel through it due to the fact that it does significant damage to whatever it is mounted in and I took a few years off from the hobby.

Anyway here are issues:

1. Severe vibration to the point that it has broken bolts and most recently (this weekend in fact) it destoyed a Slimline pitts-style smoke muffler. It also fretted the exhaust port threads to the point where there are only about a 1/4 of them left which may make this whole thing a moot point. Hopefully they can helicoil it and I don't have to replace the cylinder.
2. Poor fuel draw (may be related to the above) but it also has the problem on the test stand. The needle valve has little impact on the top-end adjustment and rpm's top out around 9300 with a 16x8. Idle is very reliable and the engine transitions very cleanly.
3. The vibration really tunes up with props larger than 15" and it appears to reach a natural frequency with a 16x8 that if left running would dismantle an airframe in minutes. I've even changed props between the Saito and one of my OS 1.20s to see if it was the prop and the OS does fine. I've also tried Top-Flite, Master Airscrew, Zinger and APC props with the same effects.


Thanks in advance for the help!

G'day Mate,
3 things, first off, the engine is still running in, & also you are under proping it, a Saito 180 should have at least a 16x10, or up to an 18x8, Check out this Saito site, for more info.
http://saito-engines.info/prop_sizes.html
And last of all, although there may be more, I would check the valve clearance, Check the above site, under maintenance.

alan is right, a 16x8 is not enough prop, a 180 should use at least a 17x8 and no less, also did you balance your spinner?

just some thoughts

As long as you are using O.S F plug and a nitro/oil content according to instructions, it should be OK.

Since the idle is reliable and WOT RPM readings are within normal limits, it sounds like you are having a pre-ignition problem. Check your camshaft timing. I have experienced it on one Saito 80 with the same problem. With wrong timing, it can develop extensive vibrations above 1/2 trottle. This timing issue can also be the reason for the poor fuel draw!

On a Saito that is experiencing an ineffective HS needle, it's usually because the LS needle is set too lean, however the shaking indicates that the LS needle is set too rich in your case.

Thanks Alan. I've had an 18x8 on the engine with the same results. I do find it odd that the Saito link that you provided recommends different prop sizes than the engine manual. The manual actually lists the 15x8 as the starting point for the 1.80 which I always found odd since I run a 15x10 on my 1.20. I'll check the valve clearance and try it again.

Thanks again!

I'm still seeing a puff of smoke when transitioning out of idle so I think that I am running rich. It going back onto the test stand so I'll give reset it and see if the fuel draw and HS needle valve improve.

Thanks!

Yep. I've balanced the spinner.

That sounds pretty close to what is happening as the vibration really tunes up above 1/2 throttle. Would seem an odd problem to have on a relatively new engine but stranger things have happened. Although I love 4-strokes there is something to be said about the simplicity of a 2-stroke!

Looks like I've got some bench time ahead of me. Thanks everyone for the troubleshooting and I'll let you all know how it turns out in the end.

One final question: Has anyone ever had the intake or exhaust port helicoiled to repair thread damage?

I had a Super Tiger 3000 that vibrated like that. It vibrated so bad after about 4 runs
on the plane,it had powdered the balsa around the hinges and the control surfaces
came loose. Turns out the spinner had been miss-drilled and it was out of round. I
had balanced the spinner, and it was off a mile, but it did balance out.

Measure your spinner with some calipers in different areas around the circumference
ans see if it was drilled true.

FBD.

I had the same problems with my Saito 180 on my GP super stearman. Do the following:

- Place this engine in simpler airframes like Extras and forget stearman.
- Use dubro anti-vibrating aluminum mount.
- Forget 16x8 props. Use props equal or greater than 17x8 APC to lower rpms.
- Change the stock muffler (that is like bell) with the alternative Saito offers that is like cylinder and the inlet is centered to the top. Use teflon tape to lock the thread. It was the only way for me to solve the muffler coming-loose problem.
- Change rear ball bearing as it is of low quality from the factory and has big tolerance that allows the crankshaft to vibrate a lot. My engine was almost destroyed because of this and I mean the rod hitting the crankcase!
- Never operate the engine at WOT continously. Alway allow small brakes for cooling. Otherwise it will burn the silicone tubing at the muffler and deadstick. It can even destroy the preassure nipple at the muffler.
- Never lean HS needle too much because you will destroy everything.

After lots of trials and efforts to conclude to the above listed, I am now enjoying this powerfull engine but I always keep in mind the limitations.

Stelios

Have you verified the timing? It sounds retarded to me.
David

It's not as retarded as it sounds....


This engine shows symptoms of "leaning out above 1/2 throttle" due to early opening of the inlet valve. If the inlet valve opens early (one tooth wrong), the mixture will be lean since the engine will get a reduced fuel draw during the suction stroke at high trottle. High load gives higher pressure and temperature in the exhaust stroke and hence more reverse flow to the inlet manifold if the valve opens early. More reverse flow gives less fuel draw and leaner mixture. Leaner mixture reduces ignition delay and can lead to extreme maximum cylinder-pressure.

I've seen it before, fixed it. Just take out the plug and check inlet valve timing vs crankshaft angle.

[8D]I have been running my 1.80 with a 16X8 prop and it runs perfectly.
Never a problem. It use it to fly a Dynaflite Super Decathlon.

G'day Mate,
OK so you are running a prop, that is ok on a low powered 20cc engine, & you are using it on a high torque 30cc engine.
Sorry, but to me that is under propped.

The 16x8 is a good choice for a Saito 1.50 but not the 1.80.

[8D]I can only relate what works for me, the engine and the aircraft. What more can I say??

I have the same engine in the same airframe. Didn't see the vibration problem, but did see the fuel draw problem. I'm assuming that your mounted inverted. If so, put a occelating pump in and the fuel draw and uneven power will not be a problem. Mine was a dog until I added the pump, now I wouldn't trade it for anything else. Ever see a stearman hang on the prop?

Marv422

First thing, you don't know enought about glow engines to get the Saito needlevalves adjusted properly. Now you can keep playing with it till you ruin the engine and a few airplanes or find someone with enough experience to set the engine for you, simpliest way. I have seen the broken motor mount screws several times before and it is always improperly adjusted needlevalves. It seems strange but that is probally what it is. Once this engine is adjusted properly it is very smooth and powerful.

Buzz, I agree, I'd like to have that engine for about 10 minutes. I'll bet with 10% or 15% WildCat and a Fox Miracle plug it would run like a Swiss watch.

I've been working with glow engines since my first Thimbledrone .049 in 1976 at the age of 10 and have owned countless engines since. So I think that I may know a little about glow engines. As I stated early on I've never seen this issue before in any of my model engines either 2 cycle or 4 cycle and was simply looking for positive assistance from fellow modelers as we all hit "road blocks" in our thought processes from time to time.

Thanks to everyone who has been helping me get past my "road block".

Hopefully it will settle down and become an engine you can like.

Stelios,

Is this the engine that you returned to England for warranty repair?

Blw

No. The engine turned back to France (not England) for warranty was a Saito-100 that I still have on the shelf although I recentrly changed on my expence the following:

- both ball bearings that were tolerating and completely rusted.
- carb spray bar
- carb low speed needle

I am now ready to place it on a plane when there will be a vacant one for its size.

Stelios

This is an interesting problem. If all other items have been checked, have you pulled the rear cover and checked the bearings for wear/slack by wiggling the crank? To remove the spinner factor, run it without the spinner. Are you setting the idle needle per instructions listed many times on the Saito club?
I'd sure like to hear how this is resolved!
Dave