bjnginge

I bought a second hand saito fa91,this is my first 4 stroke and talk about disappointed[&o]i am bench running it at the moment and cannot believe the vibrations.the prop is ballanced and does not have a spinner.am running coolpower 5% nitro.if i lean the low end any more it seems to help a little but dies when throttling.is it normal to vibrate like this or sould i try and resell it and buy a new magnum(thats all i can afford at the moment.any advice would help.

P-40 DRIVER

A Saito .91 or a Magnum .91 will shake about the same. I do not know what you are comparing it too, but any 4 stroke will get a bit loppy at low idle. Alot of vibration also depends on what you have the motor bolted to as well. I would run at least 10% nitro fuel in that engine, it will run much nicer for you. Another thing, is take everything you know about 2 stroke and throw it away, 4 stroke tunes much differently and Saito has its own little tricks on top of that. Once you figure it out, you will never fly anything else. Magnums are fairly crude motors compared to Saitos, so I would stick with the Saito if it was me.

rcdude7

My Feedback: (264)

You balanced the prop tips, but did you balance the hub portion also?

Flyer95

My Feedback: (1)

Mount it on your airplane first before you get more dissapointed. Should run smooth as a silk[sm=thumbs_up.gif][sm=teeth_smile.gif]

Running it on a bench is probably giving you a false idea about the vibrations.

Hobbsy

My Feedback: (102)

The .91 is normally a smooth engine.

w8ye

My Feedback: (16)

I have three Saito 91's and they don't vibrate any different than my Magnum or OS 91's.

You may have a bent crankshaft?

Kmot

My Feedback: (24)

Yup, they will shake a bit at idle but above that they smooth right out.

XJet

It's been my experience that some Saitos shake, some don't.

Regardless of how well the prop is balanced or how the needles are set, some are real pneumatic hammers while others (seemingly identical in every way) are far smoother.

My SA82 is beautifully smooth -- but lots of folks complain that their 82s are real jack-hammers.

My SA100 is a mean SOB. It shook one of my planes so hard that the RC gear gave up in disgust.

Because they're so light, a Saito will almost always vibrate at least a little more than the equivalent OS/Magnum or whatever. This is because there's less mass in the engine itself to resist the torque pulse created on the combustion stroke.

The best analogy is to compare our engines to rifles...

If you shoot a powerful round in a lightweight rifle it's going to have a lot of recoil.

If you shoot the same round in a heavy rifle the recoil will be significantly less.

With a model engine -- the power of the round equates to the engine's displacement -- so a lightweight high displacement engine has a lot of "recoil" and that manifests itself as vibration.

NM2K

My Feedback: (14)

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That is a good example. I'm going to use that one myself. <G>

powerlines

I have had 10+ Saitos and what I have seen is when they are new they shake like the dickens.. After they are broke in a bit it gets bettehr but not smooth. I love them. They are IMO the best made. I will run nothing but a
Satio 4 Stroke. I have 3 that I fun now. 65, 100, and 125.. All are great running motors. Never a dead stick unless it was out of gas!!






LATER and do not sell it. If you do PM me and I may add to my collection.. LOL

Kimhoff

My Feedback: (22)

If it is shaken at idle the low end is too rich. Saito's run like my Grandma's old singer and they are just like Kessler's, smooth as silk!

loughbd

No. All saitos do not Shake like C@#P. As a matter of fact I never had one that did. Mine are are quite smooth running from the little 30 up the the FA120.

DarZeelon

I don't know, bjnginge.

In fact, I have never seen C@#P shaking... I believe it just sits there pretty still...

I think it is the fuel. This is a Saito four-stroke, designed to use more nitro in the fuel.
It smooths out considerably, when slower burning, 15-20% nitro fuel is used in it.

Also, a four-stroke has stronger 'power pulses', occurring at half the frequency of those of a two-stroke engine running the same RPM, so its power delivery vibrations of the four-stroke are considerably more perceptible than those of a two-stroke engine.


Besides that, single cylinder engines are not perfectly balanced - they cannot be (without a very elaborate mechanism).
It has been discussed in length, in threads about prop balancing and internal engine balancing.
A perfectly balanced prop, or a counter-balanced one, helps very little in this respect.

The 'balancing' of a single-cylinder engine, is to find the least offensive combination of up-down vibration and side-to-side vibration.

JettPilot

My Feedback: (6)

Hahahaha,

You are wasting your time trying to balance the hub of a prop on a single cylender Saito engine. There is so much vibration comming from the engine itself, that trying to balance the prop that accurately is just a waste of time and effort.

As many are saying, a single cylender 4 stroke engine will have vibration, no matter how well your prop is balanced. The vibrations are more than a 2 stroke, they are not excessive, but the vibrations are there and will always be.

JettPilot

Chrispeace

You guys really love to use that "C@#P" word don't you! Dar Zeelon, were you thinking the same as me?

My 82 on 10% Irvine Contest vibrates less with an APC 14x4W prop than it did with it's first cheap Master Airscrew so props do matter and having one that is not balanced will not help. That said I have changed from a Hangar supplied plastic mount (Funtana40S) to an aluminium mount and this made a discernable difference but the 82 still vibrates a lot at medium to high throttle settings, so much so that adjusting the high end needle is very difficult as it is vibrating so much (it is actually feels like your holding a powerful engraving tool and blurred to look at). I use a Tacho to set the high and low revs as the manual states so there isn’t much more I can do, is there? This condition cannot be right and must be putting a lot of unnecessary stress on airframe and gear. I have reset the valve clearances post run-in but this hasn’t helped much. I have always put it down to it being my first 4 stroke and that one day I will get the setup right. Unfortunately I’ve never had the benefit of another 4 stroke operator looking at it as I fly alone at my field. Everyone says they get better with running. Great! but will the gear and airframe survive to see that day?

buzzingb

My Feedback: (2)

Before you give up or make the problem worse see if you can find someone in your area to help you set the needle valves. It is a little tricky for most people and someone who has set these fine engines will straighten it out for you and then you will know how. I have been where you are and I didn't know at the time the problem was me not the Saito. After you run 2 gallons through the engie it will smooth out even more. This problem is one of the nice things about Saitos, It is letting you know that the needles or fuel system is not set up correctly.

Chrispeace

Sound advice - we've all been there in this hobby be it engines, aerodynamics, contol setup, the list is almost endless.

Thanks

outssider

My Feedback: (23)

assuming the engine has not been damaged, saito's shake a lot at idle when set too rich. never used 5% either, that may have something to do with it.

XJet

I'm considering making up an anti-vibration mount for my SA100. I simply can't use it with the level of vibration it's producing on this lightweight model.

Flyer95

My Feedback: (1)

It is best for the muffler construction if the engine is mounted, lying on the side, on strong beams made in aluminium, hard wood or thick heavy duty composite plast. IMO the harder and stiffer the mount the better the results.

bjnginge

an update on that saito,before i get rid of it and save for an os(thought id give the magnum a miss)ive noticed that it leaks heaps of oil from around the front bearing.also it has a tiny bit of movement in the bearings.would this make it vibrate more?how difficult is it to replace them[] id like to keep it because it has less weight but leaks like a bad woman and vibrates like a bad toy.

loughbd

Bad bearings wouldn't make it vibrate as much as you say it does. I just replaced bearings in an OS 70 that were absolute garbage. The engine ran fine just sounded like it was running on marbles.

bjnginge

the vibration is like chrispeace says,it feels like you are holding the tip of an engraving tool and looks blurry.is this how they are supposed to be?[]

bjnginge

update again.i run half a tank of 15% nitro through it and it is much better.but nitro is expensive here and it will have to have a diet of 10% max.do u think this will do?

it also still spits heaps and heaps of oil out the front around the shaft.will bearings fix this?[]

Flyer95

My Feedback: (1)

If the 15% nitro helped with the vibrations then your idle needle is too rich. Try a new OS-F glow plug and set the idle needle as lean as possible, as long as the throttle response is good. 10% nitro works very good on these engines.