T.W.

Does anyone know what causes engines to throw their props? Is it normally due to a hydraulic lock, or is it that the engine has seized due to over-heating?

This is a new trick which my normally "trusty" OS .52 has just learned. It ran perfectly the last time I used it and nothing has been changed since then. Today it started-up and continued to run perfectly. I held the nose up and leaned the needle for max revs and then richened it up a few clicks until I heard the engine slow a little (as usual). The model took-off normally and flew half the tank of fuel just fine. But then the engine note changed to a metalic sort of "hammering" noise and after just a few seconds it stopped dead, throwing the prop

I thought that the noise I'd heard was a bearing letting go, but back on the ground I tightened the prop down and tried turning the engine over by hand - it was fine! I fired it up and as I reached to adjust the needle the engine again made its horrible racket, stopped dead and threw the prop

The engine still turns-over ok by hand. There's only a slight amount of end-play at the crank-shaft (normal I guess), there's no indication of damaged bearings and the engine has plenty of compression . . . . but I daren't try starting it again for fear of what damage I might do (or have done!)

Any advice would be welcome,

Tony

Kimhoff

My Feedback: (22)

It is lean. You have a fule problem or orings going bad in the carb and intake pipe.

Richard L.

My Feedback: (24)

Your high end is too lean or you have an air leak somewhere. Try richening up the high end a few more clicks.

w8ye

My Feedback: (16)

With this much back firing, The knerles on the prop drive washer may be gone also by now.

Pull the prop and look at the drive washer. Make sure it still has the little ridges.

If it is smooth, get a new one.

Enjoy,

Jim

Homebrewer

My Feedback: (8)

Two reasons why a 4 stroke throws a prop.

1. Engine is not fully warmed up and is too quickly advanced to full throttle. Remember, as in our automotive engines, an engine needs to be run richer when it is cold. Since this is not very practical (unless you actually use the choke if it has one) a warmup at a fast idle for 30 seconds or so is a good idea before advancing the throttle.

2. Engine is too learn. If you are throwing props when engine is warmed up then you definitely have a lean mixture. It can be caused by airleaks or most likly improperly setting on your needles.


This post is a good reminder to NEVER stand in front of a four stroke engine when you are advancing it to full throttle. I had a Saito 1.50 that throw a large prop and hit an individual 20 feet away in his leg. He did scar from the injury. I know am very conscious about 4 stroke throwing props and ensure that no one is in front of the engine when I'm advancing throttle or setting mixture setting.

T.W.

From what you've said it's pretty conclusive that a lean mixture is causing my prop to disentangle itself from my engine - so now I know where to start looking. Your help is greatly appreciated

Tony

Zman39

My Feedback: (6)

Start at the tank with the checking. A split in clunk pick up line would cause air and will get worse as fuel get drawn down during flight.

Z

T.W.

Today I checked all the pipes to the tank and the clunk pipe itself - all were sound. I changed the tank to a uniflow system as it seemed like a good idea. At the strip, and bearning in mind what has been said previously here, I opened the needle a few more clicks until the engine was running noticeably rich. The engine now had only just sufficient power to drag the model across the strip fast enough to achieve flight, but once in the air the rich setting wasn't a problem. I flew "steadily" and after maybe two minutes of rich-running the engine stopped "dead" making a sound like a hammer hitting something solid! The engine never "leaned-out" at all and the prop, spinner and two locking nuts were flung off

So, is it possible that a rich setting can cause these seizures? Or do you think I have some kind of mechanical problem. Plug: OS F; fuel: synthetic based 10% nitro with 3% Castor. The guys at the strip who heard the "bank" were sure the con-rod had broken. But the engine turns over normally and is as smooth as ever. I'm really puzzled by this

Tony

T.W.

Today I checked all the pipes to the tank and the clunk pipe itself - all were sound. I changed the tank to a uniflow system as it seemed like a good idea. At the strip, and bearing in mind what has been said previously here, I opened the needle a few more clicks until the engine was running noticeably rich. The engine now had only just sufficient power to drag the model across the strip fast enough to achieve flight, but once in the air the rich setting wasn't a problem. I flew "steadily" and after maybe two minutes of rich-running the engine stopped "dead" making a sound like a hammer hitting something solid! The engine never "leaned-out" at all prior to the sudden stop. The prop, spinner and two locking nuts were flung off

So, is it possible that a rich setting can cause these seizures? Or do you think I have some kind of mechanical problem. Plug: OS F; fuel: synthetic based 10% nitro with 3% Castor. The guys at the strip who heard the "bang" were sure the con-rod had broken. But the engine turns over normally and feels as smooth as ever. I'm really puzzled by this

Tony

jaka

Hello!
Sounds strange..mechanical do you say...how big prop do you have on?
12x5-12x6 or...?
I would definitely take the engine apart and have a look at it. Easiest thing to do is to remove the backplate and have a look at the big end of the con rod and the rear bearing.

Regards!
Jan K
Sweden

T.W.

Hi Jan, thanks for your input. The first prop to get thrown-off was a 12.25x3.75, but it was fitted with an 11x7 this most recent time. I'll take a look inside the engine sometime in the next few days as you ssggest. But as I said, the engine seems to turn-over as sweet as a nut now. It has plenty of compression, just like it did before it started throwing my props away. I've felt for "roughness'" and "two TDC's" when turning the engine over by hand, but it feels just fine. I've had this engine for around 8 years and it's never so much as coughed until this episode started. I'm wondering if it has something to do with the model's plumbing even though I can see nothing wrong with it. So I am thinking it would be a good idea to re-fit the engine to the model it was powering successfully previously, just to see what happens . . . . I need "more time!"

Tony

pikebishop

you might want to replace the o rings in the nv assembly. this could cause an inconsistent setting.

T.W.

Makes sense to try this whenever "engine problems" arise I guess. But on the other hand, there is no inconsistency in the needle settings at all. The needle is easy to set and, once set, the engine doesn't lean-out in flight. When I set the engine to run rich the other day, it ran rich right up to the point where it stopped "dead." I could even see smoke from the exhaust right up to the "sudden stop" too. I think before doing anything else I will re-fit the engine to the model it was previously powering successfully, just to see what happens . . . . but time is in short supply today, so this will be a job for tomorrow

Tony

pikebishop

could there be a small piece of debris in the tank that gets sucked up causing lean condition and prop throwing wich frees itself after fuel draw stops?

Kweasel

My Feedback: (29)

Forget the uniflow setup and use muffler pressure. The uniflow requires very good fuel draw from the carb, fourstrokes in general are lacking in this department. Muffler pressure should provide some positive head pressure to the carb at full throttle, even if there is a leak in the system.

T.W.

It's the first time I've tried the uniflow furl tank system. It made no difference to my current problem so I won't be using it again. Interesting idea about there possibly being a small piece of debis in the tank . . . . I've decided to replace the tank and fiel pipes, they look fine and I've replaced the pipes previously, but you never know! I removed the engine from the model today and took a look behind the backplate. The rear bearing, con-rod and "big-end" all appear ok and the engine rotates very smoothly. I'm going-ahead with my plan to re-install the engine in the model it previously powered, just to see what happens

Tony

laker500

My Feedback: (2)

Am I thinking of something else? I thought a uni-flow setup used muffler pressure, it just put it into the tank through a line with a clunk in an effort to stop atmospheric pressure from playing a role in fuel supply. I remember an article in a magazine discussing them, it sounded like it made sense but you needed to be a physicist to understand exactly why they worked better. Jeff

Julian537

My Feedback: (9)

you have had it for eight years?
I do not think anyone has mentioned this yet. have you checked the rocker arm to valve clearance?
I had a .40 os FS that was doing the same thing. the exhaust valve clearance was way off. .010 off.
check your manual or the OS web site and check the valve clearance.

I would bet the exaust valve is out of adjustment ??

T.W.

You're right about the uniflow system. The theory is that it removes atmospheric pressure from the equation by having both the pressure inlet and the carb outlet at the same height in the body of fuel in the tank. Sounded promising, but it didn't help my problem at all

I reset the valve clearances to 4thou just a short while ago - after the first time the engine suddenly stopped. "Other things" are getting in the way of my engine problems at the moment so it could be a few days before I get back to report on progress

Thanks for your help,

Tony

downunder

Uniflow works with or without muffler pressure. What it does is take changing fuel level in the tank out of the equation.

T.W.

I re-fitted the engine to the model in which it previously ran perfectly - and it again ran perfectly. This was without changing anything at all - including the needle settings. For the second flight I leaned-out the mixture a couple of clicks until it seemed to be running just right (slightly rich so just less than the max revs possible). Again it ran perfectly

I guess this proves that there's nothing wrong with the engine and that there's something wrong with the tank or fuel pipes in the model in which it would constantly throw its prop . . . . but what? I can see nothing wrong with any of it

Next I fitted the engine to my test bed and it again ran perfectly. While the engine was running at full speed I leaned-out the mixture, slowly, until the engine eventually came to a stop. It stopped normally and didn't throw its prop. I did this several times with the same result. I also slowly nipped the fuel pipe until the engine stopped running too. Again without any miss-firing or backfiring, and without the prop being thrown

I now have doubts that a lean run can cause the prop to be thrown . . . . but maybe I'm missing something here?

Over the next few days I intend removing the tank and fuel pipes from the model in which the engine did its prop-throwing, fit these items to the engine on the test bed and see what happens when I run the engine again

Any advice or ideas for further tests?

Tony

bigphil

My Feedback: (6)

It sounds like you have indeed isolated your problem to the tank or fuel supply system of the particular plane. One thing that is easy to miss is the brass tubing where it goes through the cap on the tank. Occasionally I have found the brass split but hidden within the rubber. This will still cause severe leaning especially as the fuel level in the tank drops near or below the level of the cap.

T.W.

The model in question is a new Wildcard and the tank which comes with this kit has some kind of plastic tubes, instead of the usual brass type. I intend changing the tubes to brass after first testing the tank "as-is." But I hadn't thought to look for a split in the area of tube actually inside the rubber bung, so thanks for this

Tony

T.W.

Well . . . . Summer has come and gone and my WildCard continues to produce dead-stick landings with every flight - and it is still throwing its prop every couple of flights too

I tired of trying to fix the problem and flew other models for most of the Summer, but I really must return to my WildCard and get it fixed once and for all, as it is a lovely-flying model!

Over the months I've tried several different 4-stroke engines in this model, and they all do exactly the same thing. I've tried several different types of fuel, tank, plumbing, props and plugs. I've flown with and without the cowling too

I now have a tiny 4-oz tank surrounded by a thick cushion of foam rubber (which I've never needed to use previously), as well as using an anti-foaming agent in my fuel

The result is always the same, the engine stops dead after a few minutes in the air or on the ground (usually preceded by a "hardening-off" of the engine note). oN the ground I can keep the engine running (if I'm quick enough) by opening-up the needle a little. Yet all the different engines which have stopped running while fitted to my WildCard are happy to run all day on my test-bed and on other models using all of the different fuels I've bought and any of the plugs and props I fit

This morning I was thinking about changing the engine mount to an "anti-vibration" mount (which I will have to buy if I do decide to go this route). I was thinking that I've never had to resort to this kind of mount in the past when it occurred to me that the engine mount which came with the WildCard is made from alluminium - and this is the first alloy mount I've ever used!

So . . . . has anyone experienced vibration problems when using alloy mounts - and do you think that replacing it with a "normal" plastic mount may stop engine vibrations aerating the fuel, as this is what I think must be at the root of my problem

Any comments will be appreciated,

Tony

T.W.

The weather allowed me to go flying this afternoon - and what a revelation it was! For the first time since getting my WildCard, its engine (ASP .61 4-stroke) actually sounded "just right" from the second it fired-up today

It was airborn in less than three yards and with the engine sounding exceptionally sweet I pulled the nose up until the model was vertical. I opened the throttle to full and watched as it got smaller and smaller - without so much as a cough or a sag from the engine

I flew it hard for around 12 minutes doing all the aeros I could think of, landed (with the engine still running - for the first time!), did a little dance to thank the engine gods, re-fuelled and flew again. I had three flights with this model during the afternoon and suffered not one dead-stick landing or thrown-prop, despite all the inverted, bunts, spins, prop-hanging, etc. I was extatic!

So that's it. Problem finally solved

After a lot of frustration trying to solve the riddle of my thrown props and lack of power I can now confirm that engine vibrations were at the root of the problem. They were being transmitted, via an alloy engine mount, into the airframe and managing to aerate the fuel, despite the tank being padded with foam rubber and the fuel having an anti-foaming agent in it. Even though the vibration wasn't actually noticeable it was obviously enough to cause the problem

All I had to do was fit a plastic engine mount in place of the alloy item and the problem went away. If only I'd thought to do this a couple of months ago!

Still, I'm happy now!

Tony