Why does it work?
 

We have had long discussions about my Fl 70's idle. I ended up changing the fuel and adjusting the rocker arms. The problem got much better but not disireable. A friend told me to add a few washers between the engine and the mount to tilt the engine slighlty from the horizontal position it was sitting at. Well, i did that and today when i turned the engine on it idled so low that i couldn't believe my eyes and that was without the onboard starter forcing it to run. When i opened and closed the air-bleed whole i could actually hear the rpms change at idle, this has never happened before.

I am very confused now, what has caused my engine to idle, when it didn't idle before?
This could help me in tunning other engines in the future

RE: Why does it work?
 

Ask your friend why this works. He told you to do it. Then let us all know what this does and how it works.

RE: Why does it work?
 

I think he said that it prevents the fuel from pooling on the glowplug. It only takes 2 or 3 washers between the engine and the mount on any side that you prefer. It can't be bothe or it won't tilt it. It changes the engine from being 90 degrees down to 80 or 100 dpending on the side you put the washers on.

RE: Why does it work?
 

Messing with the thrust line will have adverse effects on flight performance. May I suggest you remove the washers and go back to your original setup? If what your friend says is true, you should be able to duplicate the results by raising or lowering the nose of the model while it is idling. Personally, I would expect that this trick has nothing to do with the glow plug, but moreso with the air intake in the rear of the engine. Perhaps you are mounted too close to the firewall, or the fuel line is pinched somewhere? If the engine is lean enough at idle, it's not taking in enough fuel to pool in the plug.

RE: Why does it work?
 

This is kind of hard to explain. The thrust line doesn't change. I think i explained it wrong. It is kind of like mounting it inbetween sideways and straight down.

RE: Why does it work?
 

Not24 He's right , he did not explain it right. His engine is mounted inverted straight down and fuel is collecting in the glow plug. Their fix was to put washers on one side or the other of the mount rail to offset the engine to one side or other from complete inverted position. So intead of say 6:00 oclock position to a 5:00 or 7:00 position exaggerated.......This does not effect thrust left or right or front up or down.

RE: Why does it work?
 

That's a neat trick. Because it works there must be an explanation as to why it works.

If the engine is mounted horizontally, so that the wing and the cylinder are parallel, fuel could not pool up on the glow plug.
This would be true for an engine that is mounted vertically, with the glow plug up.

The only time you would experience fuel pooling on the glow plug is if the engine is mounted inverted.
Fine tuning and changing fuel usually corrects this.

I have a O.S. FL-70 and I think it is the most fussy engine I own. I think a lot of the problem is that the engine is non ringed and built inexpensively, not cheep, so that it is very susceptible to changes in temperature and humidity.

The engine is now on it's 3rd season and is working much better. It's had a long time to break in.

If the washer method can be explained I too would love to know why.

RE: Why does it work?
 

I agree that it all sounds a bit strange so here's my $0.02 worth (is that groans that I hear?)

Is the engine mounted sideways or inverted?
If it's mounted sideways - it may be that washer adjustment is simply altering the carb height in relation to the tank - just enough to help it idle at low tank pressures.

Otherwise
Either it is very rich at idle as Not24 has alluded to

or
the engine mount is somehow placing uneven strain on the crank case via the engine mounts (I don't know what plane or mount is involved here). this may cause some warpage as the engine heats up and may cause some sort of leakage that is affecting the idle (I know that they don't aspirate through the crankcase but who knows what happens sometimes).

Or
It suffers from the bumble bee syndrome - (nobody told the bumble bee that it can't fly - so it flys) It's the power of persuasion and positive thinking. - Either way it's always good when something works.

RE: Why does it work?
 

Okay, I understand better now which way you are tilting the engine. But it doesn't really change my thinking. I find it hard to believe that a model will sit on the ground perfectly parallel, with the engine exactly straight and perpendicular to the earth. Two washers worth of tilt is only going to be about 2 degrees, which is not enough to have that type of effect. I have heard of tilting the engine 15-20 degrees off of vertical in an inverted position to keep the plug hot, but I really don't think any less than that would make any difference. There is something else going on here, and we can speculate all day about it. I'm still thinking it is something external of the engine, and not pooling of fuel in the plug.

RE: Why does it work?
 

I don't now what it is but i did that and it worked. For some strange reason i think that what i did has someohow stopped a restriction in the air-bleed whole. If anyone read any of my earlier posts about the problem the engine always ran rich below half throttle. The engine didn't perform and differently when i moved the airbleed whole. Now, i can hear an rpm change when i adjust the airbleed whole. In turms of if i am worping the engine because of what i am doing. I don't think so. I loossened all for mounting screws before inserting the washers and the screws passed threw easily on all for. My friend does this on his inverted engines without a problem.

RE: Why does it work?
 

The plane is a Groovy 50 3a with an adjustable engine mount

RE: Why does it work?
 

Hi!
You had an inverted (180 degrees) mounted engine and changed it to a slightly less 110-160 degrees tilting cylinder...The reson this works better is that oil is acumulating in the glow plug element when you have the engine mounted 180degrees (inverted) preventing good idle.
Inverted mounting of any glow engine should always be avoided if possible.

But...never put washers under the engine! It will be to little mounting surface and the engine crankase will easily get distorted that way. All engines should be mounted so that the beams holding the engine fits the mounting lugs on the engine with as much surface as possible.
Plastic mounts should always be filed smooth and square before bolting the engine down.

Regards!
Jan K
Sweden