Buried in a posting is this little gem:

I suppose this is cheating of the worst sort, but coming in at the tail end of another thread, "TD .049 for Stunt?", was the following, first from Brett and then myself.

While Brett refers to it as a pet peeve, I'm not so sure it is even that for me, but it does give me pause to see so many "tuners" just mindlessly toss head shims at any given motor, and then to declare them in Stunt Tune.

To put a real fine point on it, if that dyno in their arm is so sensitive as to recognize the instant switch to Stunt-type power, why is it not sensitive enough to note the loss of torque as well?

The answer--or one answer--has to be they are putting a lot of emphasis on the sound of the motor, not how it is flying the model.

Anyway, I think the preceding and following thoughts might spark some conversation.

I defer to Larry. I merely wanted to point out that adding head gaskets really doesn't really help when it's an intake problem. Additionally, the reflexive tendency to "add head gaskets for stunt run" is a pet peeve.

Brett

Agreed. Back when I was flying a lot of RC, I would frequently comment it was my view that changing the needle setting ought involve a lot more work than merely a short reach and a big twist. Make changing the needle setting as difficult as, say, changing head clearance and then maybe people would first look for the real reason their perfect needle from previous flight of a sudden is now two turns lean.

It was only when beginning to fly CL Stunt that I saw the flaw in my argument, as it seemed people were tossing head shims in their engines with approximately the same amount of thought and hopefulness as goes into furiously dialing the needle when it's the fuel filter which needs attention.

Sometimes, when considering adding a head shim to a CL Stunt motor, I will first take a shim out and fly. You'd be surprised at how many times it doesn't make a lot of difference, indicating the problem might well be further upstream. Or in one of a whole bunch of other variables.

One of my ST 51s was real inconsistent until I increased the compression and decreased the bore size of the venturi.

While I would have to check my notes to be sure, I don't believe either of my two GMA ABC Fox 35s currently being flown in competition, plus the back-up motor in the tool box, have any head shims at all installed under the hemi heads. George and I disagreed about the details of my setup, but y'all can see the good results at any NW contest.

I am agreeing with you, Dan, on this element. I have a saying of my own that "If it runs like a Fox and sounds like a Fox it will have the power of a Fox". Too many people seek only the sound. Sometimes head shims need to be added or removed in 2 or three thousandths thickness. The OS head shim is 16 thousandths. When people start adding these in abundance I really cringe. One guy sent an engine to me and wanted me to tune it. He wanted more power. That wasn't hard to deliver. It had five .016 head gaskets in it. That was abut 60 thousandths too much. This is where I have some .010 head shims for these engines that allow a "mix and Match" situation. Instead of going 16, 32, 48, etc. you can go 16, 20, 26, 30 (getting too high already), etc.

>I am agreeing with you, Dan, on this element. I have a
>saying of my own that "If it runs like a Fox and sounds like
>a Fox it will have the power of a Fox". Too many people
>seek only the sound. Sometimes head shims need to be added
>or removed in 2 or three thousandths thickness. The OS head
>shim is 16 thousandths. When people start adding these in
>abundance I really cringe. One guy sent an engine to me and
>wanted me to tune it. He wanted more power. That wasn't
>hard to deliver. It had five .016 head gaskets in it. That
>was abut 60 thousandths too much. This is where I have some
>.010 head shims for these engines that allow a "mix and
>Match" situation. Instead of going 16, 32, 48, etc. you
>can go 16, 20, 26, 30 (getting too high already), etc.

Well, it's about time you and I agreed on something!

I like the statement "If it runs like a Fox and sounds like a Fox it will have the power of a Fox." I like it enough that I am sorely tempted to edit my original posting such that it appears as if you copied me...

Still, we must admit that amateur tuners got the idea from some good sources. GMA and I would frequently disagree on this, as he just automatically installed two .010 (stock) head shims in Fox 35s. Now he had different needs, that of supplying customers with an engine that would still run nicely even if mishandled in some way(s), but I never liked the low-compression/big-bore venturi setups he preferred, especially with the ST 51.

"Expansive" Dan is agreeing--Wow!!!
I was wondering about the "head Shim" thing also--loss of torque was my first thought also. OK Dan, (or other people) WHAT sequence do you use to Evaluate an engine run? I know we have alot of varibles from tank to prop. BUT give us several examples of some problems that you have had in the past and give us the sequence.
Right now I am having fits with a McCoy 19 on the"Spit". First of all I found out it was a NEW engine and had to break it in. The first 5 runs seemed OK-(The engine was accepting a consistant 2 cycle at end of break in.) I went to Pearson on the 4th and it went FAT inverted, flight -(The engine is "inverted" on the plane). Now I had tuned the needle with plane in take off position (engine inverted)--with inverted flight (engine upright) it goes fat!!! OK, we normally "move the tank 1/8" DOWN to get rid of a rich run in that position. NOW the stupid thing cuts out on the corners!!!
Dave (stumped) Shrum

Boy, do I know how to stop a thread -OR-
They are mad at us,Dan _OR_
Maybe I should just say "Duh"!!!!!!!
Whatever
YOu know this doesn't say anything about airplane stuff--OH, now its legal--I said "Airplane"

Dave,

Not ignoring you, I've simply been doing other things.

On the other hand, I can now freely ignore you: I don't do engine-run diagnosis by remote control. I mean, I have seen your NWSR and Flying Clown equipment run. Or not. There could be almost any number of things wrong with your setup.

Don't know that I have tested sequence.

What I try to do is first getting some bench-time on any engine.

With the piece mounted in an airplane, before going out to fly I will plop the model in a fixture of some sort, one of my home-made racks generally, and get a reading on the motor with model both inverted and upright. Tank is adjusted to suit, this usually gets it real close.

At the field, lap times inverted and upright are a factor, but not a huge one. They only have to be close to equal.

More important to me is what the motor is telling me through various maneuvers. Sometimes you just have to live with (slightly) unequal speeds upright and inverted.

As to tune, with the Fox 35s it is nice to hear the traditional break at the tops of loops, a variable being how soon and how the motor breaks. As a general rule, I strive for just a touch of break merely as a self-evident confirmation all is well with the needle setting.

From there it is getting some more torque and increased squeeze is a real good way to do so, as is more potent fuel. Banging hard corners one after the other--think Square 8s--will give one a real dandy way of evaluating your success or failure.

The rest is merely fiddling further with needle settings, props, plugs (maybe, the Thunderbolts just always work in two-stroke Stunt motors) fuel, line length, blah, blah...

Yup, and I gave all those racers away!!! Thanks for help, Dan. I'll keep working at it.