RL TT53H additional shims?

[Patrik J]

Hi.
I just received my TT53 engine, in the box there were a bag with two shims/gaskets for the cylinder head and a notice saying an additional shims is to be used when running in a hot climate or running with 15% or more Nitro.
I'm running with 20% nitro.

There are two shims, one thin and one thicker, I'm not sure if I should replace the original one with these two or just ad one of them onto the original one, thinner in that case?.
Perhaps I should just leave them in the bag?

Find it a bit strange that the engine can't take more than 15% nitro without lower the compression, when the manual saying that 30% is good to use.

There is no information in the manual about these shims/gaskets at all.

Anyone heard this before on the TT53?

[Mentalic]

Be happy, at least TT gives you the extra shims you might need, OS does not.

The point of shiming is to adjust the engine ignition timing. Timing is affected by the altitude you live at, precentage of nitro you use, ambient temp, brand of fuel, fuel oil content, humidity, engine temp, plug, mixture setting.. So that narrows it down nicely, eh?

I basically live at sea level, as humid as it gets, and its seriously hot here in South Louisiana. For me to run 30% cool power in my 50 Hyper I had to make and add a .005 head shim. Before the shim the high speed needle was very sensitive, engine required richer settings for higher idle up rpm, and you could hear a metallic rattle. After adding the shim it runs great for me, all problems solved.

Its much easer to detect pre ignition on an plank engine than our heli's. Plank engines that need a head shim will not have the normal sharp peek in RPM as you lean the highspeed needle and often you can hear it rattling. I've been flying planks since the early 80's and it was normal to have to shim European engine brands like Supertigre to even run on 15% nitro.