Vibe problem?

[Paul T.]

Hi all,

I've just completed rebuilding an old X-Cell gasser that I bought damaged from Ebay. The model had had a heavy boom strike, so I completely stripped it, replaced all damaged parts including mast, feathering spindle etc, and a number of worn bearings. Fitted with new blades (JP carbon), head carefully balanced, static & dynamic tracking set up, but vibrates like a bugger! I've only hovered it a couple of times as vibration is severe, the canopy is rattling round, skids almost a blur etc; increasing head speed makes it worse, lowering it makes it almost tolerable though vibes are affecting gyro. If I remove blades and run engine up the vibes disappear, which made me suspect rotor head, but I've stripped it and rechecked everything 3 times, even repalced the main plastic head block in case that might have been distorted, but still no joy.
Next thing to try is remove engine and clock up clutch/flywheel assembly; I didn't check this when rebuilding as I assumed that it must have been done by previous owner, but I felt the vibes pointed to head problem.
I've checked blades for weight & C.G. as well.

Paul.

[SRH990]

Have you flown it after you bought it or is this the first time. One of the guys I fly with has an X-Cell gasser and it vibrates something rotten. He had engine problems and fitted a new Zenoah 26cc motor, these seem to be somewhat worse than the 23cc Zenoah lump which is supposed to be smoother.

He had a chat with Dave Wiltshire at Motors & Rotors and he suggested balancing the fan/clutch/flywheel as they can be pretty poor out of the box. He hasn't got around to it yet but the vibration is so bad the exhaust keeps falling off and he's lost the front of one skid which fractured through.

[Paul T.]

This is my first attempt at flying it, so I'm not sure what is 'normal' vibration level for an X-Cell. I have a Vario Benzin which is very smooth running, although this has a different version of the Zenoah 23 engine.
What puzzles me is removing blades seems to cure vibes which led me to think it was a rotor problem, but I've checked and re-checked everything in that area.

I will take engine out next and check runout balance etc as you suggested.
Thx for info.

[SRH990]

Let me know if you manage to sort it as my friend would be very interested! At the moment he's considering selling the gasser and buying a Logo 600

[Paul T.]

I read the X-Cell manual at weekend, and in there it 'recommends' that the builder removes the flywheel from the engine to check it's balance before installing engine! Hmmm RTFM?
Doesn't inspire much confidence being told to check balance on new engine.

So today I've removed engine and attempted to remove flywheel, however I'm stuck on the first hurdle; there's a 'pulley' that fits over retaining nut that engages with pull start, according to manual it should just come off with light tap from a nylon hammer. Not mine! I've got a two legged puller on it but it won't budge, I'm afraid to apply too much pressure in case I break it. (see attatched pdf file, G230 manual. Page 4 parts 32 & 33)

Also been doing some research on web and came across this on a model boat site:

Zenoah coils
Clearance between the coil and flywheel:
0.015 - 0.016 inches( 0.38/0.4 mm). This allows a good spark and, at the same time, avoids the coil touching the flywheel which cause drag, loss of power and radio interference. If necessary, to adjust the clearance, file the mounting holes of the coil.
Jim asked Zenoah about specifications for the manufacturers coils. That's the response:
RED Coil: Secondary voltage Ignition Timing
@1.000 rpm 16KV @ 7.000 rpm 30 BTDC
@7.000 rpm 28KV @10.000 rpm 28 BTDC
GRAY Coil: @1.000 rpm 20KV @ 7.000 rpm 28 BTDC
@7.000 rpm 20KV @10.000 rpm 25 BTDC
"As you maybe know, the gray coil has good performance at low (idle-7.000rpm) and the red coil has good performance at high (over 7.000rpm) range."
"This difference is set up according to the engine purpose, red coil (G230PUH/PUM is for high power at high rpm range, gray coil G230PU) is for easy starting by propeller flipping and good power at mid (7.000)rpm range."
Komatsu said the coil/flywheel gap should be .3mm, and .2mm if you can get it. The smaller gap the hotter the fire.

I assume the writer is referring to the coil located adjacent to flywheel, on mine it's a red one which is referred to as a high power one; now in my mind I associate higher power with higher vibration? My gasser is an early one with magneto ignition, but I believe that later versions have electronic ignition, maybe to reduce vibration?

Could do with some advice from someone with more experience of Zenoah's, would it be worth trying a 'gray' coil?

[Paul T.]

Failed miserably trying to remove flywheel, eventually broke puller.
Lacking any furthur ideas as to reducing vibration, I've taken a leap of faith and bought new engine for X-Cell.
The original is an early Zenoah G230PUH, latest version is G231PUH, my reasoning being that the later one will be smoother running. Although they initially look identical, there are significant differences; the later one has four bolts to clamp cylinder on, whereas the earlier one only has two which leads to leaks around the base gasket. Earlier version has two piston rings, but latest version has only one thin ring, & smaller spark plug.
I don't know what the internal differences are, but later version peaks at 13,000 rpm, earlier version 10,000, so porting is probably different. (Interestingly my Vario Benzin has yet another different version of the Zenoah, G230RC3, which I believe is actually designed for 1/5th scale car racing, and this revs to 19,000 rpm!) I bought the new engine off Ebay, came complete with exhaust, air filter tools etc for £150, damn good price I think.

Also got the parts to convert Vario to flybarless, so going to be busy for the next few weeks....