I am running a Fuji 64 on a Kangke Laser 2000. The engine has the optional long prop hub. I am running a balanced 22x10 Pro Zinger.
Every club member at my field who has helped me in the pitts during run-up has commented that the engine seems to be producing a tremendous level of vibration.
The engine was flown very rich yesterday and the aircraft sustained a broken muffler mount 'stay' and broken cowl mount blocks. Upon leaning the motor to smooth its running, 2 club members felt the level of vibration (even with clean, lean running) was excessive.
Upon returning home, I rechecked propeller balance and used a dial indicator to check prop hub/crank run out. Prop balance was perfect. Run out at the spinner tip (Tru Turn spinner) is approx. .005". The same run out exists at the prop bolt shank. However:
Run out on the rim of the prop hub (prop flange) is approx. .015" indicating the prop hub itself may not be true. However, it would seem the spinner tip and prop bolt would be the ultimate measure of run out.
I mounted the standard short prop hub and observed almost identical measurements.
However, these are all STATIC measurements. Since like every other Fuji 64 I have seen, mine experienced contact between the flywheel and magneto throughout break in, it makes me wonder about the Fuji's crank run out during operation... is the crank shaft ill-supported leading to excessive run out (wobble) during high speed running?
I have no way to knowing if the measured run out is excessive; no way of knowing what the long prop hub is doing AT SPEED; and no way of knowing what consitutes excessive vibration except to say that every time I have flown this plane, SOMETHING ends up broken due to vibration.
The airplane was flown once today. Vibration noise (resonance) coming from the airframe is excessive and unnerving. The tail stays on the aircraft are continuously loosening, the cowl mounting holes elongating, the cowl itself is being destroyed with cracks, and servo output linkages are showing vastly premature signs of wear. The vibration is so bad, I believe the entire aircraft is at risk of catastrophic in-flight failure.
The engine is very solidly mounted to a 3/8" hard ply firewall. Please advise.
Richard Geertson

IF the crank has too much wobble, it may need to have the bearings replaced. They may have too much clearance. Hard-mouning large, single-cylinder gasoline engines is also not recommended. They really should be soft-mounted so that less stress is transmitted to the airframe.

You may wish to send the engine to us for evaluation of the crank bearings, crank, and prop spool.

BAX,
The Fuji is in the mail, along with prop shafts and detailed explanation w/pictures.
If the big Fujis are supposed to be soft mounted, why doesn't Fuji or Tower literature explain or recommend this? Are the Fujis more prone to vibration than other manufacturer's motors?
btw: Some muffler manufacturers will VOID their warranty if engine is soft mounted as they claim this leads to broken welds.
Thanks,
RCG

Hi Richard, This is mickfin I got a Fuji BT 64 N i had to send it in for the same resin vibration,
Thay sent me a NEW BT64 in the Box I tryed too ask as too what was the problem, All thay sead was not putting thear thumb down too what the problem was, Thay sead thear was a problem?? All N all i got the NEW one and i mounted it with Truck Mud flaps 2 thick on the Firewall N smooth, I got it on a Giant Stinger, Good Luck to you Richard, Mickfin