leskirkup

Hi,
I have a Fuji 64 engine ready for breaking in. I've never done any breaking in before and the engine stand that I've constructed is just plywood (where the engine is mounted on) securely screwed and wood glued to medium density fibreboard on the plywood sides. I borrowed the design idea from this guys engine stand design
(http://www.rcgroups.com/forums/attac...hmentid=917309).
I'm not sure whether the engine stand will be strong enough to withstand the vibration caused by the engine, so I hope someone with experience can tell me about it (I can't afford to get a new engine if this first one is damaged due to vibration).
Is it ok to use rubber grommets, the ones people normally used on cables and encircle it on the screw (bolts) that attaches the engine mount to the firewall?
Thanks in advance

shakeelsid

Hi,
Firstly, it is good to be cautious, without being fearful. I am sure you will be very successful in breaking-in this engine, as well as mounting and flying it subsequently.

A 64 cc engine would produce about 30 lbs thrust maximum - pull test your rig to say 60 lb if in any doubt. During initial running it will vibrate a lot, untill you get the carb set for mixture. If the prop is not balanced it would vibrate even more. Install a kill switch on the stand at an easilly accessible position so you can shut the shaker off when in doubt. Balance your prop and use a low load prop initially. make sure the stand is firm and would not move around at full throttle - and there you go.

BTW, I have test run 45 cc engines mounted to a pair of 1/2 inch sheets clamped to my bench vice - I wont recommend it to you though.

Don M.

My Feedback: (5)

For 15 years I always "soft mounted" my gasoline engines and always had vibration problems of one kind or another. This past summer after ignoring advice to hard mount direct to the plywood firewall for years I tried it on 2 planes. Guess what, the vibration problems have all but disappeared. I will still soft mount my small glow engines but for whatever reason "soft mounting" gassers does not seem to give the desired results.

shakeelsid

You are so right Don - small 2 stroke singles would have a terrible shake at low RPM which nothing but amplified with soft mountings on the firewall. This is because generally the axis of vibration (piston movement axis) is perpendicular to the mountings (which is generally isolated at the firewall). If you were to provide isolation and dampening on the same axis you can correct the amplitude.

But it would require you to have either a radial tube mount with perpendicular isolators or a beam mount engine. In most cases wooden structures are suffcient to dampen vibrations. Current practice of box engine mount is an excellent design for dampening as it has many holes and cut-outs which resonate and break the wave patterns

I would go ahead and slap the engine on the firewall and think about isolaters and dampeners only if I had severe problems.