I have a new da-50 on an EF YAK 88".

At idle, there is very noticable vibration. There is a tiny amount of epoxy on a CF spinner (which I spilled by mistake).


Does this small amount of epoxy on the spinner cause vibration?


What about the spark plug? After braking in the engine, spark plug was not changed. I just changed it and haven't tried the engine yet. Could this be a reason for the vibration?


TIA

It could cause vibration just like any dirt could. I think it might be more prevolent on a light weight carbon fibre spinner than an aluminum one.

Did you check the balance of the spinner & prop ?

Don't forget a single cylinder engine has vibration especially at low RPM.

A fouled spark plug could also cause vibration.

I hope this helps.

Thanks for the reply!

For balancing the prop, I have to admit I never got to balance one before. Do I need a special tool to do this? Anyways, the prop is new (Menz 23x8) and I used a gig to drill the screw holes.

A two cycle gasoline single cylinder engine will vibrate. There is no way to get around it. Your installation may have a resonate spot at low rpm that exaggerates the problem. Make sure the engine is secure and avoid that RPM if possible. I doubt if a small spot of epoxy on the spinner has anything to do with it.

seems logical. The vibration is huge at low RPM. The whole plane shakes hard. If I up the idle, then it becomes too fast for landing.

What about the spark plug? It is the same one that was used during engine brake-in. I opened it the other day and it was black and replaced it with a new one.

One more thing I did which I haven't tested yet. The muffler was leaking small amount of black burnt oil. I removed the muffler and installed a gasket and put it back on again.

Now I have done two things: New plug and muffler gasket. So, if the vibration reduces I would not know which was the fix

This statement is a fact, and the fact that you dont know how to balance a prop, explains your vibration. If the engine is performing to your expectations, chances are you have a good working sparkplug. Since you are going to change the plug, make sure its gapped to .020 and BALANCE that prop.

It is a cardinal rule to balance your prop.

Your local hobby shop should be able to help you out with a prop balancer.

Also you can do a search on balancing props here in RCU.

Some guys will balance the prop , spinner & backplate together.

If your plug is black you are running too rich. Lean it down a bit and you might reduce the vibration.

Now I have a new plug plus the muffler has a gasket. It seems slightly better but still vibrates at idle.

I ran the engine today and flew the yak a couple of flights. Just a brief hover and some knife edges and couple of loops. I noticed when inverted there is, but am not 100% sure, small hesitation in the engine. Would a rich setting cause hesitation while inverted maybe?

Also, the engine has just been broken in, and had only few flights (5-6 flights) with synthetic oil (redline 1:40 mix). And, there has not been any changes to the factory low/high needle settings.

and track the prop blades as well

How to track and balance a prop.
http://www.youtube.com/watch?v=1JuSu...feature=relmfu Part one
http://www.youtube.com/watch?v=uZmqE...feature=relmfu Part two
http://www.youtube.com/watch?v=ViTiJ...feature=relmfu Part three
John

Please, please, please set the needles for your airplane, prop and fuel combination and the area where you fly.

There is no such thing as "Factory set needles"! Those settings will allow you to start the engine and little more. They could be spot on or way off ..... you have no way of knowing until YOU set the needles yourself!

Many threads have been written on this subject along with the sticky info at the top of this Forum's first page.

Hi!
Did not see any tracktesting of the prop!? Do not think that is possible !

Sorry I mistyped. One simple way to see if a prop tracks is to place a tablet of paper underneath the prop while it is on the balancer. Place the paper so the prop just misses when rotated. Rotate the prop and put a mark , rotate the other half of the prop and they should match.

Basically I wanted to show a video of how to balance a prop for someone who hasn't done it before.
John

Try this thread good info http://www.rcuniverse.com/forum/m_11...tm.htm#1115188