Big single vibrating

[calt]

I have a ZDZ super 80, 26x10 pt prop. This engine idles very smooth hardly any vibration but between 2000 - 2800 rpm it vibrates bad, you can see it, hear it and feel it. Above 2800 it’s as smooth as can be expected. Any ideals how to fix this?

[BTerry]

Yup. The only way to get rid of this is to replace it with a twin. All singles have a harmonic vibration somewhere between 2300 and 3500 rpm for a range of ~600 rpm (i.e. ~600 rpm somewhere between 2300 and 3500, depending on the engine). They all do it, some worse than others. My two ZDZ 80 RV's are pretty smooth however, when compared to other engines.

[Tired Old Man]

That's why big singles were re-named "Thumpers" a long, long time ago

[KIM]

I had a BSA Thumper

[snap]

I put a Walbro carb from a DA 85 on my super 80 and its pretty smooth. Starts like a DA and is easier to tune.

[Highlights]

I have a super 80 as well and it never had a bad shake. Though it did not run consistently enough on the Tillotson so I replaced it with a new Walbro .Makes it very easy to start and tune. Mid range is great. Low Low rpm's 900 and below are really shak'n though.

Live with it.

[Show871]

	Quote: Originally Posted by calt
	I have a ZDZ super 80, 26x10 pt prop. This engine idles very smooth hardly any vibration but between 2000 - 2800 rpm it vibrates bad, you can see it, hear it and feel it. Above 2800 it’s as smooth as can be expected. Any ideals how to fix this?

Beef up your motorbox with tri stock, and carbon fiber the whole box. This really helped my sd yak with da 85!

[calt]

it has a walbro carb on it. one of my flying buddies wants me to install the prop 90 degrees to the cylinder when its at top dead center.but this will make it hard to flip the prop when starting. have you ever heard of this? is it Worth a try?

[mikeh]

Long stand offs will also add to the problem if you are using them.

[calt]

no stand offs the engine is bolted to the firewall

[zoomer260]

	Quote: Originally Posted by Tired Old Man
	That's why big singles were re-named "Thumpers" a long, long time ago

Back when I was young and indestructable, stupid if ya will, I was a dirtbike addict and we called those big single four strokes "thumpers". You could see every compression stroke on those because it would send up a roostertail of dirt. Seperate "spurts" between power strokes and exaust strokes.

The two strokes on the other hand would appear continuious with the dirt spray.

Damn, those were the days.

[pe reivers]

Most confuse power stroke vibration with engine unbalance vibration. Power stroke vibration at one rpm range will excite the airframe into resonance. Lighter frames will resonate at higher speed than heavy frames.
Large one-cylinder engines have more powerful power strokes, but so have large twins. However, the large twins have more seismic mass which also is better balanced around the shaft to counteract these strokes.
It is the nature f the beast.
At one time, someone invented the zero stroke engine, that would rev up indefinately and ran vibration free. Let's wait for some entrepreneur to take it into production.