1/2 vw engine vibration

[mikeheckler]

Hi,, I have a Hummelbird with a 1/2 vw scott castler 37 hp engine with 160 hours on it.  In early summer it quit at 2,000 ft between Lyons N.Y and Sodus Bay.  I was able to make a successful landing in a corn field without any damage to the airplane.  When I got the Hummelbird back to the hangar and remover the cowl part of the crankshaft and connecting rod had gone through the case.  I tore the engine down and found the crankshaft was broken into 3 pieces, 2 fractures right at where the counterweights were welded on to the crankshaft. I called Scott Castler about it and he said mine was the only 37 hp engine that he knew of where the crankshaft broke, however there were many 45 hp engines with the cast crank that have broken, he offered to sell me a new FORGED crank and case at his cost.  I accepted the offer understanding that the new crank would be Forged, not cast like the original.

After receiving the parts I put the engine back together and have about 50 hrs on it, but it vibrates as bad as the old one.  I had the prop dynamically balanced, but the vibration is still bad.

I saw an earlier post where the question was asked, How many IPS is acceptable with this engine when a dynamic balance is preformed, but there was no answer, .

I also saw a link to an Ipad app for vibration and ordered it and mounted the Iphone  to the instrument panel with Velcro or just pressed it against the instrument panel when I was flying.

My results on the x and y axis between 3,000 and 3,500 rpm has been in the 1.7 to 2 g range.

I would be interested in finding out if any one else has used the app to get a relative indication of vibration so we all could compare what is dangerous and what is not,,,Thanks a lot Mike Heckler,, N607SN

[kalazzerx]

What app exactly are you using - I noticed more than one in the app store.  I would be willing to run it against my 1/2 VW and compare results.  It will be a few days before I can do so as currently out of town but I am also interested in the results.

[mikeheckler]

It is just called Vibration

[mikeheckler]

Vibration by diffraction Limited Design LLC

[Sweet B]

Great post! I hope to dynamically balance my prop this weekend so I'll let you know if it happens. Currently @ 3200-3500 I cannot read the gauges because it shakes so much. Can you tell me where and how much weight you currently have on your hub? Glad you made it down safely.

[mikeheckler]

Glad you are interested a lot of people are not.

Looking from the front of the engine toward the back the weight is 90 degrees to the left of the top dead center line on the prop hub when the hub is at tdc,, in other words at the 9 oclock posisition when the tdc alignment mark is at 12 oclock, looking front to back.

I don't know what the weight weighs.

[Dan_]

Are you talking about the bob weight put on the back of the prop hub with the mass balance job done on the crank..?

[mikeheckler]

Yes it came with the crank

[Dan_]

Ok, next question...  Is it the bob weight off the old crank or did it come with the new crank..?

[mikeheckler]

With the new crank

[Dan_]

[Dan_]

OK, next question... Was the prop statically balanced before it was dynamically balanced..?

[mikeheckler]

Yes it was

[Dan_]

[mikeheckler]

 How many IPS is acceptable with this engine when a dynamic balance check is preformed, does anyone know?