prop balance

[Mark Kramer]

Cool. Wish I could find the skf app. Using something called vibration analysis by Krober. Gives two different values. For example: acceleration 1.48 m/s2 or distance 1.59 mm. To get these two examples I just shook the phone a little bit and these were the two values it offered. I was thinking I would use the distance option, but that’s only a guess. Or do I want the acceleration option? Is this app even gonna work for what I need? Any thoughts Denny? So close to flying, but I know things must be right.

[dennysleen]

Using the 4 Run Test method it shouldn’t matter what value you use as long as you are consistent.

[Dan_]

Cool. Wish I could find the skf app.

Is this it..?  https://www.reliableplant.com/Read/31459/condition-monitoring-tool

If so it is at the Play Store.  https://play.google.com/store/apps/details?id=com.skf.pulse.release

[Mark Kramer]

No, it’s not the same app that Denny was talking about earlier in this thread. He said another vibration app should do, as long as all the other parameters involved are always the same during each test run. Hope I’m not misquoting you Denny. Tried again today and couldn’t get the 3 circles to intersect. I was using a rpm that was particularly shaky. Tomorrow I will maybe try at idle, won’t have to rely on this worthless tiny tach. The input is so valuable to me, keep it coming... thanks

[dennysleen]

The SKF app that I referred to three years ago is no longer available. I have not found another one that was as straightforward and easy to use. I would do all of your test runs at wide open throttle. The circles may not and will not perfectly intersect you’re going to have to make a best judgment for their “intersection”location.

[Mark Kramer]

Ok...I have no idea what rpms wot is,(tach troubles) also engine falters at wot. Not sure why yet. Stabilized the carbs, pretty sure I have the timing correct(used a timing light). Little scary that close to the meat cleaver.
You did this by laying the phone on that flat spot? I made a bracket for the phone and attached it to the engine top. Hope it’s not shaking more than the engine. I made it as stiff as I could.
Oh, should I do this test with or with out the counter weight on the prop hub?
Thanks Denny
Mark

[Dan_]

The SKF app that I referred to three years ago is no longer available. I have not found another one that was as straightforward and easy to use. I would do all of your test runs at wide open throttle. The circles may not and will not perfectly intersect you’re going to have to make a best judgment for their “intersection”location.

If the app is for Android you can "save" it and hopefully attach it to a post here.  If it is for one of those nursing home phones I guess it reached the end of the line... 

Instructions here:  https://www.theverge.com/2019/6/12/18661705/android-apps-transfer-new-phone-how-to-legacy-old

[dennysleen]

If your crank has a balance weight on the prop hub you should always keep it there. I held my phone in place during the test runs. The SKF vibration app that is no longer available had a 5 second count down and then recorded data for I think 15 seconds and gave you a graph and an overall average. I have yet to find an app as easy to use. I haven’t looked for a couple years until yesterday when this thread caught your interest.

[dennysleen]

I found one that I will test when I get to the airport. It is called Vibroscope Lite or Vibro.LITE 
It has a three second countdown then records 20 sec of data.

[Mark Kramer]

Ok yeah, the one on my Android has a 5 second count down, pretty easy to use. Shows two values, acceleration and movement. The Mosler manual says to use the counter weight, and tells where to use it, but not the size and weight. Mine is a guess, not balanced to my engine. I want to do the test at wot like you suggested, but it falters at wot at this point. Not sure why yet. Haven’t given up on the dual carbs yet. I don’t feel like it is shaking all that much, maybe I’m looking for something not attainable? Just thinking it can be fine tuned.

[Mark Kramer]

Watched putt putt up close and personal this am, quite sure his counter weight is 1/4 in thick. Made mine 1/8, wonder if mine should be 1/4. If I could just do this shake measurement correctly it should show me where and how much weight.

[Kamcoman77]

The counterweight that comes with a lot of the 1/2 VW kit engines is 1/4" thick. Here is a drawing of one. The angled piece cut off one corner is a different size depending on the engine size.

[Mark Kramer]

Think I will make one up out of 1/4 inch stock. I wouldn’t say my engine shakes like crazy, but I would say it needs fine tuning in that department. Can’t get these carbs to stop spitting out gas. I feel like the engine would have to be perfectly still for these carbs to not spill gas.

[dennysleen]

Every crankshaft needs to be personally balanced. Mine came back from the balancer with 35 grams on the prop hub. I have seen others with the huge chunk of steel shown below. I think my engine would rip itself off the plane if I added that muck weight to it. Be careful.

[Mark Kramer]

I hear ya on the too much weight thing. Removed my phone bracket, as I think I was getting additional shake or movement in the bracket. Holding the phone directly on the engine is giving lower numbers and making a little more sense when graphing. As far as doing it at wot I’m not sure if I have the cahonies for that! Also my erratic tach makes this testing not consistent. Have tried everything possible with that sensor lead on the plug wire to no avail. Carbs are not right yet either. One plug is white while the other is tan. I have no jets to try yet, so I raised the needle one notch on the white plug side. I can now get full throttle, not as nicely as it should be though. My engine is a 40 horse 94x78. Carbs are vm26  606 4 stroke carbs. Gonna try going up a jet size. Did a compression check, right side 135, left side 160. Wonder if this difference is an issue. Need to call Scott.