AK rotor shake

[bones]

People hoping some one can help me short track the problem with a set of rotors that came with a machine to a student up here.First off, the machine rotor head i feel is fine because i put a set of my AK"s on that i knew where smooth, and sure enough no problem smooth as, double checked the stringing of the problem set and got them perfectly over the dot, put them back on and still the same shake back again.Now more details the shake feels like 11 to 5 which from memory is odd, normal shake i thought was more 2 to 8?Now some thing i thought of the rotors that i put on where 26", and the problems ones are 28", also when the 26" where on the rotor tie down until the front stops is a lot more than with the 28", so if the cone angle is too great would this be causing the shake??I also tried to "sling" the rotors, it made a small improvement but still not as smooth as the 26" rotors.The only other thing i can think of is to try shiming the bar sideways in the head, but is this a waste of time?Any ideas?? any one

[asra]

There might be a bit of tracking or balance plus the 2/per shake. Try shims under the block each way for tracking and also moving the bar sideways and see if it will come back to the 2 to 8 shake.

[bones]

There might be a bit of tracking or balance plus the 2/per shake. Try shims under the block each way for tracking and also moving the bar sideways and see if it will come back to the 2 to 8 shake.Yes well aware of all this, was hoping some one may have had this problem before.

[Ken Watson]

I bought a new set off Jeff years ago and the shake was woefull. The balance was out that much that the hole he drilled in the end block, I filled with steel to get it right. The stringline punch mark was not centered on the block in any direction and was not directly above the teeter bolt, so I punched a new one. The hub bar is rounded slightly on top and the block is flat. A bit like a matchbox sitting on a bit of water pipe. I lapped the block to fit snugg all over. I then shimmed the rotors sideways in the towers until they flew perfect. They are substantially closer to one side, but fly very nicely. Ken

[Mark Horan]

Ken is right with the matchbox and waterpipe analogy!when I bought my tandem, there was a 5 thou shim on one side between the hub bar and block. I didnt like the look of it so I tried to remedy the "hump" on the hub bar by using a bit of tool steel to "spokeshave" the bar flat. It made it flat but the rotors shook like a bstrd so I put the shim back in.I think that it is a bit of an Agricultural fix, but the blades are smoother that they have ever been.I was thinking of having the two surfaces machined together but Steve Waddell turned up and I decided to do nothing until he had completed his hub bar project. I have been lucky enough to see some of the computer modeling regarding stress on a hub bar that Steve has done and it is certainly interesting.When I bolted the block back onto the hub bar, I was concerned that overtightening may deform the aluminium, which in turn may provide a place for damage to occur to the hub bar. It still scares me, as Steve confirmed my way of thinking. I looked up torque values for the bolts, but could find nothing using aluminium as the material to be connected. When I bolted the two together, I reduced the torque number

[Brian]

The 28 AK"s I have are smooth as silk so its not the size thats the problem. Think mine have about .8 degrees pitch so check what the pitch is as if its been pitched up , they will most likely shake a bit.I got a set of 27"s that were smooth as till Geff changed the pitch to 2 degrees and now they shudder, not real bad but its annoying. Tried most things to stop the shudder but have managed to reduce it a bit.

[bones]

Well we got an hour or so to start on the problem today, and started with a standard 3/8 copper washer 0.040"

[Ken Watson]

G"day Mark. I used varying thickness of shim paper and made washers from it. I finished up making tiny adjustments. I did all the caculations and shimmed according to this to start with and it was terrible. Then I went the opposite way like you and it gradually improved. My shims were a lot thinner than yours, but I finished up with quite a few. Ken

[birdy]

it is much much better now. : :Gee ay????,...........never woulda gessed that. One o these days you young fellas will listn to the old farts.

[bones]

it is much much better now. : :Gee ay????,...........never woulda gessed that. One o these days you young fellas will listn to the old farts. What you trying to say you old fart

[Des Garvin]

What you trying to say you old fart Birdy : Just ask his kids