DA 100 throwing props/spinners

[Gary Powers]

	Quote: Originally Posted by Freddy Warbird
	I wouldn't think a backfire would cause prop bolts to shear off. IMO, Prop bolts don't know whether the engine is rotating one way, or the other. I would look into how your fastening the prop to the engine. Not every propeller has the same hub thickness, some are thicker, and some are thiner. The fasteners may not be fully seating against the plate. They could be bottoming out -ever so slightly- against the rear engine hub giving a false indication of torque. Likewise, over tightening bolts with a wooden prop could crush the hub ruining the prop. Just my two bits!

Good thoughts Freddy and thanks. If anything I am over tightening. This started with some thoughts posted by KIWI regarding the wisdom of using anti-seize or lithium grease on the bolts to prevent them galling. When it threw the prop on the engines initial start, I got to thinking maybe that was a bad idea, so I cleaned the stuff out of each hole, but it has happened twice since. Rich as the engine was, the power was very impressive. Can't wait to get a full flight in. :-)

Gary

[Gary Powers]

	Quote: Originally Posted by dmcquinn
	Almost certainly your prop bolts were too loose. Needle valve settings will not cause this. I use a torque wrench calibrated in inch-pounds (not foot-pounds). I use 37 inch-pounds for wood props. Re-tighten them after fllights 1, 4, 8, then every so often.

I do have an inch-pounds torque wrench and will check it out tomorrow. And I will give DA a call in the morning; I thought they might be monitoring this forum.

And thanks to everyone who responded! I've gotten just enough time on this airplane to know that I want a lot more and I only have the coming weekend to get this solved before its off to Albuquerque for their IMAC contest.

Gary

[Gary Powers]

	Quote: Originally Posted by Vic3D
	Hey Gary! I'm starting to think that your ignition sensor might be off, which makes your timing bad. I would get that checked out with DA, also. Vic

Ah, Vic, something I had not considered at all. OK, a call to DA first thing in the morning. And again to all, thanks.

Gary

[vernonf]

4.5 ft lbs or 54 inch lbs. torque on the bolts. blue locktite. no problemo.

[3dubya]

	Quote: Originally Posted by Vic3D
	Hey Gary! I'm starting to think that your ignition sensor might be off, which makes your timing bad. I would get that checked out with DA, also. Vic

	Quote: Originally Posted by Gary Powers
	Ah, Vic, something I had not considered at all. OK, a call to DA first thing in the morning. And again to all, thanks. Gary

How does he check the key has sheared in the DA and the boss has sliped on the shaft (throwing timing out) without pulling boss off. I know how the 3Ws work but the DA I dont know.

[Richo]

I think someone has mentioned before, check that the prop bolts aren't hitting home. If the bolts are too long, you can tighten the bolt up until the cows come home, and you will still break bolts and spit off the prop.

[Howie]

	Quote: Originally Posted by 3dubya
	How does he check the key has sheared in the DA and the boss has sliped on the shaft (throwing timing out) without pulling boss off. I know how the 3Ws work but the DA I dont know.

At TDC the magnet should be directly under the pin in the sensor. (There is a mark on the forward edge of the sensor corresponding to the pin.) Unlike the 3W's, there is no TDC mark on the hub, but it's not too difficult to find.

Except for a prop strike I have not seen a DA100 hub shear a key and slip.

My bet is the prop bolts are bottoming out. If it was backfiring hard enough to break bolts then you would hear it!!

Bolts only break if they are loose.

[3dubya]

It probably would be a miracle to start it if this was out too hey.

[Howie]

	Quote: Originally Posted by 3dubya
	It probably would be a miracle to start it if this was out too hey.

I sheared a key on my DA150 once when I was playing with a rather heavy 3 blade prop. (Turned out the prop was crap anyway.)

With the hub slipped, the engie was difficult to start and wouldn't transition at all. If the hub slips you normally know straight away there is something wrong.

[Stinger1]

The only time I had an issue with a large engine shearing bolts was when I went to a prop with a thinner hub and bottemed the bolts instead of tightening them . Now I carry 50mm, 55 mm and 60mm bolts in my tool box .

[Mokken]

Call DA..

[flyin woodbutcher]

WTF you have thrown the prop 3 times, is that correct ? That would mean you have replaced 18 bolts ? You were able to remove the broken bolts from the hub every time ? A wood prop that came off would also be damaged , along with the spinner. I can see one time ,but why not call DA right off. Respectfully I got some non belief in this situation. I apoligize in advance for assuming this is a troll if it is not.

FWB