DA 100 throwing props/spinners

[feral63]

listen to this guy. he does know just a lttle bit about these engines.

	Quote: Originally Posted by Howie
	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.

[TheTank]

What prop were you using when it was thrown? A standard Menz or Mejzlik is fine with stock bolts, but a different prop, or a crushed hub on the prop from over tightening could be causing the problem.

[3dubya]

Yer check the back of the prop, I use mezjlic props and PTs cause they perform the best, but we have had a few mezjlic's turn up in Aus where the back of the prop where it bolts on is not flat. Enough to bend the bolts and center pin when done up. Its a very rare one but some thing to always check with a new prop. It rocks when you put it on flat surface.

[plane]

Here's another angle to consider. This sounds almost exactly what was happening to my friends motor.

The hub wasn't counterbored deep enough and the hub retaining studs radiused base wasn't allowing the spinner backplate to sit flat against the hub. It was about .003-.006 away. VERY hard to see. I used a brand new backplate on the motor and discovered it.

The fix was easy. I took an exacto knife and chamfered the the center hole on the old backplate until the plate sat flat against the hub.

Problem disappeared forever.

[DATech]

Hi Gary
Sorry to hear about the problem. As asked above, what type and size of prop are you using? Are you using a spinner?

[speed8]

Three times , come on, I would have all ready called . DA has the best Tech suport . IMO

[Gary Powers]

	Quote: Originally Posted by 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

I accept your apologies. :-)

Actually I have replaced 14 bolts, two spinners and three props. I was able to recover the spinner from the first airborne deal.

I assumed that the first time (still on the ground) was because I had put a drop of oil on each of the prop bolts and they backed out. Don't remember what our thinking was the second time, but we suspected an overly rich setting and were working the low end in. The third time was the wake up call, although I obviously was still looking at the engine being overly rich.

I have two brand new DA's, a 50 and 100, and am absolutely delighted with them despite this small issue. I have been flying BME 50's and a ZDZ 60 and the DA's are, in my limited experience, a cut above. The 50 is notably more powerful than the BME and they both start a heck of a lot easier than the ZDZ.

I spoke with Brian Huffmeier at DA this morning and he suspects a prop balance/vibration issue, so we'll make sure all the obvious problems like bolts bottoming out are eliminated and then try it again Saturday. Worst case, I will send it back for their inspection and fly my 50 at the Albuquerque IMAC.

And again, my appreciation to all who have responded and shared their thoughts and experiences. While I have been a modeler on and off for over 30 years, I am fairly new to gassers and working hard to catch up on the technology.

Gary

[GremlinX]

Just dawned on me... are you balancing the prop?

[Gary Powers]

	Quote: Originally Posted by GremlinX
	Just dawned on me... are you balancing the prop?

The first one was balanced, but I cannot remember balancing the second one. Bet your bippy I'm gonna balance the one going up Saturday morning.

You know, stepping back and looking at this last couple of weeks, it could be what pilots call a "cascade of errors" with one leading to the next. I'm fairly certain it started with that little bit of oil on the prop bolts.

Gary

[FLYNYAK]

Check your prop bolt holes. After you drill it, you can slide all the bolts, prop washer and spinner back plate together nice and easy. You can hand thred them on befor you need a rench.If you have not drilled the prop perfect then you get a side lode and when you rev it up it can break the bolts.

[AHP]

Sounds like timing.

[Kevin Y]

the reason I dont think it is timing is because the slots on the pickup sensor do not allow you to advance or retard the timing enough to ever get it to backfire. It should only be enough to make the engine run hot or hard to start not actually backfire. But the timing can easily be checked. I know someone posted it before but all you need to do is bring the engine to top dead center and see if the leading edge of the magnet is lined up with the black mark on the pickup sensor.