Prop Nut & Bolt Torque Sequence Question
 

<div id="post_message_793374">I have a ZDZ80 which has 6 smaller bolts and a large nut on the main shaft for bolting on my prop. When I snug down the large nut, the 6 outer bolts get loose...so I tighten the 6 bolts, but then the big nut is loose again...so I tighten the 6 bolts. You get the picture...tightening one makes the other loose. What is the correct method for snugging down the nut and 6 bolts. When do I stop cranking on them?</div>

RE: Prop Nut & Bolt Torque Sequence Question
 

With the ZDZ80, there are the six bolts, which are the "drive" bolts... beings how the prop, nor the shaft, have splines of any kind. The proper proceedure is to tighten the main shaft nut to specs, then snug the "drive" bolts. Their only purpose is to prohibit prop "freespin" on the shaft. I would use threadlock on these, avoiding vibration movement.

RE: Prop Nut & Bolt Torque Sequence Question
 

Dude, I do what you do on my ZDZ80. I keep going back and fourth. First the center nut then the bolt circle. Just snug them up good. There will be a point where they are all snug. Stop at that point. This may take about 6 times for the nut and 6 times for the bolts. It is a good idea to recheck them periodically. In fact that is what I'm going to do now since I'm going to a flyin tomorrow.

RE: Prop Nut & Bolt Torque Sequence Question
 

On my ZDZ 80RV (silver head) I only have the 6 smaller bolts (with flat washers and split locking washers).  There is a center shaft, but no nut or even threads that stick out enough to bolt on a prop.  I tighten the 6 small bolts down using a criss cross pattern to 20 inch lbs, then retighten again to the 20 inch lbs.  I then tighten them up to 30 inch lbs, again using the criss cross pattern and then again to the 30 inch lbs.  I put a drop of machine oil and the threads.  I have never had a problem with them coming off or breaking, and any tighter seems to really start to squish the prop hub.  Tightening to the 30 inch lbs puts a little bit of squish on the wooden prop hubs, but not very much.  I do check it after a weekend of flying and they are still good.  When every I replace a prop or take the bolts off, I try to replace the split locking washers (but this does not happen every time but I try too).
If I remember correctly from a previous thread, someone mentioned that you either use the large single nut or the 6 smaller bolts not both.  A copy of the manual that I have does not mention the large single nut at all.

RE: Prop Nut & Bolt Torque Sequence Question
 

Sorry, I just checked out TBM web site for the online general manual for the ZDZ engines.  They mention the center nut and the 6 bolts as well as the correct way to tighten them.  Check out thier site www.troybuiltmodels.com  .I know the older ones (which I have) does not mention a center nut.

RE: Prop Nut & Bolt Torque Sequence Question
 

I did see the general manual, and they say to tighten all bolts. This is far from the correct way to tighten the bolts.
I see far to many pilots use their full force to tighten the bolts, compressing a wood prop way too much.
The bolts, including the center nut, should be very lightly tightened in a criss-cross pattern going round and round until all bolts hold their torque.
I cannot tel the torque, because I use my engineer's feeling. All I know is that the final torque is way below the thread damage torque. When I am done, a medium hardness grade wood prop will have compressed very slightly.
When the engine heats the wood, it will compression set again, so re-torquing is required. The heat also hardens the wood, so torquing frequencies will become less and less.
One of these days I will buy a suitable torque wrench, so I can check the final torque in my applications. I doubt it will be more thanthree foot-pound on M5 screws.

edit PS:
M5 10.9 high grade bolts have 6.7 Nm standard torque (lubed threads). That is about 5 LbFt, which would certainly compress your prop to death.

RE: Prop Nut & Bolt Torque Sequence Question
 

 about  4 ft pounds is plenty on any 6 bolt pattern
 BUT for you guys with no torque wrenches  ( Tsk tsk)
 a  T wrench  - a 3 mm or 4mm wrench  which fits your palm with the  leg of the  t extending  through middle and ring finger to the bolt  will do the  job with  regular old  wimpy  wrist  action found on typical non sports oriented  humans
 Also  all six bolt patterns should have  the bolt pattern  drilled shch that all bolts  fit  easily using fingers only to insert  and  partially thread the bolts .
 side loading the bolts is a no no  -slight clearance is dsireable  as the bolts  simply clamp  -they are  not  drive pins -tho some think they are -

RE: Prop Nut & Bolt Torque Sequence Question
 

A t-wrench like this? The first line is 3Nm torque. I use about 4 Nm on wood, and about 7 Nm on carbon props

RE: Prop Nut & Bolt Torque Sequence Question
 

40 inch pounds for those not Eurocentric;)

RE: Prop Nut & Bolt Torque Sequence Question
 

and 70 inch-pounds on carbon ()
tenfold Nm is accurate enough for general technical conversion

RE: Prop Nut & Bolt Torque Sequence Question
 

I use 38 in-lbs for wood props and 40 in-lbs for CF props

RE: Prop Nut & Bolt Torque Sequence Question
 

On carbon props you can torque quite a bit higher. Limits will be what the prop washer and bolt washers will allow, combined with the bolt grade, which should be at least 8.8 or SAE5