NR prop bolts concern

[1avidflyer 1983]

Hi all,  I have about 175 hrs on my NR two blade prop on my Kitfox 4 with 80 HP 912.  I've adjusted the prop a number of times between winter and summer, but never actually took the bolts out.  The other day I put a balance master on it, and got new AN5 bolts for the install.  Here is what I found.  I've always torqued the bolts to correct torque, but a few times it did seem like a couple of them acted weird.  Like not turning as much as I expected at the next torque setting.  I would say that apparently, they weren't tightening up to correct torque, at least some of them.  I'm back to working on my new built Kitfox 4 now, and I took the NR two blade prop off of it, so I could work on the engine and cowl install better.  I had ran this engine/prop about 15 or 20 minutes last summer, before I got side tracked.  Both times I used the bolts that NR supplied with the props.  Last prop I know of that came from them didn't come with bolts.  Maybe I'm not the only one who had an issue.  I like the prop, gives good performance, but if you are running their bolts, you may want to have a look.  First and third pictures are the 80 HP, the number two and four are from the 100 HP 912 with 15 or 20 minutes run time.  JImChuk

Edited 23 January by 1avidflyer

[Buckchop 479]

Well id say never use thier bolts, and ill bet they stopped selling bolts cause of the streching problem, they must b grade 5 or lower bolts, id pitch them in a round receptical and go buy some grade 8 hahahahaaaaa

[saskavid 47]

So what markings are on the heads of those socket head bolts? From what I've read online they are supposed to be made to a better tensile standard then grade 8.

They are supposed to be on par with ISO metric standard of 12.9 or better which makes them a cut above grade 8. 

[1avidflyer 1983]

I'll take a look for any head markings on the NR bolts.  I did replace them with AN5-36 bolts, so shouldn't have any issue with bolts going forward.  I'll have to change the clamp bolts out as well.  JImChuk

[1avidflyer 1983]

The bolts have an 8.8 marking on the heads.  JImChuk

[Av8r3400 1179]

The bolts have an 8.8 marking on the heads.  JImChuk

8.8 is similar to SAE grade 5, which is comparable what AN hardware is.

[wypaul 448]

I have ran quality 8.8 metric bolts in my props for the 912 engines without issues.  I suspect that the bolts may be counterfeit and of poor quality.  Looking at the hub there seems to be deformation where in contact with the washer’s perhaps it is just the pictures.  I guess I would need to hear about the report on the recent KF crash in AZ where there has been some doubt cast on the prop.  These of course are just my thoughts from looking at pictures which doesn’t mean much.  I do wonder what grade of aluminum is used in the hub.  Does the hub use the standard Rotax drive lugs? Mine are threaded for the 8.8 x8mm bolts but I know they are available clean bored to be used with nuts on the rear.

[1avidflyer 1983]

My NR hubs do use drive lugs.  They are not threaded, but rather have a 5/16"/8mm hole through them.  I think the bolts where the deformation shows were not tightening up correctly or enough.  Even though the torque wrench said they were tight enough.  Might be that the galvanizing (if there is any) was being squeezed off the bolt threads and galling and binding up.   

 

PS   When I submitted my first post on this topic, I put the pictures in the order I wanted them to be in, and wrote my description accordingly.  Just looked now and they are not in the correct order.   Picture one and three are the 80 HP with about 175 hrs run time, pictures to and four are the 100 HP with about 15 minutes run time.

Edited 23 January by 1avidflyer