Notification 17-05-19 Soft Engine Isolators

[rvbuilder2002]

Originally Posted by RFSchaller

it would be useful to know how this was discovered and what, if any, dangerous condition resulted.

http://www.vansairforce.com/communit...8&postcount=10

http://www.vansairforce.com/communit...1&postcount=18

[WingedFrog]

Originally Posted by rvbuilder2002

http://www.vansairforce.com/communit...8&postcount=10

http://www.vansairforce.com/communit...1&postcount=18

From the first link: "The soft isolators can not be over compressed because there is still a spacer that the bolt torques up on."
Could you elaborate on this, I do not understand.

[Piper J3]

I checked my isolators and can't find any markings on them so I suspect they fall into this notification. On the other hand, I have very little clearance between engine valve covers and cooling plenum on the left side and don't see any evidence of motor movement causing a problem. Airplane has 250TT.

[DaleB]

Originally Posted by WingedFrog

From the first link: "The soft isolators can not be over compressed because there is still a spacer that the bolt torques up on."
Could you elaborate on this, I do not understand.

Take a look at the drawing in the manual. The bolt goes through a spacer, so the bolt torque doesn't depend upon the rubber isolator. The fuselage attachment point (WD-1221), bolt, washers, spacer and nut form a solid assembly. When you torque the nuts down there will be some compression of the rubber parts, but the washers bottom out on the spacer and that's what you're tightening the nut and washer against, not the rubber parts.

The first time I checked I was pretty sure I saw no markings. On closer inspection, I could just see the very tops of the numbers along the very edge of the metal "cup". No paint dots are visible anywhere.

Is it possible to install the isolators backwards from what's shown in the drawing - in other words, male half on the aft side of the engine mount, female half forward? And if so, would it make a difference?

[WingedFrog]

Originally Posted by DaleB

Take a look at the drawing in the manual. The bolt goes through a spacer, so the bolt torque doesn't depend upon the rubber isolator. The fuselage attachment point (WD-1221), bolt, washers, spacer and nut form a solid assembly. When you torque the nuts down there will be some compression of the rubber parts, but the washers bottom out on the spacer and that's what you're tightening the nut and washer against, not the rubber parts.

The first time I checked I was pretty sure I saw no markings. On closer inspection, I could just see the very tops of the numbers along the very edge of the metal "cup". No paint dots are visible anywhere.

Is it possible to install the isolators backwards from what's shown in the drawing - in other words, male half on the aft side of the engine mount, female half forward? And if so, would it make a difference?

Now I get it, thanks Dale. Of course an alternative would be to make the spacer shorter for the soft isolators to allow for more compression but if possible it would be even more work than swapping the isolators!
I still am not convinced that a well balanced engine is at risk with the soft isolators... If something bad happens to the engine that creates lots of vibration, may be? But eh! it's a Rotax 912 not a Continental or Lycoming!

[RFSchaller]

Thanks for drawing my attention to those posts, Scott. Sounds like this is precautionary as opposed to a failure having occurred. I feel better about waiting until next oil change in cooler weather to check mine.

Rich

[rvbuilder2002]

Originally Posted by WingedFrog

I still am not convinced that a well balanced engine is at risk with the soft isolators... If something bad happens to the engine that creates lots of vibration, may be? But eh! it's a Rotax 912 not a Continental or Lycoming!

This has nothing to do with whether your engine will run smoothly or not.

As is usually the case with design details, there is usually a lot more to it than people consider.


Here is just one.....

When an airplane experiences a G's exceleration, all components feel it the same way you do.
The engine is connected to the airframe with flexible rubber isolators (the subject of this discussion).
If the correct parts are installed, the engine on an RV-12 will sag more than 1/2" at the spinner during +4 G's.
How much will it sag if isolators that are softer than specified are used? I don't know. Tests were never done to see what happens if wrong parts are used, but I will guess that it be an inch or more.

[scottmillhouse]

I have ignored this Notification with plan to address at my annual. On my last long cross country I had strange resonance noises start (around 180 hours on isolators). Grabbing the prop hub I appeared to have excessive engine movement and feared a loose bolt to engine. Removed cowling with no evidence of rubbing or anything wrong. Could find no numbers on my isolators. Reassembled and flew 6.5 hours home with no noise or problems. Called Vans and they shipped the new parts to me for FREE. Great Service!

I'm assuming vibration was being transferred directly to the mounts by the bolt/spacer.

Update: turns out I had numbers on my isolators after all but they we not visible being compressed againt the large white washers. I replaced them with new and do note somewhat less movement. Job took about 4 hours perfomed as indicated in prior posts using an engine lift. The noise appears to have been caused by the right carb throttle lever vibrating against the side frame portion of the carb tray when at nearly full throttle. Obviously with the headwind going I was at higher throttle settings than with a tail wind upon return. Quick work with a file gave more clearance.

[Dgamble]

"Called Vans and they shipped the new parts to me for FREE. Great Service!"

That's a pretty good deal. They charged me $40 to fix their mistake.

[RFSchaller]

This was tough to do without loosening the mounting bolts, but with an endoscope I was able to see the top little bit of the markings.