Motor mount question.

GEM930 · #1 07-11-2012, 02:41 AM

So I torqued the motor mounts today on my 320 to 360 engine swap and was surprised to see that I could twist the nut /bolt combination inside of one of the mounts (lower passenger side) with just me fingers. Is this normal???

RV6_flyer · #2 07-11-2012, 03:07 AM

Quote:

Originally Posted by GEM930

So I torqued the motor mounts today on my 320 to 360 engine swap and was surprised to see that I could twist the nut /bolt combination inside of one of the mounts (lower passenger side) with just me fingers. Is this normal???

No it is not normal to be able to rotate the bolt / nut on the engine mount to fuselage on an RV-6.

My RV-6 will be 15-years since 1st flight in September 2012 and has about 2,600 hobbs hours on it. I had an intermittent alternator problem for 8-weeks. Could not find any problems. I used one of the engine mount bolts for the ground pass through from the engine to cockpit. This is not best practice and the lugs did not look like they had good crimps. I redid all the large #2 wires and lugs plus moved to a dedicated ground stud. I had to use a drift pin and hammer to get the engine mount bolt out and back in. The alternator issue ended up being bad contacts in the field connector at the alternator. All the other things tests ok. Only 0.002 ohms from battery to engine on a milli-ohm meter but since the lugs and ground location were not the best practice workmanship, they were redone.

GEM930 · #3 07-11-2012, 03:26 AM

Sorry, I was not clear. The bolt /nut combination that runs through the rubber lord mounts.

131RB · #4 07-11-2012, 04:13 AM

Sounds like your bolt is to long and the nut is bottomed out on the threads. If you changed engines you may want to make sure you reinstalled with all the hardware you removed ie large area washers and such.
Ryan

GEM930 · #5 07-11-2012, 04:42 AM

Quote:

Originally Posted by 131RB

Sounds like your bolt is to long and the nut is bottomed out on the threads. If you changed engines you may want to make sure you reinstalled with all the hardware you removed ie large area washers and such.
Ryan

I thought that might be the case and checked. It does not appear to be running out of thread. Everything appears to be tight against the internal spacer. I does not spin freely, but it is possible to turn it with my fingers. I assumed all four spacers were the same length and did not check... Are the tops and bottoms different? I replaced all washers exactly as they were on the original engine. Since it is a bottom mount it makes sense to me that the weight of the engine is compressing the rubber and everything else is just lined up so there is little pressure on the bolt. I feel like if I shook the engine a little I would likely not be able to turn the bolt as things would shift and bind.

gstone · #6 07-11-2012, 04:53 AM

This should be verified before doing anything with it but had an issue with a an IO-540 (certified) mount that may apply.....

If there is a harder and softer half of your engine mount? Check to see if they are supposed to be installed with the harder half engine side bottom and firewall side top...

That takes care of the tension at the top and compression at the bottom.

Again, verify.....

GEM930 · #7 07-11-2012, 05:03 AM

Yes I believe there is a compression side and a tension side identified by a rib or a step or something (I cant remember exactly) I installed them as they originally were and then double checked them with two other RVs on the field.

GEM930 · #8 07-11-2012, 05:48 AM

The more I think about this the more I think I just don't have the nuts tight enough. I'm using metal lock nuts instead of castle nuts and the torque spec is so low I think I'm hitting it based on the bite the nut is getting on the thread and stoping before its bottomed out on the spacer. I looked at a picture of a mount and I can't see how I should be able to turn the bolt if it is properly torqued.

Ironflight · #9 07-11-2012, 07:47 AM

if you are absolutely SURE that the nut isn't bottoming out, then this won't apply, but I seem to recall that the upper and lower bolts in the standard Van's kit are slightly different lengths - if you have them swapped, you might have two that are a little long.

krw5927 · #10 07-11-2012, 09:17 AM

Quote:

Originally Posted by GEM930

The more I think about this the more I think I just don't have the nuts tight enough. I'm using metal lock nuts instead of castle nuts and the torque spec is so low I think I'm hitting it based on the bite the nut is getting on the thread and stoping before its bottomed out on the spacer. I looked at a picture of a mount and I can't see how I should be able to turn the bolt if it is properly torqued.

In order to properly torque a fastener, you need to first measure the running torque (the torque it takes just to turn the nut on the bolt, the bolt into the nutplate, etc) and ADD that to the fastener's torque requirement. Dial or beam type torque wrenches are great to have around for this reason. You can measure the running torque on the bench before you ever install the bolt on the plane.

Otherwise all your fasteners will be under-torqued, and on some you may run into exactly this problem.