Engine Mount Bolt Direction

[slowflyin]

Good afternoon,

Looking for some group wisdom.   Pulled the engine mount off of my Bravo for an IRAN while the Lycoming is being overhauled.  The bolts enter from the engine side with nuts on the cockpit side.  However, the exploded view in the parts manual shows the opposite.  This AC is a 1994 model and the log books don't indicate the mount has ever been removed.   I can't find any relevant info in the SM.  The SM adds to the confusion as it shows a mount attach points that don't match the PM.

 

[Guest]

Traditionally the nuts are forward in the engine compartment where they are visible for inspection.

Clarence

[N201MKTurbo]

You need a big beefy guy like @ragedracer1977 to bend the engine mount when the bolt holes don't line up by like 0.020".

[carusoam]

Another factory tradition we have learned about…

Make sure the carpet isn’t under the bolt heads on the cabin side…

Extra stuff interferes with the proper torquing of the fasteners…

PP thoughts only, not a mechanic…

Best regards,

-a-

[Bartman]

I used new hardware for installation. We ground down the end of the old bolts slightly and drove them in from the engine side as a guide, and then drove in the new bolts from the cockpit. I also used torque seal on every fastener. The fluorescence makes it easy to turn the lights off in the hangar and use the black light to quickly check every bolt and fitting with an oil change. 

[N201MKTurbo]

1 hour ago, Bartman said:

I used new hardware for installation. We ground down the end of the old bolts slightly and drove them in from the engine side as a guide, and then drove in the new bolts from the cockpit. I also used torque seal on every fastener. The fluorescence makes it easy to turn the lights off in the hangar and use the black light to quickly check every bolt and fitting with an oil change. 

This method certainly helps. I do it myself, but there is a time while driving the bullet out with the new bolt that the intersection of the two cross the firewall boundary that the engine mount will spring away from the hole by enough that the bolt won’t go through. 
 

My motor mount was repaired before I had the plane, so it might not be as perfectly built as a factory mount, but I’ve had this issue with other planes too.

[skykrawler]

It's probably a bad thing if you must 'drive' bolts with anything more than a tap tap tap.

 

[Shadrach]

30 minutes ago, N201MKTurbo said:

This method certainly helps. I do it myself, but there is a time while driving the bullet out with the new bolt that the intersection of the two cross the firewall boundary that the engine mount will spring away from the hole by enough that the bolt won’t go through. 
 

My motor mount was repaired before I had the plane, so it might not be as perfectly built as a factory mount, but I’ve had this issue with other planes too.

I’ve had R&R’d my mount a few times. While it is not perfectly matched to the bosses on the steel cabin structure it so close as to not require much manipulation/flex to get everything in place. I also use old bolts as locators because it holds the mount flush with the firewall and maintains alignment of the mount holes with the bolt bosses. If the mount is even slightly away from the firewall (as in you pull it away to see if the bolt is aligned) the bolt will enter the mount hole at an angle which can booger up the threads, the CAD plating on the bolt and the inside of the mount.

[slowflyin]

18 hours ago, M20Doc said:

Traditionally the nuts are forward in the engine compartment where they are visible for inspection.

Clarence

Thanks Clarence!  That's exactly what I was thinking.

[slowflyin]

Thanks for all the great advice.  As always, Mooneyspace come through!

[slowflyin]

Thought I'd share this pic as I found it interesting.  This is the nut off my lower, outboard motor mount.   I'm not questioning the engineering and understand shear versus tension.  That being said, when I removed it, I said "Wow!".  

[EricJ]

3 hours ago, slowflyin said:

Thought I'd share this pic as I found it interesting.  This is the nut off my lower, outboard motor mount.   I'm not questioning the engineering and understand shear versus tension.  That being said, when I removed it, I said "Wow!".  

Actually, that's a USB drive. 

It is kind of cool that the "critical" fasteners on Mooneys are all so small.   Never heard of any of them failing, either.

[jaylw314]

On 1/15/2022 at 3:17 AM, Bartman said:

I used new hardware for installation. We ground down the end of the old bolts slightly and drove them in from the engine side as a guide, and then drove in the new bolts from the cockpit. I also used torque seal on every fastener. The fluorescence makes it easy to turn the lights off in the hangar and use the black light to quickly check every bolt and fitting with an oil change. 

Another trick would be getting a longer bolt, cutting off the threaded portion (leaving only the unthreaded grip), then chamfering the end a little.  That way, as you're putting the new bolt in and pushing out the guide bolt, there are no threads on the guide bolt to mar the inside of the bolt hole.

I'm sure there are actual guide bolts out there that you can buy, that would be the non-ghetto strategy

 

Edited January 18, 2022 by jaylw314

[Bartman]

8 hours ago, EricJ said:

Actually, that's a USB drive. 

It is kind of cool that the "critical" fasteners on Mooneys are all so small.   Never heard of any of them failing, either.

What I found eye opening was not only the size of the fasteners, but also the torque value.  I don't remember what the torque value was but it wasn't much and it was measured in inch pound if memory is correct.

[carusoam]

Tiny, fine treads, and only four holding 200 horses in place…

And have been known to get by with only three for a while…. Until found at annual…

Actually, the bolt didn’t fail… the engine mount broke, leaving the bolt in place…   (M20C experience)
 

Best regards,

-a-