Motor mount bolts.

[garygans]

What diameter bolts are used for mounting the motor mount to the fuselage? I need to drill the holes in the fuselage/firewall for the correct diameter bolts for when I get the motor mount made up.

[scottiniowa]

What diameter bolts are used for mounting the motor mount to the fuselage? I need to drill the holes in the fuselage/firewall for the correct diameter bolts for when I get the motor mount made up.

Am just thinking out loud here "garygans"   but won't your bolt dia. be determined by the holes in your rubber bushings? Or were you wondering if you could sleeve the bushings smaller?  At one time there was talk about folks breaking these bolts (due to vibration I think) so going smaller would not seem to be prudent.   That being said- were not these bushings .375" inner hole dia.?

I tried some time ago, to investigate how the called out bushing shape did not match the drawing for the metal cone, in the end, I figured it must have been working..   I just never figured out what " it " was.  For that matter, there was discussion that the actual bushing varied greatly... from Hard to soft,  they certainly do from a cost standpoint.  From mid teens, to $3-4 each.  Humm. 

Steve, in OSH, yours sure look good, care to elaborate?

[garygans]

I was referring to the bolts on the other end of the motor mount. The end that gets bolted to the firewall, not the end that gets bolted to the engine. 3/8" bolts seem a bit big to me for such a small engine. But, I don't know and I was wondering what everybody else was using.

[Bob S.]

It is one bolt going thru the rubber mount into the engine. The bolt should have a nice large washer on the inside. The Continental rubber fits inside the aluminum spool. I believe the bolt for the VW is about 10mm on the bottom. You can use the nearest size on the top with a nylon stop nut. Or in my case I use a double nut to make SURE the nut does not work off! 3/8" is not too small!

[garygans]

Sorry for not making myself understood. I will be making a tubular motor mount that extends the engine out front of the firewall. I was wondering what size bolts go into the firewall, not the bolts that go into the bushings.

[Bob S.]

OH!  Gotcha!

I have seen motor mounts built with #3 & #4 & #5 bolts ...  on the firewall side.. non-flexing..

[s johnson]

Scott,

Thanks for the vote of confidence but my mounts were a little dried out this year. You are so.. correct on the stiffness of the rubber mounts. I got my last set from Wag Aero, Lyons WI. My geometry while fitting up station one "FireWall" is off a little bit and has caused my top right bolt "view from the cockpit " bolt to shear. I haven't had a problem since I loosened up the tension a little and don't use grade 8 bolts.
If I remember correctly you were on the right path to figuring out the proper angles and geometry....

"Scott" J. Oshkosh

[scottiniowa]

Scott,

Thanks for the vote of confidence but my mounts were a little dried out this year. You are so.. correct on the stiffness of the rubber mounts. I got my last set from Wag Aero, Lyons WI. My geometry while fitting up station one "FireWall" is off a little bit and has caused my top right bolt "view from the cockpit " bolt to shear. I haven't had a problem since I loosened up the tension a little and don't use grade 8 bolts.
If I remember correctly you were on the right path to figuring out the proper angles and geometry....

"Scott" J. Oshkosh

Ok, folks, I would CAD out a few dimensions, if anyone would like to take this off list-  This would be for the recommended rubber bushings.  you would only have to take 4 measurments of your NEW but yet unused rubber bushings... would be great also if you knew the source and cost.  This info can come privately if you want...  This is to help everyone.  I will make the info public but without names of owners.  I would show the metal part dimensions as well as the rubber bushings.

The reason I say this, is last time I worked on this I was finding a pretty large difference in figures, but was working with mfg specs and not the actual product. 

Frank J. please feel to jump in what the Verner engine is using, as it sure looked good to me at the big show, but I did not ask about it. By the way, that set up looked fantastic, hope it proves out as such.

bolts-
Now this doesn't help the fellow asking fire wall -motor mount bolt size...  There are 1000's of 180HP engines held with .375" bolts...that is the motor mount/fire wall pass through bolts.

Scott- nearing harvest soon...

[PropMan]

We are using 5/16 bolts for the firewall attach, in the end there will be 5 or 6 attach points. The mount is specific to the Verner to help isolate the effects of the radial combustion . I did not design the mount, but can get more specific if needed. Just ask and I will find the answer.