Engine mount alignment to firewall

[JDBoston]

Has anyone ran into this issue? My upper right engine mount to firewall bolt hole is not aligned well with the engine mount. The result is that there is uneven pressure on the washer even after it is tightened. Is this a big problem? The bolt goes in, but is riding to one side of the hole of the mount.

 

[Desert Rat]

I'm not building 14, but I'm surprised that the sleeve in the mount is that much bigger than the bolt. They certainly aren't on my 7. Seems like it's asking a lot for just torque friction to keep the mount from wobbling around on bolts whose shank is smaller than the hole they're going through. Are you sure you reamed the holes in the firewall for the correct size bolts? I believe those are supposed to be AN6 bolts, right?

Maybe the 14 is different, but it sure looks odd to me.

 

[RV7 To Go]

On both my 7 and 8 the motor mount holes fit the bolts with a nice slip fit. Not sure about the 14 but I would check the bolt size.

 

[Webb]

The weldment hasn’t been drill matched to final size using the motor mount as the drill guide. Once you do that, an AN6 bolt will slip right in. Also verify with your drawings but I suspect the bolt orientation is backwards In your picture.

You also stated it was your right upper mount which leads me to think all the bolts are undersized. It looks like you used an AN4 bolt which has a tensile strength of 4,500 pounds. An AN6 bolt has a tensile strength of 17,578 pounds.

My opinion “Is it a problem”…… yes and potentially deadly. I’m just an amateur builder. I’ll leave it to the professionals to validate my thoughts.

 

[iwannarv]

In addition to the above comments, on my -10 engine mount the washer used isn't a standard AN washer, but a larger OD steel washer that has much more surface area to capture the mount on the FW side..... Doesn't look like that's what you're using.

 

[Mel]

The weldment hasn’t been drill matched to final size using the motor mount as the drill guide. Once you do that, an AN6 bolt will slip right in. Also verify with your drawings but I suspect the bolt orientation is backwards In your picture.

Normal bolt orientation is "head forward". This is NOT a requirement. In this case, it is common to have the nut forward to allow for easier inspection.

 

[rvbuilder2002]

The engine mount attachment method for the RV 14 is different from all the other RV models.
The bushing welded into the engine mount is not a net fit diameter to the bolt being used. I think it’s ID is 1/2”, and the bolt is 3/8”.
It is purposely larger to accommodate for a slight amount of mismatch between the overall dimensions of the engine mount and the location of the actual bolt holes in the firewall.
During the install process, the large flange washer on the backside of each bolt location gets match drilled to the hole in the firewall which will allow it to take all of the lateral loads at each attachment joint. For the tension loads, it doesn’t matter if the bolt is a close fit to the sleeve in the engine mount, so what the OP is seeing is normal.
Double check the plans though, if memory serves me, I think there is a different washer used other than just a plain AN960.

 

[Webb]

Ironically, the 8 plans do not list the cotter pin on the drawing even though a castle nut is listed and depicted.

And Mel, we all know you prefer to put the bottom cotter pins in sitting on a stool instead of imitating a contortionist trying to install them on the aft side of the firewall.

 

[JDBoston]

The engine mount attachment method for the RV 14 is different from all the other RV models.
The bushing welded into the engine mount is not a net fit diameter to the bolt being used. I think it’s ID is 1/2”, and the bolt is 3/8”.
It is purposely larger to accommodate for a slight amount of mismatch between the overall dimensions of the engine mount and the location of the actual bolt holes in the firewall.
During the install process, the large flange washer on the backside of each bolt location gets match drilled to the hole in the firewall which will allow it to take all of the lateral loads at each attachment joint. For the tension loads, it doesn’t matter if the bolt is a close fit to the sleeve in the engine mount, so what the OP is seeing is normal.
Double check the plans though, if memory serves me, I think there is a different washer used other than just a plain AN960.

Thanks Scott this is reassuring. And yes that is exactly correct, the ID of the tube is ~1/2" and this is an AN6 (3/8). Knowing this is per the design is comforting! I will double check the washers I was pretty sure I put the correct ones in so thank you.

 

[JDBoston]

Scott, It actually is a NAS1149F0632P (AN960-616L) which is specified and that is what is on there.

 

[Mel]

Scott, It actually is a NAS1149F0632P (AN960-616L) which is specified and that is what is on there.

Maybe I'm missing something but I would not approve an installation as shown with the washer bearing on less than 1/2 of the mount tube!

 

[stigaro]

Scott, It actually is a NAS1149F0632P (AN960-616L) which is specified and that is what is on there.

You might want to recheck this. Looks like NAS1149F0663P on the forward side. The 0632P washers go on aft side of the upper two bolts only.

 

[asw20c]

Has anyone ran into this issue? My upper right engine mount to firewall bolt hole is not aligned well with the engine mount. The result is that there is uneven pressure on the washer even after it is tightened. Is this a big problem? The bolt goes in, but is riding to one side of the hole of the mount.

Jeff, it makes you feel better, my engine mount fits the same way. I didn't think it looked right either.

 

[dmattmul]

It's been a while, but the supplied nuts go on the back for the 14 as it is Nylok and prefer to keep the nut at a reduced temp, I think. They never fit exact but have some movement to split the difference between holes. There is also some "give and take" between holes. Don't try and offset ream only one hole so not to get an oblong hole. Spread out the difference and a little pushing and shoving might be in order.

 

[Desert Rat]

The engine mount attachment method for the RV 14 is different from all the other RV models.
The bushing welded into the engine mount is not a net fit diameter to the bolt being used. I think it’s ID is 1/2”, and the bolt is 3/8”.
It is purposely larger to accommodate for a slight amount of mismatch between the overall dimensions of the engine mount and the location of the actual bolt holes in the firewall.
During the install process, the large flange washer on the backside of each bolt location gets match drilled to the hole in the firewall which will allow it to take all of the lateral loads at each attachment joint. For the tension loads, it doesn’t matter if the bolt is a close fit to the sleeve in the engine mount, so what the OP is seeing is normal.
Double check the plans though, if memory serves me, I think there is a different washer used other than just a plain AN960.

well darned if I didn't just learn something new. Thanks for posting this.