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Engine mount repair

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Old 11-13-2012, 05:04 PM
  #1
rsdonomoore
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Default Engine mount repair

I have a 1/4 scale piper super cub. The motor has to be replaced and they do not make the SV 26cc anymore so I opted to replace with a different 26cc gasser. My problem is that the new motor is almost identical except for the motor mount size. The new location of mounting holes is just slightly skinnier than the existing holes. I don't think I will be able to drill new holes through the firewall because it will be so close to the existing holes. What do I do in this scenario? Do I have to cut out the firewall and glue in a new piece of wood? Any help would be greatly appreaciated. I've attached a picture of the existing setup. Thanks!
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Old 11-13-2012, 05:21 PM
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Default RE: Engine mount repair

Fill in the existing holes with the correct size "hardwood" dowel epoxied in place... smooth and redrill the new locations.
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Old 11-13-2012, 07:08 PM
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rsdonomoore
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What minute epoxy should I use, 30 minute? Also, how can I tell if the dowel is "hard wood"? Sorry, I'm new at this. Thanks!
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Old 11-13-2012, 08:59 PM
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Default RE: Engine mount repair


Quote:
ORIGINAL: rsdonomoore

What minute epoxy should I use, 30 minute? Also, how can I tell if the dowel is "hard wood"? Sorry, I'm new at this. Thanks!

Balsa is a soft wood ! So a hard wood would be Maple, Oak, Ash, Spruce, Pine, Mahogany, Pecan, Bass and etc.

Frank

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Old 11-14-2012, 10:27 AM
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Default RE: Engine mount repair

I agree with the hardwood dowel method, but also remember to make the dowels flush with the BACK SIDE of the firewall. That has to be a level surface for any fastening hardware (Tee nuts, washers & nuts, etc) to mount to in a flush manner. I have done this many times ahd have no problems, except of course to the 'first time', when I didn't make things flush with the back of the firewall.

After the new holes have been drilled where you want them, remember to fuelproof the new fresh wood on both sides of the firewall with CA or epoxy.

Just my $.02

Bob
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Old 11-14-2012, 12:23 PM
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Quote:
ORIGINAL: N1EDM

I agree with the hardwood dowel method, but also remember to make the dowels flush with the BACK SIDE of the firewall. That has to be a level surface for any fastening hardware (Tee nuts, washers & nuts, etc) to mount to in a flush manner. I have done this many times ahd have no problems, except of course to the 'first time', when I didn't make things flush with the back of the firewall.
Very good point. I was going to say the same thing as I also learned this the "hard way".

It is extremely difficult in some cases, to flush cut or sand down dowels from behind the firewall if you do not have A LOT of access.

Better to glue the down so the back is flush with the inside of the firewall.

I usually either flush cut or sand down the protruding part at the firewall front. Japanese flush cut saws are GREAT for this.

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Old 11-14-2012, 12:39 PM
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Default RE: Engine mount repair

With the mounts that close to the edge you are asking to get the engine in your face with out replacing the firewall and doing it right[:@]
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Old 11-14-2012, 04:11 PM
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rsdonomoore
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Default RE: Engine mount repair

I guess I'm going to try the dowel idea. They should have the hard wood dowels at the local hobby shop right?
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Old 12-28-2012, 03:23 PM
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Default RE: Engine mount repair

Yup or any hardware store should have poplar dowels for wood working projects [ home depot, lowes.ace, or any home improvement store.]
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Old 12-29-2012, 06:39 AM
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Quote:
ORIGINAL: rsdonomoore

I guess I'm going to try the dowel idea. They should have the hard wood dowels at the local hobby shop right?
This is a VERY easy thing to do. Use a flat tool of some king to make sure the dowel is flush on the back side of the firewall and sand the front flush after the epoxy cures. It is OK to drill out the hole on the firewall for a slightly larger dowel if needed. When I was doing some tool and die work we did this on occasion to "repair" a mistake

Ken
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Old 12-29-2012, 10:33 PM
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Default RE: Engine mount repair


Quote:
ORIGINAL: Live Wire

With the mounts that close to the edge you are asking to get the engine in your face with out replacing the firewall and doing it right[:@]
It does look a bit sketchy
seems the upper portion is likely not attached to much except sheeting.
I would drill and put some small screws in the sides of the firewall or better drill and put small wooden dowels around 1 inch long to add more security.
You do not want a 18 inch prop and engine becoming dislodged while standing in front of it.
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