Author Topic: Fox .35 Plywood shims (Read 2025 times)

Bill Little · « **on:** July 18, 2015, 12:14:15 PM »

Hi All,

I have been told by several Fox .35 gurus that it is a good idea to use 1/64th" ply under the engine mounts to allow them to crush and take up the uneven machining on the bottom of the mounts.

Best thing to do since I cannot get the mounts machined flat?

Thanks!
BIG Bear
RNMM/AMM

Ron Cribbs · « **Reply #1 on:** July 18, 2015, 10:53:37 PM »

The best thing to do would be to mount them on aluminum pads.

Fox engines are shakers, they will run much better if you mount them solid. I have never come across such an uneven surface that it causes an issue with mounting.

RknRusty · « **Reply #2 on:** July 18, 2015, 11:10:44 PM »

Ditto what Ron said. That's the way I mount all of my profile engines, with good hard aluminum bearers. I bevel the edge that butts against the crankcase so they fit square. With the Fox I like to use them on the other side of the beam too, and cover it up with a hard balsa cheek block for additional stiffness and cosmetic appeal too.
Rusty

Balsa Butcher · « **Reply #3 on:** July 19, 2015, 04:35:31 PM »

Put those 1/64th shims between the engine and the alum mount pads. May not be necessary but can't hurt.

Jim Roselle · « **Reply #4 on:** July 19, 2015, 04:45:50 PM »

Quote from: RknRusty on July 18, 2015, 11:10:44 PM

Ditto what Ron said. That's the way I mount all of my profile engines, with good hard aluminum bearers. I bevel the edge that butts against the crankcase so they fit square. With the Fox I like to use them on the other side of the beam too, and cover it up with a hard balsa cheek block for additional stiffness and cosmetic appeal too.
Rusty

What do you use for fasteners on the inboard side, T- nuts?

Jim

Bill Little · « **Reply #5 on:** July 19, 2015, 05:20:59 PM »

I had a poor choice of words wen I said "uneven". The bottom of the mounts are not machined perpendicular to the vertical center line of the engine. In some cases this can cause the crankcase to distort. Marvin "Bigiron" Denny had made a fixture to machine the mounts as they should be, but now that Marvin is gone there is no one I know that can do this. I use 1/8th" aluminum pads under all my engines so that is not a problem. The mounts didn't use to cause a problem for me when I mounted them directly to the plywood doublers on profiles. Now with the aluminum pads there is no "give" when mounting.

Thanks, Pete, I will use the ply on top of the pads!

BIG Bear
RNMM/AMM

Steve Helmick · « **Reply #6 on:** July 19, 2015, 05:44:04 PM »

When I built a "FoxBerg" racer, I made 1/8" aluminum pads to mount the engine on, with a twist. Literally, the two legs (where the engine was bolted to tapped holes in the aluminum) were tapped and bolted to the casting draft angles of the engine lugs.

The wood was then fitted to match the angles of the aluminum, epoxied down with a couple of #6 sheet metal screws ahead and behind the mounting lugs. When the epoxy set, the engine mounting holes were drilled through for clearance, and T-nuts installed. I think you'll get the idea of what I was trying to do. Easier to understand than describe.

Steve

Bill Little · « **Reply #7 on:** July 20, 2015, 01:32:21 PM »

Hi Steve,

I understand what you are saying. Marvin thought the angle was important enough to get rid of it so I feel I need to do "something" to take care of it. Marvin knew his Fox .35s! Marvin might have been the first to tell me to use 1/64th" "crush" shims, but more than one have said it. When we mounted a Fox straight to the motor mounts, the shake of the engine and compression of the mounts took care of it pretty quick. I remember having to tighten the engine hold down bolts a couple times before they would stay tight. I think it was because of the mounts taking the shape of the draft angle. The engine in question is an ABC, hemi head, stuffer, high zoot crankshaft engine Marvin built off a 40th Anniv. case for me and will be used in a competition model for Aaron.

BIG Bear
RNMM/AMM

Bill Johnson · « **Reply #8 on:** July 20, 2015, 01:54:44 PM »

I had to repair some mount beams that were inadvertantly ground down unevenly, which is similar to the problem you have, the beams and mounts not meeting up evenly. What I did is lay a thick layer of JB Weld on the mount beam. Then I covered that with a piece of Saran wrap, then put the engine in place, running the mount bolts, well greased with anti-seize, through the plastic and pulled the mount bolts up snug. The next morning, the bolts came out fine, the engine popped right out and the mounting surfaces matched perfectly.

RknRusty · « **Reply #9 on:** July 20, 2015, 02:53:14 PM »

Quote from: Jim Roselle on July 19, 2015, 04:45:50 PM

What do you use for fasteners on the inboard side, T- nuts?

Jim

Jim, if I put bearers on the inboard side and cover it with a cheek block, then yes I use T-nuts backwards against the aluminum, and a deep enough recess in the cheek block to accommodate it. The points of the T-nuts stick into the cheek so I can R&R the bolts if necessary.

I went out to the shop and looked back in time at some of my models, and I was mistaken in what I said in the above post. My only Fox is actually mounted with aluminum pads under the engine and bolted into brass inserts. I got that idea from you back when we were both building at the same time. It's holding strong with no sign of loosening.
Rusty

Dennis Toth · « **Reply #10 on:** July 27, 2015, 05:40:52 PM »

Bill,
The 1/64th plywood crush pad works great with the stock Fox 35, it keeps the case from distorting and causing overheating and lost performance. To address the vibration you can build the nose with the cross grain balsa between the beam mounts (used for the ST 60's also). The aluminum pads keep the mounts from continuously crushing down and changing the shaft/spinner position relative to the nose ring, thrust line etc.

Best, DennisT

Bill Little · « **Reply #11 on:** July 30, 2015, 04:36:58 PM »

Quote from: Dennis Toth on July 27, 2015, 05:40:52 PM

Bill,
The 1/64th plywood crush pad works great with the stock Fox 35, it keeps the case from distorting and causing overheating and lost performance. To address the vibration you can build the nose with the cross grain balsa between the beam mounts (used for the ST 60's also). The aluminum pads keep the mounts from continuously crushing down and changing the shaft/spinner position relative to the nose ring, thrust line etc.

Best, DennisT

Hi Dennis,

Ever since I saw Windy do a Big Jim Greenaway crutch motor mount set up, I have done it to every built up fuselage model I have built, regardless of the engine. I have also used 1/8th" aluminum pads. So this one will get the 1/64th" ply crush pads between the engine and the aluminum pads.

Thanks to everyone for their ideas

Bill

Bill Little · « **Reply #12 on:** July 30, 2015, 05:36:17 PM »

Quote from: Dennis Toth on July 27, 2015, 05:40:52 PM

Bill,
The 1/64th plywood crush pad works great with the stock Fox 35, it keeps the case from distorting and causing overheating and lost performance. To address the vibration you can build the nose with the cross grain balsa between the beam mounts (used for the ST 60's also). The aluminum pads keep the mounts from continuously crushing down and changing the shaft/spinner position relative to the nose ring, thrust line etc.

Best, DennisT

Author Topic: Fox .35 Plywood shims (Read 2025 times)

Bill Little

Fox .35 Plywood shims

Ron Cribbs

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RknRusty

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Balsa Butcher

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Jim Roselle

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Bill Little

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Steve Helmick

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Bill Little

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Bill Johnson

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RknRusty

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Dennis Toth

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Bill Little

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Bill Little

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