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Building Tips and technical articles. => Building techniques => Topic started by: Tom Vieira on August 15, 2018, 06:35:53 AM
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All,
So, Bob and I tried to get my McCoy 35 running last night for an RST I built for my nephew. The motor is just too tired. once warmed up, you can get almost two full revs out of her when flipping by hand, and she just won't stay running. I'm going to try to bake the piston, but, if that doesn't work............
I have a couple different engines I can run, 25FP, Evolution 36, Fox 35, and a 40LA. I even have a 46AXII I could use as well if I buy a C/L venturi for it.
But, that McCoy is a wwwwwiiiiiiiiiiiiiiiiiide motor, and I had trimmed the hardwood mounts to fit. The FP's and Evo for sure are much narrower, I haven't checked the LA or Fox yet. I can see straight through about 1/3 of the mounting holes where the mount *would* have been if not for the McCoy adjustment.
So, clamp the motor in with 3/16" aluminum? use some ply and fiberglass to rebuild that part of the mount that was trimmed out? I REALLY don't want to cut out the mounts and start over, as the plane is ready to go.....
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Retrofit bearers like the ones in this post (https://stunthanger.com/smf/building-techniques/build-cartoon-scale-mooney-mite/msg431514/#msg431514)? Then you can try different engines. The ones pictured are based on a stick of 1/2x3/16 2024 or 6061 aluminum (I can't remember which) bought from Online Metals for cheap. You just whack off lengths, do some work in a drill press, and you're done. I drill & tap the holes for the engine screws, but I know other people prefer to drill through-holes and bolt things on.
(https://stunthanger.com/smf/building-techniques/build-cartoon-scale-mooney-mite/?action=dlattach;attach=241982;image)
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Get you some 3/16 X 1/4 hard aluminum strip. Cut it to length so you can bolt it to the fuselage after drilling and tapping to fit engine of choice. Of course you have to drill new holes for the pads. This also gives more bearing/crushing surface to fuselage. If you do a search on here you will probably find better pics of what I do. D>K
Tim has better pic. H^^
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So, Bob and I tried to get my McCoy 35 running last night for an RST I built for my nephew. The motor is just too tired. once warmed up, you can get almost two full revs out of her when flipping by hand, and she just won't stay running. I'm going to try to bake the piston, but, if that doesn't work............
I have a couple different engines I can run, 25FP, Evolution 36, Fox 35, and a 40LA. I even have a 46AXII I could use as well if I buy a C/L venturi for it.
I don't know what an "RST" is, but that is a very wide array of engines to consider. Normally you wouldn't consider an Fox 35 and a 46AX for the same airplane, that is a huge range of potential power, and I cannot imagine any airplane what would work well with either.
Brett
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RST = Rugged Stunt Trainer. Available from The Corehouse. D>K
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I don't know what an "RST" is, but that is a very wide array of engines to consider. Normally you wouldn't consider an Fox 35 and a 46AX for the same airplane, that is a huge range of potential power, and I cannot imagine any airplane what would work well with either.
Brett
But Brett, he'll have plenty of line tension with the AX. You know he would. He could even go into the business of digging post holes, for people with lots of clearance around their fence lines.
I think I've held an RST in my hand once, but it may have been an earlier iteration. At any rate, Phil markets it for "35 or 25 schnuerle". If the 25FP is anything like the "good" 25LA, that's probably the go-to engine for this plane.
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He had mentioned the 25FP when talking to him, but I already had the McCoy on hand, and didn't pick up the FP's until I was nearly done building. I was hopeful I could get the McCoy to cooperate.
i'll get something hammered out. gotta keep this boy in the air! and I need to finish mine up as well....
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I had an FP25 on an RST. Flew just fine. Until my cousin butters plowed that sucker in leading edge deep.
On the McCoy, TJ; can you turn the plane over, so the exhaust is up, put a little oil (I use 2 stroke oil for this) in the exhaust, choke flip it 3 or 4 times and try to start it that way?
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Dane,
it'll run fine if it's stone cold, but the moment it heats up, looses all compression. I'm not kidding when I say you can send it through two compression strokes with a flip...
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Dane,
it'll run fine if it's stone cold, but the moment it heats up, looses all compression. I'm not kidding when I say you can send it through two compression strokes with a flip...
Oh I got ya. Sounds about right for those!
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Gave the Fox 35 a quick check, she might work without much "hack magic" involved! requires further study....
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I had the same problem TJ.
An easy fix is to epoxy strips of motor mount stock to each bearer in the plane. Use a good epoxy. I like West Systems with a 2hr pot life. It takes 24 hours to cure though.
Pre-glue the pieces, tape them in place. then mask off the bottom(left side) and pour some more epoxy on to fill any gaps. Use a heat gun to gently but thoroughly warm the motor mounts until all the glue soaks in.
1/8 or 3/16in aluminum as shown above will also work. It probably isn't quite as strong in crashes, and it offsets the motor to the right which isn't the best idea. Most profiles already have the motor too far to the right anyway. Which is a good reason to build in enough right thrust to point the thrust line towards where the spar crosses the fuselage.
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This is all much easier to fix than you think. Mount the fuselage in a drillpress and drill out the old mounting holes with a 1/4” drill bit through the plywood doublers and maple mounts. Cut 1/4” dowels about 5/8” long and epoxy them into the holes. At the same time add plywood shim to the inside of the mounts to adjust for width of the new engine. Epoxy glue to the mounts and clamp in place, when the epoxy cures, cut off the excess dowels flush to the doublers and plywood shims. When satisfied with the repair, add the aluminum spacers as noted before.
I'll add one more thing is make the new aluminum engine spacer in a horseshoe shape (or C shape) to further strengthen the nose and reduce vibration. This allows for much better engine runs.
Good luck and let us know how it comes out,
Mikey
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TJ,
On the McCoy if it has compression when cold you should check a couple things. First check that all the head bolts are tight, do this once it is hot or heat it with a heat gun so its close to operation temp (use a glove to hold the engine). While you are at it check the backplate bolts also. Next check the plug for tightness. I have had my plug leak after a flight on my Fox 35. When the engine was still a little warm from the first flight of the day it would not start, just pop, pop, pop. Once I check the plug for tightness it only took between 1/16 & 1/8 turn tight and all the leaking stopped and off it would go.
In desperation if the heat swelling of the piston doesn't do it, you can very carefully put the piston on a hard surface and tap the crown. The Red Head McCoy's had a domed piston and a couple smart tapes with a small hammer would push it out just a few thousands to tighten the fit. This is a last resort measure and if you rap it to hard could crack the piston. Go slow and test fit after a tap or two.
Best, DennisT
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TJ,
On the McCoy if it has compression when cold you should check a couple things. First check that all the head bolts are tight, do this once it is hot or heat it with a heat gun so its close to operation temp (use a glove to hold the engine). While you are at it check the backplate bolts also. Next check the plug for tightness. I have had my plug leak after a flight on my Fox 35. When the engine was still a little warm from the first flight of the day it would not start, just pop, pop, pop. Once I check the plug for tightness it only took between 1/16 & 1/8 turn tight and all the leaking stopped and off it would go.
In desperation if the heat swelling of the piston doesn't do it, you can very carefully put the piston on a hard surface and tap the crown. The Red Head McCoy's had a domed piston and a couple smart tapes with a small hammer would push it out just a few thousands to tighten the fit. This is a last resort measure and if you rap it to hard could crack the piston. Go slow and test fit after a tap or two.
Best, DennisT
Hi Dennis,
I gave it hell with that McCoy, but it just wouldn't do it... so it sits along with two others in a box of "maybe build one good motor out of these parts someday" box. slapped an OS40FP in one and Fox 35 in the other and haven't looked back.