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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › RTV silicon in your engine...
07-24-2012 01:09 AM  8 years ago
MarshallB

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Middle Arkansas

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Yamabond from the Cycle shop!
CurtisYoungblood.com
Next-D
Spyder Batteries
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07-24-2012 01:12 AM  8 years ago
Rotors Up

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Reading, Pa

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Guys, Just use "PC Fahrenheit" epoxy from Home Depot problem solved. Thank you Tim Jones for the tip!!Better now then never... Fly Skids Up!!
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07-24-2012 01:50 AM  8 years ago
mustang67ford

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Central Pennsylvania

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I use dtv as well. I dab the rtv tube with my finger then dab the muffler flange ever so lightly. Then, just bolt them up. For the first 2 tanks after an install, I'll just hover so if a burnout occurs, easy to land. The way I figure, is if there is a piece of rtv, it will come off within that time. If not, then either what remained from the install burnt off or got blown out. I don't think you can avoid a little squishing into the inside rim.

Before I learned how thin to go, I did have a piece get on the plug during the first tank and caused a burnout.

Since then, i've got rtv o. 4 different pipes and no issues.
Team HeliProz - Retired
AMA #513507
IRCHA #4011
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07-24-2012 02:30 AM  8 years ago
GMPheli

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W. Bridgewater, MA USA

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"Mckrackin The hottest place is the ring gap it breaks the continuity of the heat path. Most pistons showed seizure at the ring end gap. I have ruined a lot of two stroke pistons and most were not stuck at the exhaust port. I have had pistons that were concave after a run, but not seized anywhere."

Every seized 2 stroke engine I have seen has done so at the exhaust port
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07-24-2012 12:00 PM  8 years ago
airdodger

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Johnston USA

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GMPheli Think about it, the combustion has already cooled from it hottest condition by the time it reaches the exhaust. The ring is subjected to the combustion pressure and heat from combustion. When the mixture is ignited it does not know where the exhaust is, the piston is subjected to the most heat at the combustion of the mixture. The exhaust can't be hotter than the combustion process.
Scoring is commonly seen on the piston face directly below the piston ring end gaps. The blast of combustion can get between the large end gap of a worn out ring and burn the oil off the piston and cylinder in that area...Hence the surface scoring. In most cases, score marks can simply be sanded off of the piston and cylinder. However when ever you see scoring, it's a good idea to find the source so that it doesn't develop into a full blown seizure.

Piston seizure is a case of scoring where the oil film does not immediately return. After a few moments of constant scoring, the piston and cylinder will scratch each other hard enough to remove material from each other. This floating material grinds itself into the piston and the cylinder as it continues to grow in size. As this snowballing material grows, it will drive the opposite side of the piston against the cylinder wall with a pressure so terrific that scoring on the other side of the piston begins to take place.[quote]
Chris
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07-24-2012 02:39 PM  8 years ago
marc8090

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Long Island, N.Y.

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RTV user here. As others have said if you are putting on a one piece muffler the layer needs to be so thin it is see through. On a two piece muffler you can put on as much as you want. Bolt on only the header and then with a q-tip wipe out the exhaust port before bolting on the muffler. Since doing it this way I have never had any silicone get into the glo plug. I did years ago if it was put on too thick.
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07-24-2012 06:26 PM  8 years ago
rstekeur

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Ft Myers, FL

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I have 2 OS50's and neither one has a muffler gasket and haven't had any trouble or sighs of exhaust leakageEven a stopped clock is right twice a day
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07-24-2012 07:07 PM  8 years ago
fla heli boy

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cape coral, florida

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you must have the version with the muffler bearings....
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07-24-2012 08:48 PM  8 years ago
reddragon

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Brooklyn, N.Y.

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LOLWayne - Fly it like you stole it! You're in good hands with Runryder!
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07-24-2012 10:53 PM  8 years ago
GMPheli

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W. Bridgewater, MA USA

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Not trying to hijack the thread here, but I have seen many seized two strokes in my day, and scores of pics of them on here over the years. I am just stating that every one I have seen has seized at the down wind side of the exhaust port. Such as this one.

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07-25-2012 12:40 AM  8 years ago
dkshema

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Cedar Rapids, IA

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Flat, clean surfaces. Tight bolts using proper wrench. Fly, land, tighten while hot, repeat a couple of times.

The seal is fine, there is no glop coming from the muffler/crankcase joint, no flakes of RTV to worry about, no need to buy tubes gasket material, no need to cut up aluminum cans. The bolts stay tight and the muffler doesn't loosen up. It comes off when I want it to with a proper fitting wrench.

No, the piston doesn't score, gall, and seize, no loss of performance in the muffler system, and I don't end up with oil and junk dripping off the engine or muffler at the joint. All that remains where it should, at the exhaust deflector. Carburetor settings remain unchanged from flight to flight, motor doesn't go lean in the air. It just works. Been doing that for many years with great success.

I have had to replace one piston/cylinder along the way, but that's because a wrist-pin retainer decided it was time to migrate...

When the mufflers have been removed, there is no evidence of a bad seal, leaks, or burnt spots. Just nice, clean surfaces.

I tried the high temp RTV route for a short while, until it began to flake off and take out plugs. Even using a thin film as described above, with the surfaces being clean and flat, you still get glop that squeezes out of the joint into the exhaust. Same with epoxy, Yamabond, or any other semi-liquid material used to "seal" the joint.

Do whatever you need to rationalize the need for extra material, but in the end, you really don't need it.
-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz
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07-25-2012 02:15 AM  8 years ago
reddragon

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Brooklyn, N.Y.

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Different strokes for different folks. Whatever works best.Wayne - Fly it like you stole it! You're in good hands with Runryder!
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07-25-2012 03:15 AM  8 years ago
airdodger

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Johnston USA

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GMP I know you have enough experience as to what happened to the piston you showed in the pic.Chris
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07-25-2012 10:51 AM  8 years ago
punkin71

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illinois

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When I first started flying nitro a thin layer of Hondabond worked good for me on OS 50's Nowadays I use the align muffler gaskets.
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07-26-2012 12:41 PM  8 years ago
GMPheli

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W. Bridgewater, MA USA

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"GMP I know you have enough experience as to what happened to the piston you showed in the pic."

?????
I am just stating what I have seen. Experience has nothing to do with it. When buying a used motor most people want to see a pic of the top of the piston through the exhaust port, so they can be sure it has not seized there. And I think it is pretty obvious what happened to the piston I showed. It was run too lean, the motor got too hot and the lubrication burned off at the exhaust port. When a 2 stroke is running, 3 sides of the top of the piston are continually being cooled from the incoming charge of fuel/air through the transfer/boost ports. The exhaust side is not. Hence it runs a lot hotter.
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07-26-2012 01:00 PM  8 years ago
Four Stroker

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Atlanta

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Hey, where have all of the posts gone with pictures of burned up engines that were always run rich with plenty of smoke ? I miss them.
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07-26-2012 03:26 PM  8 years ago
airdodger

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Johnston USA

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GMP The heat dissipation by the incoming mixture is tiny compared to the heat released by the combustion. The incoming charge can't be much over a few hundred degrees or the oil would cook and the combustion temperatures are in the thousands.

Why would the exhaust side have any higher temperatures, the heat of combustion does not know where the exhaust port is? The incoming mixture in the chamber is absorbing heat, trying to maintain equilibrium. If the heat of combustion is throughout the chamber, the easiest path for the heat to escape is the exhaust port, the longest path from the other side.

When I look to see cooked oil on the underside of the piston, never have I seen it cooked on the exhaust side. Almost always under the center of the dome. That would lead me to believe that that is the area subjected to the most heat for the longest time. Which is the longest path from the piston center.

The piston is being cooled by the incoming charge underneath the piston on all areas, the top is protected by a boundry layer. The charge has already absorbed enough heat by the time it reaches the chamber it is ready to become or is a vapor.

If you have seen and believe the exhaust side of the piston is hotter, I am good with that.
Chris
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07-26-2012 06:48 PM  8 years ago
adamsz06

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Geilenkirchen Germany

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Doesn't the muffler act as an additional heatsink on the exhaust side as well?R.I.P. Roman
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07-26-2012 10:19 PM  8 years ago
Einzelganger

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Campbell, Texas

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+1 to muffler and manifold as a heat sink.
The exhaust facing portion of piston comes in direct contact with spent exhaust gas more than any other part hence showing stains more than others. Kind of like a smoker's teeth.
I bought a bird used and the previous owner had used a thin layer of J.B. weld for sealer. I never thought twice about it and use a thin layer of J.B. Quick. Works perfect.
I love the smell of nitro in the morning.
RIP Roman
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07-27-2012 12:25 PM  8 years ago
GMPheli

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W. Bridgewater, MA USA

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This is a pic of the ring from my husqvarna chain saw:

I let my brother borrow it. The needles were set too lean for the weather conditions that day. He should have known better, but kept running it until it would not run any more. I pulled the jug and found that at the down wind side of the exhaust port the ring was worn, the piston was galled, and the cylinder was covered with black burned on oil. This to me is proof that this section of the engine was hotter than the rest. AirDodger, I guess we can just agree to disagree!
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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › RTV silicon in your engine...
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