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Engine basics => Engine set up tips => Topic started by: DanielGelinas on November 05, 2012, 01:27:32 PM
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Hi everyone,
I'm running a OS MAX 35s which I purchased summer 2012. This engine was being sold as just broken in and in excellent condition.
The engine is running Brodak's 10-29 and has great compression. I flies my oriental with ease. I can easily hot start the engine. BUT there is a darkish residue on the plane at the end of each flight.
I opened the back cover to look inside the engine. It would seem like the connecting rod is rubbing on the back plate. I'm assuming this is why the oil is black...
In the connecting rod used?
Thanks for feedback. H^^
-Dan
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I had a similar issue with my RO-Jett 76, it was spitting out a black residue on the side of the fuselage. It turned out the header had come loose just a little bit. Was the muffler tight on the engine? I've also never had an OS spit black residue out unless I had a VERY lean motor run.
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Dan, it's not uncommon for the con rod to rub occasionally on engines. I see it many times on several engines. Are you using a muffler with this engine? I've seen the stock muffler do this on that particular engine especially if it doesn't fit the exhaust stack tightly. The screw that holds the strap as well can come loose making black oil. Technically there's 2 screws, one for the retention and one to hold it to the muffler. That engine also used brass end pads on the wrist pin. If these wear out it cuts grooves in the cylinder walls. Hopefully that's not the situation. One other black oil problem on that engine is a loose venturi. Not only will it make black oil, but it will make crappy runs. The rubber o-ring becomes hard under the venturi base and the venturi wiggles. Doubling the o-ring works if indeed that's the problem. Ken
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You might want to check and make sure the rod is not stuck on the wristpin and forcing the rod to rub. Some engines are very prone to the rod sticking if not run for a while.
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Hi Guys,
Thanks for the info.
I'll mount the engine on my test stand and check it without the muffler.
In this case, the tongue muffler is screwed onto holes which were taped into the case.
I'll send a picture as soon as I can.
-Dan H^^
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I though that the rods were the weak point on these engines and it could simply be rod wear rather than the rod rubbing.
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I recently got a couple of after-market metal backplates for the OS46LA. Both caused serious rubbing of the rod on the backplate. It took several tries honing down the backplate on sandpaper taped to a glass plate before the engine would run again.
F.C.
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I recently got a couple of after-market metal backplates for the OS46LA. Both caused serious rubbing of the rod on the backplate. It took several tries honing down the backplate on sandpaper taped to a glass plate before the engine would run again.
F.C.
Hi Floyd,
did you consider changing the gasket thickness? It is a lot less permanent. ;D
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Hi Chris,
I'm assuming it isn't rod wear since the engine runs so well, has power and great compression. I'm assuming the rod wear comes at the same time as the other frictional parts wear on this engine? Then again, i'm no os max 35s expert...
I'll give the engine a go on the test bench this weekend.
-Dan
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I thought I read here that the black residue in the exhaust is a sign that the engine isn't broken in yet and after a while, the exhaust clears up. Or was I dreaming?
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Hi Chris,
I'm assuming it isn't rod wear since the engine runs so well, has power and great compression. I'm assuming the rod wear comes at the same time as the other frictional parts wear on this engine? Then again, i'm no os max 35s expert...
I'll give the engine a go on the test bench this weekend.
-Dan
Dan,
I am pretty sure that the old OS 35 had weak rods and there is an after market option available for them on the 'other' forum.
And -
http://stunthanger.com/smf/index.php?topic=24921.0
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Guys,
Just wanted to let everyone know.
The problem was the tongue muffler vibrating. I tried the engine on the bench tonight without T-M and NO BLACK OIL!! #^ #^
Really glad since this is a very good engine.
Thanks for all the replies and sorry for getting back late on this...
-Dan H^^
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If you watched The X-Files you would know enough to stay well clear of The Black Oil. Don't let it get in you eye.