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Thunder Tiger 91 4-stroke issue?

Old 09-03-2021, 12:06 PM
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tljr100
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Default Thunder Tiger 91 4-stroke issue?

After 8 years I got my 91-4 stroke going again but it appears to be leaving fine powdered aluminum in the exhaust oil residue. Is my cylinder degrading or the piston, or the bearings? I am running 10% nitro with added castor oil. Any help is appreciated.
Old 09-03-2021, 03:21 PM
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Originally Posted by tljr100 View Post
After 8 years I got my 91-4 stroke going again but it appears to be leaving fine powdered aluminum in the exhaust oil residue. Is my cylinder degrading or the piston, or the bearings? I am running 10% nitro with added castor oil. Any help is appreciated.
You may want to define the "fine powdered aluminum" a bit more. Generally if there is aluminum rubbing against metal and when you add oil you get a black residue. If the fine powdered aluminum is fine and shiny something is scraping inside your engine. On model engine the cylinder sleeve is not aluminum for most brands. Even if the cylinder sleeve is aluminum it is usually plated with something like chrome or nickel. The piston usually does not come in contact with the cylinder sleeve. The piston ring is the item that comes in contact with the sleeve. One scenario that may be the issue is when you have a piston wrist pin that is gummed up, rusted or simply stuck. The connecting rod will move the piston at an angle while moving the piston up and down on the sleeve. Then the piston skirt will be rubbing on the sleeve and causing wear on the piston.

Your best bet is to disassemble the engine and make sure all the parts are moving freely and not rusted or gummed up with castor oil.
Old 09-04-2021, 08:12 AM
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I’m going to guess something in the exhaust is loose. A lot of times there is a battle in the muffler that is swagged or riveted in place a s vibration causes the aluminum to wear and shed the particles suspended in the exhaust oil.
Old 09-05-2021, 11:19 AM
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jaka54
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Hi!
Fine aluminum powder in the exhaust oil is always coming from a loose muffler rubbing against the engine.
Old 09-05-2021, 12:03 PM
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Originally Posted by jaka54 View Post
Hi!
Fine aluminum powder in the exhaust oil is always coming from a loose muffler rubbing against the engine.
Mine has always been black. I guess I use too much oil.
Old 09-06-2021, 07:06 AM
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jaka54
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Hi!
Black oil means a too lean setting!
Old 09-06-2021, 10:07 AM
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Originally Posted by jaka54 View Post
Hi!
Black oil means a too lean setting!
Life will be grand if only this one line answer will solve all the engine's ill. No black oil does not have to mean the engine is too lean. There are way too many variables involved. One of the main reasons for black oil means that a muffler is loose and the aluminum is rubbing against aluminum with some oil mixture added. That can happen when the engine is either lean or rich.
Old 09-07-2021, 12:58 AM
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Hi!
I'm sorry!
You are right! Had not time enough to give a more elaborate answer.
Old 09-07-2021, 08:46 AM
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Originally Posted by jaka54 View Post
Hi!
I'm sorry!
You are right! Had not time enough to give a more elaborate answer.
Lean run is never very good for any engines. However it does take a bit of metal wear to get the blackness in the oil. So besides the lean setting I am sure there has to be some metal rubbing. Most likely from a loose muffler or some other parts internal.

OTOH, getting back to the OP regarding the shiny aluminum powder that is most likely a loose muffler since that is the closest aluminum part to the exhaust outlet. Or that could be from something outside of the engine. It is hard to tell without adequate information from the OP.

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