stunthanger.com
Engine basics => Engine set up tips => Topic started by: Robin_Holden on May 07, 2009, 04:46:26 AM
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Greetings all...... Advice please .
I've just bought a 2nd hand OS MAX 35 - S off the infamous E-Bay. It came from a very reliable chap. It is in really good condition.
Now ..... Not knowing how much running the engine had experienced , I thought it best to first put it through a proper running - in regime , so I used Randy's advice published here . i.e. Smaller prop , 28% fuel [ around 22% castor 6% synthetic ] and starting with several really rich runs with a 5/10 minute cooling off period etc.
The engine was easy to start but would cut out after about 3 minutes rich running. Installing a new plug appears to have cured that problem.
It's now had around 45 minutes of rich running-in.
It does appear to be running ' hot ' as it does take the full 10 minutes to cool off.
Guys : In your opinion how much running in should this old timer need please ?
Any other tips about this 60's engine would be appreciated.
As an addendum , it's amazing how much has changed since I was a lad as we Brits say ! My two favourite engines , the Magnum XL 36 and Thunder Tiger 36 perform brilliantly after a sensible running -in procedure and give no problems whatsoever without any internal mods ! I must stop buying 'old' engines !
Much obliged ,
Robin [ ex-pat Brit in the Charente full of ex-pat Brits ]
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It's Robin here again about my OS MAX 35-S.
When my OS is in a VERY rich setting , whilst running-in on the bench , it will start to lean out after a couple of minutes.
I then have to richen up the needle a touch.
Perhaps that means it will need a lot of running-in maybe ?
Robin.
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My "guess"is that the leaning out is due to the fuel level dropping in the tank, which ends up lowering the pressure at the needle. Opening up the needle, as you are doing, fixes it---at least on the bench! How is the tank setup? You want to setup the tank so that the fuel level drop is only an inch or so. You could set it up as a uniflow (vent and pickup oriented at bottom of tank) and avoid any pressure drop.
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See if you get the same running problems without the muffler. I have found the stock strap on muffler is very restrictive and may be causing your overheating. It tapers toward the inside of the muffler so the outlet is narrower than it seems. Try drilling it out, carefully as the walls are thin. I prefer Big Art or Randy's tube mufflers but tongue mufflers, or hopefully your drilled out stock muffler will work as well. They do run hotter than the modern engines you mentioned but are good engines. 8)
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Hi Robin
You have good advice from Pete and Alan, another thing you need do is to put the engine in a fast 4 cycle, pinch the fuel tubing to lean out the engine, if it snapped right back into a 4 cycle it should be ready to fly. Also I too would suggest changing to a less restictive muffler, as not only is the exhaust hole very small, the strap can somtimes bind the piston-sleeve a bit
Randy
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Thanks a lot fellas ...... Much obliged you took the trouble to reply to my problem.
Randy has a point , the muffler ' strap ' does need to be pretty tightly fixed and this could affect the liner/piston fit a touch.
Thanks for that Randy ,
Robin .
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Thanks a lot fellas ...... Much obliged you took the trouble to reply to my problem.
Randy has a point , the muffler ' strap ' does need to be pretty tightly fixed and this could affect the liner/piston fit a touch.
Thanks for that Randy ,
Robin .
Robin
It is a good idea to use a thread fastener, such as "Lock Tite" when using a strap on type such as you have, this way it will stay without having to crunch it down so tight
Randy