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Old Nov 30, 2011, 03:56 AM
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The crank has been ground down as there is hardly no casting marks on it, i will shove a temp gun on the engine after its run in, its got some hellish compression at the min and my normal starter will not even turn the engine over so have ordered an dynatron still no reply from rjx hobbies yet i think the spares back up is totally rubbish and will not buy another rjx heli

The pistons dont have to be lightened to balance the crank, grinding material from the piston gives more torque but thats at high end rpm, i have had pistons lightened in the past and have failed, only things i would have done is the conrod and crank which has been done on this engine
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Old Nov 30, 2011, 04:15 AM
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Have you got any pics on the inside of your cylinder barrel and inlet and exhaust ports ?

Kev
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Old Nov 30, 2011, 06:46 AM
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Only the piston and crank are modified on my engine.

The case is stock. I tried to find a solution for this stock engine but I think i will go zenoah...
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Old Dec 01, 2011, 04:04 AM
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My Sk720 gives vibration warnings. Makes me a little leary about flying it. Maybe this winter, I'll take the engine appart to see what I can do about the balance.
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Old Dec 01, 2011, 05:17 AM
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I test the vstabi with the stock crrcpro26.

vstabi test on RJX gasser (1 min 32 sec)



Finally it is not a solution because the vibrations kill all the parts of the heli

I never tried an actual complete Crrcpro modified by Wally from Rc Aftermarket.
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Old Dec 01, 2011, 10:35 AM
That Free Gas Weirdo Huh ?
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Are you guys using those rubber shock mounts ? There are different types, finding the best elastic compromise is the trick. Some have a little air hole to make a shock absorber system like on a car.
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Old Dec 01, 2011, 11:32 AM
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I use the green glue sheet "ZEAL" from Kyosho.
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Old Jan 05, 2012, 12:23 AM
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Just got a reply back from an model boat engineering place that builds and modifies engines for marine use

A single cylinder engine will never be balanced. Balancing the crank on the engine does nothing for it, because there is nothing to oppose the force from the piston. On any real engine there are multiple pistons whose force is used to counteract the force that any one piston will make on the engine. In a single cylinder engine there is nothing to counteract the force. A counter weight will not work because the force that the piston places on the crank from combustion and compression cycles are never the same. Point being the force on the crank is constantly changing because the speed of the piston is consantly changing as it go's through the engines stroke. In a multi-cylinder engine there are other pistons going through the same phenomenon to counteract. But in a single cylinder engine there is nothing. To have the engine truley be balanced you would need a counter weight that is constantly changing its effectiveness on the crank to match the pistons g-force on the crank. But thats impossible in these engines.

Anyone can balance the parts, but having it actually make a positive effect is just a myth. Its dosent make a difference to a point. I try to get the crank close and I allways check it, but spending any more then 5 min on it is a joke. If you cant precisely measure, or duplicate the constantly changing force on the crank pin, and you cant replicate it on the engine then all your doing is just waisting time.

Not to sound negitive but its just a lame rumor that uninformed or fly-by-night motor guys spread by saying that you can balances a crank to make an engine better.


Now rjx recommend a bench run with a 16x8 prop to aviod the heli vibration, the response i got from them was if the heli vibrates then the engine hasnt been run in correctly. Dreading this now on mine, think it will be gyro pads securing all the electronics lol

Kev
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Old Jan 05, 2012, 02:21 AM
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I think you might have not read between the lines of what he is saying. Yes, it will always be out of balance. The problem with many engines are that we run them at a higher rpm than the designer calculated the balance for. By tweeking it into the actual running rpm range, the best balance can be achieved. These CRRC engines are very much out of balance, compared to my Hanson modified Zenoah.
And yes the engine will smooth out when they are broken in, and tuned. Tuning will change as its broken in.
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Old Jan 05, 2012, 08:56 AM
That Free Gas Weirdo Huh ?
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I think it could use those pneumatic rubber shock mounts that take the hard hits from each end of the motor's vibration swing. They worker well on ultralights. The motor needs to be able to swing a bit. Wouldn't a one cylinder glow engine have to vibrate the same ?
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Old Jan 08, 2012, 03:50 AM
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The glow engines of similar power are much smaller displacement. And run at almost twice the rpm. So the frequency of vibration is much higher, and of lower amplitude. Not to mention the combustion rate is slightly different.
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Old May 31, 2014, 09:06 AM
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hello I need someone to help me so that I can control and fly by helicopter rc and for programme futaba t14sg for helico rjx 90 gasser . help me please
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Old May 31, 2014, 01:46 PM
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You need to set every setting on the transmitter. With most transmitters I go through the manual page, by page. When you come to a setting you don't understand, ask about it.
If you have flown a helicopter with this transmitter in the past, the settings could be similar.
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