Hi all.
I am running an OS 70sz in my Raptor 60 and after a rebuild, it is running really hot.

I have replaced the following after the con rod broke up during a fly.
New piston and ring, con rod, piston pin, seals, glow plug (os8) and new bearings. I set the idle, mid and high range needle back to factory settings. Once all fitted back into the heli I put some fuel through the top of the head and turned the motor over with an allen key by hand a few times. Once all seemed ok,I started her up and let it idle for approx 1 min or so, all looking good. Took it out to the field and popped her up in the air showing a nice amount of smoke but after a couple of minutes of hovering, the motor very slowly started to slow down so I landed. The first thing I noticed was that the motor was really hot, I mean so hot I couldn't keep my thumb on the back plate for more than a second. I tried to richen up the mix separately using the all three screws, but only managed to get it stall at half and 3/4 throttle.
There is one thing I forgot to mention is, the fuel I am using is Optifuel 20% but it is one year old. I don't know if that makes any difference but I have just ordered some more 12% as I only pootle around.

I would be really grateful if you could help me out with this one.

Thanks

Dave

Dave

You have an air leak. http://www.osengines.com/faq/faq-q687.html

Or an obstruction in the fuel system that may be floating around blocking the fuel flow .... Have you by chance used RTV to seal the muffler to the motor?? If so , a piece can flake off and make its way into the fuel system and it winds up making its way to the main needle valve .

Whether or not you used RTV , I would take the main needle out and inspect for obstructions and then back flush some fuel before reinstalling the needle .....

One last thing , if you have not replaced your fuel lines recently it would be a good idea to do so.... Old fuel lines can get gummy over time and can partially collapse which would reduce fuel flow and cause lean runs....

Been there, done that and old enough to know better.....

Helijunki: I have to ask the obvious. Did you replace the sleeve too?

Blue Angel

Thanks for all your replies.
Flycatch, Thanks for the link. I have done some reading and this also refers to an air leak so I have been renewing all the fuel lines and checking for any damage to the tanks.

Juan, I have just stripped the carb and I did find the piece of sleeve that the mid range needle screws into (excuse my terminology) was pretty much completely blocked, so I give it a good clear out with some solvent cleaner and it opened it right out. That couldn't of helped much I think?

As for the exhaust, I only used an aluminium gasket without any compound sealant of any kind. Would this be enough to give an air tight seal here?

Blue Angel, Sorry , Is the sleeve the piece that the needle screw into?

Thanks again to you all.

Dave

Dave

rtv

What ever you do don't use that metal gasket over again...

Blue Angel was referring to the cylinder sleeve . It was not included in the list of things replaced during the rebuild.

If the motor ran hot enough for you to need to replace the piston and ring and for the lean run to cause the connecting rod to break then most likely the cylinder got scored up as well . If that is the case the motor will probably not run right . Did you inspect the condition of the cylinder before the rebuild ????

Been there, done that and old enough to know better.....

JuanRodriquez: Thanks Juan, for explaining my point exactly. I couldn't have said it any better. I just assumed "Helijunki" would understand what I was saying. Maybe the sleeve is the problem.

Blue Angel