Hello there! I have a 71 inch egde 540,it was fitted with a 120 TT pro RP,
it was climbing vertical like rocket,I had the TT second hand and it was ratteling a bit so I thought the bushes were worn out, so I got miself a brand new 2 stroke SC 120 (Super Custom), I tried it and I am very desappointed with the , power I ran 4 tanks allready trough, and still wanting to overheat a full power (revs drops) with a 16X6 apc (the same I used on the TT pro)so I still running it rich, flying does the same, flyes ok for the first 3 minutes, then the power drops,i can see smoke coming of he exhasut showing good lubricaion, I dont know if is because still stiff, or because the engine is not good, in the ground gives around 8500 revs with the 16X6 which are ok, I dont know!!, andddd the rattle still there (is not the exhasut or the frame), I guess bigger engines do have more play on the bushing thant smaller ones!!!??. any sugesstions?? how long will take to brake a 120 ringed engine??

Thanks Very much

You have ball-bearing engines. If you hear rattling, that could be due to the airframe or something loose inside.
Use a 15" prop for breaking-in the engine, 4 tanks of fuel is nothing for these engines. Be sure to use fuel with castor oil or it will take forever to break-in. Run it a bit on the rich side for 3 more tanks at WOT on a bench.
And NEVER trust the smoke trail, it means nothing.

Good luck.

G'day

A rattling or sizzling sound at mid range or above can be a symptom of pre-ignition ie fuel igniting too soon in the power stroke. It can be caused by a plug which is too hot, by too much nitro (in a high compression engine) and/or a lean mixture. It will result in damage to the engine if not corrected. An over large prop will also put extra load on the engine and can cause this effect.

I have seen one particularly bad case of this with an ASP 120 two stroke in an Ultimate Bi-Plane. The tank was very tall and narrow and if the engine were tuned at the top of the tank it would be running lean by about half way down the tank and would stop well before the bottom of the tank. If tuned at the bottom of the tank, it was way too rich when the tank was full. The solution was to fit a fuel pressure regulator such as a Cline or to use a second clunk for the vent line. This is called a uniflow tank setup. If you do a search here you are bound to find into on how to set it up.

Your Thunder Tiger engine is a high quality engine and if it just needs some bearings, they are easily replaced and will give the engine a new lease of life.

The noise Im hearing , is like the con-rod bearings they are brass on these, but reading your kind advice it sounds like timming, the reason I changed the TT was becasue the same noise I thought, was really bad thats wy I swapped it, TT wasn't overheating it was a muscle engine!!, but The only common thing on both was the fuel I am using, is the recommended by the model shop! but being both engines knocking, Im starting to doubt about it, is model technics formula irvine contest 10, 10% nitro 18% Klotz Super Techniplate Oil 72% methanol, which fuel is best fot these 120 ringed??

Thanks a lot!

Plug Im using is an OS No 8, the nose on both engines Im shure is no something else, if is under load is ok if you release the throttle is ok is just when you are cruising a middle stick, in the bench does the same, could be the worng plug or fuel?

HI again I just noticed, the very top of the thank in this plane is in line with the carburator,there is no way to move it or move the engine down.so I guess I need a Pump for it