TT .46 and heat
 

One of our students last night had a TT .46 in his plane. All of a sudden, it would quit after a few minutes of flying and he asked me to take a look. At full throttle, it started to lean out. Needle was 4 1/2 turns out. Transition was smooth.

OK so
1. His prop was a MA 10x6 that we switched to a 11x6
2. We flushed the needle valve.

After these 2 changes with the needle out 2 3/4 it was rich (oil and fuel coming out the exhaust) and wasn't running higher and higher rpms like before, it stayed constant.

Even that rich though, you could fry an egg on the head after a minute or two of running. After about 5 minutes of flying at half throttle, the engine over heated again.

Any ideas of what to go at next?


Bob

What fuel is he using? Try going to a fuel with more castor content, and/or a higher oil content. It really does make a difference.

Simple fix? Just richen it up more than usuall (maybe 500 to 800 off peak rpm instead of 200 to 300) - and live with the little less power produced but at least you wont fry the engine.

I mentioned fuel to him. We backed off quite a bit from the peak rpms (hence the rich stmt, sorry shoulda been clearer). The engine doesn't have nearly as much zip but he was able to fly with it fine. I can tach it but we went 3/4 needle turn back from peak by sound. I don't like to peak engines; just not worth it IMO.

His fuel is Byron 20% oil content (15% nitro). It's been running fine until yesterday. The needle flushing certainly helped as did the prop change but it's the heat confusing me. I would have thought 20% oil is plenty but I can certainly bring some castor for him on Saturday.

Thanks for the ideas, I'll try some castor if you think it will help

Bob

I've used Thunder Tiger 46 engines exclusively in my smaller planes and have alway had for the most part great success with them. All it takes is a minute or two of running lean to cause serious problems with an engine. Take the muffler off and look in at the side and top of the piston. If it's blue, you have had a lean run. Once this happens, your going to have hot runs with the engine.

Just thought I'd mention this as it is another thing to look at. If this is the case, the only real fix is a new piston and sleve!

Hi Gary,

so once he's had a lean run (and he apparently had a few), the engine will always run hot? When he had too small a prop coupled with some junk in his needle assembly, engine revved too high. I'm curious, why, in that case, would every run be so hot?

I'll check in on Saturday, hopefully this isn't the case.

Thanks

Bob

Bob, I mentioned to him that he might want to try lower nitro - even 5%. I had an old engine (now my wife's :D ) that started to run hot all the time and would only run with 5%.

I suggested he try and borrow a tank of fuel if possible instead of getting an entire gallon.

Nony, I was in a hurry (lunch) and didnt see the rich part :)

Byrons is oily, so I dont think it will help much... I would also then try a lower nitro content, or perhaps one .005 head shim.

Bob:

I had some problems with my TT overheating as well when the outside temperature was 30C or more. Changed from 15% to 5% fuel and added a little castor ( 2 oz. or so ) - problem went away. I believe the nitro content was the key. Also solved my problem with an MVVS .77 - simply would not run on 10% - 5% works fine.

Brian

OK,

I'll get him to try 5%. This engine is only 2 months old so not quite worn out yet. Hopefully this is an answer. I have some shims he can try too.

Thanks again guys, I'll post what we find on Saturday

Bob

Just to advise how it ended up.

Student went from an A3 to a #8 plug. We then found out that he had purchased fuel from a local shop who, unfortunately, has a habit of selling old stock that just doesn't move quickly at this place. Prices are higher. Anyway, the new student, who has since switched shops to one that most of the members frequent, had paid $28 for a gallon of old fuel that was on the shelf. He switched to some new stuff (remained at 15% as that is what he flew since he got the engine in the spring) The engine purred and stayed reasonably cool. He threw out the old fuel and chocked it up to experience.

Looks like the culprit was some old fuel :?

Just wanted to provide some feedback. Thanks to all for the ideas.

Bob