Supertigre 45--poor performance

[cudaboy_1971]

i bought my first ST45 back in '91. right out of the box it was a screamer. after an hour of break in on some crappy cheapo green 10% nitro fuel it was turning 12.5 - 13K. the thing was awesome.

unfortunately, that was the engine i cut my R/C teeth on. that poor engine (not to mention the planes it was tied to) met with more than its fair share of deceleration trauma. after cracking the muffler off so many times it would no longer seal to the head, i figgered it was time to invest in a new powerplant.

i'm longwinded i know...but, heres the point of the post:

being older and wiser (that's debatable) i broke in this engine with some 15% powermaster....3 tanks of it.

this engine just wont wind up, tho. transition is nice. lean out the high end until it sags...back it off 1/8 of a turn.

did the pinch test on the fuel line, replaced all my hoses, got a new fuel tank. i dont get it.

i mounted it to a plane and figured i'd see if it didnt get its 'legs' in the air. same thing. engine acts fine....transitions smooth. idle's nice. not blowing a lot of smoke....but it only runs about 9.5K...just wont get up and move like my first ST.

any ideas? TIA

[Dave Robelen]

Hi Cudaboy,
First, does the mill seem hotter than usual after a run? That could indicate a bind somewhere. It is also very possible over that period of time the Supertigre has made changes to the muffler and/or porting that trim away some top end. These folks change the design of their motors so often that it can be really hard to get a match after 10+ years. The other possibility is that this one is ported for more low end torque and will pull a bit more prop than the earlier one.
Regards, Dave

[cudaboy_1971]

thx for the speedy reply.

i dunno about hot. i dont have a thermometer; and i sure aint grabbing the head :)

but, after a tank in the air, the thing dang near seizes up. i know this is not right. but, i dunno what to do. i literally pull as hard as i can on the prop to break it over the top of its stroke. after it pulls over that first compression stroke, it spins normally and will start right up.

any ideas?

[Dave Robelen]

Hi Cudaboy,
It sounds like that poor thing is simply fit way too tight. I would pack it up and send it back before thevwarranty runs out.
Regards, dave

[Taylorcraft]

Cudaboy,

From what you say I suspect this engine isn't even close to being broken in, the piston expands more than the sleeve, causing the bind.

It may run too rich in the air, and/or may need some additional bench time. The prop can also be luging the engine down, causing heat to build and then the engine to "seize".

You didn't mention what prop you're using, so my first suggestion will be to check this. Our well proven TLAR-method (That Looks About Right...) says that this engine will do great on a 10x7 prop, up to 11x6. The make of the prop can also make a difference.

Also, if you have difficulties pulling the crank through the first compression stroke the engine may experience a hydro-lock, raw fuel filling the compression room making the engine close to impossible to turn over.
If so, check your carb settings and also the plug type.

I teach that an engine isn't fully broken in before it can hold full trottle for at least one full tank. Just run a few tanks of fuel through a new engine won't do.

Running the engine (ABC-style) in short bursts, leaning it out, just for some seconds first, then extending the period to up to half a minute and letting the engine cool down completely between runs, will most likely produce a strong-running mill.

Note: More lubricant here is not a good thing, no matter what you might think! :)

What we want is to "stir and shake" the pieces together, creating a unison unit out of individual parts (PFG Chinn said sonething similiar many years ago...).
So we're using the same fuel that we'll fly with, maybe a slightly smaller prop than the one ment for flying and expose the engine for some initial wear. And when the sleeve/piston has the right clearance at operating temperature the engine won't seize or sag, but run strong and hold full trottle for as long as you like.

Example:
I've bought a few old Thunder Tiger and Magnum engines, that the previous owners says were dogs, wouldn't work at all.
After a check and proper breaking in period these engines now will go on as long as there's fuel in the tank, and I've checked them with BIIIG tanks! :D

So give your engine a second try, break it in properly, check the prop size and then see if it will perform or not.

Good luck, my friend!

BRG

Taylorcraft

[cudaboy_1971]

thanks for the lengthy explanation. helped a bunch. and, now that i've replaced this engine with my worn out ST45 on my plane, the new engine is all ready for some bench time.

fyi--this engine has seen only a master airscrew 10x6 (same as the old worn out one has always run well). and the plug is a fox miracle plug.

hydrolock sounds to be the culprit in the first stroke tightness. you mention the carb and plug--what should i be looking for? too rich low speed needle? idle bar setting (never quite understood how to set that anyway)? i've always just adjusted the low speed needle for transition...and it transitions fine. and ive always adjusted the high speed needle for rpms (lean out until rpm drops, then back out 1/8 turn). if you have better advice for settings i'm all ears. thx.

[Taylorcraft]

Hmmmm.......

From the new info the engine might as well just run too lean. I use the same props myself, and the plug oughta be OK as well. Never trust just an angle setting of the needle, 1/8 turn might not be enough. Trust your ears instead. :) When idle and transitions are OK the engine gets enough fuel at low RPMs. I suspect that if you back out the needle a little bit further the problem might go away. Also consider the extended break-in process.

Setting of the carb is often individual, depending of prop, plug and weather conditions. Try to go for a steady idle and transition. Too often people will try to tweak the engine for just a little lower idle and a little higher top end. Try to go for stable settings instead, after all, the last thing you want is the engine quitting on you in the air. :D When the engine can run for, let's say, 10-20 secs on idle (or perhaps even more) and then handles a transition to full power without too much (or any) hesitation those settings are OK.

What happens when the engine is pulling your plane through the air is that it unloads, it takes more power to turn the prop at full speed on the bench, where it's stalled than in the air - wich means lower RPMs and less need for fuel. So you might have a perfect setting for a certain RPM on the ground, but when the engine revs up even further in the air, it goes lean, with less fuel and oil to cool it - a seizure is just around the corner.

A simple solution is to back out the needle even further from the 1/8 setting.

To end revs is another story. If you're convinced that this engine should be capable of more than 9.5K (it should be...), and you can't make it unwind with the extended break-in period and slightly richer setting, contact ST or the shop where you bought it.

BRG

Taylorcraft
_______________________________________
Given enough power even a brick will fly.
But, the lighter the brick, the better it flies!

[imsofaman]

Maybe your prop has too much pitch. I would change the prop to a lower pitch to achieve the higher rpm. I have had the same problem. A few of these guys guys are on the same page, even though it took half the night reading them!

Dave

[rcflier]

10x6 is definetly not too much prop for a ST .45 . Give it some more break-in at a rich 2-stroke setting for short intervals, 2-3 minutes each. Let it cool and repeat. Never let it run rich enough to "4-stroke". It that is done the engine will run too cool and you will wear out the fit between the piston and sleeve.

[imsofaman]

Well...to begin with ..I think that Cudaboy fried that engine. I would have used a 10 X 4 prop and richened it up thru four tanks of gas and taking it easy....never going full throttle or pulling too hard. Then leaned it up a bit for two more tanks. Then put on the 10 X 6 prop for two more tanks then let 'er rip!!!!! He would have never had a problem. I have broken in many engines and this seems to work for me. Everyone is different and that is what makes our sport so fun. Also it gives us an insight on what others are doing and we should all learn from it. Just take something from our mistakes and learn from it.