Hi

Two months ago, I buyed a second hand TT 120 SE.

My question is about a strange feeling when moving the propeller. It looks like if there is no compression. It is possible to move the propeller with the finger with no effort and, till now, it is not possible to start it without a starter..

When the engine is running, it goes quite well. There are only two things to comment: the idle is not very low (at least as low as I expected) and there is little difference between two positions: horizontal and nose up position (it is necessary to open the needle valve a little bit)

Do you experience the same?

Thanks in advance

The engine need long running-in and the ring will fit the sleeve and get more compression later.

Jens Eirik

My TT120 has some compression when I turn the prop over, I can start it by back flipping mine. My idle with Cool Power 15% and an APC 16x6 is about 2,200-2,400 RPM. What is your max RPM on what prop? Mine on the APC 16x6 is about 10,000 RPM.

My figures:

10% Nitro, 15% Koltz oil, 5% Castor oil Home brew fuel
OS No. 8
1,900 feet
Humidity: 55%
Standard Muffler


MA 16x8
8,800 RPM running - 9,200 peak

Mertz 17x6
8,700 RPM running - 8,900 peak

Seems ok dude ...

I would replace the ring if the compression is that low. []

FBD.

My TT 120 has had low compression for many years now. However, It runs great. Go figure ?

I would concentrate on adjusting the high end first, backing off 200 - 300 RPM, and then adjusting the idle using the pinch technique. She should idle below 2000 RPM easily using a 16x6, and 10% nitro fuel.

> Jim

thinking about buying a good used tt120 from a trusted club member ...think i will... as for UGLY AIRPLANES... well those you can "fly em like you stole em!" [>:]

I agree. You should be able to get a ring fairly cheap. The PROBLEM is actually GETTING the ring. TT is NOT known for being very good at supplying parts. And your in Spain--just to make it worse.

Your high idle is an indication of a worn ring. If you've TRULY got the carb adjusted properly, and the servo end point travel set up properly, it should idle reliably around 1600-2000RPM.

The reason why a worn ring won't idle at a lower setting--is because it just can't develope enough compression to maintain running at lower speeds. Too much blow-by, and loss of compression.

It runs reasonably well at high RPM--because the heat and pressures are increased. This compensates for the loss of compression a little. You don't really notice the loss of compression and blow-by at higher speeds.

If you opt for the new ring--and can get it. Do a thorough inspection of the cylinder when you tear it down. Check for peeling chrome and look too see if the cylinder has a blue tint to it. If the cylinder is blued or tinted blue--especially around the top end; then you've got a bad cylinder.

As long as the cylinder looks shiny and no signs of overheating--then slap the ring in and plan on a gallon of fuel to break it in.

Break it in SLOWLY. Remember--it's a ringed engine. Not an ABC that requires a fast break in at optimum engine temps very quickly.

Good luck.

My first TT 120 had very poor compression, even after several tanks of fuel, running rich on the bench. Sent it back to Ace, the importer. They said it was ok. Ran it some more on the bench, put it in the airplane (25% Edge 540), and had very erratic results with it. Added a Perry P-30 pump, with which I am familiar. Didn't help much. I finally yanked it out and sent it to Frank Bowman in New Mexico. Frank put a new ring in it, and said the initial ring was far from round, was polished from running only in a few spots. I broke in the new ring, and the engine runs great.

I bought a second TT 120 and put it in a Goldberg Sukhoi. This engine had good compression from the beginning, and pulls like a moose.

It sounds to me like you got another poor ring from TT, or else the ring is worn out. Good luck in getting it fixed.

Clair

I just went over the same problems you had and adding the pump did not help neither, I deceided to take a peek inside the engine and I found what it looks to be a coin with a hole in the center, that things is the head gasket!!!!. I removed it and the engine is running like a champ!!! I use 80/20 , zero nitro anyway.

Low compression, will not easily hand start, will not idle low means worn out ring. Ring has lost tension. Get a new ring.

Denis

Agree!! but this was a brand new engine....,Probably it would have worked fine with 10-15% of Nitro.This head gasked is particulary thick and solid...but I do not have experience with TT......
It is working fine now.

As Motorboy states, these engines take a long time to seat the ring. After about 8 liters of fuel, it should have good compression. I have a Magnum .30 that had low compression in the beginning, I had to use a starter. After some bench time the compression was so good the prop would bounce start by hand real well.

Sorry I thought we were talking about a an engine purchased used. My previous statement also applies to a new engine with a not yet seated ring. My magnum 120 2 stroke took over a gallon of fuel before it would hand start or idle well and show good compression. The cure then for your TT is to run it. But if it has been run very hot even once chances are the ring has lost it's tension and the only cure for that is replacement.

Denis