All my beliefs were stood on their head last weekend at our Rockhampton Q500 competition and I would appreciate any comments.

After the comp, the top three TT46 engines were inspected for any illegal modifications. There were none. The winning engine posted Australian record times of 76 seconds on the short course. On inspection of this remarkable engine, there was no shiny narrow band around the top of the piston side wall where it would normally pinch at TDC. The piston was badly carboned - real sooty black - indicating significant blow by on the down stroke. My TT46 is very tight at TDC and has a 1 to 2mm shiny band around the top of the piston side wall where it pinches at TDC.

The loose engine is performing better, with lower race times, on a standard muffler and 10x6 prop than my engine does on a Magic Muffler and 9x7 prop. The standard engine was running without a shim while mine had 0.005" under the head with the MM and 9x7 prop.

I had always thought that the tighter the TDC fit, the better the engine would perform. Not so in our case. In fact, its quite the opposite.

Any comments would be appreciated.[&:]

Maybe this special engine was complimented by a good pilot? could that be the reason for better times? maybe the engine is running more RPM in the air because the pilot flies smoother than the rest of you guys? And being that the engine is badly carboned, that just tells me that this guy pushes the engine to the limit by running it leaner than you guys.

What were your times compared to this 76 second run???

RB

RB may be correct, I went for a friendly pylon competition, any low wing plane with a stock 46. Day I I flew a Black Horse Twister against simple Q500 planes and low winged ones. My time was second fastest, only 1/10 off the leader who was flying a Q500 plane. On the second day I flew a GP Super Sportster and I was fastest. Reason being they all over shot the turns and with 3 pylons, they flew in a circle, I flew a triangle course.

Joe, I have had both tight and loose engines run well. A loose engine, as long as it is making a good seal at running temps will have less friction.

I would agree with Daven.. The fastest Nelson SS engine I ever raced had absolutely no "pinch" in the cylinder at all..

A lot of internal combustion engines run their best just before blowing up. Some take longer to blow up than others.

Hi Joe just thought I would share some of my thoughts
You say you have a shiny band around your piston , I see this as BAD bad bad, at most it should be a matt grey it being shiny tells me it is most likely cutting through the oil and polishing metal to metal.
Tight engines are great in cowled set ups like F3D where you can control the cooling , less air for very tight more air for loose engines doing this lets the tighter engines loosen through thermal expansion.
Your tight engine would probably best suit the hot dry conditions in Perth but in QLD with the high humidity you are almost water cooled and injected which is just over cooling a very tight engine. Try wraping the fins with coke can and give it a fly you might be surpised at how much better it may run.
What others have said about being smmmooottthhh is very important with thses planes , they are big draggy planes with low horse power and a big prop (10/6 for Aussie rules) and if you slow them down at No1 it will take the full lap to get up to speed again if it can.
One of the best quickies down here would be Jasons the OS in it has tram tracks up and down the liner and piston due to either flaking nickel or the tang of the bearing cage but it is always run a little rich so that if it is loaded up it has the fuel to not lean out and pull through the load. Also he flys very smooth other wise his caller tells him off. It is set up to do a full up turn at both ends of the coarse and can catch out some No1 cut judges as the plane starts its turn before the pylon but still makes the distance and by flying it like this it loses little speed and probable speeds up for the first few laps.
And as someone else said 2 stroke engines always seem to go there best just before blowing up or falling over the edge of performance
Hope you can get something out of this
Terry

what my dad does to produce great running glow engines and this has been proven with both my OS and TT 46 stock class pylon engines is, from out of the box engine he strips it done totally and inspects all ports for and burr dags etc etc , he then laps in the piston to linner nip using heaps of wd-40 lube and also he laps the liner to case so it fits in easy . he claims this pre run method seats the piston in alot better than it would just running in etc also the liner to case lap assists in a better heat transfere around the liner . the engine starts its run in on a full synthetic oil mixed at 20 % and no nitro, the run in consists of a simular heat cycling method of 5 minutes running rich then 15 minutes cool down and so on until 40 minutes of running has completed, he then strips down the engine / inspects and cleans all internals ready for racing with castor based oil mix. i must say these engines run very well and do have the edge on other simular engines in this class.

I shall ask this ... how is a piston or sleeve LAPPED.

say you have the piston in one hand and the liner in the other hand, you firstly need a short length of wood dowel that will slot into the inner piston conrod part this will fit snug to where the conrod normally fits when connected. now what you have is a piston with a wooden stick holding it that you will use to lap in the piston to the liner, the idea is not to just push in and out with the piston but to also rotate the piston as it goes in and out. you must use alot of wd-40 type lube when doing this so nothing gets dry also you do not force the piston up to high in the liner just let the lapping process do its job, make sure you don,t go right up to the tdc area aswell. same goes for the liner to case lap but no wooden stick is needed plus only a short lapping period is required just so the liner fits into the case without any force. normal piston to liner lapping takes about 30 to 45 minutes and must be done by hand [ no power tools ] and liner to case should only take a few minutes.

Is that kinda like what I hear some old flyers do when they run in the engine by hand? They put in some lube, turn the engine over by hand, then more lube then turn until its like XXXX number of times.