RCTecher12

iTrader: (1)

In 20 years of enjoying this Hobby (nitro the whole time), I've never worn an engine out. I had some that didn't run hat great or strong, but it wasn't due to a worn piston/liner fit. Bad carburetors are usually the biggest culprit, and poor fuel usage a close second. In my early days I ran Traxxas engines (sport .15, and the successor to the sport .15 was the Pro .15. I used Traxxas fuel at that time, and could never get the engines to run consistently. Changing to a better fuel made a significant impact on the engines for the better.

After running different engines (both surface and air) and experimenting with different fuel blends and different glow plugs did I find a much better method to run the engines and adjust them better. When it comes down to brass tacks, the best thing that promotes a long lasting engine is a nice tight pinch when new. When an engine still has pinch (piston will get stuck at TDC turning by hand) after a good length of time (2+ gallons), piston sealing is still at its best. Once the engine loses its pinch, they do run faster and make their best power, but they are also at the peak of their life. Once the pinch is gone, the engine will gradually lose its power. How quickly it loses its power is dependent on a lot of things; with fuel and how the operator treats the engine being the biggest two IMO. I don't have any scientific data to back this up, but I do trust the information I've been given from a very reputable and world renowned aircraft racing engine builder. In his words; "A tight piston fit, good fuel & plugs, and proper needle settings make these engines run the best and the longest." "A tight engine is a good engine". (Dub Jett)

And FWIW - Dub Jett's engines do not use any grooves in the pistons. He uses a specially formulated alloy for the pistons (of which he will not divulge) that promotes long life and very low failure rates. Also, all of his engines are AAC constructed due to Aluminum having better stability; when the piston/liner fit is worn to an undesirable level, he fits a new piston to the existing liner. Aluminum liners do not bellmouth when overstressed (overheated) like brass does. This is why Brass liners often need replacing or repinching when the fit is lost.

In this day and age of people wanting instant gratification, many engine manufacturers are setting their engines up with a looser fit so they break-in quicker and give peak power quicker at the expense of longevity. Compare the fit of an engine from 25-30 years ago to an engine of today and you will find a pretty significant difference in how tight they are. The two Novas I have are a good example of this; the Ron Paris BX21 pinch is pretty intense - the piston starts to stick just above the exhaust port whereas my Legend 28-8 didn't stick until it was just barely below TDC. This comparison was made before the engines were run.

So this is all mostly my anecdotal experience. I have preference to older engines due to their better fits and tolerances, but this isn't to say that modern engines aren't powerful or well made. My Nova Legend is a brutally powerful engine that is a blast to run/drive.