MikeJdad:

In racing use TBO can be as little as two minutes. Check the top fuel drag boys - a tear down after each run. The Reno racers probably have a TBO in the range of one or two hours max. And that Rolls Merlin had a rated combat life of only 200 hours.

The only model engines I've seen with a rated TBO were the early Norvels, on the instruction sheet they said six hours. And the last Fox I flew lasted less than one hour - the crank broke. But that was in a racer, so it doesn't count for sport use.

Engine life can be greatly extended by using intake air filters, my filter of choice is the "Bru-Line," available from Tower and others. If you want a really efficient air filter check the ones the car boys use. But they are big and ugly, might tend to block cooling air to the cylinder on an airplane, I've never tried one, the Bru-Lines do me very well.

I have a pair of Magnum 46 engines on a twin, they are five years old, can't be told from new, Bru-Line since new. An eight year old Diablo still has its original K&B 61, Bru-Line from new.

A recent picture of that Magnum powered twin is on page 96 of the Feb 2003 Model Airplane News.

But my old trainer is on its third engine. The new engine has an air filter, the first two did not.

My oldest plane that has not had an engine change (without accessory filters) is seven years old, twin AMD engines - these are the ones that Norvel sells as AME - they have an inlet screen as stock. But the whole airplane is probably less than two hours TT - well within the rated six hours.

Regardless, 15 hours is around 100 flights for most of us, and for most of us the planes just don't last that long. The last plane I destroyed (dumb stupid foolish error on my part) had less than 30 minutes on it. Airplane and engine four months old.

Or consider the average homeowner and his power lawn mower. He buys a new one every couple years, and throws the old one away with maybe 10 hours total time.

So actually 15 hours TBO isn't too bad, considering.

But the more expensive engines, with higher grade materials, can be made to run into the hundreds of hours without problems. Stay with at least 20% oil, always at least part castor oil, (yes, even on four stroke engines) keep them clean and not lean, and don't try for peak RPM.

Enjoy.

Twin engines old and slow? New P/L sets will make them go!

Bill.