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Teddy: The lifespan, on the newer four-strokes, is not like the life span on the older ones. Take a Honda CRF450 versus an old school XR650 or even XR400 engine. The old XR’s had a reasonable lifespan, they came with larg- er piston skirts, and most important of all, more oil ca- pacity. Back then, you could get a 100 hours or better on one of those XR motors. If you remember, we used to see big oil coolers on some of the big bore XR’s. Some of them even ran oil in the frame to get more capacity. The old ‘XR” style thump- er motors ran about three quarts of oil, the new ones only about one quart. To save weight of course, but most motor builders know that to keep a four-stroke alive, you need clean, high qual- ity oil to circulate through it and help cool it down. On the new ones, the CR’s, YZ’s, & KX’s you’re lucky to get 40- 60 hours on a motor between major rebuilds. Dirt: Isn’t that always the case though, we always want fast- er, lighter, improved motors to race with? Teddy: Sure. The tradeoff though is that you have to give up a certain amount of reliability to get that. Lighter motors mean running less oil capacity, less oil, more heat. More heat, the faster the oil breaks down. It all combines to make it even more impor- tant to change the oil regu- larly on the newest genera- tion of racing four-strokes. This latest generation of en- gines need regular Dirt: How often should you change it? Teddy: Every week after rac- ing. No exceptions. Also use a good quality oil and the right viscosity, one for the motor side and one for the transmission/clutch side. Believe it or not, some rid- ers only change one side and think they’re done. You have to change and drain both sides of the modern four stroke engine and replace the fluids to the exact measurements listed in your owners manual. I can’t emphasize that enough. Get and read an owners manual for your bike! Since these new motors operate on less oil than ear- lier four stroke designs, you have to make sure you re- place it regularly. And that you are putting the exact right amount of oil in. Other- wise, heat build up will break down the viscosity sooner, and engine wear will in- crease, significantly. Dirt: Any other things a rider needs to look our for on the latest generation of four stroke engined mixers? Teddy: Here is what I tell rid- ers that ask how to make their modern day MX four- strokes more reliable. First, you need to change out the titanium valves on the newest Knowing the right type of replacement oil filter to install on your machine can spell the difference between winning or losing. Or blowing up. Watch the video! www.dirtillustrated.com