Don’t Let it Happen to You

A few short years ago the off-road world was enamored with 2-strokes thanks to their reputed simplicity and performance. Then, seemingly overnight, the four-stroke mill resurfaced and has since taken over nearly every aspect of the performance-quad segment. To many long-time 2-stoke devotees, the concept of valves, cam chains, and wide, flat pistons threw them for a loop.

There is no denying the reality that more moving parts equals higher rebuild costs, but there’s no reason to forget everything you’ve learned throughout the years in diagnosing a tired engine as a result. The following report is designed to shed some light on what to look for specifically if you’re uncertain whether or not it’s time for a four-stroke rebuild. Remember that it’ll save you money if you catch the problem before it actually fails.

A Game of Hours

If you just brought home your new ATV, take advantage of the fact that it’s yet unridden and pick up an hour meter. If that’s beyond your means, keep a log of time spent in the saddle. There’s no more an accurate means of determining when you’re due for a rebuild then by keeping track of the hours on the motor. Your ATV’s owner’s manual will provide intervals (usually on the conservative side) as to how often you should be freshening up the internals. Keep in mind that racing will speed up wear while gentle trail riding will extend service life.

Condition Induced Guilt

In keeping with the first entry, be honest with yourself (even if the hour meter says you’re still in the good zone). Have you been neglecting oil changes or racing with caked on mud? Have you flogged your quad in the sand/ dust? Have you let air filter maintenance slide or ran the ATV without realizing it was low on coolant? These are all factors that can greatly accelerate time between rebuilds.

Lend Me Your Ear

Especially detectable at idle (beneath the rumble of the exhaust note); listen for clunking, thumping, or rattling sounds in the top-end. This is especially important if a sound you don’t remember hearing before suddenly pops up during a ride. Remember that not all four-stroke noises mean catastrophe: A loose flywheel or stretched cam chain are common culprits to the rattles. However, in either case, tightening down or replacing the worn bits can avert a full-on engine failure.

Compression Depression

Sorry to break it to you, but that old compression gauge that told you when the piston in your 2-smoke was due for a replacement doesn’t work on a modern four-stroke. This one has become a shop specialty, as most will have a leak-down tester capable of measuring static compression.

Read Your Oil

In the modern four-stroke, there are few indicators as valuable or as accurate as reading the lubrication-fluid that had just spent time circulating among the engine’s internals. If you’re suddenly spotting excessive debris in the bottom of the oil pan after a change it could very well indicate trouble. Also smell the oil being drained (even if it still looks fairly clean). If it smells burnt or like fried-clutch, it may be time to freshen things up.

Clearance Items

It turns out the manufacturers don’t provide the clearances of certain engine components just to be fancy. By checking these numbers, you can easily tell if things have worked themselves out of whack. Begin with valve lash and work your way into the internals with piston ring end gap, skirt clearance, and rod and valve guides.

Hard Starting

Four-stroke engines will often let you know something’s wrong a little bit before a full meltdown by refusing to fire up. If your quad suddenly seems harder to start or requires much more cranking than usual, take heed. Poor compression or improper valve clearance are often to blame.

The Rest of the Quad

If you’re still in the dark as to whether it’s time to consider a rebuild, take a look at the rest of your quad. Have you burned the knobs off the stock rear tires? Have you replaced the original brake pads yet? Is everything else in need of a refresher? A simple way to get a rough estimate as to how many hours are on the motor itself is to factor against the more-frequent maintenance performed.

No Smoking Zone

Yes it was perfectly natural to trail exhaust smoke in the 2-stroke days but if your four is puffing clouds, not a good sign! If your quad suddenly decides to take up the smoking habit, it’s possible the valves/ guide seals are starting to fail. Even more likely is that the piston rings have worn to the point where they no longer seal against the cylinder wall.

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