4-Stroke Engine Life Expectency.

I'd run a compression check or leak down test...or both. If your valves are to spec, it may be your rings are worn to the point where they aren'tfully compressing the fuel air mixture to ge a more efficient burn. I always put a fresh piston and rings every year in the winter whether it needed it or not.

The winter project was a tear down, adjust valves (usualy just confirm that they are right) new piston and rigs, new cam chain-VERY cheap $40 insurance, and clean internal oil screen. That way I was more likely to have a summer of care free riding with no issues. Motor advice is always a dime a dozen, but I was once told that worn pistos can lead to blown cranks in 4 strokes. With the short skirts on 4 stroke pistons, when the piston starts to wear it will travel within the cylinder at a slight angle (the skirt does not keep the piston straight like on a long skirt 2-stroke piston). This angle, if allowed to get to large could translate to very edge of the piston hitting the cylinder head on the intake or exhaust side. This contact transmits the shock through the piston and rod to the bearings and can cause failures in the bottom end...grenade failure. I'm no expert but it makes sense. If you put a piece of clay on top the of edge your piston and check the clearance to the head...you will be surprised how little there is.

Preventive maintenance is fun for us old guys, and after you've done it for a while, you find out that it really pays off in the long run. When others are fixing this and that...you're riding. Besides riding, whats more fun than a few beers in the garage with your favorite gas powered sweetie? lol
 
If he has kibblewhite valves, are they titanium or stainless? Titanium valves wear out on the intake side faster because of dirt! Keep the dirt out and they will not wear nearly as fast. Im talking not even dust. Titanium valves can be shimmed for break in of valve seats and carbon build up. But if they are subjected to dirt ingestion the hard coating on the titamium is worn off almost instantly and then the soft titanium wears really fast. If he OP has stainless kibblewhite valves which is a popular mod for hondas, stainless valves can be shimmed and will last for years if the valve guides are still good.

Waiting until the bike doesnt start is the worst thing to do for the life of your valves, and if you do, your right in saying they should probably be replaced, its too late to save them. Proper valve clearance is important to valve life. The valves are cooling when they rest on the valve seats between strokes of the engine. If you do not have proper clearances they will not rest on the seat for the proper amount of time which increases wear.

In short, keep your air filters clean and oilied, airbox clean and check your valves regulary. How often depends on how many rpms you turn with engine, if you are banging it off the rev limiter all the time or running at top end rpm all the time you will have to check more often, if you trail ride or dont rev the engine that much then you can go futher before checking the valves. The rest of the engine depends on oil for longevity, change it regularly and oil filters too. type of oil isnt as important as everyone makes it, just keep it clean and changed regularly.

OP may have tried to break in his new JE piston and rings with synthetic oil, that will not work. Use regular mineral based non-synthetic oil for break in of four stroke pistons and rings.
 
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