Basic Thumper Overhaul

[Shawn007]

How about a general guide to overhauling the new 4 strokes?
Besides checking the valves, at how many hours should what parts be replaced?
I know "EVERYTHING" varies, but there's got to be some kind of GENERALLY AGREED UPON MAINTENANCE.
If a bike runs great until it has 40 hours on it, does that mean EVERYTHING should be replaced? What is everything? I have a '03 YZ450F with 40 hours and it runs perfect. 30 hours are practice and 10 hours are racing. Nonetheless, do I blindly replace the Valves, springs, timing chain, piston, rings, oil pump etc.. ORRRR, tell the mechanic to just replace the parts that are beyond the spec limits? Now here's the second part of my need----Between the massive depreciation and the massive amounts of money on overhauling, I can't believe we have accepted this 4-stroke
movement. Plus, I can't see spending $500-1200 on a going on 4 year old bike. I look at 2 strokes in a whole "new" enticing way... Please help with my rationale????????????

 

[RMZRIDER]

well, you should check your valves every 17-20 hrs, but check them now and if there fine leave them, obviously change your oil and filters regularly, you might want to put new rings in it also, if someone said 500-1200 dollars on maintenance for your bike, your getting ripped off, most of the stuff you can easily do yourself, i think its called a micrometer? to check valve clearence, i got one at napa for cheap

 

[Ol'89r]

Nonetheless, do I blindly replace the Valves, springs, timing chain, piston, rings, oil pump etc.. ORRRR, tell the mechanic to just replace the parts that are beyond the spec limits? QUOTE]

Shawn.
Everything in your engine has spec limits. The way you ride the bike determines the life span of the parts. If you are a pro that keeps the bike pinned against the rev limiter, then you may want to use the guidelines recommended in the manual. Of course cost will not be a factor since your sponsors will pay for everything.

If you are the average weekend warrior that only races occasionally or just trail rides, then you can go much longer on these parts.

Find a mechanic that knows how to inspect and measure your engine for wear. Many mechanics are only parts replacers and go by what the manual says regardless of how the bike is ridden.

Rings are a no-brainer and should be replaced every time the engine is taken apart. Valve springs get weak and pistons wear and should be checked often. Leaving your piston in for too long can result in a broken piston and serious damage to your engine. Most everything in your engine can be checked for wear and replaced as necessary.

The main thing is to service your bike often. Like RMZRIDER said, check your valves and change your oil and filters at the required intervals. Learn how to do as much of this as you can. It will save you many dollars in the long run.

Many of these expensive repair bills that we keep hearing about on the new four strokes are due to people not doing the required maintainance on their bikes and waiting until something goes wrong or the bike stops running. Then it is too late.

Just my $ .02

Ol'89r

 

[Mudd Slinger]

I trail ride and plunk around (race days are over). If it runs good, leave it alone. Change the oil on a regular basis (I change my oil and filter every 10 hours). Check the valves per the manual's recommended intervals and shim as needed. If you have to go into the engine for something, change all the heavy wear items as a no brainer rule (rings, valves, valve springs, timing chain, etc). Measure everything else as a general rule and replace when out of tolerance. Use good judgement. i.e. If the piston is close to out-of-spec, replace it. I use the manual as a guideline and appy good common sense. I don't rebuild engines every day but did a few in my life time.

If you race the bike, it will wear faster.