Thumper maintanance

dkortje

Sponsoring Member
Joined
Aug 30, 2002
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#1
Alright, I might finally fall and buy a 4 stroke (YZ450F) :scream: . My question is what type or maintenance does it require. I am used to changing rings every 10 hours and piston every 20 in my 125. Do you still have to do this with the thumpers. How hard is that. I know freq engine oil change is important. Anything else. Thanks!!
 

nikki

Moto Junkie
Joined
Apr 21, 2000
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#2
Oil changes are about the only routine maintenance needed. Change your oil every 3 rides and you should be good to go.

If the bike begins to be hard to start, this is usually a sign to check the valves, which isn't as complicated as I thought it would be. Basically, you remove the tank/shrouds, pull off spark plug cap, take out 2 bolts in the valve cover, pull it off, get the piston at TDC (through little TDC site hole), and slide a feeler gauge (buy at any auto store for a few bucks) between the cams and valve caps and hope the clearance is in spec. The exhaust valves have one spec limit and the intake valves have another (it's in the manual).

If they aren't in spec, then you need to loosen the cam chain (through the chain tensioner), remove the cam chain from the cam sprockets (use a paint marker to mark where in lines up with the sprockets and tie a wire in the chain so it doesn't fall down into the case), remove the cam holders (just some 8 mm bolts, but don't drop the half washer spacer thingies), remove the cams, pull off the valve caps (use magnet), and replace the current shim with the size needed to get in spec.

Replacing pistons and/or rings is a pretty easy deal, too. Its basically the same as a 2-stroke except you have to do the above with removing the cams but the good thing is you have no powervalve to deal with. But trying to hold like 5 rings in place while you slap the cylinder back on can be fun. Luckily you can go a lot longer on pistons/rings in a 4-stroke. Clutches seem to last a lot longer, too.