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Cowles52

Engine rebuild?

9 posts in this topic

I have 115 hours on my 2010 Yamaha YZ 450f and want to know when I should look into re building it? I have no issues with the bike; it runs like its new still and starts with no issues but I don't want to wait till I have an issue. Any tips or advice?

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I would say that if your pushing 115hrs on a completely stock motor with zero replacements or adjustments ever made :jawdrop: (just fluid changes)...you are running on borrowed time. Some guys i know who just trail there 450s are rebuilding at around 60hrs, if you race or ride it hard id say around 45. I suggest popping off the valve cover and check your valve clearance. Im pretty sure if you get your hands on a repair manual it'll also have a page (some times two) with a big chart on it to tell you what to check and what to replace at what Hour. The chart is just general though, your bike could be different, depending on if you babied your machine or put her through the paces. Ither way it'll give you an idea of when about to check or replace some parts.

I mean a complete top end rebuild can never hurt you!....except your wallet....it can hurt the shit outa your wallet

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Thanks for the info. That helps a lot! I do race but I'm a beginner. I'm not pushing it like a lot of guys on the track. I'll have to open it up and figure out if I'm still in spec or not. Thanks

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At around 100 hrs, I replaced cam chain, piston, clutches. Knock on wood, valves were still in spec. I mic'd everything and piston was only thing out of spec. Book says replace the piston every 18 hrs but that seems a little short but im not bouncing off rev limiter much.

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i rebuilt my 2010 at 110 hrs, i couldnt even tell it was rebuilt. i too have never had to adjust valves or anything, so i reused the valves, got new springs, piston kit, and timing chain, everything was still well withing spec, and i have been racing my bike pretty hard in the open expert class in my local desert series. these bikes are amazing.

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I'd say your due now, I've been doing 80 hours myself for a new piston rings wrist pin. I do timing chains pretty often, at least 3 during that 80 hours, here only $20 and stretch quickly. Inspect your crankshaft side to side clearance and compare it to spec. Inspect your valves before your start disassembly. If they are out of spec you can shim them once. After that first time they move around pretty quick when that coating wears off. You should be good to go another 100 hours then

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Well a friend of mine is at 170 hours on his 2010. He brought it new and even his valve clearances haven't changed! We are going to tear it down soon for a rebuild, I'll measure it all up and let you all know how it looks .

The thing runs like new, amazing motors.

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Thanks guys! We get some nasty winters here so I think I'll turn this into a winter project. Hopefully I don't have any issues till then. But like I said before it still runs awesome.

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