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Chansharp

wierd problems...need some In put before I go on a buying spree

12 posts in this topic

So here's the deal..I have a 2010 yz450f. starting a few days ago it was impossible to start. It would fire a few times and motor would rotate but die. Can push start it but even after warmed up I stop and let it idle and it dies. If I leave the cold start out it stays running but idk for how long. I haven't moved the idle speed ever. Also my motor is losing oil. There is no visible leaks and i have never seen any smoke. A month or 2 ago I did the valves and I know one intake valve moved within 2 weeks. ( I only ride Saturday and sunday) so I'm gonna check the valves when I get home from work today. I'm expecting my valves to need adjusting but I'm also thinking I may need to buy new valves..just don't know how many. I'm wondering if I should get valve stem seals and springs. and possibly a top end. It is a used bike and have no idea if the previous owner had put in a top end or new valves since new.

Hopefully someone on here can confirm my thinking due to symptoms and have some input

Thanks guys

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Well my intake valves have no measurable gap between lifter and lobe. So I imagine that has a big part to play in the hard to start/not running catagory. My exhaust were between .20mm and .23mm (no in between sizes) so I'm thinking I should probably replace both intake valves. But would could cause me to lose oil? Should I go ahead and replace valve seals for all 4 and springs for the new intake valves?

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I'd get a high compression weisco piston and new timing chain while in there. I used fast heads for my valve work. 90 hours on my head. Starts first kick. No valve movement

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I've considered going to high compression but didn't really want to have to buy race gas..would you choose wiseco over vertex? And update I dropped down from 1.85 to 1.75 shims and 1.95 to 1.85 shims and still only measure .05mm gap. They must have been VERY tight

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At 13.5 to one my bike runs great on premium. My guess is that your valves will tighten up on the next ride and you'll be back to square one. I put 60 hours on the last wiseco and it still looked brand new. The price is good too.

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ok so here is where I'm at. today i figured id go change my oil and measure to see if there had been any loss. sure enough i was about 10 oz low..and i am warming up my bike and blip the throttle a few times and on the deceleration here come smoke.. I've never paid attention during warm up cuz i usually start it up and walk away and don't touch the throttle. I've read on a few post that this is most likely due to leaking valve stem seals. Which i am hoping because I'm not wanting to do a top end. so i have ordered 2 new intake valves, 4 new valve seals, a timing chain. and gasket kit so i can at least inspect the piston and rings while I'm in there. So my next question is about my timing chain.. there seems to be a lot of noise like it is loose. i did make a little mistake replacing the tensioner and didn't get it all the way tightened down before it sprang back. so i then tightened it all the way down. retracted the spring...and let it pop back again. Could this allow it to not set back to correct tightness?

Edited by Chansharp

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Why wouldn't you go ahead with a new piston? It should be replaced at least every 100 hours or so. Most manuals say 15hrs!!

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Why wouldn't you go ahead with a new piston? It should be replaced at least every 100 hours or so. Most manuals say 15hrs!!

after more thinking.. I'm just gonna go ahead and do it. i was try to be cheap and cut corners but thats not how you keep a bike nice. 

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should i be measuring something before i order pistons? people are debating about how stock pistons are more reliable and will last longer? I'm above my head here.

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All modern bikes have a hard coating on the cylinder walls. You don't bore them out and use oversize pistons anymore. So unless it has a big bore cylinder, it will be stock size.

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