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Zach Hanson

03 yz450 valve timing and shim

25 posts in this topic

After some research, I'm confident to do my own valves. Before I tear everything apart, I want to make sure my timing is correct and I am at TDC. How does this look? Sorry of the bad pic quality. That's the I mark not the H.ImageUploadedByThumper Talk1434060805.620604.jpgImageUploadedByThumper Talk1434060685.445456.jpg

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I'm just a little worries because when the mark is perfectly centered, the dimples on the camshafts aren't perfectly strait. The right one sits below the head and the left one is perfect. Take a look from this angle.ImageUploadedByThumper Talk1434063620.850286.jpg

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Chain's old.  Besides, they never really line up just exactly.  When you look at it, ask yourself whether it would be closer to lining up or farther form it if the timing mark was on the next tooth over. 

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Ok thanks! So, I should trust the mark in the sight hole for TDC? I'm getting some feeler gauges soon to measure my clearances so, I may need some guidance on that and ordering new shims if needed.

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You can check the mark for consistency with TDC by probing down the spark plug hole with a long Phillips head or similar.  If it's off significantly, you should check the flywheel woodruff key. 

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Ok my manual says that the exhaust valve spec is supposed to be .20-.25 mm. And the intake valve spec is .10-.15 mm. After using my feeler gauges and carefully inspecting them, I got .127 .102 .127 for my intake valves and .152 for both exhaust valves. I have the chart in my manual that compares the number on your shim to the clearances and tells you what shim to buy. It says all my intake clearances are in spec. I and yet to remove my exhaust can and look at the shims. (Will do tomorrow) the whole reason I decided to do this was because the bike was backfiring and popping a lot and my idle wouldn't stay. So I figured the valves were screwed up. Could my out of spec exhaust clearances be to blame? Or am I wasting my time?

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Your exhaust valves are out of spec, so you are not wasting your time reshimming them.  They are not the likely culprit in your problem, however.  Look into your carb.

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Ok, where should I start in the carb? I already replaced all hotstart components, and did a carb rebuild with a moose racing kit and it still did not help. Fiddling with the air screw did not help either.

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I have no idea how the accelerator pump works so maybe it's that? Is there an adjustment or a common problem with them???

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Probably a simple matter of cleaning it and adjusting the idle mixture.  Just spraying carb cleaner on stuff won't open a clogged pilot, though. 

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Chain's old. Besides, they never really line up just exactly. When you look at it, ask yourself whether it would be closer to lining up or farther form it if the timing mark was on the next tooth over.

How do you know the chains old grayracer? The slight wear on the outside of it?

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If your popping and backfiring....my 2003 did the same.

A carb rebuild, a metal hot start nut on carb from zipty racing....and new header exhaust gasket, midpipe exhaust gasket, and silencer repacking cured it.

It was backfiring quite a bit. After i cured it....it had the typical small backfiring thats normal for em.

Ive heard...and gray can back me up on this.....that backfiring when letting off Can be both exhaust gaskets or silencer packing. They are cheap to replace.

Edited by soulsedg3

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I literally just bought a silencer packing kit, carb kit, and a metal hotstart nut! Haven't installed the repack, but hopefully it will help. How much were the gaskets? And where did you get them?

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I got the oem gaskets from my local mechanic. I think the total cost was like 50 bucks canadian or something.

I cant quite remember...but they were oem yamaha.

Grayracer suggests using a certain size copper wire for header gasket that butts ends perfectly...but i didnt go this route.

I would definitely do the midpipe and header gasket though. Then ya rule everything out. :) let us know how it goes :)

Edited by soulsedg3

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I'm still waiting on my shims to arrive! Once I get them and install them, I'll start to eliminate some factors that could cause it. My muffler only had half the packing left in it and I am certain that the header pipe has a leak at the head because I recall seeing some smoke come out when I first cranked it one morning. Is it possible for me to make my own gasket with gasket paper? I have a ton laying around.

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Cant make an exhaust gasket with paper gasket maker. But you can use bared 4g copper wire

Like gray suggested

 

EIGHT (8) gauge.  :banghead:

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