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tommyr21

11 yz450 valve check

4 posts in this topic

Hi lads,

Picked up a 2011 yz450 about a month ago. had a few rides on it and it goes great. only problem is, and from what ive read its quite common, is the bike gets pretty hard to start once its warm.. Normally starts within 2-3 kicks cold, but when hot, ive sat there for up to 5 minutes kicking the thing...

The bike had a top end rebuild and had only done about 1 hour before i bought it. After reading a few posts ive found out that valve clearances should be checked after run in, which hasn't been done. So i took it upon myself to get in and have a go (first time)

Turns out, as everyone has said that checking clearances is a piece of piss... Only problem is, all 4 clearances are out of spec and on the tight side.. so obviously this is whats causing my "hard to start problem"

Exhaust - 0.18mm & 0.17mm - Spec = 0.20 - 0.25mm

Intake - 0.09mm & 0.08mm - Spec = 0.10 - 0.15mm

Anyway, i just have a couple of quick questions for the more experienced valve gurus...

1. When checking clearances, how tight should the feeler guage "feel?" Is it just a tiny bit of resistance or should it be reasonably hard to push through??? im pretty sure it just needs to feel the slightest bit of resitstance, but not 100% sure so thought i better ask...

2. Whats the trick to getting the valve lifters and shims out without the "special tool" described in the manual.. im sure there has to be a simple way. but thats whats stopped me from going any further tonight...

3, When choosing the right shim to get clearances back into spec, where should i be aiming to be? on the tighter side? more clearance? in the middle??

Thanks in advance for your help.

Tom

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1) The idea of the feeler gauge is to determine when there is a gap between parts that is the same size as the blade used. When using feelers to measure valve clearance, understand that you can wedge a gauge under the cam that is as much as .002" too big to fit, raising the valve off its seat in the process. With that in mind, you should have the same resistance at the gauge as you would if you rest the end of a 19 - 22mm box end on the gauge on a clean bench and pull the gauge out from under. You want it to drag, but "just". Also bear in mind that the angle you have to work from makes the gauge bend as it runs under the cam, and that can influence the feel a little.

2) I looked for the special tool you mentioned in the manual and didn't see it. Haven't had the top of a four valve YZ open yet, but on the older ones, I just grab them by the edge when a good pair of bent needle nose pliers and pull them up. A strong magnet may help you, too.

Something that works in a pinch if you run into a stubborn one is to push down on the lifter with a tool of some kind, and then slide the tool off the edge, letting the lifter "snap" back up sharply as the valve slams shut. A brass or aluminum punch is best, but a steel one with a bit of a rounded nose will work. Just remember that your piston is at TDC. This trick will often pop them up just far enough to get a better grip on them.

3) The ideal is to stay on the tight side. Yamaha builds them that way because it's easier on the valve train. But keep things in perspective: the specified range is only .002" wide, so how much difference will it really make?

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I used a telescopic auto magnet on the buckets and shims and worked great,they came right out with the shim in one piece.

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Hi again,

thanks for your replys..

I ended up using the magnet technique which worked great, bucket and shim both came out together no problems...

After measuring the existing shims i went down to the dealer and got what i needed to get them back into spec.

After putting it all back together i checked clearances again and they were all pretty close to where they needed to be.. except 1. one of the exhaust valves ended up being about .05mm out still, so i pulled i tapart again and got another shim to get it right... obviously pays to measure a few times to get it right..

Anyway, all back together now and seems to start pretty well... started it up and rode around for 5 minutes to get it hot, then killed it and started it about 10 times... started first kick every time...

Now just need to get out on the trails and see how it goes..

The only thing i havent done is tightened everything back up to the correct tourqe... its all nice and tight but didnt have a tourqe wrench so just went by feel without going to hard and stripping threads. Ill bring home a tourqe wrench from work tommorow and go over everything to make sure its right..

Anyway, after checking and adjusting clearances, i can definetly say that its pretty simple and anyone with a basic mechanical aptitude could do it easily. So i encourage everyone to save some labour costs and get in and do it yourselves...

Thanks again for your help.

Happy riding

Tommy.

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