2006 YZ450 kICKSTART STUCK WHEN PLUG IS IN

[jhuerta]

Hello Everyone,

I was out riding in GLAMIS for about 2 hours when we stop for a break no more than 10 minutes. I went to start the bike and the lever would not kick down for nothing! It’s like stuck. So the bike went for a ride on the back of my truck :( . Came home and started to look at. I can set the bike in neutral and it moves freely. I removed the plug it kicks perfect, so good engine is not seized. I changed the plug and nothing; stuck again. I set the timing because I had screwed it up due to removing the chain tensioner and pushing down on the kickstart lever :bang: Before I put the plug back on and while the valve cover is off I pushed down on the kick lever with my hand and perfect. So I put the plug and tried it again; stuck again. I took a look at the decompression mechanism but I really can tell if it’s bad because I don’t know any better. So for the sake of piece of mined I remove the cylinder head everything looks good nice and smooth. Which sucks because now I have too perform a top end buts is okay since I have not done one since I owned the bike that is 3 years. So due to all other things working I think it might be a bent valve or the decompression mechanism. But this is where I need the help of the experts. YOU. ;) Im not a mechanic but I like to work on engines so I do what I can at home and I have done some builds and repairs. I don’t think it’s the valves because if the valves were bent then I don’t think it would work even if the plug was off. I started to think that maybe it’s the valve seat which need to be re-shimmed. It looks like the decompression mechanism rides on top of the valve seat to release decompression. What do you think?

Thanks.

 

[jhuerta]

Any one!

 

[sharky243]

I have an 03 yz450f that does that once in a while. If the engine stops at just the right spot, you will be trying to kick against full compression because it stopped just past the decompression stage. You say you have taken the top end apart and everything looks ok ?, no signs of impact on top of the piston or in the cylinder head ? Make sure the decompressor on the exhaust cam is not stuck closed. Thats the mechanism that pivots outward on the cam sprocket and pulls in the pin on the one exhaust lobe.

 

[_JOE_]

Sounds to me like the auto decomp isn't working.

 

[jhuerta]

Thanks guys. I started to put it back together with a new cam chain and I am going to take a close look at the decompressor on the cam. I spoke with a shop and he said to take a look at timing again. The guy mention to me that he had a bike in not too long ago with the same symptoms and the issue was that exhaust cam was off by one tooth.

 

[_JOE_]

If that were the case it wouldn't roll over with the spark plug out......

 

[jhuerta]

I found out what the issue was. After checking the piston, both cases right and left I went back and checked the valves clearance and adjusted the timing again. This time I did not follow the link counts on the diagram from the Yamaha manual image. I followed what it said and that is to have the two dots be above the line. That did the job. I valves were out of spec which did not allow the decompression to engage. Therefore causing it to be hard to kick and lock when the spark plug was in. I had never experience this before so this is why I decided to check everything. Since I was not sure what had caused the problem or if it was going to start I did not replace the cylinder gasket and now I get a lot of smoke which leads me to believe that oil or water is sneaking into the cylinder head. So that being said always replace them if you cylinder is removed. This was a hard lesson to learn. I won’t make this mistake again. I will always make sure timing is correct first and valve clearance is good.

 

[jhuerta]

Thanks Joe and sharky243.

 

[sharky243]

Yes anytime a gasket has been disturbed, it should always be replaced with a new one. Even if the bike was never started. And you're quite welcome jhuerta !

 

[jhuerta]

FYI - My crank bearings when out and it cause lots of issues. Maybe the crank was going bad causing all these cam chain issues. I had to adjust the cam chain twice in row. I would ride for about 2 hours and it would not want to start again. Now I need to replace crankcase, cylinder, piston. I'm not sure if these are signs. Maybe a weak bearing was causing the chain to wobble. Something to take into consideration.

 

[BSWIFT]

Ouch!

 

[jhuerta]

I’m finally putting my bike back together. Got everything fixed and installing new parts. That crank caused all sort of issues. Good thing my head was undamaged. I will post some pictures of the broken crank later.

 

[jhuerta]

My BIKE has been running since Thanksgiving 2013 and it rides awesome. It starts right up with ease. It was a lot of work to rebuild the engine but I saved a lot of cash and learned a lot! I replaced the Crank with HotRods and all other parts were OEM(piston, rings, o-rings, other). I didn't want to hassle with piston hitting valves or any other issues. I have decided to keep this bike as stock as I can; Well not true( I jetted the carb, KN filter). I been out to the desert and it sounds and rides great. Anyhow if any of you are having issues like this and it has been about 3-4 years before you got a bottom end I suggest that you replace your crank. Do a full bottom and top end rebuild! I think I spent about $1000 just in parts. This includes that crank case which I had to purchase (new lucky I found one side on ebay). It would have been about 200-300 less. Now I need some radiator braces. Hit a bolder going down a valley between to mountains. Sand sucks! (sometimes lol)