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Discussion Starter · #1 · (Edited)
Well, after my rebuild everything was almost perfect. Quad running great, just cosmetic crap I was caring for. Heck, it was almost ready for it's first run to the Dunes in Indiana this next coming weekend.

I was practicing doing whillies in the field out back. Had them almost down to PERFECT. When I brought the front end down, it started acting like it would get any top end power at all. Bogged real bad when I'd hit past 1/4 throttle.

Brought it back to the garage, thought it was dirty carb. Cleaned it and my air filter, and started it back up. IT hit real nice a few revs, then died.

Put my hand over the exhaust, and felt it both sucking and blowing when I tried to start it. Pretty much knew right then I had jump a timing tooth and bent the valves.

Got her open last night and sure as hell, the exhaust valves are screwed. The intake ones look fine, but the Cylinder head has 1/4 circle indents from the exhaust valves. I SHOULD be able to file the indents down and it'll be ok. I'll get a new set of valves ASAP, but the main thing is how to stop this from happening again. I got lucky and just barely marred the cylinder head. It could have been a lot worse. I'll throw up some pics later on.

What do I need to replace to make damn sure the stress of jumping and other things doesn't let this happen again?

My list so far

1) CRF 450 timing chain Part# 14401-MEB-671 (have been told it's the same as the 400ex HD chains for over 100$. This one is only 29$)
2) Cam chain guide
3) Cam chain tensioner
4) Lifter assembly tensioner
5) New set of 4 valves (both intake and exhaust)
 

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Well, after my rebuild everything was almost perfect. Quad running great, just cosmetic crap I was caring for. Heck, it was almost ready for it's first run to the Dunes in Indiana this next coming weekend.

I was practicing doing whillies in the field out back. Had them almost down to PERFECT. When I brought the front end down, it started acting like it would get any top end power at all. Bogged real bad when I'd hit past 1/4 throttle.

Brought it back to the garage, thought it was dirty carb. Cleaned it and my air filter, and started it back up. IT hit real nice a few revs, then died.

Put my hand over the exhaust, and felt it both sucking and blowing when I tried to start it. Pretty much knew right then I had jump a timing tooth and bent the valves.

Got her open last night and sure as hell, the exhaust valves are screwed. The intake ones look fine, but the Cylinder head has 1/4 circle indents from the exhaust valves. I SHOULD be able to file the indents down and it'll be ok. I'll get a new set of valves ASAP, but the main thing is how to stop this from happening again. I got lucky and just barely marred the cylinder head. It could have been a lot worse. I'll throw up some pics later on.

What do I need to replace to make damn sure the stress of jumping and other things doesn't let this happen again?

My list so far

1) 450EX timing chain (have been told it's the same as the 400ex HD chains for over 100$. This one is only 29$)
2) Cam chain guide
3) Cam chain tensioner
4) Lifter assembly tensioner
5) New set of 4 valves (both intake and exhaust)
you ever hear the old saying...'' you get what you pay for '' ?..well..for a 29 dollar timming chain..thats why it did what it did !..lol..i use d.i.d timming chains..they are as good as stock..if not better..just make sure your slack adjuster is good...and working right when you put it back together.
 

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Agreed ^^^^^ also invest in some new timing chain guides they are neoprene and wear too!
KB Motorrsports sells a nice KibbleWhite set of valves for the 250X pretty reasonable too!!
 

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Discussion Starter · #4 ·
Well, after my rebuild everything was almost perfect. Quad running great, just cosmetic crap I was caring for. Heck, it was almost ready for it's first run to the Dunes in Indiana this next coming weekend.

I was practicing doing whillies in the field out back. Had them almost down to PERFECT. When I brought the front end down, it started acting like it would get any top end power at all. Bogged real bad when I'd hit past 1/4 throttle.

Brought it back to the garage, thought it was dirty carb. Cleaned it and my air filter, and started it back up. IT hit real nice a few revs, then died.

Put my hand over the exhaust, and felt it both sucking and blowing when I tried to start it. Pretty much knew right then I had jump a timing tooth and bent the valves.

Got her open last night and sure as hell, the exhaust valves are screwed. The intake ones look fine, but the Cylinder head has 1/4 circle indents from the exhaust valves. I SHOULD be able to file the indents down and it'll be ok. I'll get a new set of valves ASAP, but the main thing is how to stop this from happening again. I got lucky and just barely marred the cylinder head. It could have been a lot worse. I'll throw up some pics later on.

What do I need to replace to make damn sure the stress of jumping and other things doesn't let this happen again?

My list so far

1) 450EX timing chain (have been told it's the same as the 400ex HD chains for over 100$. This one is only 29$)
2) Cam chain guide
3) Cam chain tensioner
4) Lifter assembly tensioner
5) New set of 4 valves (both intake and exhaust)
you ever hear the old saying...'' you get what you pay for '' ?..well..for a 29 dollar timming chain..thats why it did what it did !..lol..i use d.i.d timming chains..they are as good as stock..if not better..just make sure your slack adjuster is good...and working right when you put it back together.
Naw man, I'm not sure of the timing chain on it. I meant the 100$+ HD chain they sell for the 400ex is supposed to be the exact same as the stock 450ex chains which are only 29$ish. I'll have to research it more, but I'm alsmot sure I remember that mentioned here or on exriders.com

Yea, the chain might be original along with slack adjuster and I KNOW the tensioner and guides are original. I should have replaced them when I did my rebuild. Oh well, like I said it could have been worse.
 

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your sure right about that..lol..when you rebuild it..check everything..guides..chain..slack adjusters..cam sprocket..cam..all of it..or you will be right back where you are now...oh..and make sure when you put it back together..that you torque everything down good..if you don't get it right..your timming chain won't fit right...just don't go to tight..or you will break a bolt off inside something...lol..been there sooooo many times..lol.
 

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Discussion Starter · #6 ·
your sure right about that..lol..when you rebuild it..check everything..guides..chain..slack adjusters..cam sprocket..cam..all of it..or you will be right back where you are now...oh..and make sure when you put it back together..that you torque everything down good..if you don't get it right..your timming chain won't fit right...just don't go to tight..or you will break a bolt off inside something...lol..been there sooooo many times..lol.
Thanks for the heads up. Truth to that for sure. I make sure to try and do everything by the book. Locktight on the cam sprocket bolts, the works.

I'll get the 2 new rails, new cam chain, and new tensioner. File down the indents on the cylinder head and hopefully I'll be good to go with new valves.
 

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Quick question What amout of breakin time did u give it before u went out scalding the earth......
 

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Discussion Starter · #8 ·
It's got 10hr on the rebuild.

Did the normal motorcycle break in, warm it up and ride it like you stole it pretty much. Had to re tighten the head bolts after the first 20mins. Then just been somewhat easy on it, changed oil at 1.5-3-10 hours. I've been pretty nice to her, but I have cracked her open as well.
 

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Your are broke in!! I berak them in like i am going to run them WIDE OPEN after the motor warms up.
 

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Discussion Starter · #10 ·
Quick question. How do I determine if I have the +1mm valve kit? Should I just take out the valves and measure them at the top then compare to the service manual?
 
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