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crf 450 top end

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#1
i was out at the track the other day practicing for my next race and i came around a corner too much wait on my front and wound up sliding out! no biggie! when i got up i tried and tried and tried to kick start my bike but it wouldnt start! finally one of the flaggers came over and tryed kicking it for me. he also was unsuccsessful. he gave me a push and i poped it in gear and it started right up. he mentioned that i might need a new top end cuz it seemed harder to start than most bikes. its a 2003 crf 450 and i bought it used. when i got it the valves needed to be adjusted and shortly went completly out of spec! i replaced them with kibble white stainless steel black diamond valves and there double spring lightweight racing spring kit! when i had the bike torne down i didnt have the money to put a new piston and rings in it! but i did lower the piston and inspec the cylinder walls and they looked spectacular!! i put the bike back together and it runs insanely well! it doesnt smoke at all, has all the power and torche i need! its very easy to kick when its cold or hasnt been runing at high rpms for long! but once i have ran it for a wile it gets hard to push on the kick start! does anyone know if this is a symptom of a worn piston and ring?? i have no idea how long its been since the top end was done! any help would be great! thanks
 
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#3
The only way to tell is by doing a compression test. But, by all means, check your compression release and you valve clearences. My guess for your on track soil sample would be that you flooded it and it took a little while to clear it out.
 
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#4
Britt Boyette said:
My guess for your on track soil sample would be that you flooded it and it took a little while to clear it out.

That would be my guess too. If you pull the hot-start lever and it still wont start, turn the throttle wide open and hold it open. Then kick the bike through about 6 to 10 times and then release the throttle and try to start it again. This will clean out the flooded engine and make it easier to start. Don't twist the throttle or it will flood it again.

When you kick your bike you can't feel the compression in your engine because of the automatic compression release. To check the compression you have to disable the automatic compression release first or you will get a false reading. Back off the adjuster on the compression release lever inside the top cover before checking compression.

While you have the top cover off, it would be a good time to check your valve clearances like Britt suggested.

If you have never inspected or replaced your piston, you may want to do that. The piston in your bike has a very short skirt and less rings than a normal 4 stroke. They wear very quickly and should be replaced at regular intervals.

Just my $ .02
 
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#5
Ol'89r ok i didnt know my bike had an automatic compresion reslease! but what would cause it to become harder to kick? i visually inspected my cylinder but i did not pull it off and check the piston! my cyinder looked great like the day it was assembled in japan!! is there anything that can be adjusted or something that could be going wrong with the comrpression release cuz thats what i feels like is im kicking over full compression!!
 
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#6
oh and ya my valves r always inspec at .19mm!!! they havent moved at all since i put them in! THANK GOD FOR KIBBLEWHITE!!
 
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#7
2003_CRF_450 said:
Ol'89r ok i didnt know my bike had an automatic compresion reslease! but what would cause it to become harder to kick?is there anything that can be adjusted or something that could be going wrong with the comrpression release cuz thats what i feels like is im kicking over full compression!!
A good place to start would be to check the adjustment on the compression release arm. It is the arm on the right side exhaust valve with the adjuster and lock nut on it. After you check and adjust your valves, check and adjust the compression release arm to .014 clearance at TDC. If this adjuster has too much clearance, the bike will be hard to kick.

Ol'89r
 
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#8
ya ive checked it and adjusted it but that was it i need to go threw my bike and check clearences and stuff!! so we will find out! is there any other options?? so if i check my compression how do i know if my top end is bad? wouldnt a loss of compression also result in a loss of power?
 
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#9
Who put the kibbles in your head?The biggest concern I had when we took the 06 apart was the small end of the rod showed the piston to be rocking,SIDE TO SIDE!Eric Gorr has some top notch reference on what to watch and some priceless insight to rebuilding.
 
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#10
2003_CRF_450 said:
i didnt have the money to put a new piston and rings in it! but i did lower the piston and inspec the cylinder walls and they looked spectacular!! i have no idea how long its been since the top end was done! any help would be great! thanks
I would not even bother to check compression. You may have decent compression but your piston may be ready to break.

If your piston has never been out since you have owned the bike and you bought the bike used, I would suggest taking the piston out and replacing it. When you have the piston out, look at the lower part of the skirt. You will be able to see the wear pattern from the piston rocking in the cylinder.

As I mentioned, these pistons wear very quickly due to the fact they are so short. They will start to rock in the cylinder and eventually break. Then you will have a very large repair bill. While you have the cylinder head off, pour gasoline in the ports and look at the valves. If your valves are not sealing correctly, you will have gas leaking from around the valves. If your valve job was done correctly, there will be no leakage.
 
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#11
i had a local machine shop lindsay machine cut and lap my seats and valves! i put them in my self though! im going to test my compression asap but like i said wouldnt a loss in compression equal a loss in power?? my bike has just as much power as ever and would it maybe be burnning oil or something due to worn rings?? cuz my bike doesnt burn oil at all!!
 
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#13
Aluminum piston against a chrome bore,who would you pick to show wear.Your motor will run killer,until a loose piston frags,up to you,and there is the timing chain,chain guide and tensioner,what kind of cam?And do not forget the oil pump!High wear items pretty much get all changed at the same time.Anybody seen an aftermarket rod with a needle bearing yet?
 
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#14
whenfoxforks-ruled said:
Your motor will run killer,until a loose piston frags,up to you,QUOTE]


They run best just before they blow. :yikes:

2003_CRF_450.

Just tell us what answer you are looking for and we can stop wasting our time. :bang:

This is typical. You guys come here asking questions and when you get an answer that you don't want to hear, you keep asking until you get the answer you want. :coocoo:

Next month when you explode your piston you will come back and attack four strokes and everyone that rides them. You will complain about how much it is going to cost you to repair your POS four stroke and how the OEM's are screwing poor guys like you and ruining the whole damn sport. :yell:

Or, you could just change your piston. :nod:

There are two ways to correctly determine what is wrong with your engine. You can dissasemble the engine and inspect and measure everything or, you can let it go until it takes itself apart and the problem will be much more obvious.
 
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#15
hahahahhaah hey chill out im not coming to get the answers i want to hear!! im here to find out whats going on and what i need to do!!!! my bike is coming apart tomorrow so its all good!! i race for a team we have sponsers and get discounts i have a job and have money!! my bikes not a piece of **** i love my bike!!! things wear and have to be replaced! thats the nature of the sport!!!
 
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