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cam chain failure, did I get lucky

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Okay, here is the deal. I was out practicing for a race and heard a weird noise coming from the motor. At first I thought it might be a loose bolt so I shut it of and checked to see if anything was loose. My bike started right up And I putted back to the truck and took the valve cover off and noticed the cam chain was very loose :) . The old tensioner failure. Well other than the noise the bike was running like a champ. Wont be able to tell if it jumped timing until I get the tensioner and install it. Right now the timing mark goes from being dead on to the mark on the sprocket being above the other mark. If it did jump one tooth is there enough clearance to allow everything to operate without the piston hitting a valve. It was running great so I cant imagine anything being bent. I really dint want to tear down the whole engine if it is not necessary. What do you all think? I was on a cross country race so I wasn't revving the motor just using the lower rpm range. :)

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Were you racing TCCRA at Pittsburg by chance. You would have heard the piston hit the valve. Pull out the tensioner, you may just have broken the tensioner spring. If so you can set it manually using your old tensioner.

HTH

Ian :)

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Why yes I was with TCCRA at pittsburg. Been looking forward to this race for months and I got to ride a few hundred yards. What a disappointment. There was alot of noise coming from the motor. How could you tell the difference between the loose chain and the piston tapping the valve. Although it did sound alot like a loose chain. Also how can you tell if your cam chain is bad. I see you are a firefighter. Where? I am a firefighter/medic in Tyler.

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If the valve touches the piston it will bend it enough so that it won't seal good and starting will be nearly impossible. Thats what mine did when the tensioner failed and the valves played patty cake with the piston. As long as the valves are sealing ok then just fix the tensioner and check/reset the cam timing and you'll be ok. BTW, my piston was ok and is still in use.

There are several ways to fix the tensioner; buy an new OEM, shim you old busted one, or buy a manual cam chain tensioner.

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My experience says that the chain can skip/jump one tooth in one direction and be OK. Symptoms: Hard to start. Seems like a ton of compression.

If it skips/jumps the other direction, the valves WILL play pattycake with the piston and usually this ends up with loud expensive knocking noises. Shut'er down immediately!

If it starts right up, your probably OK with the valves and the noise is the loose cam chain slapping around. A new chain tensioner assy will take care of it. I doubt you even need to replace the chain..........hope this helps :)

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very interesting? on my 2nd lap 045A at pittsburg my 03crf450 started making that same sound. I think cam chain tensioner prob. will open it up tue eve.to see. hope you have good luck with yours.

H616

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My dads 450 recently jumped a tooth (to make a long story short, a metal clip got stuck in one of the gears). The bike was absolutely unstartable even though it was just off one tooth on the ehaust side.

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Had the same thing happen to my 05 CRF 450R. Was out riding and one of my buddies wrecked, so I slid up to him and killed the bike. When I went to start the bike it was very hard to start( lots of compression). Finally got it started and was heading back to the truck when the motor started making a very high pitched metal on metal sound. To make a long story short after ripping the motor apart I found that the timing was off and that the cam chain had failed. Piston and valves were fine. Oh yeah when putting the motor back together remember to tighten all the bolts. I forgot to tighten one of the cam bolts and it backed itself out and through the valve cover. Had to tear the motor back apart to clean all the shavings out. Im getting pretty damn good at tearing the motor apart.

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I skipped four teeth in a whoops section on my 04, the intake valves hit the piston, it lost a lot of power, It wouldn't rev all the way up in 3rd gear. I should have shut it down, but the checkered flag was only 200 yds away, so I shifted into 2nd and pinned it. The intake valves hitting the piston at high rpms make a very bad sound. I pushed the bike back to the pit, and after cooling off for a few minutes, I started the bike to determine what all the racket was, and it started on the first kick. Upon tear down I was surprised at how little damage occurred. The piston was scarred from hitting the intake vales, but the valves weren't damaged. I did put in a new head w/ stock valves, a new piston, timing chain, and tensioner.

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