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When it all goes BANG!

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I understand what you're saying, but it's too perfect and clean and doesn't look like typical impact damage to me, IMO. Even if it hit the piston that could have been after the other valve failed which may have then caused a tensioner failure to create the smacks. Sux no matter what, but seeing as it was a recent rebuild on a relatively low-hr motor, my bet is on a lock issue (bad parts, bad install, wrong parts, etc.) or valve stem busted.

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     The install was not long ago at all. And both valves kissed the piston just one more that the other. The other intake valve looks like one of those awesome offset valves. lol. Infact so did the exhaust.

     We know it was the tensioner because of the slapping noise the customer had told me he had herd before the big bang. This was a stainless valve that are very hard to break the head off of, but you can see that the valve head got bent back and forth a few hundred times before the motor stopped. This is like taking a thin peace of metal and bending it over and over again. Soon it will break.  

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Better change al the valves now thatits opened. Don't wanna risk breaking another valve.

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20130909_092836_zpsb2d34b20.jpg

 

Hard to see in the pic but at the bottom of the valve you van see the kiss of death.

 

If the valves were not shimmed exactly the same it would cause one to travel further than the other and thousands make the world of difference when it comes to engine parts crashing.  

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Jeff,

 

I just recently rebuilt the top end on my 09 CRF450R.. new 13:1 wiseco forged piston, new valves, springs, retainers, int/exh port work, stage 1 hotcam, MRD pipe, etc..  

 

What kind of valves do you plan to use on the rebuild.? Let us know when you bring this head back to life and how it runs. 

 

JL

0903131408.jpg

0903131419b.jpg

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Better change al the valves now thatits opened. Don't wanna risk breaking another valve.

 

 

lol... its gonna need more than just valves

:)

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How would it bend one intake, but not the other not be touched at all? I bet the intake head popped off, then a cycle later the exhaust starts to open, broken valve head smashes into the exhaust valve, destroying the chain/tensioner.

 

 

as they stated, ALL the valves were damaged.. after the cct failed. A valve breaking off isn't going to "take out" a cam chain tensioner.

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Its all fixable. 

this is true but a new head can be had for probably the same amount of money, if not less, and its new. Unless of course the ports have been worked on. 

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20130906_103622_zpsd083c807.jpg

This is that happens when you OEM cam chain tensioner gives up in 4th gear. 

 

 

With just 1 or 2 pics its mostly just a guessing game. If that valve stuck or got tight in the guide you could be looking at the same photo and damage, thats one of the reasons not everybody agrees with the tensioner failing as the beginning of all the damage to the head. Was it a new head or did you recondition the old one?

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how would having a valve break cause a tensioner to fail ?  If a valve breaks, and the tensioner is working, it just keeps on spinning the the cam sprocket and camshaft.. if a cct fails, stuff starts hitting that should be.

If the head of a valve breaks off the cam could continue to turn until something else stops it, but the crank/piston will come up against resistance from the broken piece being wedged where it doesnt belong and that would cause the crank/piston to suddenly slow down and stop soon after. The tensioner could easily be damaged, in a way its similar to chopping the throttle at high rpm. The crank speed slows down fast and the timing chain tension is on the back side of the chain loading up the tensioner to much. What do you think, yes, no, maybe?

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If the head of a valve breaks off the cam could continue to turn until something else stops it, but the crank/piston will come up against resistance from the broken piece being wedged where it doesnt belong and that would cause the crank/piston to suddenly slow down and stop soon after. The tensioner could easily be damaged, in a way its similar to chopping the throttle at high rpm. The crank speed slows down fast and the timing chain tension is on the back side of the chain loading up the tensioner to much. What do you think, yes, no, maybe?

 

i think the plastic chain guide flexes as well.. the cam chain isn't in a solid/tight position. the cct pushes against the cc guide, which flexes some. Maybe its' possible a tensioner could break from massive force of busted parts, but i have not heard of or seen that happen. A motor breaks a valve, piston, crank, etc.. or.. an auto tensioner fails and then everything else breaks.

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i think the plastic chain guide flexes as well.. the cam chain isn't in a solid/tight position. the cct pushes against the cc guide, which flexes some. Maybe its' possible a tensioner could break from massive force of busted parts, but i have not heard of or seen that happen. A motor breaks a valve, piston, crank, etc.. or.. an auto tensioner fails and then everything else breaks.

 

Here a link to a good thread about tensioners. The tensioner is supposed to keep the slack out of the chain and a keep a pre determined amount of tension on the chain, its not supposed to back up and when it does theres a problem depending on how the engine is being run. The rear chain guide is plastic bonded to a metal backing, if there was any significant amount of movement or flexing of that guide the plastic would break or become separated from the metal backing plate.

 

http://www.thumpertalk.com/topic/1036007-how-does-a-cam-chain-tensioner-work/

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We know it was a tensioner do to the slapping noise coming form the motor that my customer had told me about. The head was brand new OEM head with all new Bigborethumpers.com Stainless steel valve kit installed. With valves in hand you can see where they all kissed the piston. When the old tensioner was installed that had gone threw 8

+ years of heat cycles The spring did not have the proper tension on the 8+ year old cam chain. This causes the cam timing to move in the danger zone. And yes probably a good throttle chop and BANG. Only going by the word of the customer. But going by our track record on valves we have yet to have one fail without aid.  

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