[mehrab101]

Hey guys. Recently bought a 02 CRF450R that needs a rebuild because it dropped a valve. There's obvious damage on the piston so that's going to go. I was looking at the head and wondering if the head can be machined and saved. I think the valve dropped and then kick back into its port.

[JimDirt]

Welcome to the site !!

Ken would be the real one to answer that question , as he does them all the time (the owner of the site).... BUT .... from what it looks like in the picture , the dents should not cause a issue , as they are not going to affect anything but maybe a slight turbulence disruption of flow , but what I see is the lip of the valve guide is bent from the impact , so at the very least the guide would have to be replaced , which is usually done with a full head job anyway ....so with that I think the head is salvageable ....

However , when a valve hits a piston ,you will need to replace the crank ... 99% of the time when a valve hits a piston , it damages the rod bearing from the impact and lockup , it puts a flat spot on the actual bearings themselves , so what will happen is you will end up with a rod knock , not to mention if the rod was bent during the sudden lockup , and failure down the road is inevitable if you don't replace the crank as well ... it is most likely going to be that the first time you fire it up , it will have a knock .... I have seen it a dozen times , when people don't want to replace the crank after a catastrophe like that , then you end up tearing down the entire engine after the top end was put together , because you did not replace the crank/rod in the first place ...

[mehrab101]

Welcome to the site !!

Ken would be the real one to answer that question , as he does them all the time (the owner of the site).... BUT .... from what it looks like in the picture , the dents should not cause a issue , as they are not going to affect anything but maybe a slight turbulence disruption of flow , but what I see is the lip of the valve guide is bent from the impact , so at the very least the guide would have to be replaced , which is usually done with a full head job anyway ....so with that I think the head is salvageable ....

However , when a valve hits a piston ,you will need to replace the crank ... 99% of the time when a valve hits a piston , it damages the rod bearing from the impact and lockup , it puts a flat spot on the actual bearings themselves , so what will happen is you will end up with a rod knock , not to mention if the rod was bent during the sudden lockup , and failure down the road is inevitable if you don't replace the crank as well ... it is most likely going to be that the first time you fire it up , it will have a knock .... I have seen it a dozen times , when people don't want to replace the crank after a catastrophe like that , then you end up tearing down the entire engine after the top end was put together , because you did not replace the crank/rod in the first place ...

Thank you so much for that input. I've been looking into fully redoing the bottom end but I was hesitant because the previous owner has receipts that he got it redone in February. Nonetheless, I think I'll have to do it. Is there anyway to check for damage without taking the case apart?

[JimDirt]

You might be able to try wobbling the rod side to side , and up/down to see if there is movement , but sometimes you can't really tell till compression is on it , and that is what takes it out ..

There will be some side to side movement , it should say in your manual what the allowance is

And regardless of what WAS done , what matters is after the valve issue , its like saying , "my tires were new before I ran over that nail" , the nail is what damaged the tire , just as the valve cutting loose is what did this damage ..

But overall the 02 is a great bike , I had mine from 2008 , till just last November when I got my 20 ... so I went from a 02 to a 20