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Discussion Starter #1
Any guesses as to what caused this?



I swapped in a JE 11.5:1 stock bore piston (shown) and a 2002 CRF 450R cam.

The valve on the left broke loose and caused the damage. Both sides were hitting the piston.
 

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yeah the timing was off....did you get the timing chain a couple of teeth off maybe.

Did it run at all, or is that just from kicking it over? Juding by the carbon build up, I would say it ran for a short time....now thats what does not make since..

Unless your timing chain fell off while you were riding....maybe thats the answer.
 

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Discussion Starter #3
It ran at St. Anthony Idaho (hard sand dune riding) for two days before this happened. Probably about 5-6 hours in the sand, plus about 1 hour of easy break-in at my house before the trip.

We checked the timing pretty carefully, and are pretty sure that it was correct. The timing chain was still on the sprockets when we took it apart. No visible damage to the sprockets or chain. Tensioner still working.

My impression of the bike after the install was:
- Harder to start.
- Loss of bottom end power
- About equal top end power (maybe a bit more)

Has anyone else used a '02 CRF cam?

Jon
 

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I wouldn't have recommended a CRF cam in the first place! The reason for the loss in bottom end is that a bike weighs a good 100lbs lighter and doesn't need as much bottom end as a quad. A bike only has one tire approx 2-3 inches of tire hitting the ground whereas a quad has two with each one having approx 8-9 inches of tire hitting the ground. You def want to go with the HRC or Curtis Sparks cams. Hopefully you didn't do too much other damage!
 

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Discussion Starter #5
I was told the '02 CRF cam is almost exaclty the same as the HRC cam. The thing that I was thinking is the CRF piston has a different strokeand with the CRF cam in a TRX, the vavles could hit the piston. Bad theory?
 

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the only thing I can think of that would cause that is....like I said a broken/fallin off timing chain....or it was slightly out of time to begin with....

because you were able to drive it for so long, I think the valves where hitting the piston the whole time....and it finally took its toll....

The one thing I know from building Honda engines is that they have the specs about as close as you can get them before there is contact like that....If that timing is off a little to much....you find this issue....I generally like to think that you would have to be a tooth off or something to do that much damage but who knows.

Or maybe it was just simply the wrong combination of parts....the CRF cam lobes are just a tad to high. So that is throwing your valves even closer to the piston....and say that piston is just a tad taller then the stock one...there your even closer again.....you can take it from there...but thats all I can think of that could cause that problem...someone else may have better answers.
 

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Discussion Starter #7
Knowing what I know now, I would never have gone with a CRF cam (even if it didn't cause this problem). And I wouldn't recommend a HRC cam is it is truly that close to the CRF cam that I was running.

The valve busted up the head, but we are hoping to change the valve seats, clean it up and be OK without having to get a new head. Since I am having the head worked on, I was thinking about having a bit of porting done and maybe doing an angled valve (3-5 angles?) job. Thoughts?
 

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Your time tensioner could have let loose. I had the same thing happen to my 400ex but it was a 180 degrees off and it took 2 days for it to blow up. Good luck to you man and I am very sorry this had to happen to you. That really sucks!
 

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That almost looks like my EX piston when i was finished with mine.... just mine was a lot worse....... :D

I had an over-rev and my exhaust valves both just seared of compleatly and my piston and head both looked like someone took a claw hammer to it......

Pretty wild... i will try to get pics of it up.....

Good luck with your stuff man......
 

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I have been riding for 20 years and the set up I have now is totally awesome.
CrowleyOffroad, The hotcam is great, in my opinion the way to go! My carb gave me low end and the cam gives me mid and top end and the pipe helps all the way around. I wouldn't change a thing that I did. If you need any help let me know. Glad to help! :D
 

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When this happen to my 400ex, my whole engine was destoryed. I had a huge hole in my piston not to mention the valves were totally destroyed. Also, there was nothing left of my head. Had to buy a new head. It was the worst I have ever seen. My engine basically granatited like a bomb.
 

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was the piston a CRF or a TRX piston? even though the engine is very similar, i believe they are different. if so that would have made a huge difference
 

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Did you notice any abnormal valve noise after rebuilding the engine?

Would have been a ticking like valves were slightly out of adjustment.

My guess is that you didn't have enough piston to valve clearance with that setup - it's a good idea to clay the piston to valve clearance when swapping parts like this.

With the valves lightly rubbing the piston, it would have likely lasted a little while - and probably broke at a high RPM point - possibly when the valves floated or maybe just when that one valve had enough stress that it finally gave up.

CRF cam -- I haven't measured the cams myself, but I've been told by a top engine builder to not use the CRF cams - the TRX engine needs more low lift duration than the CRF cams provide because of the differences in flow characteristics of the head (TRX has smaller ports). I was also told that the CRF cams are pretty different than the HRC - may not appear that way if you look at basic lift and duration specs, but are very different when you look at the actual lobe profile. He also went on to say that it's very likely you would actually lose power with a CRF cam.

180 degrees out --- It is not possible to set the cam in a 400ex or a 450R 180 degrees out. In fact, it is not even possible to determine what would be 180 out on one of these engines. 90 degrees out is a possibility & would cause immediate and serious problems.

Trying to keep from replacing the head --- price a new cylinder head before putting any time and parts into your old one, with the price of a TRX cylinder head being as low as it is, you machine bill will quickly become greater than the price of a new head.
 

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Discussion Starter #15
Originally posted by 86atc250r@Jul 1 2004, 11:36 AM
Did you notice any abnormal valve noise after rebuilding the engine?

Would have been a ticking like valves were slightly out of adjustment.

My guess is that you didn't have enough piston to valve clearance with that setup - it's a good idea to clay the piston to valve clearance when swapping parts like this.

With the valves lightly rubbing the piston, it would have likely lasted a little while - and probably broke at a high RPM point  - possibly when the valves floated or maybe just when that one valve had enough stress that it finally gave up.

CRF cam -- I haven't measured the cams myself, but I've been told by a top engine builder to not use the CRF cams - the TRX engine needs more low lift duration than the CRF cams provide because of the differences in flow characteristics of the head (TRX has smaller ports).  I was also told that the CRF cams are pretty different than the HRC - may not appear that way if you look at basic lift and duration specs, but are very different when you look at the actual lobe profile.  He also went on to say that it's very likely you would actually lose power with a CRF cam.

180 degrees out --- It is not possible to set the cam in a 400ex or a 450R 180 degrees out. In fact, it is not even possible to determine what would be 180 out on one of these engines.  90 degrees out is a possibility & would cause immediate and serious problems.

Trying to keep from replacing the head --- price a new cylinder head before putting any time and parts into your old one, with the price of a TRX cylinder head being as low as it is, you machine bill will quickly become greater than the price of a new head.
I noticed a light ticking noise......

I'll check on the price of a new head. Thanks for the heads up.

Jon
 

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Just looked it up (price from servicehonda)

It appears they raised the price a little from last time I looked, but it's still reasonable

12200-HP1-670
$201.75
 

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Why does 86atc250r know so much? The differences in cam compatibility comes from the longer stroke on the trx motor. The dwell, or how long a piston lingers near top dead center, is a function of crank pin offset (stroke) and the length of the rod. When you change either it changes the geometry that changes dwell near TDC. A little bit of modeling clay can save a LOT of money! Next time you assemble with a different cam put a little clay lump in the pistons valve pockets, oil the valve faces , and assemble enough to turn the engine over by hand (don't kick it) . After rotating, disassemble and check the clay thickness in the valve pockets - anything less than .060" can cause you a very sharp pain in your wallet! All that being said, my SWAG puts your timing at 1 tooth advanced pre-catastrophe.
.............mixxer
 

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Discussion Starter #18
Originally posted by mixxer@Jul 5 2004, 09:23 PM
Why does 86atc250r know so much?  The differences in cam compatibility comes from the longer stroke on the trx motor. The dwell, or how long a piston lingers near top dead center, is a function of crank pin offset(stroke) and the length of the rod. when you change either it changes the geometry that changes dwell near TDC.A little bit of modeling clay can save a LOT of money! Next time you assemble with a different cam put a little clay lump in the pistons valve pockets, oil the valve faces , and assemble enough to turn the engine over by hand (don't kick it) . After rotating, disassemble and check the clay thickness in the valve pockets - anything less than .060" can cause you a very sharp pain in your wallet! All that being said, my SWAG puts your timing at 1 tooth advanced pre-catastrophe.
.............mixxer
mixxer,

If I was one tooth advanced, what would I have felt power-wise?

Jon
 

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Actually, advancing a cam usually gives you more low end. Without a baseline run at straight up timing there would be no reference to gauge power shift from. The increase in timing from the stock cam would have caused more low end loss than your mild compression increase could have compensated for.....mixxer
 
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