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Discussion Starter · #1 ·
Hey guys, looking for some direction here.
I went to replace my clutch plates tonight and when I removed the cover I found these massive chunks of rubber with some metal shavings in the bottom of my motor. Then I noticed my cam chain guide and tensioner look pretty worn. Also not sure if this link should look like it does in the photo. Is it safe to assume these are from a worn out chain guide and tensioner?
My machine is a 2004 400ex.
Thanks!
 

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The engine needs rebuilt. The damage is from a worn out cam chain and the chain is dangerously close to breaking (it's already broke on one side, it simply has not broken on the other side) - that chain was due for replacement years ago.

I have seen similar damage in "PERFORMANCE" engines that had a CRF450R cam chain installed - some monkey determined that a CRF cam chain was a performance "modification" because it was cheaper than a TRX400 cam chain. Not only is it cheaper, it is wider and lighter and wears out faster. The CRF chain is lighter and wider as the plates are thinner and the pins are smaller diameter. The CRF chain is intended to be replaced more often as it is a 'cost of racing'. The CRF engine is rebuilt every 30 hours of racing as routine maintenance.

Since it is wider than the TRX chain, it drifts side to side on the cam and crank sprockets, cuts the flange off the guides and will contact the side of the cylinder head, cylinder and engine case depositing glitter sized particles of aluminum in the oil to be distributed throughout the engine. Most will be caught in the oil filter, but there is a quantity of particles that will be distributed by splash and collect in non turbulent oil areas of the engine.

Another cause of the damage you are examining is caused by improper cam chain tensioner pusher installation or an improperly adjusted manual cam chain tensioner.

I hate to say it, but if that were my engine I would scrap the quad and just get a newer one that parts may be available for. Nothing older than 2012.
 

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Discussion Starter · #4 ·
The engine needs rebuilt. The damage is from a worn out cam chain and the chain is dangerously close to breaking (it's already broke on one side, it simply has not broken on the other side) - that chain was due for replacement years ago.

I have seen similar damage in "PERFORMANCE" engines that had a CRF450R cam chain installed - some monkey determined that a CRF cam chain was a performance "modification" because it was cheaper than a TRX400 cam chain. Not only is it cheaper, it is wider and lighter and wears out faster. The CRF chain is lighter and wider as the plates are thinner and the pins are smaller diameter. The CRF chain is intended to be replaced more often as it is a 'cost of racing'. The CRF engine is rebuilt every 30 hours of racing as routine maintenance.

Since it is wider than the TRX chain, it drifts side to side on the cam and crank sprockets, cuts the flange off the guides and will contact the side of the cylinder head, cylinder and engine case depositing glitter sized particles of aluminum in the oil to be distributed throughout the engine. Most will be caught in the oil filter, but there is a quantity of particles that will be distributed by splash and collect in non turbulent oil areas of the engine.

Another cause of the damage you are examining is caused by improper cam chain tensioner pusher installation or an improperly adjusted manual cam chain tensioner.

I hate to say it, but if that were my engine I would scrap the quad and just get a newer one that parts may be available for. Nothing older than 2012.
Alright so finally got an update. I decided to go against your advice. Not because I don't think you know what you're talking about but because I couldn't admit to my wife I made a bad purchase.
So I tore down the top end. Valves looked a little crusty but sealed up good. Cam and journals looked ok. Cylinder, piston, and rings all looked good.
Took off the clutch and replaced the cam chain, guide, and tensioner. Put it all back together and it runs fantastic compared to before.
It took me like two months just doing this on weekends and discovering different tools and stuff and having to wait until I could aquire them but I finally have a functional trx400 again!
 

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I've had this exact issue. That guide can break up and leave long stranded chunks in your motor. Luckily it didn't damage much in my case. Just new used guides, new can chain and new uses tensioner. Probably should just buy a new tensioner in my case but I'm cheap.
 
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