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good day, having some timing chain issues. first off the bike is a 2015 yz 450f with about 40 hours on it. a guy brought me the bike with a damaged head, cam and a broken valve. the head was beyond repair so I found him a head off of a 2014 yz 450f (exact same part number) put the bike back together and it ran flawless for about 10 hours. he went for a ride and shut it down and the bike would kick over. so he brought it over and I pulled the valve cover off and noticed the intake came had spun out of time 180 degrees. after resetting the timing I put the chain tensioner back in and the chain was a little loose so I tightened it up a little more with a screw driver and put it back together and the bike ran flawless again. after 3 start ups the bike did the same thing again so I pulled the valve cover off again and the intake came had spun on the chain 180 degrees again. the chain had come slightly lose again. reset the timing again, put the chain tensioner in again and had to manually tighten it more with a screw driver again. bike now turns over and runs again. I suspect the chain tensioner is toast. could it be the chain has stretched beyond the limit of the tensioner with 40 hours? looking for some insight before we start to order parts as the closest part store is 1200 km away. there doesn't appear to be any damage on the piston or the valves after an inspection. any input would be greatly appreciated. thanks

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The gear(on one) or gears (on both) of your cams are are spinning. THATS how you're losing time

Either buy new cams

Or press off, retime, press on gears, and spot weld them.

Its easier and more professional to buy new cams. Just not cheaper.

Theres no way you spin 180 out of time. Thats even a lot for a gear to spin. But the only other reason would point to tensioner. So START by buying a brand new cam chain, and a new cam chain tensioner. And take your cams to someone who knows their ish. Ask them if they think gear has spun. Cause it would only take me a quick glance and I'd see.

Or post pics of the cam facing the gears as if it was "in time"

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i looked at the cams and compared them to another set I have and they do not appear to be spinning. I thought the same thing when I pulled it apart as I have seen cams do that before. does not seem to be the case on this one. they may not be 180 out but there more than a few teeth. the piston hit the one valve but just while we turned it by hand it didn't sound like it hit while the bike was running but were going to pull the head off to inspect to make sure. its just weird that if you line up all the timing marks the bike runs flawless for awhile then it seems to loosen up and knock the timing out

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7 hours ago, corndogg said:

good day, having some timing chain issues. first off the bike is a 2015 yz 450f with about 40 hours on it. a guy brought me the bike with a damaged head, cam and a broken valve. the head was beyond repair so I found him a head off of a 2014 yz 450f (exact same part number) put the bike back together and it ran flawless for about 10 hours. he went for a ride and shut it down and the bike would kick over. so he brought it over and I pulled the valve cover off and noticed the intake came had spun out of time 180 degrees. after resetting the timing I put the chain tensioner back in and the chain was a little loose so I tightened it up a little more with a screw driver and put it back together and the bike ran flawless again. after 3 start ups the bike did the same thing again so I pulled the valve cover off again and the intake came had spun on the chain 180 degrees again. the chain had come slightly lose again. reset the timing again, put the chain tensioner in again and had to manually tighten it more with a screw driver again. bike now turns over and runs again. I suspect the chain tensioner is toast. could it be the chain has stretched beyond the limit of the tensioner with 40 hours? looking for some insight before we start to order parts as the closest part store is 1200 km away. there doesn't appear to be any damage on the piston or the valves after an inspection. any input would be greatly appreciated. thanks

The first thing I would have been looking for is spun gears too (Like NotE),  but I can't believe it would run good after just aligning the timing marks again.  Call me a chicken,  but even if I found that it was a bad tensioner that chain is getting replaced too.  Run it through the test measurements that yamaha perscribes at the very least would be my suggestion.

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i couldn't believe it either. I told the guy to buy a lotto ticket because it looks like there was no internal damage. going to rip the head off this weekend to verify but everything seems to be working smooth with no noises it just looses chain tension after a bit and knocks the time back out. it was the original chain from the bike when the head swap was done yes it only had maybe 30 hours on it tops

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I bet nothing's wrong with your chain. Buy a new one. Cheap investment then youll have a new one. And compare lengths new vs old chain. This is an obvious observation. If its longer there's your issue. If its the same size. Then I'd look into buying a complete, brand new, tensioner assembly. Worth $80. If you're absolutely certain your timing marks/lobes are good, then replace tensioner if not chain as well. 180 is really far out of time. Were talking one or two teeth. 180 degrees is like ten teeth. How has your piston not mashed your valves? You says it did hand rotating...Id do a leak down test with new chain/tensioner in.

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Sounds like a possible faulty tensioner? kinda hard to believe but never know, You've gotten lucky no further damage id say :ride: definitely get new one and chain maybe then try again :thumbsup:

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48 minutes ago, Motox367 said:

Sounds like a possible faulty tensioner? kinda hard to believe but never know, You've gotten lucky no further damage id say :ride: definitely get new one and chain maybe then try again :thumbsup:

if its all good lucky is an understatement. like I said when we reset the timing the bike runs flawless has lots of bark. I have never seen this situation before, going to work on his bike again this week and try a few things out but a new tensioner is a definite. going to pop the head off still and check it out for him he does have extra valves. when the bike ran there was no piston slap sound or valve noise. both times it was running great then shut down with the kill switch and would not kick over after being shut down. there was almost a whooshing noise of the chain turning on the gear heard on the second shut down then It was seized but not tell after the killswitch was killed.. loosened the chain tensioner and the cam cover rotated the cam reset the time and all was good bike would run perfect again. my mind is bottled lol

Edited by corndogg
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3 minutes ago, corndogg said:

if its all good lucky is an understatement. like I said when we reset the timing the bike runs flawless has lots of bark. I have never seen this situation before, going to work on his bike again this week and try a few things out but a new tensioner is a definite. going to pop the head off still and check it out for him he does have extra valves. when the bike ran there was no piston slap sound or valve noise. both times it was running great then shut down with the kill switch and would not kick over after being shut down. there was almost a whooshing noise of the chain turning on the gear heard on the second shut down then It was seized but not tell after the killswitch was killed.. loosened the chain tensioner and the cam cover rotated the cam reset the time and all was good bike would run perfect again. my mind is bottled lol

Hope mine never does that lol where's gray when you need him 

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Just now, Motox367 said:

Hope mine never does that lol where's gray when you need him 

I have been waiting for him to chime in lol

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If you know what your valve clearances were before,  one that "grew" clearance will tell you if your have a bent valve.   I find pressuring up the combustion chamber with with about 15 lbs of air on a 4 stroke and listening and spraying soapy water tells me a lot.   If I don't have any references to what the rig was doing on a leakdown test before,  it is actually handier. 

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21 minutes ago, ossagp said:

If you know what your valve clearances were before,  one that "grew" clearance will tell you if your have a bent valve.   I find pressuring up the combustion chamber with with about 15 lbs of air on a 4 stroke and listening and spraying soapy water tells me a lot.   If I don't have any references to what the rig was doing on a leakdown test before,  it is actually handier. 

I was tought at school long ago to lay head upside down .fill combustion chamber with wd40 if didn't leak thier good lol those were mostly old two value engines or xt,xr type 4 valves. Oh you mean with engine still together my bad

Edited by Motox367

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1 minute ago, Motox367 said:

I was tought at school long ago to lay head upside down .fill combustion chamber with wd40 if didn't leak thier good lol those were mostly old two value engines or xt,xr type 4 valves

taught the same way. once we get a chance to look it over again I will let you guys know what we come up with. thanks for all the feedback guys.

 

23 minutes ago, ossagp said:

If you know what your valve clearances were before,  one that "grew" clearance will tell you if your have a bent valve.   I find pressuring up the combustion chamber with with about 15 lbs of air on a 4 stroke and listening and spraying soapy water tells me a lot.   If I don't have any references to what the rig was doing on a leakdown test before,  it is actually handier. 

never thought of the clearances growing for the bent valve that's a good idea thanks

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4 hours ago, Motox367 said:

Hope mine never does that lol where's gray when you need him 

As it happens, "Gray" is up to his receding hairline with getting his house on the market, taking days off the job to deal with contractors, agents, house cleaners and appliance repair "proffesionals" :rolleyes: , then trying to get a week's work done in two days.  That's where he is.

The two things that lead to a cam chain skipping most often are a chain that has any stiff links:

1) The chain must be absolutely free of friction when oiled, and you should be able to drag it over a pencil and have it follow that tight a curve without a fuss. 

2) A weak tensioner.  Most people misunderstand how these work.  They don't actually put the tension on the chain, they just take out all the slack.  The crank pulls on the front cam, which pulls on the rear cam, and then the run of chain going up from the crank to the rear cam has no load on it. The spring in the tensioner then turns a screw gear that forces a plunger forward against the tensioner shoe and gets rid of the slack so the chain will track onto the rear cam correctly.  If the spring is weak, or the screw gear won't turn smoothly and freely, it can't do its job.  They aren't very expensive, either, so I'd replace the thing if there was any question.

3) I know, I said two.  This one doesn't come up very often: High lift or long duration race cams and heavier than stock valve springs can go beyond the tensioner's abilities to hold things together, but even then, the stock auto tensioner usually works OK.

 

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16 minutes ago, grayracer513 said:

As it happens, "Gray" is up to his receding hairline with getting his house on the market, taking days off the job to deal with contractors, agents, house cleaners and appliance repair "proffesionals" :rolleyes: , then trying to get a week's work done in two days.  That's where he is.

The two things that lead to a cam chain skipping most often are a chain that has any stiff links:

1) The chain must be absolutely free of friction when oiled, and you should be able to drag it over a pencil and have it follow that tight a curve without a fuss. 

2) A weak tensioner.  Most people misunderstand how these work.  They don't actually put the tension on the chain, they just take out all the slack.  The crank pulls on the front cam, which pulls on the rear cam, and then the run of chain going up from the crank to the rear cam has no load on it. The spring in the tensioner then turns a screw gear that forces a plunger forward against the tensioner shoe and gets rid of the slack so the chain will track onto the rear cam correctly.  If the spring is weak, or the screw gear won't turn smoothly and freely, it can't do its job.  They aren't very expensive, either, so I'd replace the thing if there was any question.

3) I know, I said two.  This one doesn't come up very often: High lift or long duration race cams and heavier than stock valve springs can go beyond the tensioner's abilities to hold things together, but even then, the stock auto tensioner usually works OK.

 

Dam contractors :ride: lol 

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They're cheap insurance/maintenance items, anyway.  Last time I bought one of either,they were $22 for the chain and $34 for the tensioner.  Considering the amount of grief either one will cause if it fails.....

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15 hours ago, grayracer513 said:

They're cheap insurance/maintenance items, anyway.  Last time I bought one of either,they were $22 for the chain and $34 for the tensioner.  Considering the amount of grief either one will cause if it fails.....

thank you. going to start by changing out his chain tensioner the chain does not appear to have any stiff links or stretched as the timing marks almost line up bang on when reset. also im going to recheck the torque on the cam covers to make sure they are not putting to much resistance on the cam causing it to bind up. thanks for the input fella's cheers

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Cam cap torque on the 5 valve heads was CRITICAL.  I haven't heard of any trouble with the four valve heads in that regard yet, but there's no sense in pushing one's luck.  Always seat the caps by hand or by gentle tapping with a plastic or wood tool handle or mallet. Never draw them down with the bolts.  Be sure the threads are clean, and tighten them in the specified sequence in 3 or four steps, that is, tighten all to 35 in/lb, then 55, then finish them.

I notice an interesting difference in the torque spec for these and the 5 valve head.  Industry standard practice is that unless the manual specifically calls for the threads to be lubed, sealed, or whatever, the assumption is that the torque spec is for clean, dry threads.  On the 5 valve, the manual specified oiling the threads, and now on the 4 valve they don't.  I mention this because lubing the threads will result in roughly 20-25% more clamping force applied by the bolt when run down to any given level of torque, and I always felt that 87 inch pounds (7.2 ft/lb) was too much for the cam caps, just going by feel.  I used 75 in/lb on all of my YZF's and never had a problem.  That would be about equal, in terms of clamping force, to what you would get from clean dry threads. 

What I'm getting to is that you should either be sure the threads are clean and reasonably dry, or approach the torque limit with some caution.

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