Have any of you guys ever swapped out your automatic cam chain tensioners with a manual one? If so, how do you know when you have reached the correct amount of tension? I read about an 06 yz250f that blew up because the engine was downshifted at high rpm and the automatic tensioner failed letting the valves come in contact with the piston. I was told that that if there was a manual tensioer on the bike this wouldn't have happened.
Installing a manual cam chain tensioner
- Thread starter JustinC
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Yes, if the spring loaded oem tensioner fails, it can be a mess. However, I can't say I've ever heard of one failing. If you are checking your valves on a regular basis, I think it would be easy to tell if the tensioner felt like it was getting ready to fail, or wasn't working properly. It should have a distinct slam when you turn it to release the load.
Now, a spring loaded tensioner provides a progressive loading on the chain. In other words, as the chain loosens from wear, the spring loaded tensioner will compensate and move in with the chains loosening and progressively apply tension on the timing chain.
The hard stop type of tensioner can only be adjusted to one setting. And when you run it in to place a bit of tension on a new chain, it will not move from that point. And even if the chain grows a bit from wear, it will simply get sloppy on the cam and crank sprockets, and will see less and less tension as it grows, as the tensioner is not moving in with it.
If you mount up a hard stop type tensioner, be certain that you check it often and keep a good tension on the chain. Not super tight, but taught.
I wouldn't trust myself with the damage that can occur from just a slight bit of neglect of the hard stop tensioner. I like the progressive tension the oem apparatus provides, and since the anecdotes of them failing seems to be few..or void...I opt to use the stock part.
Now, a spring loaded tensioner provides a progressive loading on the chain. In other words, as the chain loosens from wear, the spring loaded tensioner will compensate and move in with the chains loosening and progressively apply tension on the timing chain.
The hard stop type of tensioner can only be adjusted to one setting. And when you run it in to place a bit of tension on a new chain, it will not move from that point. And even if the chain grows a bit from wear, it will simply get sloppy on the cam and crank sprockets, and will see less and less tension as it grows, as the tensioner is not moving in with it.
If you mount up a hard stop type tensioner, be certain that you check it often and keep a good tension on the chain. Not super tight, but taught.
I wouldn't trust myself with the damage that can occur from just a slight bit of neglect of the hard stop tensioner. I like the progressive tension the oem apparatus provides, and since the anecdotes of them failing seems to be few..or void...I opt to use the stock part.
Jaybird said:
They fail all the time Jay. On the CRFs we recommend people change the cam chain tensioner every season especially on 2022 & 2003 450 models. The 2004 and newer tensioner is a better design but I'd still toss it after a season of hard riding to play safe. There is something about the single cam setup that really seems to excite the cam chain.
Early model Yamaha YZF450s tensioners are prone to failure, but the later versions seem much better. YZF250s seem to hold up pretty well but replacement every few years (along with the valve springs) is a good idea. Guys who don't change the cam chain every season on their YZF250s seem to have the most problems with tensioners. Probably because the cam chain starts the kink when it wears.
I've never seen tensioner failure on the YZF400 & 426 engines but after a few years it's cheap insurance to change it anyway.
RMZ450s have a manual tensioner stock that needs to be adjusted in the first few hours of running and checked about every 10 hours or so after that. Guys who don't rev them hard don't seem to have issues after the initial early hours adjustment. As for the RMZ/KXF 250 and it's much heralded valvetrain :rotfl: well lets just leave it at :bang:
As for going to a manual tensioner on an engine that had an automatic tensioner to start with. I'm afraid you are blazing your own trail here my friend. Good luck with that. For the record, if you downshift ANY current four-stroke near redline and mechanically drive it past the rev limiter long enough and hard enough with the back wheel you are going to hurt the valve train, I don't care what kind of cam chain tensioner you are running. Nothing can be foolproof because fools are far to ingenious. ;)
The short history of what I've seen with cam chain tensioners. :cool:
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- #4
Thank you for the responses guys. Rich I know that you post over at Thumpertalk.com sometimes, do you know who Kelstr is? I belive he is an engine builder from the Phoenix AZ area. There is a thread that is going about a guy who said his son's 06 yz250f blew up on hard deceleraton, Kelstr responded and said he had one of his own personal 06 yz250f's blow from the same thing and belives it was the cam chain tensioner that failed. He said his bike was completely stock, but he usually always installs manual tensioners and recommends them. I am not trying to start trouble or anything here, he seems like a pretty knowledable guy, I have heard a lot of good things about him at gomxracing.com. The who reason I asked this question is because I am probably going to buy a 06 yz250f and was kind of paranoid that's all.
All I can tell you is it can be VERY difficult to determine the EXACT cause of an engine failure after the fact, but it is fairly easy to speculate. Even those of us who have been looking at broken parts for a very long time are regularly fooled by the exact causes of a problem. If the 2006 YZF250s have cam chain tensioner issues it's something new and from my vantage point (whatever that is worth) not too wide spread . That doesn't mean there can't be an issue or that Kelstr is wrong in his diagnosis, but the previous years did not have a history of tensioner failure so I would personally want more facts before condeming the current tensioner design.
crazy4nitro
Member
- Aug 31, 2005
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steve125 said:
Great quote from Rich..... :ohmy:
Crazy
Ga426owner
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- May 10, 2001
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I am a advocate of replacing the CCT at the time of a new top end - for $30.00 it is cheap insurance....I have yet to see or have one fail on any of my 400/426 or 450 yamis...I would not replace for a manual CCT...as more maintenance is not what I want...