HEADS UP!!!

Site upgrade in progress... Core site functions are working, but some non-critical features/functions will be temporarily unavailable while we work to restore them over the next couple of weeks.

Please post any bugs you encounter, but before you do, check to see if it's already listed.

Thanks for your patience while we work to improve the community.

Sign in to follow this  
Followers 0
rporter44

2008 YZ 450 F Motor Failure

27 posts in this topic

I am new to this forum so please be paitent with me>>>>

Here is my question. I am a X full time motorcycle mechanic. I come from the old School days of Motorcross being 2 strokes.

I have a good friend of mine that brought me a Motor from a 2008 YZ 450 F that he reported just died and when it did it actually blew out the part of the valve cover gasket that covers the cam shafts. I pulled the head and it was not a pretty sight. All valves bent or broke one of them actually stuck in the head. I do know for a fact that all the service work has been done due to I did it all. I dont want to order all the parts until I find some kind of reason for the failure. From what I can tell it broke one of the valves at the retainers and the rest was history. Is this a comon problem with the YZ??? If so this is very sad. and others should beware.

Thanks for reading and any responces

Share this post


Link to post
Share on other sites

I would agree, but all the timing marks were in line when I pulled it apart. Thanks for your input.

Share this post


Link to post
Share on other sites
but all the timing marks were in line when I pulled it apart.

Then explain the contact between the valves and piston unless the rod is broken.

I'm not buying.

10:1 the cam chain is full of tight links.

Share this post


Link to post
Share on other sites
Is this a common problem with the YZ??? If so this is very sad. and others should beware.

Not to sound like a jerk but you're insinuating that the public needs to know that YZFs are unreliable machines. I'm not buying that either. :thumbsup:

If it was the timing chain - how many hours were logged on it prior to its failure?

Share this post


Link to post
Share on other sites

However, any four stroke does have the potential for this. As stated the cam chain is a strong suspect. How many hours where on it, how often was the oil changed etc? This is one of the battle cries for the 2 stroke.

Share this post


Link to post
Share on other sites

I'd say YZ's ARE reliable motors, however (after reviewing many posts on the topic) it seems that some '08's had timing chain problems (like Gray said, prone to kinking.)

I bought my '08 used, and replaced it's original chain as a precaution. The original had some tight links/minor kinks in it.

Share this post


Link to post
Share on other sites

I have no proof of anything, but my personal experience with cam chains kinking up in '06-'08 models is this:

  • No one using my maintenance schedule and oil recommendations has had a problem with this.
  • Everyone I personally know who has had this problem was using some other oil, and/or changing at a longer interval.

Not truly enough to draw a sound conclusion from, but it does make me suspicious...

For reasons unknown, the '08 was particularly susceptible. Probably a vendor related issue with the chains.

Share this post


Link to post
Share on other sites

Thanks for all the responces. I am not questioning any body experiences or knowledge. I am simply asking if this is an issue before I go and spend a large amount of money on the machine with out some kind of warm fuzzy feeling of the cause. I am in no way shape or form saying that the Yamaha is a bad product or that they are unreliable. With that being said. After a little more investigation I have come up with the reason for the failure and it doesn't indicate that it was a Yamaha issue at all nor was it a Maintenance issue either. More a a freak of nature.

Thanks

Share this post


Link to post
Share on other sites

Well it sounds like it dropped a valve. You said one was broken at the retainer.....My buddy's neighbor had that happen to his 07' YFZ450. It dropped a valve into the cylinder....smashed the piston, head and nuked the rest of the valves. And the top section of the valve that broke gouged the exhaust cam. I think he was about 1500.00 for parts....including a new (used) head.

Share this post


Link to post
Share on other sites

I have an '08 and im going to do a top end rebuild this winter. What chain should i use? A 2009 chain?

Share this post


Link to post
Share on other sites
  • No one using my maintenance schedule and oil recommendations has had a problem with this.

can you briefly elaborate please?

Share this post


Link to post
Share on other sites
can you briefly elaborate please?

Sure. Bear in mind that the statement you quoted is scientifically considered an "interesting observation", and could be pure coincidence, but nevertheless:

http://www.thumpertalk.com/forum/showthread.php?p=2685432#post2685432

My specific oil of choice is Amsoil MCF.

The problem could also be simply a bad run of chains. The thing that makes me doubt that is that Japanese manufacturing is set up altogether differently than it is in the US. GM and Ford work on the idea that it's cheaper to buy things in big lots at today's prices, so it doesn't surprise me to see a defective part turn up and persist in the system for a year or two. Japan, in general, doesn't have the space available to pile up a lot of inventory, so they order things in smaller batches as they are actually needed. Given that, I find it somewhat incongruous that a problem that shows up from '06 through '09 would be related to that. Then again, cam chains are small and easily stored. Hard to say.

To me, the logical candidates are:

  1. Maintenance, as stated.
  2. Bad run of chains
  3. Basic specification of the the chain called for by the design is not adequate (I think this unlikely)
  4. The timing chain does not oil as well as it should (making item one more important)

That last item, I think, finds some footing in the fact that this was not a problem the occurred with as great a regularity in the first generation YZ450's, or any previous model. The tensioner was also changed in some unspecified way in '06, and could be a contributor.

Share this post


Link to post
Share on other sites
Then explain the contact between the valves and piston unless the rod is broken.

I'm not buying.

10:1 the cam chain is full of tight links.

I was told by a dealer and a mechanic that the piston wont touch the valves on that particular engine if it jumps time.

Mechanic had fast kid who crashed so hard said it jumped 4 teeth and no damage was done and thats how he found out.

Anybody know for certain if theres any truth to this?

Share this post


Link to post
Share on other sites
Mechanic had fast kid who crashed so hard said it jumped 4 teeth and no damage was done and thats how he found out.

hmmm a crash caused the timing to jump four teeth??...no expert here, but I think he was stretching the truth a bit...well a lot..

Share this post


Link to post
Share on other sites
I was told by a dealer and a mechanic that the piston wont touch the valves on that particular engine if it jumps time.

Mechanic had fast kid who crashed so hard said it jumped 4 teeth and no damage was done and thats how he found out.

Anybody know for certain if theres any truth to this?

None. Or some. It depends on how far which cam jumps which way. They will definitely hit.
hmmm a crash caused the timing to jump four teeth??...no expert here, but I think he was stretching the truth a bit...well a lot..
I think he's making things up to explain the coincidence. It would be more likely that the bike jumped time and that lead to the crash.

Share this post


Link to post
Share on other sites
Mechanic had fast kid who crashed so hard said it jumped 4 teeth and no damage was done and thats how he found out.

:banana: My BS meter just exploded.

1 person likes this

Share this post


Link to post
Share on other sites

Since we are on the subject and I have never left an engine alone or had a bike long enough to have a chain failure but what is a good interval for chain replacement? I use MCF and change oil usually around 8 hrs sometimes less. Would a 100hrs be pushing it? I plan on full teardown at this time for preventive maintenance.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0