45 hours, 2 bent exhaust valves..... replace or complete stainless rebuild


11 replies to this topic
  • lftdjeep426

Posted August 25, 2009 - 06:28 PM

#1

Well...... this 07' has been giving me problems to put it mildly. I had a bad wiring harness...... which led me to take the top end apart looking for a potential problem. I put a new piston in and buttoned it back up. Ran great, raced a motocross grandprix, rode one weekend and a valve stuck. Just pulled the head tonight and one exhaust valve is all the way down and more than likely bent, the other exhaust valve is 1/2 the way out and probably also bent since neither of them will seat. I'm a intermediate class rider so I don't need Uber performance..... should I just replace the two exhaust valves with titanium at $140/valve or spend $425 on a Kibblewhite Stainless rebuild kit? I will have to get the valve seats cut (what the kit says to do). I have no ideahow much this will cost. I really want to do the work myself to help with costs but I have never done this before. I have good mechanical skills but I don't know what all this involves.

What would you guys recommend? Should I take this on? Are there any special tools I will need? Will I have to lap these valves in and what exactly does that entail? Am I giving up any reliability by just replacing the bad valves?

Sorry for the million questions, I just got a big paycut at work and don't have the cash to just pay someone 2 grand to do a full valve job; however, I don't want to try to do this myself and end up costing myself more in the longrun.

:)

I know I'm not the first one that this has happened to nor will I be te last. But I can't say it enough, I came back to Blue to get away from the problems and look at where I'm at. It just kills me when I do all of the maintenance.... 3 hours on an oil change, clean air filter every ride, keep bearings greased, ect... and I have friends that treat their bikes like you know what and they run forever with no problems......:ride:

I need some comfort......:lol:

  • 642MX

Posted August 25, 2009 - 07:57 PM

#2

If it was my bike, I would replace all the valves with SS and have this guy (http://www.mxtime.com) do it.

  • lftdjeep426

Posted August 26, 2009 - 04:11 AM

#3

When I pulled it apart, there seemed to be an excessive amount of debris on the top of the middle of the piston, on the middle of the head and in the exhaust port. I have no idea what this would be from but it wouldn't surprise me if that is what jammed the valves. A piece of that crap getting into one of the guides maybe? What would all this sediment be? It didn't seem to be metallic at all; however, when I pulled the head the carbon build-up on the original piston was MUCH less and it had 45 hours on it. This piston maybe has 5 if that. I did run 110 octane during that race to keep the engine cool since it was a fresh top end with about an hour and a half of break in. Think that could have caused the excess build-up?

  • KJ790

Posted August 26, 2009 - 04:37 AM

#4

You can get OEM exhaust valves for $79.88 from Yamaha of Troy, and I'm sure they can be found cheaper. Honda East Toledo also sells complete valve kits with all 5 OEM valves and springs for $308.47. You will need to buy the retainers and keepers, but they are only a couple dollars.

Typically when all of the exhaust (or intake) valves are bent it means they contacted the piston due to incorrect timing. It is possible that your cam jumped timing and your valves hit the piston. I would replace the cam chain and tensioner to be safe.

  • lftdjeep426

Posted August 26, 2009 - 04:42 AM

#5

I don't think it jumped time because when I pulled the valve cover I checked to make sure that at TDC the index marks were lined up with the top of the head on the cams. They were all lined up properly and the lobes on the cam were in the right positions (to the naked eye) so I don't think it spun the cam gear on the shaft. I really think that some of all that debris might have got in the exhaust guides on exit and locked them up. Does this seem possible?

  • 08YZ450Derek

Posted August 26, 2009 - 05:07 AM

#6

Why would you use 110 octane race gas when Yamaha recommends running 91 octane pump gas? Maybe that caused your engine problems?

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • lftdjeep426

Posted August 26, 2009 - 09:36 AM

#7

I wasn't aware that Yamaha didn't want you running race gas. Again I know it runs cooler and it was supposed to be close to 100 degrees that day and I knew I would be riding it hard on the race so I thought I was doing the engine a favor by letting it run cooler temps.

Do you think that the higher octane could have led to the excess debris in the chamber? Could it be that i kicked it over a number of times with the valves wedged open. This debris concerns me. :ride:

  • clutchless

Posted August 26, 2009 - 09:56 AM

#8

i always thought higher octane gas ran hotter and burned cleaner.

Most racers run a mix of premium pump and U4 mixed 50/50.

unless you have a ton of work done to your engine you shouldn't need it at all.

  • grayracer513

Posted August 26, 2009 - 10:17 AM

#9

I wasn't aware that Yamaha didn't want you running race gas. Again I know it runs cooler and it was supposed to be close to 100 degrees that day and I knew I would be riding it hard on the race so I thought I was doing the engine a favor by letting it run cooler temps.

Do you think that the higher octane could have led to the excess debris in the chamber? Could it be that i kicked it over a number of times with the valves wedged open. This debris concerns me. :ride:

Let's straighten this out a little. The octane number of a fuel is a rating of the fuel's resistance to being ignited by heat and pressure, or any other source of ignition other than a spark or a flame. That tells you how resistant it is to detonation, and how high a compression ratio it can be used with, and that's all. It has nothing whatsoever to do with the burn temperature, burn rate, flash point, volatility, energy content, or any other characteristic of the fuel at all. The idea that high octane fuels burn cooler is is completely false. Some do, and some don't, and in either case, it has nothing to do with octane number at all.

Was the debris carbon? Was the bike burning oil?

  • lftdjeep426

Posted August 27, 2009 - 10:15 AM

#10

I think I might have found the cause of the problem but not the root. I believe the debris to be dirt/sand. Here in Florida everything is sand but I haven't figured out how it got in the engine. I'm always VERY careful about my air filter (cleaning, oiling and new grease ring after every ride). All I can think of is that the air box boot wasn't on good enough, which I doubt because it is a PAIN IN THE BUT to get on so I am always very conscious to it being completely on before I tighten the ring. Are these bikes known for the "sucking" of sand through vent hoses?

  • cowboyona426

Posted August 27, 2009 - 10:21 AM

#11

I think I might have found the cause of the problem but not the root. I believe the debris to be dirt/sand. Here in Florida everything is sand but I haven't figured out how it got in the engine. I'm always VERY careful about my air filter (cleaning, oiling and new grease ring after every ride). All I can think of is that the air box boot wasn't on good enough, which I doubt because it is a PAIN IN THE BUT to get on so I am always very conscious to it being completely on before I tighten the ring. Are these bikes known for the "sucking" of sand through vent hoses?

Some have had issues with sand getting sucked up the vent hose and into the head, yes. Yamaha sells a kit to re-route the vent hose into the fresh air side of the airbox, or you could just run the hose into the airbox and put a small PCV breather on the end like many here have done.

  • grayracer513

Posted August 27, 2009 - 11:00 AM

#12

It is possible under certain circumstances to draw sand up the breather, but whether it did or didn't it could not have gotten from there into the combustion chamber. Look at the joint of the air boot to the air box.

Also, if it's sand, I think you've found out why you have seized/bent valves in only 45 hours. :ride:





Related Content

 
x

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.