Power Valve Removal

[cdn280]

After 100hrs of flawless running my 2006 300 did an odd thing. While running the road at a good clip the exhaust note suddenly changed and the next thing you know the engine is locked up and the back wheel is skidding. In with the clutch and pulled over expecting it had seized, but found neutral and it kicked over fine with normal compression, but when it started it was rattling like a SOB. Sounded like a piece of metal rattling inside the expansion chamber. DNF for the first time.
During the teardown I'm expecting to find a broken clutch tab, piece missing from the piston, or something obvious.... nothing. In fact, the clutch, cylinder and piston all looked in great shape for approx 100hrs use.
What I did find was something possibly odd with the power valve. When you hold the flapper stationary, you can grab the lever plate (the part that the actuator rod attaches to) and move it about 15-20degrees without too much effort. Should this not be one rigid piece ???
I would think thats whats causing the rattle, but I still don't see any indication of where anything hit together to cause it to lock up. (no marks on the piston or flapper)
I'm trying to remove the whole pv assembly now and I've pushed out the one rod that is under the allan bolts that hold down the bearings, but I can't pull out the stupid pv assembly on the right side. Any tricks to get it out ? or any idea what could have happened ?

 

[iancp5]

Have you pulled the piston out to check?

That really does sound like a seizure and yes they often do start again and the compression "feels" the same at the kickstarter. I have had exactly this happen to mine. I had it jetted lean to stay clean in tight woods (which I forgot about) but one day was riding down the road at about 50 mph and the symptoms were just like yours. The moment I stopped it was locked up but it kicked free and started. Although there was no rattle on mine but hey anything could've happened. I rode it back no problem at about 20 mph but as soon as I pushed it on a bit it would nip up again. On disassembly it had clearly seized.

 

[cdn280]

Have you pulled the piston out to check?

Yep. Piston, rings, wrist pin and bearing are fine. The cyl still has a fine cross hatch everywhere with no scrapes and only a few very fine normal looking scratches that you can't even feel with a finger nail.

 

[widebear]

Sounds like a crank main gone south.

 

[cdn280]

Sounds like a crank main gone south.

Don't think so, it spins without any rumbling or roughness.
There was a change in exhaust for about a min or so before it locked up, which leads me to believe that its something with this sloppy power valve. Can someone confirm something for me ?? If you hold the powervalve flapper stationary in the exhaust port, should you be able to move the lever plate at all ? There is a 15-20 degree movement there, and I can't seem to pull the assembly out of the right side. Any tricks to get it out? I have the pivot rod out (the one behind the allan bolts), but I can't pull out the assembly on the right side (step 9 in the instructions posted by MattR)

 

[GMP]

cdn,

That sounds about right to me (the play, not your problem). The flapper has a slot at an angle, and the rod between the two drums rides in this and forces it up and down. There isn't a whole lot to go wrong. There will be some slop even between the two drum valves. The flap should not be able to hit the piston and did not in your case.

To remore the right side drum, thread an M5 bolt back in the drum and pull it out with vise grips. Most come out easy, if its stubborn warm the area with a propane torch (carefully).

I have an idea. Have you removed the primary cover yet? If the PV linkage came loose, either the setscrew on the belcrank, lower end of the rod, or the entire mechanism from the case, the PV would just float and be under no force, that would explain the change in tone. It would also explain the rattle on restart. Now, if something is loose in there, it could have caused a lockup. Just a thought, not a normal issue by any means, but worth checking out. This is an interesting one.

 

[cdn280]

Update... I found a very good priced 250 top end from another inmate (thanks Rick !) so I figured I could accomplish a few things with it:
1- try a 250 for a while
2- have a spare in case I ever did pooch a cylinder/piston
3- see if the powervalve is the issue.
Well I mounted up the 250 top end in late fall and although it fired right up, and the same rattle was still there. So the loose pv in the 300 cylinder is still a mystery, and the bike has been in hiding since I had a foot operation shortly after that, then the cold fall was excellent for trials riding and recouperating the foot well into Nov. Winter then kicked in and I've only just got back to working on it. I've stripped the cases to find that Widebear was right.... the right side crank (ball) bearing is in real bad shape, very rough and a bit pitted. The left side roller seems better, but its seal had some gook in it that appeared to be silt/mud from the water. I think the oil passage to the bearing must have been plugged with the crap causing the bearing to get oil starved and destroy itself. New crank bearings are ordered and also the bearing behind the clutch (a 6205 bearing) which is obviously unrelated but it also is on the rough side. I happened to have another new quality NTN 6205 bearing kicking around that I had for either a wheel bearing or an idler wheel for a snowmobile, and it doesn't seem much smoother. I cleaned them both out and blew out with compressed air but it just doesn't seem to be a very smooth running bearing. The new one is slightly better but are they supposed to be that loose rolling and rattley? The other bearing on that side is a similar sized 6203 and it plus all the other little bearings in the case seem much smoother, so I'm looking for an alternative.

3 lessons learned ...
- will now take a different route no matter what to avoid waist deep water
- don't shut off the motor to walk the bike during a deep water crossing
- once spooge starts coming out of the header/cylinder junction get new O rings (probably where the water got in)
Will report again once its all freshened up.

edit: GMP - the linkage and actuator are all fine. The problem is that I can hold the flapper steady and still be able to move lever arm several degrees. The 250 pv is rock solid with no movement. I'll get that 300 pv out some day to find its problem.