Dropped Valve...... Why........

[Boyko]

So I was roughing in the tuneup on the low buck Attack, had it on a track stand and was getting it in to boost. Lots of stuff to watch, it looked like low 12s on the air fuel and around 12 psi boost at 10,000 rpm which all sound pretty and nice. I fired it up the next day and it ran like crap and had a ticking sound from the top end. Pulled the plugs and did a comp test and # 3 was dead, nothing there.

I just got the head off and it dropped a Ex valve but looks like the valve locked in the gide and did not bang things up to much at all.

I am missing a stem lock....WTF, the shim and the other stem lock were sitting under the lifter cap,

This thing has got 1200 km on it and was wrote off not that being wrote off would cause it to lose a stem lock.

I will look again for the missing part but why would this happen?

Should I just toss a new valve in it and run it? I will take some measurements from the deck to the piston to see if it is crunched up.

Edit..
It has to have 2 stem locks there is no way for the valve to stay in with just one.

 

[Ted Jannetty]

I can only theorise, that some one has been in there forgot to install one, they can't just fall out, there is no where for them to go.

Hopefully the guide is not damaged and you can just replace the valve, valve locks, and shim bucket.

 

[HURRICANE]

I have seen that happen if the valve lash gets to wide.The shim will get bouncing around in there untill it pops out and then it will push the retainer down alowing the keepers to pop out.That is assuming that the other keeper is in the engine some place.Be sure to check all the valve lash when you repair the head

 

[wantboost]

dave what kind of lash are you using on the turbo motors.i remember seeing something about setting it on the high side of the factory spec

 

[HURRICANE]

That's where you want to be with stock cams.The lash is alittle tighter with our turbo cams

 

[Mountaintech]

I would consider yourself lucky.

 

[Boyko]

I would consider yourself lucky.

Ya no kidding, didn't sleep to good last night because of the horseshoe up my butt.

Thanks Dave your sharp like a tack, the thing must have been lashed out fat, if I get time I will try to straighten the valve out on a lathe and measure the lash as it was setup before to try to validate that fault.

Yo Ted I first thought that it was missing a valve lock but it would be very difficult to assemble it that way, so my motor must have ate the lock. I will see if I can fish it out somehow

 

[Mountaintech]

First place I would look is flywheel. Take mag side cover off and remove flywheel. I've found them on the inside f the flywheel stuck to the magnet. You can also get a telescopic magnet into the sump from that side from what I recall.

 

[Boyko]

First place I would look is flywheel. Take mag side cover off and remove flywheel. I've found them on the inside f the flywheel stuck to the magnet. You can also get a telescopic magnet into the sump from that side from what I recall.

That's an Idea , makes sense. What do you mean "I've found them on the inside the flywheel stuck to the magnet" have you had keepers flying off your head to?

How common of a problem is this?

 

[Mountaintech]

My situation was a bit of a fluke......happened years ago so I wouldn't call it a common problem. If I were in your shoes though that is one of the first places I would look.

 

[powderlites]

VALVE KEEPERS

Seen a sled come in our shop with keepers missing and 2 valve shim in bottom pan!
You have to check valve clearances when done before valve cover goes on.

http://www.powderlites

 

[Boyko]

Thanks again for the replies,

So I checked the lash on the bench and all the lash clearances are on the tight side, I know torqueing the head down will effect it. I will loosen up the lash so I can pound the valves into the head with some good old fashion detonation (just kidding but I will loosen them up). I do not think any one has been in this motor before, when I did the cam timing I checked a few lifters and assumed they were all ok. Why does Yamaha keep the lash tight, is it to keep the valvetrain noise down. Don’t the valves settle in and tighten up the lash even more?

 

[mbarryracing]

Loose valve lash = less valve lift... They don't open very far to begin with so the tolerance ends up being a good % of lift?

There is a reason that Yamaha doesn't require a lash check for many many miles, there is very little pound in.

 

[Boyko]

Setting them loose is only about 1/1000 of a inch

I am still concered why this happened is it probable that one valve was lashed loose enough to cause the valve to drop. Did I over rev it and float the valves, I did not hear the rev limter.

 

[mbarryracing]

What is the total lift?