Idiot! Bent valve.

[Ed89]

In that order.

Was trying to remove shim to check thickness.  I thought, hmmm, maybe I turn the crank to compress the valve, then stick in an appropriate allen key between the bucket and the cam to keep it compressed, then turn the crank again to get some room and I can get the shim off!  Brilliant!

Not!!!

Right intake valve now bent.  Not confirmed yet but I am 90% sure.  (1) the valve clearance now goes from less than 0.038mm to 0.56mm (2) there is almost no compression with the finger-to-spark-plug-hole test and (3) there is some blow back on the right carb intake (it suck then the pressure is released, unlike the left one which just suck, damn, I wish it just plain suck only      )

Can I be sure about that if I remove the head to look at the valve?  How hard is it to replace a valve?  Any hint how much that'll run me up DIY?


Cheers,
:guns: e.

[dgyver]

A bent valve is very likely. Really will not be able to tell until the head is off. Does not take much to let the in/ex valves hit.

Valves are around $30. They are actually very easy to replace. You will need a tool to compress the valve spring. A large c-clamp and a piece of pipe with two notches cut in it works for me. If there is not a pic of one in the manual let me know and I will take some pics. The fun part is putting the two valve keepers back in.

[Rema1000]

Brilliant!

Not!!!

Right instake valve now bent. .

I could have sworn that I had read of a similar procedure successfully used by one of the racers here.  Perhaps you inserted the key, and it depressed the "cam follower" (bucket)... but also accidentally pressed on the shim itself?  I can see how that would bend the valve.  If so, then perhaps the Motion Pro tool is a safer bet.

[The Buddha]

That procedure you said is standard for the XJ series yamaha's... BTW why would valve clearance change if the valve is bent... it will be very high but that change ... Also compression test with finger ... did you hold the throttle open when you did that.
Take the carbs off and loook into the intake side and see if you see a bent stem... and turn the motor over by hand and see if the valves open and shut... and look at its stem as it opens... if they all reveal a straight valve... you are fine.
Cool.
Srinath.

[Ed89]

dgyver:

Thanks for the hint.  Clymer talks of a valve compressor, so I suppose that's what it is.  I think there is a pic of the compressor tool on pg 133 (pics 104 and 105, uh, mine's the 89-96 version, so newer/older edition might have it on different pages/pics).  If you can get a pic of the home made pipe-compressor that'll be great.

Rema:

I was over adventurous on that valve.  I used a 8mm allen key that compressed the valve too much.  The other two valves I used the same trick but only with a suitably placed 6mm allen key and those valves were not bent.   :guns:   So, I suppose if anyone wants to try this "brilliant" procedure of mine, don't use an allen key more than 6mm.  Not that it is much of an advice.  :mrgreen:

Srinath:

Well, if the valve is bent, it is prolly not closing fully, which would explain the lack of compression, the carb blow back, and the extra clearance I have.  I did not hold the throttle open for the finger test, although the left (good) cylinder has a hell lot more compression than the right (bad) one.  The bad cylinder has almost zero compression.

I also looked at the carb instake hole and the stem looks straight and it does open and shut when I turn the crank.  But the bent could/must be really slight since it is just making the valve not sit by 0.5mm.  Any more test you can think of I would be happy to do.  Otherwise the head is coming off.  (And I hate that since I have an 89 and I have to do the drop-the-frame-just-a-little trick.  :guns:)

Cheers,
e.

[Blueknyt]

wait wait, rotate crank till cam lobe pushes down on valve, insert tool between cam and edge of bucket reverse rotation on crank enough to move lobe away from shim, remove shim, put in new shim, rotate cam back releaseing tool recheck clearence.......  sounds about right with most shim over bucket valves.   did you continue to rotate crank so the opposite valve opens on same cyl while the tool was still in?  there is room for valve to be open with piston at top dead center, so unless its a highlift cam, or supper shaved head or domed high compression pistons, the only way to bend a valve is with its corrisponding valve in same cyl. that being the case your likly to have 2 bent valves.     check your gaps again, pull the exhaust pipe and carbs off,  shine a light into sparkplug hole, if a valve is bent you will see light from intake or exhaust port all the time.

[The Buddha]

Yea the light trick or I was going to suggest the reverse compression tester trick... AKA poor mans leak down at TDC compression stroke connect the compression tester spark plug unit to the suspect cylinder but dont connect the guage... then blow into it...
Cool.
Srinath.

[Kerry]

there is room for valve to be open with piston at top dead center

Really?  I always thought that one of the reasons to be VERY careful about getting the camchain on right was so that you wouldn't bend a valve (because it was down when the piston came up).  But I suppose the valve could get bent because of another thing you said:

the only way to bend a valve is with its corrisponding valve in same cyl.

Your thoughts Blueknyt (or anybody)?  Do you know of any info sources that will back up the first statement above?  I guess I could try Clymer and Haynes....


Meanwhile, I've been re-studying the animation on this HowStuffWorks page.  I realize that the valve actuation shown is a bit different from the GS's OHC configuration.  But if you ignore everything above the manifolds it's pretty accurate, yes?

Now, Blueknyt's explanation below makes sense to me, and it sounds a lot like something I read from Bob Broussard long ago.

rotate crank till cam lobe pushes down on valve, insert tool between cam and edge of bucket reverse rotation on crank enough to move lobe away from shim, remove shim, put in new shim, rotate cam back releaseing tool recheck clearence.......  sounds about right with most shim over bucket valves.

Here's my question:  IF we're unsure about the piston-to-valve clearance at top dead center, would it add an extra measure of safety to rotate the crank FORWARD after inserting the shim tool for INTAKE valves, and BACKWARD after inserting the tool for EXHAUST valves?

[Ed89]

Blueknyt:

I just did the light check on the intake valve, and... light!  
I am going to do the exhaust valve after dinner.  And if I see light, it is YOUR fault.  :mrgreen:

But it could be what you said--both valve screwing each other up.  I did not reverse the crank to remove the tool since clymer says to rotate it clockwise.   :guns:  Clymer.  

Thanks for the tip.  I guess now I am more sure.  It remains to be seen if it is just one or two valves.  But first, food.

Srinath:

I have no compression tester other than my finger.  And my face is a little too big to fit onto the plug hole directly. :mrgreen:  But since I have at least one bent valve, I guess the head is coming off anyway.  That's the halloween "trick" for me.


Cheers,
e.

[Ed89]

OK.  Good news for the night.  Exhaust valve seems OK--i.e., no light.

Head's coming off now, and then it's to the suzi dealer for a new valve.


Cheers,
e.

Edit:

Blueknyt:

Looks like you are right.  Got the head off and the intake valve is slightly off center, atmost 0.5 mm.  And the way it is off center looks as if it might have been pushed by the exhaust valve.  If it had been pushed by the cylinder instead, it would probably be off center in the opposite direction.  The valves are awfully close to each other.  The good news is that the exhaust valve looks good--centered and passes the light test.  Maybe the intake valve was really sticking out when it got pushed by the exhaust valve, thus the contact point could have been close to the center of the exhaust valve.

I wish I could stick out the intake valve again and push it in the opposite direction to straighten it.  It looks so doable.  Bummer.


Thanks for everyone's help!  You guys rock!    

[Ed89]

dgyver:

I think I know what you meant by the slot in the pipe now--it is to access the keepers.  I think I can manage that.

Cheers and thanks!

e.

[Rema1000]

Here's my question:  IF we're unsure about the piston-to-valve clearance at top dead center, would it add an extra measure of safety to rotate the crank FORWARD after inserting the shim tool for INTAKE valves, and BACKWARD after inserting the tool for EXHAUST valves?

I think I follow you, Kerry; and there's another reason that might be good:  the rhythm of the valves opening should be "exhaust, intake, (pause...), exhaust, intake, (pause...)".  During the pauses, both valves should be closed, so keeping the intake open longer (or opening the exhaust early) should be safe from either the piston crown or the opposing valve (if I'm seeing this correctly).

When changing the intake shim, you would hold the intake open late by:
-rotate crank until cam lobe depresses the bucket
-insert tool
-rotate crank forward slightly until you can get the shim out (intake open late)
-swap shim
-rotate crank backwards slightly until you can get the tool out

For exhaust, it would be the opposite:
-rotate crank until the cam lobe depresses the bucket
-insert tool
-rotate crank backwards until you can get the shim out (exhaust open early)
-swap shim
-rotate crank forwards until you can get the tool out

(NOTE: this is just a theory... don't run out and try this until someone knowledgable comments on it)

Ed, can you clarify which shim you were replacing when the intake valve got bent?  And you mentioned that you moved the crank "forwards"... is that "forwards, then swap shim, then backwards", or is that "forwards, then swap shim, then forwards some more"?

[Ed89]

It is my intake valve that is bent.  Of course, I had no idea that I bent it until I had a hard time starting and idling the engine.  So I can't say for sure at which stage I messed up.  My guess is that I bent the intake valve while keeping the said valve open.  I _always_ rotated forward (clockwise), and that valve is the only one I tried the 8mm allen key on.  Come to think of it, I never did the exhaust valve on that side (right side) because it was up to spec.

I also did take out both shims on the left side, but only using 6mm allen key and there doesn't seem to be any damage to those valves.  I also only rotated the crank forward for those two valves.  Here's my procedure for all the shims (left IN and EX, right IN) I removed:
- rotate forward/clockwise to depress valve
- insert allen key
- rotate forward/clockwise
- remove shim
- measure shim and reinsert shim
- rotate forward/clockwise
- remove allen key

Cheers,
e.

[Blueknyt]

piston comes up pushing spent gases out the open exhaust valve, the Exhaust valve begins its closure few degrees BTDC At TDC both Exhaust and Intake valves are half open (this is called overlap) ATDC the exhaust valve is closed and intake is fully open for the pistons travel down.

mind you this only takes about 30 degrees rotation of the crank, give or take a few. if you pull one came out and lock the other where one valve is open, you can spin the crank all day long and it wont hit the valve. the problem comes in where the valves hit eachother when opening.

if he left the tool in  then rotated leaving the valve open, the other cam would open the oposite valve and they would hit, the valve already open would bend as the one opening would push straight..

[Kerry]

Thanks all - this is some great info.

I plan to take some photos and/or measurements that compare the purpose-made shim tool with a 6mm Allen key and an 8mm Allen key.  It sounds like the 6mm is OK to use, and the 8mm is too thick.  I'd just like to know where the spine of the shim tool fits in the thickness scale....

If I understand correctly, you inserted the Allen key so that the 2 "legs" contacted the underside of the camshaft, and the bottom of the "V" (the 90-degree bend in the key) pushed down on the bucket.  Right?  So I'll need to guess the diameter of the camshaft and allow for the open space between it and the bend in the Allen key.

[Rema1000]

I _always_ rotated forward (clockwise)

This meant that the valve you pressed-in was open through an entire cycle of the opposing valve.  That should normally guarantee bent valves, but I guess the 6mm key was just holding the other valves 1/2 open, and you managed to not bend the other valves.

It sounds like there are a few options:
1) use the MP tool

or

2) prop the valve open with a tool, and:
(2b)turn the crank forwards-then-backwards (intake) or backwards-then-forwards (exhaust) to get the shim out (note: do NOT turn the crank through a full revolution with the tool in place)
(2c)use a thin tool to depress the bucket, like a 6mm hex key, which is thin enough to (probably) avoid valve-valve interference

You could combine 2b and 2c, just to be on the safe side; reverse direction, AND use a thin tool.

[Ed89]

Yep.  Rotating forward always would guarantee a bent valve if the valve sticks out far enough.  So I was lucky with the other valves not stickout far enough to come in contact with each other.

I agree with Rema:

(IN valve):
- rotate forward (cam lobe down) + insert tool
- rotate forward (60 degree cam lobe) + replace shim
- rotate backward (cam lobe down) + remove tool

(OUT valve):
- rotate backward (cam lobe down) + insert tool
- rotate backward (cam lobe 60 degree) + replace shim
- rotate foraward (cam lobe down) + remove tool

Explanations:
(a) The first step can always be forward or backward, I just tried to make it easier to remember.
(b) For every 90 degree rotation of the cam lobe, it correspond to BDC->TDC (or TDC to BDC).
IN valve: cam lobe down (roughly TDC)
EX valve: cam lobe down (roughly BDC)
(c) For IN valve, we can safely rotate 120 degrees forward after inserting tool, but for uniformity, I put down 60 degrees (which looks like it would be easy to eye-ball from a wrenching point of view).

In any case, I think it is most likely that the piston will not come into contact with the EX valve.  IN valve, maybe, but I doubt that as well.

$0.02 from the guy that bent his valve.  Use this info at your own risk. :mrgreen:

Cheers,
e.