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Both INTAKE valves are stuck opened

11K views 17 replies 6 participants last post by  paan009 
#1 ·
Both IN. valves are stuck opened in the #2 cylinder.
No contact with the piston, but this definitely explains
why I couldn't get the motor to fire this past summer.
Any ideas and/or suggestions? Since I'm parting the motor,
I just want to know how I can sell the head in this condition.
Is it junk or just a valve keeper gone bad?
 

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#2 · (Edited)
My 2 cents but if the valves are stuck in open position it most probably is bent. They look tweaked at the valve head. This is likely to be a result of piston contact or perhaps dropped valves. Either way, it would require replacing the valves and valve guides. Hopefully someone with more experience will chime in and give you some options.
 
#3 ·
Thanks for the reply: I carefully inspected the #2 piston and didn't see
any marks on it. Never had both valve do this, but I did float 1 valve and it
took out the piston and valve head on an over-rev when I missed a shift!
 
#5 ·
As said above you will need to remove the vales for inspection.
If they are not visibly bent by eye or with a machinist square you will need some tools like this.

A indexing collet punch grinder


and a Height Guage with Dial Indicator attachment


A extremely flat surface will also be needed, A granite inspection table is the best but something level and flat should work.

The Valve will go in the Indexing Holder. Set the height gauge on the valve. and rotate the holder. This will give you a read out on the indicator and you can see if the valve is bent. You will see the dial indicator read from a positive to a negative number back and so on.
Or you will see very little movement on the gauge.
I have no idea what type of tolerance Yamaha has on the Valves but almost all dial indicators read out to .ooo1 of an inch

If you have any Tool and Die or machinist friends that will be the quickest way to get access to those tools.

Hope this help.
 
#9 ·
what about the valve buckets for those 2 valves? Are they cracked? (the things the camshaft lobes hit to push the valve spring/valve downward). IF so, the head is JUNK.
If the valve is just bent, and the bucket easily comes out from on top of the spring, i suspect you can use a spring tool to remove the retainer/keepers, take the spring out, then beat the valve out. From there just replace the valve guide and valve..
 
#11 ·
so not cracked, are they froze in the bore or will they slide out nice and easy with no sign of scuffing or scraping on the sides or in the bore? use a magnet to pull out those individual buckets. remember there are shims underneath.
 
#14 ·
Thanks for the replies. I was finally able to shine a light down the intake runner and saw both valve stems obviously bent in the forward position. Surprised I didn't see nicks or damage to the piston.
 
#15 · (Edited)
as the guys early on in this thread speculated, it is highly likely they DID make contact.. they are out of the way enough that it didn't break the heads off the stems. You are very lucky the valves were in the down position. I had a engine failure recently. Con rod bolt broke. with the rod shoved through the front of the block by the crank, and the piston at TDC. the valves had nowhere to go, and the camshaft lobes cracked the buckets. When the buckets split, it tore up the bore the buckets ride in, and nobody services those, so my ported head was/is junk.

Do you know if you floated the valves with an overrev?? On a high mileage motor, it's possible the springs were not able to close the valve fast enough, the piston made just enough contact to bend the stem, and bingo. Stuck valves. was everything else in tact? cam chain tight, pistons didn't crack, etc.
 
#16 · (Edited)
I bought the bike from a kid this summer that forgot to mention he over-revved the motor and bent valves! Luckily I got it for cheap when I saw that he didn't have a complete bike and parts were missing. No worries on my end. If anyone is interested in a great parts cylinder head, this is it! I have all parts/hardware to boot. PS- I also over-revved a $1000 Mototune epoxied/ported cylinder head on a built motor and snapped the valve and ruined the piston. They're both sitting on top of my toolbox as a reminder NOT to miss a ship or Ka-boom!
 
#17 ·
not difficult to believe that is exactly what happened. I wouldn't be surprised if it was a recent GP shift convert, and he went down a gear thinking he was going up. There is no rev limiter for the rear tire turning the motor.. and ba-ZING. Valve float, and the heads of the valves can touch the pistons. This was a best case in actuality. they didn't break off. Are you sure the camshaft lobes and buckets look good for those two valves? not that I need it, just curious.
 
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