Valve Length?

[blue giant]

I'm in the process of rebuilding my engine and have dicovered a bent exhaust valve. No big deal I have a spare head. So I pull one of the exhaust valves from the head, clean it up on the wire wheel, insert into the head and give it a quick lapping. All is good, reassemble the valve with the spring and clips. Install the bucket old shim and exhaust cam to check the clearance.

WTF? This valve stem appears shorter then the original. I check it and it is!

Now what? Is there different valve lengths for different years? I did a search but turned up nothing.

At this point I'm ready to push this thing off a cliff. I'm sure I could be driving a new bike for what I've spent on this thing!

Thanks,
Paul

[79XS11F]

They are different part numbers at Bike Bandit
Rob

[blue giant]

They are different part numbers at Bike Bandit
Rob

Rob the numbers are the same on the Yamaha site except for the first 3 digits which as I understand dictates year.

I'm confused!

[79XS11F]

Is the valve fully seated in the head? How much shorter is it?
I really only know the 78 and 79 models but would have guessed that the valves were the same in length across all models. Perhaps the thing to do is use the entire head with its matched valves if it will go with the pistons that you have on their way.
So a bent valve. That's the Compression issue answered and the lack of performance you noticed in Vermont.
Option is to send a quick note of to Andres and see if he has any valves. You only need the one?
Rob

[blue giant]

Yes, Just one. My engine is an 1980 btw. The valve I pulled from the spare head does not have the Yamaha symbol on the face.

Paul

[blue giant]

Rob, it's about an 1/8th of inch shorter. More than a valve shim can correct!

[79XS11F]

According to Yamaha's site 1978 & 79 are the same part number starting with 1J7 and 1980 & 81 are the same but start with 3H5. I am pretty sure that there was a valve size change in there somewhere but not sure when.
The head you were given is an 80 as well isn't it?
Maybe pull another valve out of it. Perhaps some one was messing with it and did use some wrong parts in the past.
Rob

[79XS11F]

Rob, it's about an 1/8th of inch shorter. More than a valve shim can correct!

an 1/8! That can't be right. Try another one from that head unless some one can confirm that they are different.

Rob

[blue giant]

According to Yamaha's site 1978 & 79 are the same part number starting with 1J7 and 1980 & 81 are the same but start with 3H5. I am pretty sure that there was a valve size change in there somewhere but not sure when.
The head you were given is an 80 as well isn't it?
Maybe pull another valve out of it. Perhaps some one was messing with it and did use some wrong parts in the past.
Rob

I was sure the head was off an 80 as the cam number start with 3h5. That head also was a valve bender so It was just for parts. I did try a second valve as well, still shorter.

[blue giant]

I'll bet Prom knows!

[79XS11F]

Is there any chance that the head on your bike is not an 80 to match your engine. It did come off a blown up engine right? The pistons I gave you were 1978 and if valves were changed in 80 they shouldn't have worked with the 78 pistons. I seem to remember that somewhere along the way the valves were changed in size to be bigger then the earlier models but I don't know about length. Of course there are also some cam changes along the was as well so if the cams have higher lift the valves might have to be shorter to some degree.
Rob

[TopCatGr58]

Hey Giant,

The 78-79 valves were 31mm and 36mm diameter, the 80-81 valves are 32 and 38mm diameter.

The prefix on the part #'s isn't just a year thing, it's an indication of a CHANGE made in a part, otherwise they would use the same prefix in the later year engine, like the tranny gears ie!

I can't find any specs on the actual length of the valves, just the clearances, guide, stem thickness, etc.!

Hopefully this can help you verify what size valves you have and what year/ head you have on that 80 engine!?
T.C.

[Big Daddy Funk]

Seen it before

I ran into a length problem like this also and ended up getting an aftermarket valve. If I remember correctly there was a change for the 80 model year and the valves were not interchangeable. I have some exhaust valves here. If you measure yours and I have a match you can have it. Rick

[tw1980]

Hey giant I went out and measured an extra I have out of my 80.3 11/16 inches long.I replaced my valves last year when I rebuilt engine.PM me if you want one.Terry

[81xsproject]

Big Daddy Funk, where'd you get the "aftermarket valve?" I wasn't aware that anyone sold them.