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Still getting nowhere posting pics, lol.

I took the head to a shop today and the machinist pulled out the bad valve. The valve of course is toast but the seat looks ok. He said I might be able to get away with just replacing the valve, cleaning and checking/surfacing the head. He didn't have tools small enough to cut the valves and the seats, but I don't think I need to do that if a new valve will seal in that old seat.

Any thoughts?
No, absolutely not. The seat has to be matched to the new valve, seat width must be correct and seating area must be correct on the valve seating area.
Get it done right.
 

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That seat doesn't look bad at all. That head looks surprisingly sooty. I wonder if a small piece didn't get wedged under the valve causing a slight leak that turned catastrophic. Valve heads are softer than the seats and can burn like that rather quickly.
 

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I've seen a small bit of carbon get stuck under a valve. But it was on an old low reving, carb fed car and it was running on three. I think modern engines are much less prone to this.
 

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Doubt we'll ever know...can't the valve be lapped to the existing seat?...assuming the new valve angle is cut to the same angle as the burned one.
 

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Doubt we'll ever know...can't the valve be lapped to the existing seat?...assuming the new valve angle is cut to the same angle as the burned one.
Back in the day, we hand cut valve seats to a 45 degree angle, then did two cuts at 30 and 60 degrees using engineers blue to ensure the seat was the correct width and in the correct position on the valve face. Valve seats can recess in the head over time. You could possibly do that with grinding paste, but generally we didn't have a week to spare for a valve job. I'm surprised a cyl head specialist doesn't have cutters of the right size.
 

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I think you will find out pretty quickly if you can just lap in a new valve or if the valve seat needs to be re-cut.
After cleaning out the carbon and inspecting for obvious pits and holes, do a light lap with fine paste. The hand tool is perfect for this, as long as you can get one the right size. If you get a nice continuous thin line on the seat, you are good to go.

Sometimes it takes a bit of lapping to get the line and it may put a groove on the valve. If you have a valve re-facer, you should do that before doing one last fine lap. (or buy another valve - depending on cost of re-facer). Don't leave a sharp edge on the valve, it will just start burning again.

If you have to re-cut the seat I'm not sure how far down you can go, but you will need to find a shop that has small cutters - some bike shops have them, but do they know how to use them??? Been there.
 

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Discussion Starter · #47 ·
I found another head shop that specializes in motorcycles and I am going to drop the head off on Monday morning. They quoted me about $180 plus any parts that are needed. Hopefully I won't need more than just 1 exhaust valve.
 

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Discussion Starter · #48 ·
Well, I dropped the head off this morning, and got a call a few hours later. The head was disassembled and I was told that I could probably get away with a new exhaust valve and stem seal. The machinist also said that he has never seen exhaust valve seats that were so poorly machined from the factory. They are so bad that I am going to stop by tomorrow morning so he can show me. He said that it wasn't from wear, it was from poor factory machine work.

We spoke about cutting the seats, but then the concern will be getting the valve adjustment correct when I go to reassemble.

More updates tomorrow!
 

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Sorry but I do hope yours was just a glitch...seems the Japs may be going down the same route the Britsh took back in the 70's...poetic really
 

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I found another head shop that specializes in motorcycles and I am going to drop the head off on Monday morning. They quoted me about $180 plus any parts that are needed. Hopefully I won't need more than just 1 exhaust valve.
"Head shop" meant something entirely different to me back in my formative years...

Good luck!

[On the Internet no one knows you're a dog]
 

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Discussion Starter · #51 ·
I have pics, but I'm not smart enough to post them, lol.

I went and looked at the disassembled head this morning. The machinist pointed out the issue. The valve seats on the exhaust side are cut so inaccurately it is crazy. It looks like the seat cutter went in at an angle and cut the seats all crooked. All of the intake valves and seats are fine, but every exhaust seat has an issue.

He is going to try and cut the seats, but he warned me that he may not be able to fix the original problem.

I would love to have another head disassembled to see if this is a fluke or an actual problem with the whole engine line. It very well could explain why almost everyone has tight exhaust valve lash specs before the factory recommended checks.
 

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Pics would be good. I can't imagine how an engine with 4 non concentric valve seats could run. I'm not sure how factories cut seats today, but they always used to use a spigot in the valve guide to centre the cutter.
 
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Just to the left of the video film strip icon is a box icon - should be able to put a jpg in with that - lets try a snippit :)
Text Font Logo Brand

Not the most friendly but it does seem to work.

Hearing that the seat cuts are missaligned is bad news. That means their tooling for doing the machining is junk or they were trapping machining chips on the pilot surfaces or... etc etc
It means we are all riding on luck.
It means they cut too many corners and have poor inspection processes or the people doing that job are being distracted with their cell phones instead of focusing on the job and doing it right.
Just not a good situation, specially when you add in cracking clutch housings

Had to fix my '01 Bonneville which developed low cylinder pressure on one side. Found the seats suffered from machine chatter, which left the seats slightly rippled. Took a lot of lapping to fix that.
 

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Or... it could just be an example of "shit happens", a one in a million mistake that makes it through inspection.

[On the Internet no one knows you're a dog]
 

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Considering the rarity of actual valve problems, I'm not going to lose sleep over this.
 
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I would be contacting Yamaha direct to see if they can shed any light on this....also if they would at least let you have a new complete head free of charge.
 

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Discussion Starter · #57 ·
I disagree with people complaining of valve problems. I think the average person hasn't put enough miles on this motor to really show it's long term issues. We all know that the exhaust valves go tight on these motors way quicker than they should.

I would never expect Yamaha to do much of anything about this, at least right now. What I would love to do is get another couple of heads torn apart at different mileages to see if this is a common issue. I doubt anyone would be interested in pulling their engines out and removing the head, right?

The good news is that my machine shop guy was able to get the seats cut properly. I am now waiting on a new exhaust valve and valve seal. Once I get those then I can reassemble the head and move on to fixing the transmission!

I will try one more time to post pics. I did try posting through the little icon, but half the time it wouldn't do anything and half the time it said the file size is too large.
 

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In the picture, the exhaust valve is closer yes?? The seat looks really wide on it... the book has a spec of 1.2mm for the nominal width and a limit of 1.8mm on a re-cut. I think they use a measurement using blue marking fluid on a valve pressed onto the seat.
The book also does not show a 3 angle cut on the seat, so if the seat is too wide, it may be possible to add a lower cut (60° included angle) to narrow the seat up. It will depend on if that cutter hits the head somewhere else.
That is a really clean head, nice job getting all the carbon out.
 
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I think we're all forgetting that the OP isn't the first owner. How do we know some butcher hasn't had a go at that head?
 
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