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Two destroyed exhaust valves [with pics] - replace valves or entire head?

  • Thread starter Thread starter TheDuke
  • Start date Start date
T

TheDuke

Guest
Soooo...went ahead and took the valves out in preparation of some cleaning and lapping and realized that two of the exhaust valves are completely shot. I'm wondering if you all would recommend just buying two new valves or if replacing the head is easier/cheaper. I figure I will have to have the new valves and seats machined, so I'm trying to take that into account when making my decision. Any advice is appreciated.

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First clean the carbon off the combustion chambers then re-post with the new pictures.
 
That has to be the worst burnt valve I have ever seen:eek:
If you get a new head you should have a valve job done anyway IMO. Find a couple used valves and lap them in.
 
As suggested, clean the carbon so we can see what's left.

The seats are remarkably durable, but not impervious, they might have survived.

If you find the seats in decent shape, I think I have a couple of valves that should work.

.
 
The one that Steve had with the glowing red header was pretty bad.
 
Wow those are the worst I have seen in a long time. What was the mileage on the head?

You could be lucky with the seats but it hard to tell without a bit of cleanup, as the others mention. As they are generally harder to wear out, I'd suspect you would just need a couple of valves, however. At worst a couple of seats too but certainly no need to replace the head unless its cracked or otherwise damaged .

Clean her up and let's see.
 
spyug said:
Wow those are the worst I have seen in a long time. What was the mileage on the head?

You could be lucky with the seats but it hard to tell without a bit of cleanup, as the others mention. As they are generally harder to wear out, I'd suspect you would just need a couple of valves, however. At worst a couple of seats too but certainly no need to replace the head unless its cracked or otherwise damaged .

Clean her up and let's see.
Click to expand...

Has nothing to do with miles, has everything to do with valve clearance adjustment.

The seats don't get as hot as the valves. They might be OK.



chef1366 said:
The one that Steve had with the glowing red header was pretty bad.
Click to expand...

This one?

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That kind of $hit pis$es me off. Damn hacks ignoring basic maintenance. Good thing it's just the engine and not the wheels or something. Stupid previous owner would be dead now.
 
Any advice on the best way to clean her up for her second photo shoot?
 
chef1366 said:
The one that Steve had with the glowing red header was pretty bad.
Click to expand...
I was going to post that, then I saw that Tom beat me to it. :D



TheDuke said:
Any advice on the best way to clean her up for her second photo shoot?
Click to expand...
Some of the pros might shuder, but I have used a wire brush in my drill.

Light pressure will take off the carbon, just don't push hard enough to take away any metal. :eek:

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Don't have a picture handy of the head, but here is how the pistons ended up:
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.
 
Ebay is a little light on exhaust valves for the '79 750 at the moment. Anyone have any for sale???
 
TheDuke said:
Ebay is a little light on exhaust valves for the '79 750 at the moment. Anyone have any for sale???
Click to expand...
Did you happen to notice post #4? :-k
Steve said:
If you find the seats in decent shape, I think I have a couple of valves that should work.
Click to expand...
If you are interested, I will go out to the garage and verify.


By the way, you can expand your search a bit, here is a list of other bikes that use the same valve.
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Last edited:
Steve said:
Did you happen to notice post #4? :-k
Click to expand...

Must have skipped past it. I will get her all cleaned up this weekend and post some more photos for collective forum analysis. If valves are all I need we can chat about price. Thanks for the offer.
 
tbh without the cam caps the heads is more hassle than what it's worth... clean up yours and see if it's damaged. buy nothing til then imo
 
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