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Old 05-15-2006, 07:13 PM   #1
datchew OP
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how do I know if i have a burnt valve

What are signs of a burnt valve?

When i took off the cover, one "chamber" is clean as a whistle (the back one...intake) and the exhaust is...well, charred kinda. Like a little soot in there.

The pushrod-rocker arm gap was pretty good, no major adjustments.
Just wondering.

thx.
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Old 05-15-2006, 08:39 PM   #2
R-dubb
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Not a problem. Just like comparing inside a carburetor to inside an exhaust pipe. One clean, the other dirty. Signs of a burned valve will be ragged edges and low compression readings, out of balance running on a twin, hard starting (or more likely no starting) on a single. Very unlikey based on what you describe.

R-dubb screwed with this post 05-15-2006 at 08:49 PM
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Old 05-15-2006, 08:54 PM   #3
RocketJ
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On the exhaust side, the oil gets hotter and, I think the word is carbonizes. No big deal, maybe bad if it doesn't.
Probably the first thing you would notice on an airhead is the exhaust valve clearances would be tighter each time they are checked/adjusted. In my experience the next would be high rpm missing/backfiring. They don't so much burn as receide. The seat just disappears. I have a good example of which I will take some pictures tommorrow if anyone wants.
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Old 05-15-2006, 09:19 PM   #4
Hltoppr
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I found out mine were fried when I did a compression test and came up with 50 psi in one cylinder and 20 in the other, pulled the heads and yup...toasty.

Symptoms were stalling at idle. Adjusting the carbs was next to impossible and did not cure the problem.

....new heads with valves, guides, seats and springs should cure the issue...sitting atop a rebuilt engine and new cylinders is nice too...

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Old 05-15-2006, 09:42 PM   #5
hogmolly
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Quote:
Originally Posted by datchew
What are signs of a burnt valve?

thx.
A warped or cracked valve face. Low compression without oil consumption.
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Old 05-15-2006, 09:47 PM   #6
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Dat: go for a compression test, it'll tell you a few things. Just disable the electronic ignition first 'cause you have to spin her over w/ the plugg leads disconnected of course-- can't fire the ign ungrounded on these

check Haynes, Snowbum etc for proc

you mentioned having a VW 1600cc, you prolly already have a tester-- if not i've had fine results with the Sears unit. Has the correct spark plug thread adapter, and a good quick-release fitting
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Old 05-15-2006, 11:46 PM   #7
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How about a leak down checker. This just pumps air into your cylinder (while on top dead center) through the spark plug hole and measurer's the percentage of air escaping. If I recall it should be no more than 10 percent.

If you have a large amount of leakage you can hear it out the exhaust...exhaust valve, or carb...intake valve, or oil fill cap...compression rings. Just another way to diagnose a problem. I think you could probably rent one. A little expensive to buy from Snap On. bye
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Old 05-16-2006, 05:43 AM   #8
datchew OP
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thanks guys.

Feel better.

Mug, my 66 bug is a 1300cc. Just don't remember it being that dirty on the exhaust side, but... (shrug)

RocketJ I would like some pics if you get a chance.

I've done leakdown checks on more modern cars (my 85 318i) but i borrowed the tools. Mebbe i'll invest in the tool you mentioned from sears.

thx all.
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Old 05-16-2006, 07:10 AM   #9
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here's the one i've used for years:
http://www.sears.com/sr/javasr/produ...seBVCookie=Yes

but these days you can get well-made examples many places-- like all Pet-Boys, Advance, etc. If you like to give yr bizness to WallaceWorld they probably have it for $2 less than anywhere else.
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Old 05-16-2006, 11:48 AM   #10
datchew OP
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sears has been good to me. i'll probly pick up one of those.

thanks for the link.

Appreciate all the help guys.
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Old 05-16-2006, 05:30 PM   #11
RocketJ
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If the top one looks like your discoloration, no worries.

[IMG][/IMG]
If your exhaust valves look like this, worry.
[IMG][img=http://img49.imageshack.us/img49/1765/1230057hz.jpg][/IMG]
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Old 05-16-2006, 06:23 PM   #12
RocketJ
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valve recession

First one didn't take.
[IMG][/IMG]
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Old 05-16-2006, 06:30 PM   #13
datchew OP
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I didnt' take the heads off to look at the back like that.
However, mine is a bit darker. Going from performance issues that you guys said would arise if i had valve problems, I think i'm good to go.

I'm not sure what i'm looking at on the second picture.
I mean... i'm not sure what part of the picture shows damage.
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Old 05-16-2006, 08:34 PM   #14
RocketJ
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The exhaust valve, on the right. should be flush, like the intake. This one has recessed about 4mm. You should not be able to see any seat around the valve.
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Old 05-17-2006, 05:18 AM   #15
datchew OP
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oh, i see it now. thanks.

sheesh that ain't good.
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