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valve adjustment / rocker clearance
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shenan-agon
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PostPosted: Tue Jun 05, 2007 9:29 pm    Post subject: valve adjustment / rocker clearance Reply with quote

So, I've known for a while that my engine (2.1) has so-so compression, especially bad on cylinder 2. I tried a valve adjustment at some point last year, which actually made things a bit worse; never really figured that out (why would backing off on the preload lower the compression?).

In any case, I popped the 1-2 valve cover this afternoon to take another swing at it - engine was warm. First reading on cyl. 1 was ~106 - I loosened the adjuster screws from their current setting (1/4-1/2 turn in) and gapped to .006. Compression went up to ~130. Not a bad start...

Looked at cyl. 2, which read 80psi. I backed off the adjusters on this one (also 1/4-1/2 turn in), and saw no improvement. Then I noticed something strange - usually, you can tell if the screw is touching by tapping the rocker back and forth and seeing if it has any play. On the exhaust valve, no matter how far I backed out the screw, the rocker still wouldn't budge; I looked a little closer, and it looked like the spring retainer was actually butted up against the rocker arm. Tried to slide my .006 feeler in there, but no dice - there's no clearance.

Exhaust valve:
Image may have been reduced in size. Click image to view fullscreen.


Intake for comparison:
Image may have been reduced in size. Click image to view fullscreen.


Now bear with me, because I'm still kind of a dumbass with this stuff...does this mean either the valve seat has been cut down to the point that it's sticking out this far, or the valve has streched that much? On a scale of "1" to "Totally F*cked", where does this sit?

Full disclosure: these are AMC heads, put on about 3-4 years ago by the PO (I've had the van about 2 years). So I have no idea if the standard AMC valves were kept, but I'm guessing they were.
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glutamodo Premium Member
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PostPosted: Wed Jun 06, 2007 2:50 am    Post subject: Reply with quote

Looks to me like you have valve issues in that cylinder. Probably a bad seat - used to happen all the time on aircooled vanagons, but watercooled ones are usually more durable (it's the damn head gaskets that suck on those) I've known AMC heads to be just so-so in quality.

I'd completely unbolt the rocker arm, then compare the height of the 4 valve springs. I'll bet that one is sticking out a lot further than the rest. If so, then plan on replacing that head Crying or Very sad

So were you planning on leaving your hydraulic valves set without preload, or was that .006" setting just for your testing?
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shenan-agon
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PostPosted: Wed Jun 06, 2007 8:41 am    Post subject: Reply with quote

glutamodo wrote:


So were you planning on leaving your hydraulic valves set without preload, or was that .006" setting just for your testing?



I did it as a test, but I may leave it that way for now and test again in a bit. I understand this is a whole can of worms, and there are lots of different opinions on valve adjustment...all I know is that with any preload, compression is significantly lower (at least on these two cylinders). In fact, if I put any preload on the cyl. 2 valves, compression quickly drops to zero.
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glutamodo Premium Member
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PostPosted: Wed Jun 06, 2007 9:00 am    Post subject: Reply with quote

shenan-agon wrote:
In fact, if I put any preload on the cyl. 2 valves, compression quickly drops to zero.


Yeah, sounds like a bad head to me. Pull that rocker arm off and compare the heights and see how bad they are.
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shenan-agon
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PostPosted: Wed Jun 06, 2007 9:12 am    Post subject: Reply with quote

glutamodo wrote:
shenan-agon wrote:
In fact, if I put any preload on the cyl. 2 valves, compression quickly drops to zero.


Yeah, sounds like a bad head to me. Pull that rocker arm off and compare the heights and see how bad they are.


Is it possible it's just the valve that's stretched, and/or the keeper grooves worn? I've been reading up on this - some good information at at benplace:

http://www.benplace.com/amc.htm

Sounds like pretty much what I'm seeing.


In any case...I'll probably drive this thing until it explodes, then do a Subaru swap. Very Happy How much time do you think I have?
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MarkWard
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PostPosted: Wed Jun 06, 2007 10:14 am    Post subject: Reply with quote

The heads may have the wrong springs installed. I came across this once before. The lifters would over come the springs and hold the valves open.
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JunkYarDog
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PostPosted: Wed Jun 06, 2007 5:28 pm    Post subject: Reply with quote

The spring caps look wrong>???
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shenan-agon
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PostPosted: Wed Jun 06, 2007 9:37 pm    Post subject: Reply with quote

JunkYarDog wrote:
The spring caps look wrong>???



What do you mean by "wrong"? What are they supposed to look like?
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?Waldo?
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PostPosted: Wed Jun 06, 2007 9:50 pm    Post subject: Reply with quote

If you don't care if it explodes, then shim the rockers where they attach to the head. Wink

If the valve is indeed stretching, then you can look forward to a really exciting moment when it finally drops the valve head into the cylinder. Just imagine the noises and wreckage. Laughing Not quite as exciting as a tossed rod, but almost.

If the valve isn't stretching, then you will have "fixed" it and it will last a good long time. Very Happy

Any chance your pushrods got too long? Maybe your lifter pumped up too big? Your cam lobes swelled? Alright, I'll stop...

Andrew
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