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Tractor Talk Discussion Forum

GMC/Chevy valves

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tlak

03-31-2005 15:45:58




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88 GMC P/U with 305. Whats the common procedure to change the valve stem seals w/o removing heads. Do you use air or rope to hold the valves up and what kind of spring compressor is used?




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Earl-IL

04-01-2005 07:57:51




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 Re: GMC/Chevy valves in reply to tlak, 03-31-2005 15:45:58  
On high mileage engines, that oil pushrod to rocker arm, I have found that if the pushrod and rocker arm pocket gets worn they will flood the top. As covered in other post, the returns need to be clear. Start up with valve covers off if it squirts oil over the side of the engine you need rockerarms and pushrods.The "o" ring when installed correctly wedges in the retainer below the keepers. Correct order when installing the "O" ring compress the spring install "o" ring ,install keepers, try to keep retainer centered so not to damage "o' ring when you release the spring. Earl In Illinois

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Mike M

04-01-2005 07:13:26




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 Re: GMC/Chevy valves in reply to tlak, 03-31-2005 15:45:58  
Service Bulletin # 91-6A-167 use GM part # 12511890 seal kit list price of $51.73 This should take care of smoke at start up.



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1945 A

04-01-2005 06:08:25




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 Re: GMC/Chevy valves in reply to tlak, 03-31-2005 15:45:58  
I did this a few years ago on an "81 GMC that I had, but, my problem was a broken valve spring.
What I did was use the air adapter like others have said, but, I took all the spark plugs out, then turned on the air, and removed/replaced the broken spring real easy. My thinking was that the plugs out would help By allowing more air volume on the back side (face) of the valve----don"t know if it made any difference, but, it was a pretty easy job, as I recall.
Good Luck!

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george md

03-31-2005 21:58:08




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 Re: GMC/Chevy valves in reply to tlak, 03-31-2005 15:45:58  
tlak,

Chevy uses an oring trapped between the keepers
and the valve spring retainer , and a metal shroud out over the spring, neither of which go
bad ,if you have an oil consumption problem I
think you should look elsewhere. Maybe the oil returns are stopped up and flooding the guides .
Crank case vent sys plugged will make crankcase
pressure and cause oil consumption.

george

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Mike M

04-01-2005 07:09:50




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 Re: GMC/Chevy valves in reply to george md, 03-31-2005 21:58:08  
His 88' should also have positive oil seals,there is a service bulletin on them.



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Allan in NE

04-01-2005 04:51:21




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 Re: GMC/Chevy valves in reply to george md, 03-31-2005 21:58:08  
George,

The square-cut o-rings set underneath the keepers and seal against the inside of the retainer slug. They have been notorious for hardening up and leaking ever since this engine design came on the market in 1955.

Like tlak says, the first sign of bad valve seals is that "puff" of blue smoke after setting overnight. I think he is exactly on the right track.

Allan



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tlak

04-01-2005 04:36:55




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 Re: GMC/Chevy valves in reply to george md, 03-31-2005 21:58:08  
If it sets overnite it smokes on start up, which to me commonly meant oil seeping pass valve seals.
I dont know if chevy changed something but the last one I did you compress the spring removed the the keepers and took the spring off revealing a little o-ring seal. Always thought the unbrella ones were better.



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RJ-AZ

03-31-2005 17:49:31




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 Re: GMC/Chevy valves in reply to tlak, 03-31-2005 15:45:58  
That lever type spring compressor is about the easiest way to go. You can get one at most any parts store, it is a K-D brand tool that I have had for years. The spark plug air adapter is available through K-D also if you don't have stuff to build your own. I use a regulator and guage on mine to limit the air pressue to just enough to keep the valve in place. Be CAREFUL not to let the air push the piston down past TDC.

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Allan in NE

03-31-2005 18:00:37




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 Re: GMC/Chevy valves in reply to RJ-AZ, 03-31-2005 17:49:31  
Hi RJ,

Boy, dunno. You want all the air to it you can muster so that valve won't drop, so I sure wouldn't use an air regulator.

And, the piston will automatically rotate the crank to the bottom of it's travel anyway.

Allan



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e

03-31-2005 17:44:02




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 Re: GMC/Chevy valves in reply to tlak, 03-31-2005 15:45:58  
I would suggest air to hold the valves closed. I have a friend who used the rope method and upon pulling the rope out, a knot was formed. Not a good senario! Just my $.02 worth.

E



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Allan in NE

03-31-2005 16:22:26




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 Re: GMC/Chevy valves in reply to tlak, 03-31-2005 15:45:58  
Tlak,

I use air and this tool I made out of an old piece of strap iron.

Allan

third party image



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tlak

03-31-2005 16:46:20




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 Re: GMC/Chevy valves in reply to Allan in NE, 03-31-2005 16:22:26  
How much pressure?



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Allan in NE

03-31-2005 17:04:04




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 Re: GMC/Chevy valves in reply to tlak, 03-31-2005 16:46:20  
I just rigged up this hose and hook it directly to the air compressor or shop line.

If you want to spend a few bucks, NAPA has a nice little twist-knob spring compressor that works pretty sweet and fits into tight places better too.

Allan

third party image



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