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post #1 of (permalink) Old 10-13-2007, 02:34 PM Thread Starter
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4.0 valve stem seal question

Alright, my '93 ZJ has 240K+ miles on it, and still runs strong. But the poor girl smokes when you let it idle for any period time over a couple minutes. I'm thinking worn Valve stem seals, maybe even Rings. hey, what do you expect after 240K miles.

Anyway. Question is, What's involved in changing out the Valve stem seals? I've had a set sitting in the Center console and a valve cover gasket under the back seat for about 2 years now, just never got around to it.

anyone have a step by step, or is it not that easy.

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post #2 of (permalink) Old 10-13-2007, 03:33 PM
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Not that hard....assuming you have the right tools.

On each cyl you have to rotate the engine so that cyl is on the firing stroke (both valves up). You then use a tool that screws into where the spark plug goes and you apply air. This keeps the valves from dropping down into the cyl.

You can now remove the valve spring and replace the seal.

My personal opinion...240K miles? I would check the compression first. If all cyl's are within 10 PSI of each other and at least 145PSI....then yea, replace the seals. But if lower, not worth the effort....time to rebuild.

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post #3 of (permalink) Old 10-13-2007, 03:45 PM
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A little trick - sometimes you don't have air handy - or if it quits -- ooops!

- Remove all the plugs - find TDC on the cylinder you are working on.
- Back the piston down about 1/4 turn on the crank.
- Stuff as much 1/4" cotton clothes line rope in the plug's hole as you can - leave the tail out!
- Gently rotate the crank back up to shove it up against the valve. The valve cannot drop now.
- Replace the seal and springs, then rotate it down and pull the rope out.

I was amazed when I saw it done - simple, easy, cheap.
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post #4 of (permalink) Old 10-13-2007, 09:46 PM Thread Starter
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So there' sno adjusting the valves or anyhting like that, just remove and replace?

DDawg, you're right at 240K it may not be worth it, but I have all the parts, and if the job is that easy, then why not is what I figure. I had a Compression check done about 50-60K miles ago and the engine was ok, not great, but ok. #1 cylinder was a little lower than I would have liked to have seen, but she still ran fine and has.

It may be a waste of my time to do it, but an enigne is about the nly thing I haven't been into Mechanically on either of my Jeeps and it would give me a littl eexpereince.

now, how about adjusting of valves, are these of the variety that don't need/have adjusting?

thanks

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post #5 of (permalink) Old 10-14-2007, 01:57 AM
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They are hydraulic....self adjusting......

It's actually quite simple how they work....

The lifter has a spring it in...mainly to give some lift in the absence of hydraulic pressure and to have a little give when in the no lift position (valve seated)

When the lifter is down on the non lift portion of the cam lobe, there is a port on the side of the lifter that lines up with an oil passage...as the engine is running, oil is pumped into the lifter/

As the cam rotates around to the lobe, the lifter goes up and blocks the oil passage....this traps the oil in the lifter basically making it almost like a solid lifter and thus pushing up the push rod which rocks the rocker which opens the valve.

The hole in the top of the lifter lets out a small amount of oil which eventually works its way up the pushrod and lubs the rocker.

In most cases when you get a noisy lifter its because either the spring has gotten weak or the lifter is not holding in the oil as well as it should.....or, you just have real bad oil pressure....

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post #6 of (permalink) Old 10-14-2007, 07:11 AM
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Correct, except that the oil is trapped in the lifter by a check ball, not by the port closing as the lifter comes up.

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post #7 of (permalink) Old 10-14-2007, 08:55 AM Thread Starter
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cool, now, what kind of valve spring compresor works best or is required for the 4.0?

The belief in a supernatural source of evil is not necessary; men alone are quite capable of every wickedness. - Joseph Conrad
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post #8 of (permalink) Old 10-14-2007, 10:30 AM
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From the '78 FSM, here's the factory tool.

temp.jpg

And the tool in use.

temp1.jpg

It's designed so that it can be used with a ratchet handle above or to the side, which is just icing on the cake. No reason you can't make something like it that will work from wherever it's convenient. Just a bar with a slot in the end to go under the rocker stud nut, a hole to get at the keepers, and a handle. It looks like the part that presses on the retainer can swivel, but that's probably just icing too, although it will make it easier to get the keepers in and out.

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Last edited by Jim_Lou; 10-14-2007 at 10:36 AM. Reason: Clarification
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