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Unread 11-21-2009, 05:36 PM   #1
leroy-yjeep
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Replace valve stem seals with head still on?

I have a 4.2 I-6, and i think i need to put new valve stem seals in. Is it possible to do it with the head still on?

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As we hooked the strap onto the jeep, i realized i couldnt remember how many times dad had actually towed me home. Ahh the beginning years of Jeep ownership.

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Unread 11-21-2009, 05:41 PM   #2
Mean Max
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I haven't done it in a Jeep, but back in the day I used to be a Mercedes-Benz dealer tech. We used to do it all the time by removing the valve train (so intake & exhaust valves are both closed), putting the piston at BDC and screwing an air line into the spark plug threads & pressurizing the cylinder.

Carefully remove the spring & replace the seal & reinstall.

Max
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Unread 11-21-2009, 05:48 PM   #3
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Here's the catch: if you have oil sucked in through the guides, seals are NOT going to solve it. Oil ONLY gets sucked down the guides when the valve to guide clearance is too great; the solution is either or both new valves or a valve guide job. Either way, the head needs to come off. It's possible the new seals alone would reduce or prevent oil being sucked through the guides for a short time... but the problem will always come back unless you address the PROBLEM, excessive clearance, rather than the SYMPTOM, oil being sucked through the guide.

In addition, if there's significant wear to the guides, likely the springs, valves, guides, and seats all need freshening... in other words, rebuild the head. Since a full head job costs as much or more than a NEW loaded head... consider a replacement head as an option. Alternately, a good head shop can do a performance valve job which can net a bit of power without losing any torque, or even mild porting for more gains, but the cost benefit on porting our heads is pretty marginal.
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Unread 11-21-2009, 06:06 PM   #4
Mean Max
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Quote:
Originally Posted by Boodyrider View Post
Here's the catch: if you have oil sucked in through the guides, seals are NOT going to solve it. Oil ONLY gets sucked down the guides when the valve to guide clearance is too great; the solution is either or both new valves or a valve guide job. Either way, the head needs to come off. It's possible the new seals alone would reduce or prevent oil being sucked through the guides for a short time... but the problem will always come back unless you address the PROBLEM, excessive clearance, rather than the SYMPTOM, oil being sucked through the guide.

In addition, if there's significant wear to the guides, likely the springs, valves, guides, and seats all need freshening... in other words, rebuild the head. Since a full head job costs as much or more than a NEW loaded head... consider a replacement head as an option. Alternately, a good head shop can do a performance valve job which can net a bit of power without losing any torque, or even mild porting for more gains, but the cost benefit on porting our heads is pretty marginal.
All good points.

Remember, I was a dealer tech and these were late-model low mileage cars with defective seals.

I would have to agree with Boodyrider, after reading his post & giving it some thought.

Max
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Unread 11-21-2009, 06:38 PM   #5
leroy-yjeep
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[IMG][/IMG]
spark plugs #6 on left, #1 on right
[IMG][/IMG]

I removed all of the spark plugs and then did a compression test on each cylinder. #1 got 150, #2 got 150, #3 got 150, #4 got 125, #5 got 130, #6 got 140.

When i first start the jeep up, it runs fine, no miss. then after a little while, it starts to miss. After it warms up all of the way, it runs pretty good. I checked the ignition and everything seemed to check out. So this all lead me to believe something is leaking into the cylinder. I thought oil
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As we hooked the strap onto the jeep, i realized i couldnt remember how many times dad had actually towed me home. Ahh the beginning years of Jeep ownership.

1990 YJ, 350 TBI, 5 speed, NP 241, XRC winch, 8.8 LSD rear, 30 LSD front, 37" MTR's, ....lots to do.
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Unread 11-21-2009, 06:48 PM   #6
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1, Take those fancy plugs and throw them away, regular copper plugs work best in the Jeep.
2, You probably need to rebuild the Craptastic Carter carb and clean the idle tubes.
3, Perform the Nutter bypass.
4, Perform the Team Rush upgrade.

Report back with the results.
Dwayne
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Unread 11-21-2009, 07:00 PM   #7
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Quote:
Originally Posted by 4.7stroker View Post
1, Take those fancy plugs and throw them away, regular copper plugs work best in the Jeep.
2, You probably need to rebuild the Craptastic Carter carb and clean the idle tubes.
3, Perform the Nutter bypass.
4, Perform the Team Rush upgrade.

Report back with the results.
Dwayne
this isn't my first set of plugs, i've tried "unfancy plugs". I already swapped to a mc2100 carb. I also already have a CRT HEI distributor.
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As we hooked the strap onto the jeep, i realized i couldnt remember how many times dad had actually towed me home. Ahh the beginning years of Jeep ownership.

1990 YJ, 350 TBI, 5 speed, NP 241, XRC winch, 8.8 LSD rear, 30 LSD front, 37" MTR's, ....lots to do.
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Unread 11-21-2009, 07:08 PM   #8
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To me that looks like a spark delivery problem. If #2, and perhaps #3, were oil fouled it would be uniform fouling all over the plug, but it appears to be dry carbon buildup and just localized as a result of misfiring. The other plugs look just fine indicating neither rich nor lean carb settings if they've been in there for any amount of time so your carb appears to be fine.

Check your #2 and #3 plug wires for solid connections, or they could be arcing if too close together. Best, shoot a little WD40 into the plug wire boot, slide it up the wire and make sure you have a solid mechanical connection to the plug, then slide the boot back down; the WD40 is non-conductive and will evap, it's just there for lubrication.

Also check the distributor cap sockets for corrosion, cracks, etc. Better yet replace the cap and rotor. This really looks more electrical than mechanical to me.
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Unread 11-21-2009, 08:04 PM   #9
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Quote:
Originally Posted by Mean Max View Post
All good points.

Remember, I was a dealer tech and these were late-model low mileage cars with defective seals.

I would have to agree with Boodyrider, after reading his post & giving it some thought.

Max
I don't know. I have replaced seals with the head on also. And yes it was a older car. Although why not give it a shot on a YJ the parts are cheap and the only real loss would be time. I think I would give it a shot first.

To answer the original question, Yes you can replace the seals without removing the head. Air is pushed into the cylinder and then you push down the springs, remove the valve clip and remove spring, place on new seal and repeat 7 more times. Then reinstall the rockers and adjust.

You do not have to put every cylinder to TDC because when you remove the rockers it does not matter. In fact the air may push the clyinder down.

The tools are not expensive. I bought mine from JC Whitney for just a few dollars. I would bet you auto parts store would also have them.
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Unread 11-21-2009, 08:11 PM   #10
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I agree I would check cap, rotor, or wires. It would be nice to know the kv's on the wires. You could also ohm the wires. Being a tech I can tell you that nothing will run right with Bosch Platiums, the germans don't even use them. If you were using enough oil to cause a running issue it would be smoking like a train. Even then I have seen cars run ok. It is definatly a fuel/spark issue.
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Unread 11-21-2009, 08:36 PM   #11
leroy-yjeep
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Ok, i already ohm'ed the wires, and checked the cap and rotor etc. everything checks out. I guess im gonna try swapping a couple spark plugs around and try and find out if its those.

thanks for all the help

Edit: oh, and it does smoke pretty good when its cold.
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As we hooked the strap onto the jeep, i realized i couldnt remember how many times dad had actually towed me home. Ahh the beginning years of Jeep ownership.

1990 YJ, 350 TBI, 5 speed, NP 241, XRC winch, 8.8 LSD rear, 30 LSD front, 37" MTR's, ....lots to do.
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Unread 11-21-2009, 08:41 PM   #12
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Are you sure it is smoke or is it condensation for the catalytic converter doing it's job. You may want to check for vacuums leaks also.
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Unread 11-22-2009, 04:13 AM   #13
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Quote:
Originally Posted by pasinbuy View Post
I don't know. I have replaced seals with the head on also. And yes it was a older car. Although why not give it a shot on a YJ the parts are cheap and the only real loss would be time. I think I would give it a shot first.

To answer the original question, Yes you can replace the seals without removing the head. Air is pushed into the cylinder and then you push down the springs, remove the valve clip and remove spring, place on new seal and repeat 7 more times. Then reinstall the rockers and adjust.

You do not have to put every cylinder to TDC because when you remove the rockers it does not matter. In fact the air may push the clyinder down.

The tools are not expensive. I bought mine from JC Whitney for just a few dollars. I would bet you auto parts store would also have them.

I've heard of a poor mans way to hold the valves closed when compressed air was not available.
Simply remove the spark plug for the cylinders relative to the valve seals you want to replace, lower the piston to BDC and then insert as much cotton rope as possible through the plug hole, leaving a few inches hanging out for retrieval later. Now you can slowly bring the piston up snug.
The rope will now hold the valves closed and you can then remove the valve springs and replace the valve seals while the rope holds the valve stems up.
After the seals and valve springs are replaced, slightly relower the piston and pull the rope out of the cylinder.
I've never did this but it makes sense how it would work.
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Last edited by alilredjeep; 11-22-2009 at 04:20 AM.. Reason: more info added
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Unread 11-22-2009, 08:00 AM   #14
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Quote:
Originally Posted by alilredjeep View Post
I've heard of a poor mans way to hold the valves closed when compressed air was not available.
Simply remove the spark plug for the cylinders relative to the valve seals you want to replace, lower the piston to BDC and then insert as much cotton rope as possible through the plug hole, leaving a few inches hanging out for retrieval later. Now you can slowly bring the piston up snug.
The rope will now hold the valves closed and you can then remove the valve springs and replace the valve seals while the rope holds the valve stems up.
After the seals and valve springs are replaced, slightly relower the piston and pull the rope out of the cylinder.
I've never did this but it makes sense how it would work.
Huh, Well how about that?
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Unread 11-22-2009, 08:05 AM   #15
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I have used that trick for many years works fine.

Dwayne
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