Head Gasket Replacement [Archive] - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

: Head Gasket Replacement


psu_nuc
03-27-2007, 11:05 PM
Hey guys,
I am new to this forum and to Trailblazers so I was hoping someone here could help me out. I am looking to swap a rebuilt head and valvetrain on my '02 4.2 L because I have a pretty solid valve tap and I think the gasket is blown. Has anyone ever pulled their head for any reason (head gasket, valve job, etc.)? I want to know if there is a need to pull the front engine cover off to access anything required to loosen the timing chain. From the pictures I have seen it looks like there might be enough room to remove the sprockets without removing the front cover. Also, does anyone know if there is a shop (Auto-Zone, Pep-Boys, Checkers) where the cam holding tool can be rented? Any advice is appreciated. Thanks in advance.

ghoster
03-27-2007, 11:28 PM
To be honest, I can't recall ever hearing of anyone doing this!! Its not a common repair on these engines. I am sure SOMEBODY has done it. I looked to see if I could find anything on it and I got nada. Good luck with it!! Take lots of pics and post them up!:cool:

ScarabEpic22
03-27-2007, 11:30 PM
How loud is the tapping? The I6 taps like crazy when cold, but mine goes almost completely away once warm. Are you sure you need to replace it?

MTPockets
03-27-2007, 11:32 PM
..I have a pretty solid valve tap and I think the gasket is blown..

These two concerns are not at all related. Top end concerns are pretty much unheard of on the atlas 4.2L. Try a search for engine tap, tick, knock for a TON of threads, info.

Joel

PROSPHOTO
03-28-2007, 06:54 AM
These two concerns are not at all related. Top end concerns are pretty much unheard of on the atlas 4.2L. Try a search for engine tap, tick, knock for a TON of threads, info.

Joel

:iagree: These engines are, for the most part, bulletproof...although they do exhibit a range of noises when first starting. I would definitely do some more research & diagnosinghttp://www.aimoo.com/forum/images/messageicon/excalmatorymark.gif

balloonman73
03-28-2007, 07:23 AM
I recently had the head removed to fixed a cracked exhaust manifold. The head was removed because of broken bolts. The front cover did not have to be removed.

MTPockets
03-28-2007, 02:56 PM
I recently had the head removed to fixed a cracked exhaust manifold. The head was removed because of broken bolts. The front cover did not have to be removed.

Ahh the nightmares associated with an all aluminum engine! They NEVER come unbolted without a fight. Good to know about the cam drives. It looks like about half of the cam drive sprockets will be exposed once you pull the cam cover off. Do you remove the sprockets or break the chain?

Joel

psu_nuc
03-28-2007, 10:14 PM
I know the two problems are seperate (valve tap & head gasket) but I think I am dealing with both. I have read everything I could find on forum concerning cold taps and piston slap hoping that was my problem. My tap does get a little quieter as the engine warms up but never goes away (which is what a bent valve would do in my experience). Once warm you can barely hear the tap with the hood open even when reving the engine, but when its under load it is much louder. Valve tap is the only thing I can come up with. Any simpler fixes would be great.

ScarabEpic22
03-28-2007, 10:28 PM
I know the two problems are seperate (valve tap & head gasket) but I think I am dealing with both. I have read everything I could find on forum concerning cold taps and piston slap hoping that was my problem. My tap does get a little quieter as the engine warms up but never goes away (which is what a bent valve would do in my experience). Once warm you can barely hear the tap with the hood open even when reving the engine, but when its under load it is much louder. Valve tap is the only thing I can come up with. Any simpler fixes would be great.

What oil are you running? Use a full synthetic like Amsoil or Mobil 1 and see if it goes away. Mine immediately went down noticeably in volume when I switched from Pennzoil to Amsoil. It also came right back up just as fast when I switched back to dino oil for 1500mi after I seafoamed my engine. Changed the filter and oil back to Amsoil, and presto the valve tapping went down again.

PROSPHOTO
03-28-2007, 10:31 PM
There's a GM bulletin that may help:

On rare occasions, an upper end tick noise may occur inside of the engine when cold and/or hot. This noise may be due to a collapsed lash adjuster (s). In some cases, replacing the lash adjusters may temporarily correct the noise but it may have returned shortly after with collapsed lash adjusters again.

This may be due to Dexcool coolant in the engine oil, which is not as obvious as convention ethylene glycol coolant (green) in the engine oil. Since some of the evidence will break down and / or volatilize at operating temperature, an engine oil analysis may not indicate that there is Dexcool in the engine oil. Typically, the only visual evidence of Dexcool in the engine oil is significant black or brown sludge deposits that appear to be the result of not having the engine oil changed even though the oil has been changed according to the maintenance schedule / engine oil life monitor. If the sludge is a result of Dexcool in the engine oil, a low cooling system level will be found with no external leaks.

Check you're coolant level; if it's low, you may definitely have to pinpoint the "Coolant in Engine Oil" condition :D

If it's not low, then just repair the noise concern (possible lash adjuster) :yes:

psu_nuc
03-29-2007, 12:13 AM
Does synthetic make that much of a difference? I have also heard that you can have valve seal problems when going to synthetic in an engine that has been running conventional for a long time (91,000), any truth to that? I dont think it is a lash adjuster problem because the sound is right on top of the engine not the front.

ScarabEpic22
03-29-2007, 12:29 AM
Does synthetic make that much of a difference? I have also heard that you can have valve seal problems when going to synthetic in an engine that has been running conventional for a long time (91,000), any truth to that? I dont think it is a lash adjuster problem because the sound is right on top of the engine not the front.

I switched at ~45K and never have had a problem. Now at 72727 and havent had a problem. As long as there are no mechanical issues, switching back and forth isnt an issue.

PROSPHOTO
03-29-2007, 06:46 AM
The lash adjusters are essentially the lifters in the engine...noise on top of the engine, not up fronthttp://www.aimoo.com/forum/images/messageicon/excalmatorymark.gif
This bulletin is not referring to the timing chain tensioner http://www.unixboard.de/vb3/images/smilies/sm-nachdenk.gif

What you've heard about switching to synthetic is a rumor...no truth to ithttp://www.aimoo.com/forum/images/messageicon/excalmatorymark.gif

Anyway, there is another bulletin:

On rare occasions, the oil gallery plug located between the number 1 cam journals may come out of position causing insufficient oil to the lash adjusters. This will result in a tick noise at all times from multiple lash adjusters.

cliffwilson
03-29-2007, 01:46 PM
Removal of the cylinder head on the 4.2 requires disassembly of the front cover. Since the front cover is T sealed with the oil pan, the oil pan must be removed before the front cover can be separated. To access the front cover; the fan, fan shroud, water pump, and crankshaft pulley must be removed. The timing chain and camshaft sprockets must be removed. Finally, the head has 17 bolts that cannot be reused. The new bolts must be torqued to yield specs. Bottom line, removal of the 4.2 head is not a shade tree mechanic job for a relaxing Saturday afternoon. As others have suggested, general engine noise is best initially approached with an oil and oil filter change, using high quality products and the correct oil viscosity.

psu_nuc
04-01-2007, 12:36 PM
If it is lash adjuster or the oil plug deal what can be done to fix it? Would you still have to pull the head? Also, as far as the head being T-sealed to the fron cover, are you sure there is no way to remove the head only. Tha shop manual is not to clear about this. I am gona go grab some Mobil 1 today. Thanks for all the help guys.

PROSPHOTO
04-01-2007, 02:17 PM
You do not have to pull the head to replace/inspect the valve lash adjusters; but you will need a specific valve spring compressor to allow you to remove the valve rocker arm and valve lash adjuster w/o removing the cams :yes:

If you have a few specific J-tools (manufacturer specific special tools), you can replace the head gasket w/o removing the front cover. Unless you know for certain that the head gasket is no good, I would not recommend performing the head gasket replacement. A valve tap is not a good reason for doing the job :nono:

Raj
04-01-2007, 08:52 PM
If you decide to pull the head, hit each head bolt with a large hammer and punch a couple of times. Very common for head bolts to snap off on these motors.

cliffwilson
04-02-2007, 07:42 PM
You do not have to pull the head to replace/inspect the valve lash adjusters; but you will need a specific valve spring compressor to allow you to remove the valve rocker arm and valve lash adjuster w/o removing the cams :yes:

If you have a few specific J-tools (manufacturer specific special tools), you can replace the head gasket w/o removing the front cover. Unless you know for certain that the head gasket is no good, I would not recommend performing the head gasket replacement. A valve tap is not a good reason for doing the job :nono:

How is this done? With the front cover unremoved, I'm having trouble visualizing how one can release the timing chain tensioner shoe and dismantle the two cam sprockets so the head can be lifted. While I'm familiar with special tools to hold the position of the cams during repair, this is the first I've heard of tools allowing the head to be removed without pulling the front cover. I appreciate any further information you can point me to. It's a tremendous labor saver!

PROSPHOTO
04-02-2007, 07:55 PM
The tool required is: EN-48464 Lower Timing Gear Tensioner Holding Tool

This gets inserted down behind the front cover...

http://memimage.cardomain.net/member_images/7/web/2551000-2551999/2551515_81_full.jpg

and gets wedged against the timing chain

http://memimage.cardomain.net/member_images/7/web/2551000-2551999/2551515_82_full.jpg

This is the basic idea, but there is a significant amount of info in the service procedure

psu_nuc
04-05-2007, 12:34 AM
Great pictures of the timing chain tool. Where did they come from, the manuals? I have the Chilton Manual and they don't have them. Where can you order these tools from (ie. cam holder tool and others). Also, If it is the lash adjusters would there be any other symptoms that would help me determine if it is the lash adjusters? How much different would adjusting/replacing them be then doing rockers? Thanks in advance.

Jozuah
04-05-2007, 01:44 AM
I know the two problems are seperate (valve tap & head gasket) but I think I am dealing with both. I have read everything I could find on forum concerning cold taps and piston slap hoping that was my problem. My tap does get a little quieter as the engine warms up but never goes away (which is what a bent valve would do in my experience). Once warm you can barely hear the tap with the hood open even when reving the engine, but when its under load it is much louder. Valve tap is the only thing I can come up with. Any simpler fixes would be great.

i may be off base here , (joel wadda you think)

If you just had an exhaust gasket changed, maybe there is a SMALL leak thats causing this "valve tap" noise, you mentioned that its most noticeable under load.
this to me sounds like a leaking gasket.

Also i have seen internal head gasket leaks (between cylinders) and not leak oil or water , and the damn thing sounded JUST like a wrist pin slap, but again only under load.

any input to this idea would be welcomed.
Josh:thumbsup:

PROSPHOTO
04-05-2007, 06:28 AM
Great pictures of the timing chain tool. Where did they come from, the manuals? I have the Chilton Manual and they don't have them.
Thanks; GM service manual. Usually the aftermarket manuals (Chiltons, Mitchells, etc.) only have about half of the info of the OEM (if that); that's why, you'll find that a handful of guys around here did pay for the OEM :yes:

Where can you order these tools from (ie. cam holder tool and others).

http://www.unixboard.de/vb3/images/smilies/sm-nachdenk.gif Try calling NAPA or your dealers parts dept.

Also, If it is the lash adjusters would there be any other symptoms that would help me determine if it is the lash adjusters? How much different would adjusting/replacing them be then doing rockers? Thanks in advance.

I don't think you're going to find any other symptoms. But, I've heard some really loud lifter tapping before all b/c the hydraulics failed in the lifter :duh:

i may be off base here , (joel wadda you think)

If you just had an exhaust gasket changed, maybe there is a SMALL leak thats causing this "valve tap" noise, you mentioned that its most noticeable under load.
this to me sounds like a leaking gasket.

I think that an exhaust leak (yeh, could be mistaken for a engine tap) would remain consistant under all temps...his gets quieter as it gets warmer http://www.unixboard.de/vb3/images/smilies/sm-nachdenk.gif

Also i have seen internal head gasket leaks (between cylinders) and not leak oil or water , and the damn thing sounded JUST like a wrist pin slap, but again only under load.
any input to this idea would be welcomed.
Josh:thumbsup:

I guess possible, but extremely uncommon with these engines :confused:

psu_nuc
04-06-2007, 02:26 AM
Thanks for the info guys. I am pretty sure the tap is coming from under the valve cover. How would I know if the lifter/lash adjuster was bad? And is there any way to repair them or would it need to be replaced? How much are we talkin to replace one/all of them? Would this all be covered in the OEM shop manuals? Thanks again.

PROSPHOTO
04-06-2007, 06:18 AM
:yes: The OEM manual will cover the entire procedure.

One way to tell is to try and push the hydraulic center in...you won't be able to move it :no: There's no repair

Make sure you inspect your oil for contamination...If you have contamination, and you don't repair that problem, you could wipe out the new lash adjusters :duh:

One more note...After you remove the Camshaft cover & b/f you replace the lash adjusters, inspect for a missing oil galley plug as shown. I found another bulletin that states that if this plug is missing (it will cause multiple lash adjusters to tick b/c there will not be enough oil to them), you have to replace the cylinder head :eek:

http://memimage.cardomain.net/member_images/7/web/2551000-2551999/2551515_86_full.jpg