I recently acquired a 2002 Trail Blazer LTZ from a relative that I knew had problems and thought would be a quick fix... not so.
Engine: Vortec 4200 - 4.2 Liter L6.. 188,780 Miles

Came to find out that I had zero compression on #2 cylinder. I bought a Service manual and read that in order to remove the head and front cover, I need to remove the oil pan.. please say it ain't so. Surely it'* possible to get the front cover off & back on without dropping the pan. It seems like the oil pump is strategically placed behind the front cover to avoid pulling the front drive axles and dropping the pan.

Hope you GM experts can enlighten me. I may have some tool questions and need to have someone reference check my manual with their edited and improved manual. I suspect mine may be a first edition.

Thanks for reading...

How in the world is pulling the head and front cover, a quick easy fix?

What is wrong with the vehicle?

What diagnosis told you to go in this direction?

I remember this engine in a Ranier, and it was a nightmare to work on.....I seem to remember one guy taking a head off and he snapped the head bolts.....I think he later found a TSB stating you had to shock the bolts before removing them....

Hope you find someone with experience on this engine.....IF I remember right, that oil pan removal is a nightmare...

I don't see how removing the head & front cover is an easy fix either. The hoped easy fix was for a misfire on #2 Cylinder. I checked fuel and electrics before I went further. Everything checked out good there. Found zero compression on #2 cyl. and wet #2 exhaust port. I was hoping it'* a burnt valve initially, but now wondering if there'* a hole in the piston or broken rings, additionally. Maybe the valve is good. I'll have to pull the head to find out. Either/or/and isn't an easy fix.

So it'* impossible to pull and install the front cover without dropping the pan?

I didn't want to drop the pan for fear that if I had to pull the front drive axles, I would pull the engine and rebuild it. I was hoping to repair it in-frame and get it on the road

I'm the only mechanic my vehicles have seen or ever will see. Not in the dark, being and old Cummins tech and worked on practically every on & off road; big & small. Just need pointers on specific peculiarities per OEM insanity (my second personal GM)

lol, I don't doubt you on the nightmare. Thanks for the heads-up on the head bolts... and thanks for your reply

Did you do a cylinder leak down test and see where the air comes out? The head can be removed w/o removing the front cover. there is a wedge that goes between the chain tensioner and a boss in the block to wedge the chain and tensioner. Hit the head bolts hard to loosen the threads, don't mess up the hex in the bolt head. If the bolts break,it'* no big deal they come out easy. I use a reverse twist drill bit and they come right out. Have done lots of heads not to many lower end issues. Note: the valve stems are small and will bend easily. Some times it'* easier to put the cams in after the head is on especially if you putting the head on by yourself.

Thanks for the info. I didn't do a leak down test. Either the #2 exhaust valve or piston is the problem (or both). I've stripped the front of the engine down to the front cover, but the cam cover is still on it to keep it clean. Although one of the first things I did was to replace the cam cover gasket to fix an oil flooded spark plug recess and replace a dead #2 coil, hoping that would fix it. Then found out I had zero compression on #2 and squirting oil in the cylinder didn't make a hoot of difference. I may make a smoke machine and/or a leak down tee to have around for the future, and test them on this engine. I have to work around the rain this week; calling for it until Wed., at least. Garage is too full and it'* parked in front of the door.

Was initially thinking of replacing the timing chain, related parts and oil pump, since I have to pull the head and there'* a lot of miles on it. Now weighing whether I should just pull the engine and rebuild it. Don't want to do that later since I'm this far along... So this is definitely a project vehicle...

My manual says that a J-41478 is a front crank seal installer; in the "special tools" section, but references it in another place as a crankshaft balancer installer. Yet the front crank seal installer is J-44218. Does it require a special tool to install the crank balancer?... I think my manual may be wacky.

Front seal installs like any other.nothing special. I usually just use a hammer and walk it in,or use a socket if I don't have an installer.Oil pan has to come off to remove the front cover because the pick-up bolts to it and the pump with the cover. If your that far the pistons aren't that much further. The front diff actuator likes to corrode into the oil pan as does the carrier so be careful when removing from the oil pan. parts are available if you brake the actuator in the oil pan. Only parts to repair are available from the factory and assemblies after market are pretty pricey. Only the upper ball joints need to be seperated and remove the 10mm bolts that hold the brake line bracket and release the one retainer that holds the wss wire to the spindle and that will give you enough to remove the 1/2 shafts from the carrier and actuator. Hope this will help.

Thanks, dpieroni3, it is a help. I figured it would be simple to install the front crank seal. What I questioned was, the manual had 2 different part #'* for the same purpose tool. I couldn't imagine why a special tool is required to install the crank balancer:





This is the regular seal installer:

Do you have a scope? If so you could see at least the condition of the top of the piston and maybe look for other clues.

No, I don't have a scope. We use to have one at Cummins; like a doctors ear scope. Pretty neat tool.

Darn. If it'* in your budget they are getting pretty inexpensive these days at Home Depot and the like. I have a Ryobi unit that pairs with my phone so I can take pictures and share etc.