Jeep head gasket replacement: Follow-Up

Hello. First I want to thank everyone who answered my compression question so quickly and knowledablely. You guys are the best! (Please see "What does "No compression mean?" thread for a refesher) Anyway, today after work I torn the engine down to the cylinder head gasket and there was indeed a 1/2"+ gap between the 2nd and 3rd cylinders. So tomorrow I shall replace that gasket plus the intake/exhaust gasket. But I have a few quick questions which hopefully some of you guys can answer before I head out tomorrow. I am worried about damage elsewhere as the Jeep got driven 3-4 days after it began misfiring but only at low speeds (20-30mph) and only like 20 miles total over the 4 days. I don`t see anything that looks bad. All the push-rods are straight. No visible problems with the rockers, springs etc. I put it in neutral and turned the crank with a ratchet and all the pistons move up and down with no noticable resistance or problem. The #1 & #6 go up together. The #2 & #5 together. And the #3 & #4. I am assuming that is the correct pattern? As long as I have this thing apart what else should I do? There`s a bunch of carbon on top of the pistons. A lot of the push-rods although they are straight are covered with a crusty black substance which seems to come off if you spray it with parts cleaner and use a rough scrub pad (Not steel wool those green pads)..Any input before tomorrow will be greatly appreciated. I am a rather poor soul and it would be wonderful if I put this back together and it runs good.

Reply to
Programbo
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Check the head and block for warping with a machinist's steel straight edge and feeler gauge before putting it back together. If you have more than (check your shop manual, but something in the neighborhood of .002-.003") gap at any point between the straightedge and the block or head surface more work is required. Otherwise it is up to you whether you want to have the head redone or not. Since you say that the gasket was failed, unless you have the head completely redone I probably wouldn't bother having the head magnafluxed for cracks - you already found the failure. (if you insist on doing everything 100% right, and can't sleep at night unless you have perfect confidence that absolutely every procedure has been followed to the letter, ignore previous sentence.) I wouldn't bother trying to decarbon the pistons, you may do more harm than good. If you like you can give it a seafoam treatment after it's back together. If all the pistons are moving up and down, that's good - and if they weren't, something would be horribly broken.

Make sure you chase-tap all the threaded holes in the block and blow them out with compressed air. If oil or debris sits in the bottom of a blind hole you can crack the block when torquing the head down, and even if you don't a loose head bolt will just let the head gasket fail again. If any holes look slightly "pulled" (threads pulling above the block deck surface due to overtorquing by a previous mechanic) chamfer them with a large drill bit. Also make sure the head bolt threads are clean and thread easily into their holes. Use a torque wrench and follow the shop manual torque sequence for the bolts. Other than that, not much to it but to do it.

good luck

nate

Reply to
Nate Nagel

I have read before in books about rebuilding engines, always use new head bolts. cuhulin

Reply to
cuhulin

DON'T USE THOSE PADS ON THE PISTONS. They can cause problems if they leave residue behind. As for how to de-carbon the pistons. Here is the easy way. Turn the crank some so the piston drops down a bit. Now coat the bore with some grease (any kind as long as it's thick and gooey), now rotate the crank the opposite way so the pistons pass up through the grease to TDC. Then use a scraper to remove the carbon (NOT real hard, you don't want to score the pistons). Now clean off all the loose crud. Once your done rotate the crank to drop the piston down. Then clean off the grease. It was there to stop any carbon from going down the gap and will grab any that is on the sides of the piston.

I would check the head surface and block with a straightedge. What you want to watch for is damage in the area where the gasket failed. Only 3 days shouldn't have done any BUT it's best to check.

Also might want to pull the valves and clean the ports and lap the valves to make sure they seal good. Replace the valve stem seals and throw in a new thermostat as well.

Follow the torque specs EXACTLY. Clean the PCV system and make sure all the vacuum lines are in good shape.

Reply to
Steve W.

And DO change the oil and coolant before you start it back up again!

Ron

Reply to
no_one

It can't hurt to use a carb cleaner or parts cleaner on those components while it is open. Try not to clean the dirt ring too much at the top of the cylinder sides where the piston stops.

I highly doubt any damage occurred from the blown gasket.

Be sure you use a spiral torque pattern on both the head and the manifolds. They are very long and need a good torque, preferably in a couple stages.

I recommend you do a retorque of the manifolds after you have driven it for a few miles to fully heat it up. They are notorious for coming loose after a re+re.

Those long valve covers also need to be super clean at the mating surface, same for the head. I use and recommend a brake cleaner spray or acetone as a final wipe because even a fingerprint can mess up the job. I then use a skim of Permatex Ultra Black 'sensor safe' RTV on both sides of a cork gasket and assemble it immediately as directed and leave it the 24 hours called for to cure it. This way they 'don't' leak.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > Hello. First I want to thank everyone who answered my compression
Reply to
Mike Romain

Reply to
Steve

That's only necessary for engines with "torque to yield" head bolts that are deliberately stretched on installation (usually on aluminum head engines) so that the elastic coefficient of the bolts is what determines the clamping force. The Jeep 4.0 has an iron block and iron head with conventional reusable head bolts, although they should be inspected for any sign of stretching.

Reply to
Steve

I had heard the same - replace head bolts every time you have the heads off.

I think this theory started because head (and main cap and connecting rod) bolts are torqued within an "inch" of permanently deforming normally, and if the motor has been serviced in the past you can't guarantee that the bolts were: re-torqued properly, dropped, installed dirty, etc... so it's cheap insurance to replace them. If I was building a race motor worth $10k, sure, I'd be replacing the bolts, but if I'm just R&Ring a head on a regular car, I'll re-use the stock bolts, especially if I believe the last time the head was off the block was when the motor was originally assembled and everything looks clean, but if I have any doubts about them, I'll replace them.

Small block chevy head bolt set from summit: $25 for stock, $240 for the most expensive ARP kit.

Ray

Reply to
ray

GUYS, ANY INEXPENSIVE MODS THAT ARE WORTHWHILE TO DO WHILE DOING THIS HEAD GASKET JOB, I.E. CHANGING THE HEAD FOR SOMETHING WITH BIGGER OR MORE VALVES OR SOMETHING? i HAVE A '96 4.0L H.O.

Reply to
greenstartree

The H.O. 4.0 is about it. Nothing even remotely inexpensive about either of your suggestions.

I would replace any vacuum lines, heater hoses, upper and lower radiator hoses and the serpentine belt. Probably wouldn't hurt to clean out any carbon or crud in the intake system and have the injectors cleaned and flow tested. Replace the plugs and wires, cap, rotor with GOOD new parts (if the ones on it are over a year old)

I would probably also pull the rest of the engine, steam it clean, pull it apart and check the bearings and rings and replace the gaskets. But that is if it was mine.

Reply to
Steve W.

Nope, the 4.0 is pretty much maxed out as it sits.

There are things you can do such as a blower or going all out and turning it into a 4.7L stroker by using the guts out of the old CJ engine, the 4.2L or 258, but none of those are 'inexpensive'.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:
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Reply to
Mike Romain

I assume that the 4.0 also would respond well to mild smoothing/porting/polishing of the intake and exhaust passages, since it responds so well to boring out the throttle body. But then again, that's not exactly a cheap 1-weekend kind of job.

Reply to
Steve

Hello,

I have very similar symptoms to this. Same cylinders and everything. How did this turn out for you. Thanks

Reply to
ChairOKey

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