First, I am not a mechanic. Second, I've rebuilt from the ground up 1 VW Transportor, and it's engine, a 1500cc w/1600 heads, and ran it on gasoline, and propane. Another engine I rebuilt was a 258 AMC Jeep Cherokee engine, just for fun. Another was a head job on a 1700cc Ford Courier, and it's installation. Point is: is that there is some controversy regards head-replacements, and whether there is a need to do the lower, or not. Type of gaskets, head bolts, etc., and the ever forgotten to do.., in service torque check(s).
Many obtain a used head from a yard, and I have! Some say only new, and too, I have done so. I have 'ground' my valve seats, and have let machine shops do it.
If you get a used head from some yard, either by pulling it yourself, or off of their shelf, take it home. You can do a couple of checks if you have some tools. You can remove the valves, and look for some burn spots.., i.e., major differences in colorizations along the head valve seats, and edges of valve rim/seat. You can look for melted away spots at/or on each issue. At the same time, you can look down into your cylinders to see if there are any melted areas on the top edge of any piston.., and can look for terrible scuff/stratches on the cyl. walls. That's another determination for a different thread. If you do not want to pay for the valve removal/installation tool, (always buy a good one, [hundred bucks, +/-], or rent), then at the very least, before you take it to an automotive machine shop, set it upside down, i.e., springs down, and with a can of WD-40, and a sheet of glass you can do a "warp-check". Bubble-Level out the head on the support stand, table, etc., and then spray all gasket flatsf, i.e., just spray the whole thing, and then carefully lower the clean sheet of glass down onto the head. What happens when you have an unwarped head is that the contact surface of the glass on the WD-40, will spread out evenly. If warped, the glass will not contact the WD-40, and you will see that. There are some technical details about how much 'surfacing' can be done before you have to make some spacer adjustments on the opposite side. Usually, if the oem head is not to warped, it'll probably be ok for a little surfacing. I've done surfacing on several heads with nothing more than a good file, and carefully making constant checking with the glass sheet. Using a magic-marker to delineate progress works well. If you look at the other side, and the valve rims/seats to head valve seats look ok, (use a magnifying glass), you are in good luck. That would indicate that all the springs are within spring values, and the used head did not experience damage severe enough to go have them, and the valves replaced, and the surfacing done. You can do all aspects of the job as heretofore mentioned.., as long as everything is good, i.e., you are just cleaning, and checking, slight surfacing, and possibly replacing oem parts, if needed, and again, with good luck you will not need to do that.
Here is where there is some controversy. I do not claim to know which is best. However, if you can, get a pressure gauge to fit your spark plug holes into the head, on the engine, and turn over the engine, (without firing it up, and over, i.e., just around 4, 5 quick turns, and read the gauge, write it down for that cyl. You will look in your manual to see the values for ok readings. It will all be explained in the rather inexpensive Haine's Man., or the more expensive official super-duper OEM, (for your year), Service Manual(which you shoul get anyway, or visit your library, and get lucky, lol). If the pressure values are within allowance, you are good to go with the 'clean used head'. If the pressure values are skippy bad on one or more cylinders, then you are looking at some replacement rings, and perhaps piston wrist pins, and perhaps some rod bearings. In either case, a replacement head that is tighter due to replacing with new parts might be too much for the lower to deal with, i.e., more pressure to deal with than what the skippy cylinders can handle. In which case you would get a lot of blow-by, and other issues. The idea is to 'match' top and bottom as per being able to handle the explosions. I know, it's controversal, but that is the way it is. Two camps. My suggestion is to make those checks on the used head, and if that is good, and your cyl. pressures on that check are ok, you can probably, with confidence, get away with putting a used replacement head, on what is a used engine, i.e., both have around the same mileage to better match. The ONE THING you better not forget to do is to obtain brand new OEM HEAD-BOLTS. Search the forum(s), for the best head gasket for the 4.0. Also, after about a couple, or three, or four gasoline tank refills, take your valve cover off, and check the torgue values of those new bolts, i.e., loosen them up a quarter turn, and re-tighten to specifications again. This latter proceedure is often overlooked, or forgotten, or dis-ed, etc., but it is very important. Things stretch, (bolts), and warp, (head), and after a bit of driving the possibility of those happenings to happen are paramount, making it, (IN SERVICE), necessary to re-check, to prevent.
To me, the only bitch is all the crap around the head, i.e., electrical/fuel/manifolds, etal, that stand in the way, causing time, and removal problems. In a way, with father and son trips.., I'd get together, have a discussion about what the deal is all about, i.e., what pluses, and minuses, possible hold-ups, broken studs, etc., can cause as per attitudes, and adjustments, thereof. (Both should study up so as to fill in any proceedural memory gaps). Drilling a hole into a broken stud, using an 'easy-out', and having that break, can cause possible grief. However, the rational, logical thing to do, is then take the head, or other parts to some mechanic that has other options/tools/knowlege to better deal with those so-called minor issues, lol. As Tim_MN said, it's a good thing for your son to get involved, for his own sake, too.
While you are studying the forum(s) thread(s), you can obtain a manual, and begin the tear down process in an orderly manner, labelling everything, using plastic sandwich bags, egg cartons, etc., to place all parts neatly someplace. Having rather dedicated places to place tools will help too, since wasting time looking for tools, or parts, will be frustrating.., and remember, time is money. I could do some head work in several hours in the old days, lol, but now with all the complicated easy to break connections, I's say the 4.0 will take longer. Perhaps someone, or more, will break in and share the hours it takes to do the job on average. I do not have that automotive time/data before me.
My hope is that the two camps will offer up a small debate, and/or make other suggestions, pro, and/or con to mine, so that you can write down in a note book what will be your judgement call alone, and perhaps with your son.., on what we input, and then make a shopping list. Best wishes for future happy trails:us:
