So You've Got A Blown Head Gasket - Here's What You Need To Know To Make It Right

I worked in a machine shop for 5 years doing nothing but cylinder heads, never seen surface like that. One thing I would strongly recommend for anyone is to use a straightedge long enough to span the entire length of the head and use feeler gauges to figure out the straightness , checking in the middle and both sides and in a x pattern, especially on a straight six.

That was a Friday afternoon at the factory head and the guy could already taste his first beer.

Nicely done Tony. Back to the UTG of old, simple explanations for the newbies at this kind of thing. 👍

Somebody has been in there before you, i have never seen factory machine work that bad.

The mill or decking machine had a worn saddle that holds the work surface or table. It's rocking as it passes center, so the tool is back cutting.

Your tip about not using a "ziz-wheel" (die grinder with a "rol-loc" scotch brite disc) is a good one. I have dozens of hours of experience using one and it still gives me great concern putting one to mated surfaces because gouging is such an easy thing to do. If you know what you're doing, are pressed for time and take the care, ok but otherwise, i have a scraper handle that holds a standard razor blade and that works great with a torch, just like you said. It's easy to want to "be like the pros" and pick up die grinders and other power tools but, they can get you into trouble just as easily as they can get you out. "Take your time" is one of the best pieces of advice you can give to a home mechanic/hobbiest. 😊

Tony,there is no way that head came from the factory like that. It’s been off before and some jackwagom machine shop screwed it up.

I would only use a straight edge that is long enough to hang past each end of the head and the deck surface. And I would check valve guides before I would send it out . And I would do pc press on seals . Valve job ? Or just lap them . I always spend to much time and money. Lol but I don't have come backs . Have a great day sir !

Still raining.....good weather to work on the Jeep!

the weak points in the drivetrain as a tow vehicle is the short whellbase. the rear driveshaft angle will wear out those small U joints pretty quick. The short wheel base will also cause handling issues with the rear suspension being so soft the trailer is going to push the car around.

Tony - Back in the day I had a '67 Chevy panel truck (a suburban without side glass). It came to me with a 250 straight six (one barrel carb) and a 3 speed manual. I installed a 400 turbo and hitched up a 2800 pound travel trailer and probably another 500 pounds or more of gear in the back of the truck, and hauled it around for two years while my wife and I traveled an itinerate circuit with other artisans. The only time I really questioned my mission was going up Jellico mountain in Tennessee with my foot to the floor going 45 mph. However, I figured I wasn't doing too bad at that since I was still passing many a semi rig! Made it over the mountain just fine, and never dropped below 45 mph. I think your Jeep will get you where you want to go.

Jeep fanatic here. It's overstated I know but the 4.2 and 4 ltr are up near the top of best motors ever. Glad to see you playing with one. I've had about every jeep but an old CJ 5 with a built 4.2 grew on me. Not many sports cars would compare IMO.

GREAT wisdom on "reading" the gasket! I'll be pulling the head on a straight 6 with poor compression and will keep this in mind!

For those who replaced everything (stock parts of course) in your cooling system but still run hot, the beginnings of this type of HG issue is your likely culprit. Mine wasn't totally blown out like this but was starting to in the middle (like cyl 2-3 and 4-5 on this one). New HG, head resurfaced and no more running hot issues.

I honestly thought you were gonna let it ride like that. Either the cutter was incredibly dull or the feed rate was set at light speed. I'm blown away at how gnarly that machining is.

Good idea would be to check the depth on the threads in the block in that area

Tony, Invest in a TRUE machinists straight edge. Yes they are pricey, but the cost is offset by the accuracy and peace of mind that what you've checked is true. Years ago I knew I would be doing head gaskets and other work requiring one. I bought a Starrett 48" machinists straight edge, accurate to 0.0002, it was about $500. For "truing-up" heads, I got a large piece of polished granite building cladding that was a scrap piece from a commercial stone building supply house. It was about 3' X 4' and an inch thick and was damaged because a small corner was broken off of it. I think I paid about $50 for it. When I checked it with the straight edge, it was dead flat and true in all directions ! For doing heads, I lightly fog some 3M "77" spray adhesive on the granite and then, using a rubber Formica" roller to glue down sheets of 3M "Tri-m-ite" sheets of wet / dry paper to it, no over-lap, just edge to edge. I use water for aluminum heads, light oil for cast iron and lay the head on it and work in circular motions, a poor mans way of lapping. A friend of mine has an optical comparator ( owns a machine shop ) and I've gotten surfaces finer than 30 RA this way. ( RA is Roughness Average, measured in microns. millionth's of an inch.) Needed this RA for using 6 star HG's for earlier Subaru's that were built to stage 2, notorious for HG failures. NEVER had one come back. Automotive machine shop head grinders typically end up at about 100 RA, maybe 90 RA in a perfect world. 30 RA looks like a mirror.

Here comes a daily series!!!

I surface a head like that myself with sandpaper. I cut open a belt sander belt, then glue it down to something flat ( a piece of glass, stone counter top, tombstone, ETC). Then I just slide the head around on the sandpaper until all the dark marks are gone. The head won't have to be disassembled, I don't have to wait on the machine shop, and it saves cash. I do own equipment to do a valve job, so I usually do a valve job at the same time, but it isn't always necessary.

Thanks Tony. Great how to video. It seems like you were fairly thorough. You touched on important things to look for at time of tear down. Nice job. 😊