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Thread: 1968 Nissan 720 Z24 pickup - head gasket issue

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    Better than that "other" place Not Verified Feedback Score 2 (100%) x2xtreme360's Avatar
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    1968 Nissan 720 Z24 pickup - head gasket issue

    A buddy of mine has had a 720 pickup Carburated Z24 engine that has been sitting for a year. Never has really driven it. One day last week, he drove it, and it overheated and started smoking white really bad and shut down. So immediately I'm thinking head gasket.

    Today rolls around and I decide to do a compression test for him. Cylinder 1=0psi. OK, move on to number two. I left the plug out of number 1, and when we go to test number 2, a GREAT stream of coolant shoots out of number 1. At this point, I start pulling the head. There's no point in testing any further.

    I finally get the head off, and to my amazement, I see cylinder 1, 2, and 3 with about 1/2" of coolant on top of every piston. Cylinder 4 is a mix of coolant and solid black oil.

    The coolant is a no brainer, it's either just the gasket, or a warped head or block, or both. The gasket was trashed, it was obvious. Two head bolts came off with ease, so it wasn't even torqued all the way.

    My concern is cylinder 4. It's highly unlikely that all that oil got in the cylinder via the piston rings, but would it be possible?

    I honestly wish I took pictures. The engine looks clean as hell... bolts came out extremely easy, even on the exhaust manifold (unlike all of our cars), it would be a shame if the engine was destroyed. I will be putting the straight edge and feeler gauges to the block and head later this week. Interested to see how this pans out.

    On a side note, whats the best way to clean block and head surfaces of old gasket material? I don't want to contaminate the pistons or heads with any type of burrs.

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    Forum User Not Verified Feedback Score 2 (100%) RealMcCoy's Avatar
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    A lot of the oil and coolant probably drained into the cylinders after you loosened the head... I wouldn't worry about that much. The block is iron, you won't be able to scar it up easily, just use a scraper and be careful. On the head, I'd use a razor blade scraper, and be careful not to gouge the aluminum. When you get it pretty clean, you can finish up by dragging a fresh razor blade across the surface at a 90 deg angle. It can't dig in that way, but it will remove the remaining material.

    Try to plug the drainback holes to the crankcase so you don't drop stuff into the pan.


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    Quote Originally Posted by RealMcCoy View Post
    A lot of the oil and coolant probably drained into the cylinders after you loosened the head... I wouldn't worry about that much. The block is iron, you won't be able to scar it up easily, just use a scraper and be careful. On the head, I'd use a razor blade scraper, and be careful not to gouge the aluminum. When you get it pretty clean, you can finish up by dragging a fresh razor blade across the surface at a 90 deg angle. It can't dig in that way, but it will remove the remaining material.

    Try to plug the drainback holes to the crankcase so you don't drop stuff into the pan.
    Thanks for the advice.

    The head was the biggest concern, the block is iron so it's tough. The coolant was definitely in the cylinders the entire time. I know because of the geyser of coolant the shot out during the compression test. Not sure on the oil.

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    There is 3m sanding disks that you can put on a high speed drill. They work PERFECT for cleaning mating surfaces.

    You can buy the kit to get the piece the disk mounts too, then buy extra disks. They come in a variety of coarsnesses too.

    Its not metal so you don't have to worry about metal burrs either.

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