Another 12ht long block build (1 Viewer)

roma042987 · Nov 20, 2020

My first 12ht build thread Builds - 1987 fj60 12h-t h55f conversion
is getting convoluted with two other 12ht builds so I thought I would start a separate thread for this one. This is my 4th 12ht to rebuild and the 1st engine I acquired and initially swapped into my 60. I had driven it approximately 2300 miles immediately after installing it when it broke down on me in Maple Creek Saskatchewan Canada. It seemed to have lost some oil pressure and locked up. After cooling off, it had restarted with alot of smoke but, I didn't drive it again with the exception of moving it into the garage. I built another 12ht for that truck and this one has set in a box for a few years. I've recently decided to tear into it to see what happened and rebuild it before all the spares for these engines are entirely gone.

roma042987 · Nov 20, 2020

This will be a SLOW build because I have a ton of other projects going at the moment and two little ones along with a full time job that demands alot of travel. I started about two months ago by pulling the head.

roma042987 · Nov 20, 2020

The rocker assembly came apart, I inspected the rocker faces for wear as well as the shaft. No grooves or pitting so a thorough clean, lube, and reassembly. The head was stripped of paint and sent to the machine shop.

roma042987 · Nov 20, 2020

The cylinder head came back with new push rod tubes, seals, and other wise a clean bill of health. A quick clean, acid etch, and some tedious taping before applying KBS engine coater.

roma042987 · Nov 20, 2020

12 new exhaust studs

I'm stashing everything away in this big pelican case to keep it organized and away from dust and humidity since it's going to be a drawn out build.
The valve cover will come back out for a vapor hone cleaning.

mongoose2231 · Nov 25, 2020

Another of your great rebuilds!
Awesome...

roma042987 · Dec 27, 2022

A few weeks ago I finally got the short block up on the engine stand. Timing cover, rear seal retainer, and oil cooler came off on there way to the vapor hone. Lifter covers and oil pan were removed to access the internals. I started pulling the pistons and instantly found the culprit. #6 rod bearing had spun.

roma042987 · Dec 27, 2022

Bearing material blocking the oil orifice.

The rest of the rod journals as well as the mains look like this.

The factory pistons show no signs of ring damage, which is common on high mileage 12ht's. The cylinder walls have no scoring and nice cross hatch is visible. All bearing sizes are standard size as well, which leads me to believe this one has never been apart before and is relatively low mileage. All the bearings seem to have a rough texture compared to any I've come across before. It's as if something corrosive had perhaps at some point was introduced into the oil. The camshaft lobes look great but the journals do have some scoring.

roma042987 · Dec 28, 2022

Using a couple of pieces of wood the camshaft plug is removed followed by the cam bearings.

roma042987 · Dec 28, 2022

By drilling a small hole in the center of the front oil galley plug I was able to pull it with a seal puller. Then using a really long 3/8 extension, drive out the rear plug.

roma042987 · Dec 28, 2022

In this state everything is removed with the exception of the coolant freeze plugs and the machine shop will be able to flush all of the oil passages of any remaining fod. The cooling system on this engine wasn't corroded like one of my others so there is no need to remove the coolant plugs. I cleaned all of the old gasket material off the gasket surfaces and wire wheeled the coolant galley behind the oil cooler to remove the scale and crud. It's off to the machine shop for a once over. The cylinder walls will be examined closer to determine if a bore is needed or a hone will suffice. The camshaft will likely be ground as well but I will wait until they tell me how much will need to removed, then compare that with what size bearings are available. The crank shaft and #6 rod are going to a crankshaft specialty shop up north. I did advise the machine shop that I wanted all of the paint removed from the block and asked them to ring me after it has been through the hot tank once so, I could come by with some paint stripper and apply it before another rinse. I had to do some paint stripping on my last build after the machine shop did their work and found it difficult and less than ideal at that time.