1981 CJ7 Restoration - 2021.09.09

Getting back to engine assembly, the next step is installing the crankshaft. This involves a few steps like installing the main bearings and the rear main oil seal, then laying the crankshaft and measuring bearing-to-journal clearance with Plastigages.

Per the machinist, no oil or other lubricants should come between the block and the block-facing surfaces of the main bearings since this will add dimension and create big problems with crankshaft journal clearance. So, I cleaned the surfaces and wiped them down to be sure they were clean. During use, engine oil will eventually get in there, but that's fine after break-in.

Clean bearings and surfaces ready for installation.

All main bearings and the rear main seal halves installed.

When laying the crankshaft, the first thing is to make sure the journals are clean. When measuring the clearance, it has to be done dry. You place a piece of Plastigage in the journal then install the cap and torque the bolts to spec. You then remove the cap and measure the smashed Plastigage against the ruler on the package to see how much clearance you have.

A closer look at the above photos shows one main bearing that wraps around the cap and its home in the block. This is the #3 main bearing and is also a thrust bearing. It is manufactured within a certain tolerance to allow the crankshaft to move ever so slightly along its axis. This end play can be measured with feeler gauges or a runout gauge.

This crankshaft will never look like this again.

I did the clearance measurement for all 7 journals, one by one. They were very consistent and measured 0.002" which is in the ideal range of tolerance. The machinist knew what he was doing.

All clearances check out.

After measuring the clearances with the Plastigage, carefully scrape off the smashed Plastigage and clean the journal surface without scratching it. Now that all of the measurements are done, we lube the bearings and journals and reinstall the crankshaft, then tighten the main bearing caps to spec. Check that the crank rotates smoothly after tightening each main cap.

Lubed and ready for final installation.

For the rear main seal the service manual recommends an anaerobic gel like Loctite 518. An anaerobic gel is a sealant that will cure in the absence of air, so it's a good solution for a sealed environment. It's also very thin so it shouldn't add any dimension unless too much is used. The gel is used to create a dam to prevent oil leakage around the rear main seal.

One other thing, many times mistakes are made by installing rear main seals the wrong way. There is a groove on one side and this should face the oil - the inside of the engine. Installing this backwards will allow oil to be easily pushed out the back of the engine.

Anaerobic gel (Loctite 518) applied.

All main bearing caps installed and torqued to 80 ft-lbs.

Interesting markings on the crankshaft.

1981 Jeep CJ7 - Engine Rebuild - Crankshaft Installation

All done and the crank rotates smoothly. Ready for pistons.


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