Custom Search
Post-Header Content
Home --> Archives --> Auto Repairs--> Engine Mechanical--> Rebuilding An Engine
Installing a new crankshaft to fix a connecting rod knock.

Fix A Connecting Rod Knock - GM 4.3 V6:

Engine Rebuild Part 5 - Installing A New Crankshaft

May Also Apply To Chevy / GMC
350 Cubic Inch V8 Engines

In This Article:
The upper main bearing shells are placed in the engine block and the crankshaft is set in place. Main bearing caps are installed with Plastiguage, torqued, and removed to check the clearance. The crank is then re-installed with assembly lube.
Related Articles:
Skill Level:
4 (Advanced)
Time Taken:
2 - 3 Hours
Bruce W. Maki, Editor
Project Date:
August 2011
By Bruce W. Maki, Editor
By Staff
Start >>


Before the crankshaft is installed for good, the bearing-to-journal clearances must be measured with Plastigage. I bought a foot-long piece of Plastigage for about $3. Once I have verified that the main bearing clearances are acceptable, I can install the new crankshaft with assembly lube.

Note that I did not perform many procedures that are typically recommended when rebuilding an engine. I did not get the engine block cleaned in a hot tank, I did not bore the cylinders to a larger size, I did not get the engine block "decks" machined, and I did not get the crankshaft "tunnel" align-bored. Heck, I didn't even use a micrometer to check the diameter of the main bearing bores. But then, I didn't see any signs of trouble with the crankshaft main bearings, just two of the rod bearings. The old crankshaft turned freely, and so did the new one.


Installing Main Bearings:
Installing main bearings in engine block.

I inserted the new main bearings in the engine block, after I wiped the bearing pocket with a paper towel sprayed with brake cleaner.

The main bearings were marked "upper" and "lower". The upper bearing shells go in the block, the lower bearing shells go in the caps.



Note how the tang on the bearing shell aligns with the groove in the casting (arrow).

Tang on bearing holds it in place in engine block.


Crankshaft set in place to measure main bearing clearances.

After all 4 upper bearing shells were installed, I carefully set the new crankshaft in place.



I pushed the lower bearing shells into place in the main bearing caps.

Installing bearings in main bearing caps.


Plastigauge set on crank main journal to measure main bearing clearance.
Checking The Bearing Clearances:

I placed a small piece of Plastigage (red arrow) on each main bearing journal before installing the cap.



I installed the main bearing cap and tightened the bolts to 77 foot-pounds.

Tightening main bearing cap bolts.


Measuring width of Plastigauge on main bearing journal after removing cap.

Then I removed the bearing cap and compared the width of the squashed Plastigage to the scale on the package.

In this case, the Plastigage had flattened out a bit wider than the scale for .002 inches, but narrower than the scale for .0015 inches. That meant the clearance on that bearing was a bit less than .002", perhaps .0017 inches or so. All four of the main bearings had very similar clearances.


The Haynes book says that the GM 4.3 liter V6 engine, for model years 1996 to 2000, should have main bearing clearance between .0011" and .0023". Except for the number 1 main bearing, which should have clearance between .0008" and .0020", which is three ten-thousandths of an inch tighter.

I checked all four main bearings in this manner, doing just one at a time.


Your Ad Here - #1


Installing A New Rear Oil Seal:

Ideally, the rear oil seal would be installed when the new crankshaft is set in place, but I didn't do it that way, as explained below.

Removing old rear oil seal from seal housing.

To remove the old rear oil seal, I placed the metal housing on two blocks of wood to support the edges, and I used a small pin punch and a hammer to pound the seal out.



I cleaned up the oil seal housing with mineral spirits.

I used carb cleaner for the stubborn oil stains, then I rinsed it with brake cleaner, which leaves no residue.

Rear oil seal housing with no seal, GM truck engine.


Installing new oil seal in housing, GM 4.3 V6 engine.

I installed the new rear oil seal by tapping on the edge of the seal with a block of wood and a hammer.

I tapped all around the perimeter to make sure the seal went in straight, not crooked.



I removed the crank and scraped off this old gasket that goes behind the oil seal housing.

I cleaned up the mating surface on the engine block.

This gasket removal should've been done earlier, but I missed it.

New gasket for rear oil seal, GM V6 & V8 engines.


Oil seal installation tool set inside rear seal.

This plastic ring came with the gasket set.

This ring is folded into a "C" shape and inserted inside the rear oil seal to keep the seal lips spread apart during assembly...



... Like this.

But installing the oil seal at this point didn't work for me... I could not keep the seal on the end of the crankshaft and get the seal housing over the stud on the back of the engine block.

I had to wait and install the rear oil seal when I could get the engine off the stand, which meant when I was ready to install the engine and had rented a hoist.

Installing rear oil seal on back of crankshaft, while crank is out of engine.


My Mistake:

GM uses three bolts and a stud to fasten the rear seal block to the engine. I failed to realize that this stud could probably be removed without much trouble, if an impact wrench is used.

With the stud removed, it should be possible to set the crankshaft in place with the oil seal dangling from the end, and then push the oil seal block into the gasket on the engine block.


Installing The Crankshaft, For Real:


Applying assembly lube to main bearings before installing crankshaft.

I applied a bit of assembly lube to each main bearing.

Then I set the crankshaft in place.



More GMC Jimmy / Chevy Blazer
Car Repair Articles:



Most Popular Car Repair Articles:

Our Most Popular Pages:

Build A Basic Workbench (From


Before you hurt yourself, read our disclaimer.









I applied more assembly lube to the crank main journals, and installed the bearing caps, starting at the rear.

I tightened the bolts snug with a large ratchet, then I torqued each main cap bolt to 77 foot-pounds.

After installing each main cap, I turned the crankshaft back-and-forth a bit, to make sure the crank was not binding.

New crankshaft set in engine block, installing main bearing caps.


GM 4.3 V6 engine with new crankshaft installed.

The crankshaft after installation.

If there is a lot of assembly lube oozing out, that's okay.

The crankshaft should turn freely at this point, although the highly viscous assembly lube gives the shaft a "sticky" feel as it's turned.



Next Page: Part 6 - Cleaning The Pistons, Installing New Rings, Installing Pistons In The Engine Block

Previous Page: Part 4 - Honing Cylinders

More Info:
Tools Used:
  • Torque Wrench
  • Socket: 5/8"
  • Misc. Sockets
  • Narrow Punch
  • Small Hammer
Materials Used:
  • Remanufactured Crankshaft Kit with Main Bearings and Rod Bearings
  • Plastigauge
  • Assembly Lube
  • Rear Oil Seal
Do you like this article ?






A portion of this code needs to be generated anew on FB, with URL of new page
 [Top of Page]



Custom Search