Second Chance Garage
All About Car Restoration
Second Chance Garage
All About Car Restoration


How to Rebuild a Corvette 454 Engine — Part 7

While selecting my engine components I decided to go with new I-beam connecting rods. Although they are similar in shape to the stock rods, they're quite a bit stronger. I also chose rods slightly longer than the stock connecting rods (6.385" vs. 6.185"). I chose a longer rod because the new pistons I decided on were slightly shorter than the originals. In order to have the top of the new piston travel to the same height as the old piston I needed to go with a longer rod. Lastly, I decided to go with bushed wrist pins instead of press-fit, this was simply a matter of preference.

Corvette 454 engine connecting rods

The wrist pins I purchased are held in the piston by using devices called Spiro Lox. The Spiro Lox are thin coils of steel that resemble a spring when the ends are pulled apart. They're installed into grooves in the wrist pin bore and prevent side to side movement of the wrist pin.

Spiro Lox

After installing two Spiro Lox on one side of the piston I determined the proper orientation of the connecting rod (one face of the connecting rod should be stamped, this face should be toward the outside of the block when installed). I also determined the proper piston orientation. Once I had the rods and pistons properly orientated I oiled one wrist pin and slid it into into the pin bore until it bottomed on the Spiro Lox. After getting the pin in place the remaining two Spiro Lox were put in place.

Installation of all the Spiro Lox was pretty much a pain in the butt. After a few I developed a feel for it, but with 32 of them all together my thumbs and fingers were pretty sore by the time I was done.

Installing Spiro Lox

So, after several hours of work, below is a typical piston and rod assembly. Next step, get them installed in the block, right?

Piston-Rod assembly

Well, hold on! Before I can install the pistons, I needed to get the crankshaft in place. With all this work new main bearings were definitely in order. I decided to go with Speed Pro (Federal Mogul) competition bearings that feature a 3/4 groove (as opposed to stock 1/2 groove) for improved oiling. I also purchased 0.001" oversize bearings since my main bearing bores had been align honed at the machine shop.

Speed Pro Main Bearings

From the start I knew I planned on Plastigaging the bearings so my first assembly was simply a dry run. With that in mind I placed the top half of the bearings in the block and did not oil them. Once I finish with the Plastigage I'll remove and clean everything one more time before final assembly.


Here's the crankshaft back from the machine shop all cleaned up and ready to be installed. Originally when I took the crankshaft to the machine shop I was a bit concerned because there were several small knicks in the journals. Lucky for me the machine shop was able to polish them out and the crank came back looking great!


With the help of a friend I got the crank placed in the block. Of course we were very careful to set it evenly into the block and took care not hit the journals against anything during installation.

crankshaft in place

With the crankshaft in place it was time to break out the Plastigage. Plastigage is precision formed piece of wax that is placed between the crankshaft journal and bearing. The main bearing cap is then installed, torqued to specifications and removed. After the cap is remove the oil clearance can be determined based on the amount the Plastigage deformed or "squashed".

Plastigaging must be done with the journals and bearings dry, so that means don't spin the crank or you run the risk of damaging your bearings! The first step is to install and torque all of the main bearing caps except for the bearing you plan to Plastigage. A strip of Plastigage is then placed across the journal an the bearing cap is installed, torqued to spec (in 10 ft-lb increments), and then removed. Again, don't spin the crank or you'll have to start over since this will smear the Plastigage.

ready to receive the Plastigage

Torquing the mains

The Plastigage comes in a sleeve that doubles as a measuring tool and is used to come up with the oil clearance. Below you can see this bearing has an oil clearance of 0.002". I'm shooting for 0.0025" so this is just about where I want to be. After cleaning the Plastigage from the bearing and journal the main bearing cap was reinstalled and torqued, and the adjacent cap was removed and the process was repeated. I checked each of the main bearings and clearances ranged between 0.002" and 0.003". This is about as good as I could expect so I'll go ahead and complete final assembly of the main bearings.

using the Plastigage

After removing the crank one last time, the bearings were removed and the block and bearing mating surfaces were thoroughly cleaned with lacquer thinner. It's important these surfaces are clean and dry, any oil or grease on these areas can lead to a spun bearing sometime down the road. And yes, that was a bad pun :)

Cleaning the bearing surfaces

Making sure that both mating surfaces are clean

After a thorough cleaning the bearings were reinstalled. With the bearings cleaned and back in place I moved onto installing the rear main seal.

Fel-Pro main bearing seals

I installed the seal in accordance with Fel-Pro's directions and offset the seal parting lines 3/8" from the bearing cap and block parting line. I also applied a thin film of RTV black sealant to the ends of the seal and cap flange to help prevent any leaks. Lastly, I coated the seal lip with a thin layer of grease. The picture below is of the seal in the bearing cap.

Main bearing seal in the bearing cap

Once the bearings and rear seal were in place I oiled the crankshaft journals and main bearings and installed the crankshaft. After torquing bearing caps one through four to specifications I aligned the thrust bearing by prying the crank back and forth a few times. This is necessary because the rear main bearing is flanged, doing this ensures the two bearing halves are aligned vertically.

aligning the thrust bearing

So, this is it. The crankshaft is in and torqued to specs. You'll notice that I got rid of the stock main bearing cap screws and replaced them with studs. Studs allow for more accurate torquing and also lead to better main cap alignment. They are also considered by many to be stronger than the stock bolts.

New bearing cap studs installed

Boy, this was a busy weekend, but it's not done yet. On to the piston installation! Similar to before I cleaned the bearing mating surfaces thoroughly with lacquer thinner before installing the connecting rod bearings.

Thoroughly cleaning bearing mating surfaces

Installation of the connecting rod bearings is pretty simple, similar to the main bearings the two halves can easily be pushed into place with finger pressure.

pushing bearings into place

Next I submerged each piston in a small container of oil to ensure the rings, connecting rod and wrist pin were all well oiled prior to installation.

Making things slippery

After allowing the oil to drip off in a separate pail for a few minutes, I verified all the ring end positions, adjusted them as necessary, and then used a ring compressor to compress the rings. After oiling the connecting rod bearing the assembly was ready for installation in the block. I should also note here that having a very clean work area during this process is especially important. All these oily parts act like dirt magnets. With this in mind the first thing I did was thoroughly clean my work area and then put down a clean piece of cardboard as a working surface. This is a messy process and I didn't want to get a bunch of oil smeared all over my bench.

piston inserted into ring compressor

To facilitate installation I rotated the engine block so that the cylinder bores were as close to vertical as possible. I'm starting with piston number one so I also rotated the crankshaft to bottom dead center for that piston. After double checking for the correct piston orientation I set piston one in bore one taking care not to scratch the cylinder wall with the connecting rod.

installing piston with great care

Using the wooden handle of my rubber mallet I gently, but firmly, tapped the top of the piston to drive it out of the compressor and into the block. Don't hit too hard or you'll risk breaking a ring or knocking the bearing off of the rod. In a few cases I had some difficulty with pistons not entering the bores and getting hung up, I simply removed them, reset the ring compressor, and started over. I figured doing so was a lot easier than replacing broken rings. Once the piston enters the bore be sure the connecting rod clears the crankshaft journal properly. This can be easily forgotten leading to a heavily scratched journal and a lot of headache!

Tapping piston into place

With the piston set into the bore and the connecting rod set against the crankshaft journal I installed the connecting rod caps (with plenty of oil) and torqued the rod bolts to manufacturer specs.

Torquing to specs

Phew! This took a while, but here are a few shots of the end result, it's really starting to come together now!

Looking good

from the top

I'm not quite sure where else to put this, so I'll add it here as a point of interest. At this point I've not mentioned anything about balancing the rotating assembly and thought I should. Engine balancing is quite an involved and important process that, unfortunately, some people overlook. A complete balance job includes dynamically balancing the harmonic balancer, crankshaft, connecting rods, pistons, rings, wrist pins, flywheel, and clutch pressure plate. Simply weighing each component separately and balancing each part is not sufficient, the process must be dynamic (the whole assembly must be spun) to be accurate. I was fortunate enough to have the machine shop owner spend about a half hour explaining the whole process to me and it's quite something.

Anyway, stay tuned there's more to come soon! I'm off to the machine shop to pick up the roller cam!

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