Engine Assembly: Installing The Pistons

Next task on the assembly list was installing the pistons. First they needed to be ringed though. The ring gaps had been inspected so I got on with it. Oil ring assembly was first. They were made from spring steel so installation tools were not needed. I just spread the expansion ring and pushed it in the bottom groove. The side rails followed. I was not worried about the gap positions for now. I'll set them right before installing the pistons.

The compression rings are a bit harder so I bought pliers for them. They were only a few euros and made installing the rings really easy. I just had to make sure the moly faced ring was installed to the top groove and that they were installed the correct side up. This was indicated by a dot on both rings.

Then it was time to insert the pistons to their cylinders. Before the final install, I wanted to check the bearing clearance though. I did that only for the first piston as testing all of them would have been somewhat pointless. First the bearings.

Then pieces of rubber tubing over the bolts to protect the bores.

And installation. I had a cheap ring compressor that I screwed around the piston. I sprayed WD-40 on everything and then tapped the piston in. The compressor unfortunately got stuck a bit and broke as I pulled it out. So much for cheap tools. At least I got the clearance measured with Plastigage again.

As with the main bearings, the result was about 0.002 inches. Acceptable range should be 0.002 - 0.003 inches so I was fine.

I did some reading and apparently the best tool for installing pistons is a tapered aluminium ring that is precision tooled for a single bore size. So I went an bought one by Moroso.

You can only use it for 4.030 inch bore size but I don't think I'll be building another engine any time soon. After pulling the first piston out again, I prepared it and the crankshaft for final install. This meant spreading some assembly lube on the journals and bearings...

...then turning the correct journal to bottom dead center (BDC), oiling the bore, locating the ring gaps and using the tool to tap the piston in. For ring gap positions I used the ones instructed in Millers book.

I have to say that the installation ring was an excellent tool! I did not have a single problem with any of the pistons. They just smoothly slipped in the cylinders. I pushed the piston in until the bearing contacted the journal.

Final step before placing the cap on the rod was checking that the locating tab on all the bearing faced towards the center of the block.

This meant that the rod had been installed correctly on the piston. Everything was OK in that front so I torqued the cap nuts to 24 ft-lbs. And after a few hours of work, all the pistons were in!

Turning the crank was naturally much harder now but everything still moved smoothly so this job was done!

Engine Assembly: Main Bearing Clearance

My crank was just machined but I still wanted to check all the bearing clearances just in case. I do not own micrometers or bore gauges so I had to settle for Plastigage. I've read that it is not that accurate but should be enough in my case as the machinist should have measured everything.

Before installing the bearings, I cleaned them and their bores. Then I cleaned the crank journals and finally pushed the bearings in place. After carefully setting the crankshaft to the block, I installed and torqued all but number one cap. For some reason Tom Monroes book says that before doing the measurements, all other caps must be installed. They should not touch the crank and so should not make any difference but I followed the instructions anyway.

I had a strip of green Plastigage that measures clearances from 0.001 to 0.003 inches. I cut a piece of it and carefully set in on the first journal.

Then I installed the main cap, tapped it in its groove and torqued the lubricated bolts to 65 ft-lbs. After removing the cap again, I checked how much the Plastigage had deformed with the supplied scale.

Bearing 1 clearance

Result was about 0.002 inches. Finally I cleaned the bearing surfaces and installed the cap again. Then it was time to repeat all the steps four more times.

Bearing 2 clearance

Bearing 3 clearance

Bearing 4 clearance

Bearing 5 clearance

Every bearing had maybe a bit under 0.002 inches of clearance. The acceptable range is 0.0005 to 0.0024 inches so I should be fine.