The Stovebolt Site Forums The Shop Area Engine Shop Rod bearing clearance check using Plastigauge

1958 Chevy 235cid.

I am slowly making progress on my rebuild and I have the crank installed. It's tight but it turn without binding.

Next I am installing the piston assemblies and I want to check the rod bearing clearances before finally torquing them down. Should I install the pistons on the rod and just slide them down the bores, without rings, and but them on the crank? Then check the clearances with plastigauge and proceed accordingly?

The mains were the easy part. How do ya'll check the rod bearings? Thanks for the tips!

Was the crank turned at a machine shop, or checked for size and out-of-round by you?
If so, I would put the rings on the pistons and install them in the block. If you do it as you are suggesting, you are doubling the chance of nicking the rod journals with the rod cap bolt ends as you install the pistons.
When checking the rod bearing clearance, you put the plasti-gauge between the cap and the rod journal, torque them down, remove the caps and measure how wide the plasti-gauge squished. Easy as pie.
Carl

Always get a short piece(2") of fuel line to slip over the rod bolts as you insert them to keep from nicking crank.

Ed

Let me clarify. The crank has been machined and the block made ready by a machinist here in Dallas. I know to put some tubing, or what not, on the rod bolts to protect the cylinder bores. What I was wanting to know was, do you go ahead and install the pistons with the piston rings and just continue installing towards the crank, then measure with plastigauge when you get there? Or does any one just install the rod by itself to check the clearance before final install?

I guess the more I talk this out it makes sense to install the pistons, rings, and rods with bearings to check clearances and then go from there. Correct me if I'm wrong, please. (clear as mud....)

If you've got the reground crank and the rods out on the workbench, it's as lot easier to do a clearance check that way. If the crank is already in the block just check the clearance as you install the pistons with the rings on them. You did get the rods reconditioned, right?

Plastigauge is kind of a SWAG- - - - -better than nothing, but it's only an estimate. When I assemble the 261 our fearless leader is working on right now, I'm going to measure the OD of the crankshaft journals and the ID of the bearings (rods and mains) with a dial bore gauge and whip out my calculator. That's how we did it on the 700+ HP round track engines.
Jerry

1st check to make is the piston to cyl gap, do this without assembling the rings and rods (if you haven't already). IIRC you don't want anymore than .002 clearance (its in the manusl).. If thats right carefully assemble your piston assemblies. Be very careful when torquing the wrist pin nut down so as not to twist the rod. A vice i very helpful. Also there are markings on the top of the piston that mark the front facing edge. The wrist pin hole is not exactly centered on the piston so you want the pistons oriented correctly. The rods also install a certain way. On my 54 235 engine there were markings on the rod caps that should be oriented toward the cam side. Make sure the rod caps go on the way they came off.
I also plastigaged my mains and rod bearings. I did the mains and tested rotation before I installed the pistons then I installed the assembled piston assemblies and plastigaged them installed. I also oiled the pistons/rings and gave the cyls a light oil coating since I would be turning the crank many times during assembly.
Good luck and hopefully the machining is spot on.
Dave

Sounds like you have everything ready to go in. You have answered your own question. At this point, anything more than installing the pistons with the rings on them, then checking the rod journal/cap clearance with plasti-gauge would be extra, unnecessary work.
I have put a number of different types of engines together after spending a lot of money on parts and machine shops, but still, my shorts ride high every time worrying about what I am about to screw up, so I feel your pain.
You've got this! Good luck.

@Hotrod Lincoln- I have not had the rods reconditioned. I'll get them to my machinist and have them take care of them. It doesn't cost much at all. I don't have the fancy gauges and mics so I will have to do it the SWAG way.

And thank you everyone, looks like I have my next direction to proceed in!