Piston rod cap torque sequence

[Jt1776]

First I have to say I'm a cabinet builder building a motor for the first time. So tolerances are quite different. I'm building a 4bolt main chevy 350. I just put the pistons in and want to torque down the caps. There has to be a sequence to tightening down the caps. I tried starting with #1 then #2 but that doesn't work. I do that and it won't move. It must be something I'm doing wrong. I do know that I have the pistons and rods going the right way. Please help the wood wright. Thanks jerry from the motor city.

 

[Customblue]

What do you mean it wont move? The crank? Did you put oil on the piston before you installed? What are your rod bearing clearances?

 

[bedwards]

Sounds like you need to get some plastigauge and check all your clearances on the mains and the rods first before you move on. Don't mean to insult but the rods are matched sets, you do have the matching ones and turned the right way?

 

[Jt1776]

It's OK you aren't insulting me. I'm new to this engine building. I just took them all out and the problem is they were mislabeled from the machine shop. I already put them back in and it turns very easy. What a learning experience.

 

[shiftpro]

Whew, good. And welcome to our place.
There is no order to torque down the rod caps, but I like to set my torque wrench at half the value and torque down, then crank it up to the full value and finish them off.

There is of course a torque sequence for heads (very important) and intake. And you will need to re-torque the intake a few times after a few heat lso your exhaust/header bolts will need re-torquing.

 

[Dutch Rutter]

I went through this whole process myself and while I've built this same exact block a few times now I picked up a cheap online (download) book and it helped out so much.. learned several tricks and avoided many problems and mistakes very worth it if you don't already have one. However, it wouldn't help in this situation.

Good find on a pretty stressful problem!

 

[Snoots]

Welcome from Georgia

You must be registered for see images attach

 

[bedwards]

assemble it with oil =]

 

[Jt1776]

Ok here is were I'm at now. I'm thinking I have the wrong size bearings. What is my clearance supposed to be on a standard 350. I checked it with plastgage and it was . 025. I thought that was good, but when I torque it down I couldn't turn the crank. So I'm guessing my bearings are to big.

 

[Snoots]

There should be a number on the back of the bearing. Was your crank turned? Were the rods resized?

 

[Dutch Rutter]

What snoots said above, those bearings should be sized for both the rods (bearing outer diameter) as well as the crank (bearing inner diameter). Could also have an out of round rod and cap. Where they checked out by the machine shop?

This is all also assuming the crank turned easily with the mains tightened and no piston rods bolted to it. And that everything is well oiled and greased up.

Edit: Could even be a siezed wrist pin bearing but that would have been noticed before putting the pistons in.

 

[QBuff02]

Are you putting everything together with assembly lube? Or heavy weight engine oil at a minimum? Also were the connecting rods numbered as it was disassembled? meaning #1 rod is matched to #1 rod cap and so on through #8? Are you installing the pistons/rods in the correct holes? The connecting rods have a large chamfer on one side that is supposed to match the radius of the crankshaft journal. So looking at the front journal on the crank (where #1 and #2 connecting rods go) the chamfers should be to the outer radius of the journal on the crank. Chevy engines are even down one bank and odd down the other. So if you look at the engine from the front the left side (passenger) is 2, 4 , 6, 8 and the right side (driver) is 1, 3, 5, 7. I know im just clearing a few things up. because i'm assuming you meant .0025 clearance on the plasti-gage which is a good bearing clearance to shoot for in most stock to performance builds. Generally I install the rods and start everything at half torque. I'll install one piston/rod assembly at a time, torque it to say 25 ft lbs and then torque it to 45 ft lbs. when I do the initial torque, i'll wiggle the rod and make sure it has some movement, and then step up the torque to final and repeat. and i'll usually rotate the engine at least one revolution to make sure everything moves as it should. and i'll do this for all 8 pistons/rods. I'll bring that corresponding journal down to the bottom of its rotation (in theory the egine is upside down to torque them, that's how I do it.) and i'll hold the rear rod away from the front on any one journal and wiggle the front rod on that journal to check it, then i'll hold the front rod away from the rear rod and wiggle it to make sure they can move independent of each other, then i'll hold them together and wiggle them together to make sure that they can move together. you want to make sure everything has clearance as you assemble. found a few bent rods this way over the years. Either way, going one at a time will point you to the problem. This is assuming everything is assembled back exactly as it came apart. Any pics? Pics can help show the complete story and help us get you in a direction.

 

[1973c10]

Go get a copy of How to Rebuild Your Small-Block Chevy by David Vizard
it will walk you though the whole process

 

[Jt1776]

They are the wrong size bearings sent from summit racing. First they sent me rings for a 305.

 

[Jt1776]

Thanks everyone. Ok here is what's up. First I do have all the Pistons and caps going the right way. So here is a picture of my bearings. I don't have a mic, but the new bearing is thicker than the original.

You must be registered for see images attach