coled18

Hey all. Am rebuilding my 72 cutlass S 350 rocket and my crank won’t turn. Right now the motor is just the block, crank and pistons. I re ringed the pistons and without torquing the rod bearing cap nuts I am able to spin the engine normally. However once I torque down the nuts I cannot turn the crank. I made sure to oil only the journal side of the rod cap bearings... I’ve replaced the bearings because I originally thought it was bad bearings but maybe not? Please help?

66SportCoupe

Sounds like the wrong size rod bearings

1970cs

Are you turning by hand? By the time you get the mains and rods torqued. There is a lot of friction to overcome. You should try to clean under all bearings and the mating surface before installing. I also turn after each main and rod cap is torqued. I usually use two flywheel bolts and a decent pry bar to turn the crank.

Pat

coled18

How would I go about getting right sized ones? This is my first time so I’m a bit confused.

coled18

cylinders are honed, everything is cleaned pretty well. I tried turning it by hand and it turns with a good amount of resistance but there are two pistons that when torqued down it won’t turn, so I might try swapping those two in case I accidentally swapped them before. If it doesn’t work I think I might have bad new bearings. Though I am confused because I torqued just the first piston down afterwards and the crank didn’t turn at all, and the first piston never had any problems before.

deadeyejedi

I would plastiguage each rod bearing individually and see what your clearance is . If you have factory connecting rods perhaps they are out of round and binding . What prompted you to do the rebuild ?there are experts here that know more about this than I do and should be able to help you out . Good luck

Sugar Bear

Any chance the bearing caps were swapped?

66SportCoupe

You said you replaced the bearings. Did you mic the crank and get the correct rod bearings?

1970cs

Agreed, plast-gauge and measurements. Did you stamp numbers on the caps and rods?

Pat

Greg Rogers

I hope you marked everything and are putting back in the same spot, that is important...

66SportCoupe

He needs to know what the crank journal size is at first. What is the part number of the new bearings? It's sounding like he possibly has std. crank and got oversized bearings.

skyhigh

After you did the cam bearings did the crank turn fine?

Owen Miller

My thought exactly.....

70W-32

Or the rods are in the wrong position, allowing the bearings to hit the crank camphor

coled18

Turns out a few of them were switched by accident. However I got to 6 and 8 and had a bind. With 6 torqued down all the way, the crank would turn but only with a lot of force. With 8 torqued down all the way the crank wouldn’t move at all. I tried swapping caps and pistons just to see but to no avail... should I just get new connecting rods/pistons?

BillK

Coled,
Take your rods and pistons to a local machine shop. They should be able to match them up for you to their original positions. Its not hard to do if you know what to look for. If the engine was running fine before then there should be no need to buys new rods etc. Dont make it any more complicated than it needs to be.

Sugar Bear

Glad you found it. Follow BillK's advice.

Good luck!!!

coled18

For me it’s not a matter of matching anymore, however will a shop be able to recondition them so that they’ll allow the crank to spin when torqued down to spec?

Loaded68W34

The new rod bearings should be stamped on the back side with std (standard) or the size the crank has been cut to (.010, .020, etc.) It is rare, but I have seen rod bearing sets with one or two bearings that were the wrong size. This happened to me years ago on a Cadillac, it was a set of standard rod bearings with 1 rod half bearing that was .010 under. Didn't realize it until the rod was torqued and the motor would not spin. First check the stampings on the back side of the bearings, then as others have said use plastigauge to check your clearance. I don't think you ever answered the question; is your crank standard or cut undersize? If cut, how much?

66SportCoupe

Hello this what I've been saying all along. He hasn't given part numbers for bearings or anything. His bearings are not matching his crank. Not rocket science!

Loaded68W34

I realize you have been saying this (the reason I included "as others have said"), but obviously this is his first build and I don't think he understands what you were asking. I was merely trying to explain to him what to look for and be a little more specific so that he may understand the problem.

66SportCoupe

If anything locks up and doesn't rotate means nothing has been measured. I understand he's new to this. However when anyone buys parts they need to know what they are getting into. Some of the stores don't help.

Loaded68W34

Agreed. Usually because many of the employee's have no real experience working on cars in general let alone classic cars. More about being able to look up something on a computer. Tell the counter guy you need a part for a 65 cutlass with a 455 and a 200r4 transmission and watch him scratch his head.

coled18

I thought I had answered, but I forgot to send!! I made sure the bearings were all standard size, my crank has not been ground down or anything. I plastiguaged the bearings since my first thought was maybe I had bad bearings but they were all in spec, even the bearings on the pistons that didnt want to move once the caps were torqued on. Granted, they were on the tighter side but still within spec. I think I will have to take the two units giving me trouble and go to a machine shop, hopefully they will be able to recondition them.

Cutlass Fan

You never did say if the rods and caps were all kept in order and replaced in the same order. Is it possible that they got mixed up or even that 6 and 8 might have gotten turned 180*?

Sugar Bear

In post #15, OP said the caps were switched.

Sugar Bear

coled18, Take the pistons, rods, caps, bearing inserts, bolts and nuts when you go to a machinist.

Good luck!!!

Tedd Thompson

It is so rare that bearings would be miss matched that I would look there last. My money is on the caps or rods being swapped. You are putting the caps on like they came off all in the same direction , some aren't reversed end for end?.....Tedd

Vista67

I recently had a similar experience that was due to one bad rod bearing shell in the set. If you are still having binding issues also check the shells for quality. I put a replacement crankshaft and new bearings in a 468 beater engine that I keep as a spare. I was doing this with the heads still on so there was no way I switched anything around. Everything was going fine with the mains but as I went through each pair of rod bearings the engine locked up when I torqued down #6. I took the shells out and they were labeled with the correct size but it measurement showed one of the bearing shells was thicker at one end and must have been the cause of the binding. This was a set of China made Engine Pro CB542P8-10. The Engine Pro bearings had come with the 10/10 crank I had picked up with a pile of parts from somebody's abandoned project. I took all the Engine Pro bearings out and chucked them and put in the USA made Clevite's with the same part number. I should have known better.

zzcruzin

X2,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,rods and caps should have been number stamped before disassembly. Rod studs should have small rubber protectors on them when installing, to protect nicking the crank. OIl is ok to lube the bearings with, but assembly lube is better. Have to ask also,,,,,,,,,,,do the pistons have a notch in them to face forward? Maybe.

coled18

I will do this today! Hopefully that fixes everything. Thanks all, and I will keep you updated.

madmax442

If it’s not mismatched parts or wrong bearings you might have a bent crank.

coppercutlass

Are the rods properly installed there is a bearing off set the chamfer has to face the cheek of the crank throws. This happened to me before. I didn't number the rods properly and the machine shop assumed I numbered by cylinder.