I've finally got all my clearance problems solved for my 383 (I think), but I ran into a totally unexpected problem today. This is my first engine, so I could be making a lot out of nothing, but I figured I should check. I dropped the two back pistons into the engine and tried turning the crank by hand by pushing on the counterweights. The crank barely turned, but I did manage to get it to make a full rotation eventually. Then I dropped the next two pistons in and now I can't turn the crank at all. I tried tapping the counterweights with a rubber mallet and the crank still barely budged. What's the deal with this? Should I try installing the balancer bolt and turning the crank over this way?? I don't know what else it could be. Please help!!

 

Paul,
When you start installing pistons, the rings will create friction on the cylinder walls, and the more piston/ring assemblies you install, the harder it will be to turn.

Hope you used some oil on those cylinder walls, and some moly lube or like assembly lube on the bearings, crank, etc.

If you'd like some reassurance that all is cool (I hesitate to use the word "groovy" here), uh, pull off a rod cap, pull the piston back out, remove the main cap on that cylinder, and looky around. No grooves ?

Must be hokay. Don't be torquing, then loosening, then re-torquing these mains and rods too much - uh, like no more than a one-time check.

High-quality rod bolts and mains will let you get away with it, but the "budget" stuff, like many kits use, will have a tendency to stretch and set rods and mains after they are torqued once. Keep loosening and tightening, and you will fatigue/stretch/ruin the bolts.

Relax champ - you're most likely just fine. The crank is hard to spin once you start installing pistons. A better question might be as follows:

Before you had any pistons in, did the crank spin pretty freely after it was torqued down?
It should have. Let us know. Good luck.

BOR

 

BOR has you going in the right direction. Main question as BOR asked,,, was it turning freely before you put the pistons in. If you're not using at least Plastiguage to check your machinist's work,, go get you some. I take it the 350 block has been notched fot the 3.75 crank,, right? If you have good tolorences at the bearings,, sometimes aftermarket 3.75 cranks will kiss the bottom of the piston at the wrist pin boss, I'd check that. Hope everything is Ok,, keep us posted.

[This message has been edited by BadSS (edited October 14, 2000).]

 

Paul
Here are some general guidelines to help you evaluate your progress as you assemble an engine.
The crankshaft alone should be turnable by hand, once breakaway sticthon is overcome.

The camshaft itself with a bolt in its nose, being turned with a wrench should turn easily & smoothly.

Once you start installing piston/rod assemblies, ring drag on the wall will significantly start increasing crankshaft turn-over effort. When installing the piston/rods, you should really have a bolt in the nose of the crank so you can use a wrench to bar over the engine. After every piston/rod assembly you install, I like to bar over the engine at least 2 revolutions to make sure of free rotation (no chopiness or binding).
Once the short block is assembled, meaning all pistons & the cam & timing chain, measure the torque to turn the crankshaft with a beam style torque wrench. I'm not talking the torque to start turning the crank, but the torque to keep the crank turning. I'm going from memeory here, but the torque to keep the crank turning should be around 25-30 ft-lbs if I'm not mistaken.
I'll make the general statement & say you should be turning over the crank each step of the way when assembling the engine.
Regards, FJK

 

Thanks for the tips guys....the crank spun freely before I started dropping in pistons and I already had to have the piston skirts shaved to clear the counterweights. I'll let you know how it turns out.

 

I ran into the exact same problem a few weeks ago when I rebuilt my stock 350. I put some of the pistons in backwards. I dont know about your rods but mine had little "skirts" on the side of the bolts that needed to face the crank weights. Well I had mine facing each other. LOL Best way to verify this would be to insert a feeler gauge between the two rods and see if you get about .018 clearance. If you can't stick anything between em, then most than likely you got em on backwards, mine were so tight I couldnt do it, so I knew there was something wrong.

[This message has been edited by Blade (edited October 15, 2000).]

 

That could be it!! I had my machinist install the pistons onto the rods, so you never know. I didn't measure it, but it looked like there was no room at all between them. I'll have to recheck when I'm home from school again next weekend.
Here's another question for you guys. On all of my pistons, the middle ring doesn't rotate around the piston when it is compressed. It seems to get hung up in the same spot on each piston. I though the rings were supposed to rotate on the piston?

 

Hmm... strange. Are these new pistons we're talking about ?

 

Yes these are new pistons. When I first noticed it on the first piston I thought maybe the pistone got distorted when the skirts were shaved, but it happens on the same spot of each piston. Anyone else have any ideas?

 

One thing that I keep seeing come up which makes me go ! Please, do not use a bolt in the crank to turn the rotating assembly. This is a lasy a$$ way of doing things. Get yourself a crank socket to turn the assembly. If not you could (and probably will happen, I've seen it) fatige and bust the bolt in the crank and the crank could be wasted because you didn't want to spend $12-$20 on a crank socket. These are available through most Performance shops.

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George P. Lara
1994 Z28 LT1 T56
1984 Z28 High Output
Member: SCCA, SCFB, SC3GFB

 

yeap, listen to 'MRZ28HO'.


BTW: When I finished my 350, I was able to turn the bottom end at around 35FP, and I was tight on the tolerances with pressed pistons. Plasic gage every 90 degrees, and check the gap on your rings.

Good Luck,
Ron C. Terry

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'82 Trans Am
'81 Camaro Z-28
'94 Vette LT1 Coupe