I am currently assembling a 1994 350 LT1 engine. I just put the main bearings and crank in the motor. I havent torqued them to spec yet. The crank doesnt want to turn by hand. I can take a soft hammer handle and leverage a journal on the crank and get it to move but it doesnt free up. A friend of mine mentioned something about setting the "thrust bearing" by using a soft mallet and smacking the crank a few times from both ends. Can anyone explain this to me what its doing, what the thrust bearing is/where it is. Im going to get some plastigage tomorrow to check my clearance with torque. Only after I take the crank back out and make sure all the bearings are in properly of course. What should my clearance be on a stock crank with standard bearing surfaces and new bearings. Is there anything special I should be aware of during this assembly? I am a rookie motor builder at best. I havent attempted something this in depth since high school vocational class.

 

you should never try to turn the crank without some oil or lube between the bearings and the crank. And you shouldn't have any oil or lube on the bearings or crank when using plastigage.
You're looking for 0.002-0.003" clearances. Anything looser or tighter is cause for concern.
The rear main bearing is the thrust bearing. No need to stress about it, this is still just a SBC as far as bearings go.
Stop using the mallet on the crank, there's no legit reason to use it here.

 

As advised, keep it under 0.003 and closer to 0.002 if you can. Also check for OOR condition. The mains should be no more than about 0.0004 out of round or you'll be line boring or honing and fitting spacer bearings, or possibly installing new caps and boring.

But before you get excited about new caps and machining, the tight crank may not be a problem. Be sure the block and caps are clean before installing the shells. Lube the journals as advised then torque the caps in the three steps required. The shells may not be fully seated until the caps are torqued. Once everyting is seated the crank should spin with about a foot pound or less of effort once it is moving, in my experience.

 

Also make sure the caps are not on backwards. I have seen many people do this including myself. If the caps are on backwards it will not turn at all.

 

If you already had the rods installed I'd say the best guess is that rod bearing caps are on backwards or a rod is in backwards. The chamfer on the rod and bearing need to be against the journal, not against the opposing rod.

Since you only have the crank sitting in the block, I'd say you have the wrong bearings installed or as mentioned above, a main cap may be on backwards. Are the bearings standard or undersized? Have the mains on the crank been machined? If you use undersize bearings on a crank that hasn't been machined, it will be too tight.

There's more to building an engine than simply installing parts. To make an engine last a long time, there are a lot of tolerances to check and a lot of assembly and disassembly for different machine work before the engine is completed. Even though I've been a mechanic for 30 years, I don't having the tooling to properly build a bottom end. I sent my short block to a good machine shop to have them put it together.

 

he's using assembly lube

 

I ended up breaking a main during assembly. I sent the block back to the machine shop with 3 caps I bought off ebay. They chose the one that fit the best and line honed it for me. I started assembling today. I need the vehicle running badly as the transmission in my truck and my wifes car have taken a crap in the last 3 months. (Wifes car as of this weekend) So this will be a VERY fast build from here. I already have the heads cleaned with new seals installed. I have the crank, cam and pistons all installed as of today. I have the day off tomorrow so I will be spending the day finishing the build and installing it in the car. Atleast thats the plan. All going well so far. I will try to update tomorrow. possibly with pics....