The Stovebolt Site Forums The Shop Area Engine Shop Plasti-Gage

Rebuilding my 1956 235 and it time to plasti gage the bearings. Should I gage the crank prior to installing the rear rope seal? Should I lube the crank or gage it dry? What are my options if it reads tight or loose..

I check bearing clearance without a rope seal in place, it gives a more accurate reading. Do the check with the PG on a dry spot on the shaft, as it tends to dissolve when it comes into contact with oil. That's intentional, so any residue doesn't contaminate the lube system. Too tight- - -get your machinist to polish the shaft for a bit more clearance. Too loose- - - -regrind the crank to the next smaller undersize.

A more accurate method of determining oil clearance is to measure the inside diameter of the bearing with a dial bore gauge, and measure the crankshaft diameter, and do the math. That's how we build race engines. Plastigauge is a good compromise for checking street engines.
Jerry

I set the crank into my 1956 block and all was great until I torqued #3 main. The crank could not be turned. I loosened the cap and the crank can be turned. Polishing the crank will give additional clearance but I am wondering if shims can be added to this cap to get the same result.

NO! Do not shim that bearing for clearance unless it's the older design with a dowel built into the upper bearing shell. If it has tabs at the parting line where the block and cap meet, it's not designed for shims. Is there a possibility the cap might have been installed backwards? The anti-rotate tabs should be on the same side, block and cap. I don't remember if that cap can be reversed or not.

I'd remove the crank and bearings, torque up the main caps without anything installed in them, and check the problem bearing bore for diameter and roundness with a dial bore gauge or an inside micrometer. I can PM you the main bearing bore sizes if you need them. It might be necessary to line bore the block to correct the problem. You can also use a thin layer of Prussian Blue on the bearing to identify where the tight spot is located. Good luck!
Jerry

Double check your torque valves and compare your torque wrench with another one to make sure yours is not off.

I new a mechanic that tightened his connecting rods to ft lb when the book called for in lb. Then the crank shaft would not turn.

Seems my block has both....dowel pins in the caps and bearing tabs on the block bearings. The block is late 1956 from the block numbers....can I shim?

The 1956 engine wasn't designed for shims. There should be dowel pins only in the rear cap and caps 2 and 3 should be marked F and R (sometimes you have to look for these) showing which goes forward and which faces to the rear. Let us know if you need more info on this...
Jon

Thanks found the F&R marks...caps are in the correct direction. The second cap back [from the front] is the tight one and it does have a dowel pin to hold the bearing....block bearing has a tab..when I remove the cap the crank turns as it should...next move?

Have you checked the clearance with plastigage? It sounds like there is a high spot somewhere or the crank wasn't turned enough. As Jerry said you can use Prussian Blue to tell you where that high spot is. Did you check the crank to see if it was straight when you had it turned? A bent crank will do the same thing.
You'll have dowel pins in the bearing caps. These fit into the recessed holes in the bearing caps. You should only have dowel pins between the cap and the block in the rear main cap...
One other thought...and this is really a long shot...but make certain there isn't anything in the recessed hole of the bearing cap or stuck to the bearing surface of the bearing cap or the back side of the bearing itself (like a sticker) that would be causing your bearing insert to be pressed against the crank journal.
Jon

Thanks....Jon / Jerry..you guys are always a click away when anyone needs help.....I will keep on trucking...and hunting for my problem...and solution..not sure what prussion blue is and were to get it or how to use it..I guess we have another teaching opportunity.

Good point. Any debris (even a strand of hair) between the bearing shell and the cap will eliminate the oil clearance, at least in one place. If the engine was running before without issues with that bearing, something to do with the assembly process has created the problem.

I recall a crankshaft-lockup problem with a Chrysler 426 Hemi we were assembling for a pull truck. Even after line boring, the thrust bearing cap would lock up the crank when it was torqued down, but substituting a lower bearing shell without the thrust flange would free it up after torquing. It turned out the car the engine came from had been in a nasty wreck, and the thrust bearing cap was bent back .010" in the middle from a hard lick on the front of the crankshaft. Another main cap (and another line bore) solved the problem.
Jerry

Sorry...I meant you'll have dowel pins in the bearing inserts. My fingers were outrunning my brain there.
Prussian blue is...well here is an example:

http://www.oreillyauto.com/site/c/d...h_N0408_-1_-1&pt=N0408&ppt=C0139

Hope the link works. Permatex makes some and O'Reilly Auto Parts sells it (along with lots of other places). Think of your dentist. If you've ever had a crown installed or had a tooth that had to be reduced in height to keep from hitting the tooth above or below it, the dentist had you close your mouth and wiggle your teeth on a piece of blue paper. Essentially the same thing. The blue left on your tooth or the crown tells the dentist where the high spot is.
Jon
Jon

That ad lies! Prussian Blue is anything but easy to clean up! It stains everything it touches a dark blue that's VERY persistent! Great stuff for doing precision fitting, though! I use it instead of lapping compound to check valve-to-seat contact width.
Jerry