I am in the process of assembling a 410 engine now that it is back from the shop. The crank was fine and only needed a polish after 153,000 miles. As some know an FE block rarely needs to be aligned honed. ell I checked the clearances on all the mains and it was at .002+ on all five. Yet when all five were torqued down the crank wouldn't turn at all. So removed #5 and you could forced the crank to move if you pried on it a bit. Removed #4 and now you could turn the crank by hand as one would normally be able to do. Been examining the new bearing halves and see a few shiny spots on those two but not much different from the other three. bearings were well lubed during assembly. So far I see nothing that jumps out at me short of bringing the whole thing down to the machine shop to give a look see.

 

Probably the first thing to do would be to take out the bearings and make sure that each cap is in the correct position on the block. You can do this with a magnifying glass and a bright light. Look at the tool marks made in the block and the cap when the block was originally machined at the factory. The marks vary in a unique pattern and when the right cap is placed in the right spot they match.

If they are in the right places, the crank is straight within a couple thousandths and the clearances are .002 then you'll have to look at the alignment of the housings.

A couple of years ago I had a customer who ran into this on a Chevy 6.0 LS engine that he was building into a 408. Had .002 and the crank wouldn't turn. Crank was straight. I line honed the block, gave it .002 clearance and the crank turned perfectly.

What you'll find when line honing is that you can take a block, cut each cap and make the housings the same size within a few tenths. Then run the hone through the block a few strokes, 4 or 5 and then check it. Sometimes one of the housings will be getting big much quicker than the rest. Some guys will loosen that cap and that's the wrong thing to do. With the line hone we're not just trying to make the housings the right size but also we're getting those housing lined up. What I do it take that cap off and cut it again to make it match the rest. Then usually it'll come right in with the rest of the group. That's the housing that was out of alignment with the rest, using up the bearing clearance and causing the case to bind up.

 

I'm not a machinist, and while all of this above ^^^^ makes perfect sense to me, perhaps it's not the miles (153K), but the years. Maybe things have moved around "just enough" on your block...

Did you save/do you still have the old main bearings? If so, maybe put them in as a test.

 

I think that's exactly what happens, things just move around over time and because it happens very gradually the bearings just wear a bit and everything is fine. Then those worn bearings get taken out and new ones are put in their place. The new bearings don't have the wear to compensate for the out of alignment on the saddles and it locks up or is hard to turn.

The 6.0 Chevy was an odd one for me because it wasn't that old of a block but since that time I've fixed a few more of those that were doing the same thing.

 

I did a re-ring, bearing, cam, and gasket job on a 352 that was in a 74 F100 I bought off of an old farmer (not original, obviously) back in early 1994. When I put it back together, the crank wouldn't turn when the #5 main was tightened...even just a little. Oh well....torqued it down and went!

I pull-started it with a tractor the first time because the starter wouldn't do it, did the camshaft break-in, then shut it off. I drove it 14 miles to school the next day (starter turned it begrudgingly from stone cold), stopping at the gas station first. Well, after filling the tank when warm, it wouldn't turn over with the starter again so I got a friend to pull it with his pickup. It fired right up and I drove it a few blocks to school. After school it started and I drove 14 miles home again with no more tightness exhibited ever again after that.

I probably put 40,000 miles on that engine over 7 years and sold it to a college instructor in 2001 when I built a 390 instead. He put it in a '65 F250 and drove it every day.

Am I lucky it didn't spin a main bearing? Oh yeah. That engine was a beast though for what it was. A Crane Energizer cam, single plane intake, headers, 4 speed. I was a stupid kid but dumb luck for the win! It lived at 3500-5000 RPM from 1994-1996. Then it sat for 2 years through basic/overseas tour, drove from Montana to Louisiana and back (pulling a car trailer with a 67 Mustang back to Montana in 100 degree heat 18 months later) and then the first two years of college before pulling it, replacing it with a 390, then selling it.

 

It doesn't take much to make an engine go from turning to locking up.

A few years ago a customer who is a good mechanic was working on a flathead Packard straight 8 engine for one of his customers. The engine ran just fine but if the car was driven somewhere and shut off it would not restart until it had a chance to cool for 45 minutes or so. It just wouldn't crank fast enough to fire up. They thought that the starter was dragging, cable ends were bad etc, nothing would fix the problem. One day he decided to drive the car to warm it up and then he pulled it into his shop and shut it off. Sure enough it wouldn't start. Just for fun he tried to turn the engine using a breaker bar and he couldn't turn it!

The next day he pulled the engine and tore it down. It had been rebuilt, crank ground etc. He brought the parts in to our shop for inspection. All the bearings and the journals looked like brand new. The mains measured fine but the rods were right at the high side of .010 under. The rods had been rebuilt too. With a bearing installed I torqued up the bolts and set the bore gauge on the pin hone to the size of the journal so that I could read the clearance. The vertical bearing clearance was right on size, zero, not even one tenth. I just used the pin hone and opened up all of the rods to the high side of the spec. This gave it about .00015 or so clearance. He put it back together and it has been fine ever since.

When it was warm it would get tight enough that the starter couldn't turn it but yet it seemed to run ok and the bearings looked great.

 

This catches my attention so much so that I am going to load the block up and bring it down to the shop to check out if alignment is good or not.

 

I did take pictures of the bearings which was almost one year ago. First two main #5 cap then saddle. Next #4 cap then saddle.

 

Next is #3 cap then saddle / #2 cap then saddle / #1 cap then saddle. As I look at the pictures I can see the variation in wear.

 

The caps got mixed up at the factory. I had one like this back in the 80's. #'s 1, 2 & 4 are the suspects. This is why I make sure when I take one down now, the numbers on the caps match the postion they're in. Swap # 2 & 4 and torque it down again. If not swap #1 & 2, or 1 & 4

 

When I took my caps off each one went into its own separate labeled baggy. The machinist then stamped each cap with its number from the baggy. Anyway since I have several engines due to be rebuilt I have ordered myself a 2-3" outside micrometer and 2-6" dial bore micrometer.

 

Turns out there is no issue with mains 1,2, and 3 when installed. Crank turns easy. Main 4 in now you have to really work at it. Main 5 in and you would need a pry bar. So checking those two this weekend after familiarizing my self with a dial bore gauge.

 

The dial bore gauge may or may not tell the tale but at least you'll know if they're happens to be a housing or two that are out of spec size wise. I had a 390 FE block one time long ago before I did line honing that was right at .002 below the low side on all 5 positions. I took it to a shop that did that sort of work and it didn't even need to have the caps trimmed just honed a bit to get it up to size. That would be an easy one.

 

Took me a bit to get consistent with the touch on the micrometer and dial bore gauge. I get clearance of .0035, .0028, .0027, .0028, and .0020 from one to five. Middle mains good, #1 on the looser side while #5 is on the too tight side.

 

.002 is not too tight. That's right where you want to be for most applications.