Hi all,

This is my first post here but you've all helped me along the way as I performed a restoration on my grandfathers '74 f100 shorty for my son. Getting down to the end here and have run into an issue while rebuilding the 390. We purchased a dissasembled 390 with "most" of the machine work done. Crank is good and reground 10/10, pistons are standard. We got the crank bolted and torqued to spec and it wouldn't rotate, out came the crank and the block was off to the machine shop for a line hone. Got her back and bolted in and the crank turned by hand. So far so good. Installed the pistons today with 10 over bearings and once they were all in the crank was hard (very hard) to turn with a 3' breaker. Removed a couple of sample rod caps to check clearance, it's ~.001-00125, seems okay to me. Next I loosened all of the caps to 10lbs and tried to turn the crank, better but still seems much too difficult to turn. When when I torque the harmonic balancer nut to 90lbs I don't need to hold the crank like I did on the old 360. I've built a few small block Chevys but this FE stuff is new to me. Any help is appreciated. Rod bearing journals are ~2.426, the caps are all correctly matched, pistons are new standard as well as the rings.

Thanks,

Jason...

 

My 390 was fairly difficult to turn after all the pistons were in. I think the combined friction of rings for 8 pistons in freshly honed bores is more than we realize.

Do this. As you install the pistons and rods again, rotate the motor over after you install each one. If it gets progressively harder to rotate with each piston installed, it's probably just rings. If, however, you get one that seems to hold up the works, then it merits investigation.

 

I'm not positive, but .001 -.00125 seems way too tight on the rod bearings. I think they should be closer to .0025 or so.

 

is that side clearance your measuring or plastigauge ? side is .010 - .020 max of .023
Did you check ring end gap ?
Plastigauge for main caps is .0005-.0025 desired .0005-.0015 dont see anything for the rods right of hand (seems I recall checking mine)..might have gotten the number here ?

 

.001-.00125 is the rod bearing clearance, seemed a little tight to me but I can't seem to get a straight answer anywhere on this number seems to be some kind of voodoo around it :-) . Side clearance seems fine (same rods and and crank) so it hasn't really changed in 35 years. However, I may need to get the space in the right spot, but I figured loosening the caps woul alleviate any binding in either of these areas. Maybe the rings?

 

The first engine I built myself was a 292 Y-block back in '67. One of the things I decided to do was to put my torque wrench on the crank snout and measure the torque to rotate the engine - not static to start rotation, but dynamic torque to keep it freely turning after static friction was broken. First, just the crank, with only the main caps finger tight; then after torquing each main; then after installing the cam; then after each rod & piston assembly. I was pleased to note that the number climbed very slowly in even increments with each rod & piston. I do not remember the final number, but it was so low, even with the rings installed that I would probably start an arguement if I posted it.

I still do this, but my arm is now a little better calibrated, so I just do it by feel. I have built several engines that were, by plastigage, near the lower limits, so I doubt that even .001 clearance would cause a problem if everything else was in order and properly lubed with assembly lube. I will list all the possibilites I can think of and invite others to add to the list. (I will list possibilities that may not apply in this particular case for the other people that are reading this thread for information.)

o Ring end gap problems and other ring-related problems such as problems with assembly of three-piece oil control rings. Is the carbon cleaned from the ring grooves in a used piston, or are the ring grooves deep enough in a new piston?

o Piston fitting. Did your machinist fit your pistons to each bore & number them? Sometimes if all the pistons are not the same they will do this, but they should remind you not to assemble the engine randomly. (If they put the pistons on the rods, then putting the rods in the right place would take care of things unless someone was thinking Chevy numbering and someone else was thinking Ford.)

o Problem with a bearing not seating fully in its bore. This could be a piece of dirt or a metal burr on the bearing. It could be near the cap joint and still give a good clearance at the plastigage part of the clearance. I notice that you did not plastigage all bearings, so you could have one or more that are tighter.

o Rods that are not straight - upper & lower bores not parallel. Did you have the big ends of the rods re-done? If they are out of round, things can be tight across the cap-joints and be OK at 90 degrees to that plane.

o Eccentric rod journals (not in this case, with a ground crank).

o Cam bearing bores not in alignment; not a likely problem in an FE, but I did run across it in a small-block. Did the cam slide in easily?

o Main thrust bearing issues; did you pry the crank forward & back before torquing that main cap?

o Rear seal installation-related problems.

I do not mean to insult anyone, by listing all of these, but I guarantee that some very nice persons have managed to have made every one of these mistakes one time or another.

 

I guess I should have asked the question if this is normal. How hard/easy should it be to rotate a crank when fresh bearings, pistons, rings and cam have been installed? Should it rotate when I torque the balancer nut to 90 or am I just being overly cautious? I don’t want to drop it in and find that the starter can’t even turn it over. BTW I’m trying to rotate with no plugs in also, so there’s no compression force. Here's a quick pick of the "Old Brown Bomb" and please disregard the pom poms, women...

Thanks again,

Jason...

 

Nice Truck.. Mine on the stand with just the rotating assembly in was pretty tight with fresh bore/hone. After cam/timing gear assembly was together it took an arm to get her to roll over. But I dont think it was 90lb maybe 50-60. The walls/pistons are coated in oil? Ring end gap checked all the way down stroke zone of the bore? This is a must.. Rings on the correct way (dot to the top, end gaps offset)? Did you notice anything odd while rotating the assembly to install the pistons (get harder all of a sudden after a set)?

 

Jason, something is very wrong. Start disassembling and check each part one at a time as you work. And yeah, those rods bearings are way, WAY too tight. I like to see .0025~.003 on my engines, and would consider anything tighter than .002 not usable. JMO DinosaurFan, @ work on lunch

 

I'd be worried something isn't quite right.

My 390 was about 40-50 lbs to rotate on the rebuild. I did a mock assembly with no assembly lube and I couldn't get the motor to move. Tore it all back down (was planning on anyway) receaned it all, lubed it up as it went together, and when all was said and done it took a very heavy arm on an 18" breaker bar to spin it over. I'm between .002 and .003 on all of the bearings and 18 on the end gaps.

Justin

 

Which direction is the large radius facing on the big ends of the rods? There is a flush side and a radiused side. If the radius isn't "out" away from the other rod, the fillet in the ground crank is dragging on the flush side of the bearing....Did you assemble the rod/piston? 1-4, radius forward, 5-8 radius rearward. It can't be a misnumbered set of pistons to bore because the shop didn't bore a standard bore engine......Check the radii. And I agree those beaning clearances are way too tight for me. You may have gotten some strange plastigauge readings IF the bearings were being "cocked" over due to the radius problem...........aMP

PS: don't even imagine the starter will loosen things up. 90lbs torque and the engine didn't turn is way WRONG. One more thing, what is the ring end gap, and what type pistons?.......You did use assembly lube, right?

 

My book shows the rod journals at 2.438 standard. So a -.010 should be 2.428.?? If yours are in fact 2.426 you should have a great deal of clearence, like .004????aMP

 

when building my first FE I put half the pistons on the rods backward and when installed in the block made the rods backward, which in turn made the motor hard to turn. Just make sure the oil holes are toward the cam.

 

Well, I'm out of town until Thursday but when I get back I'll investigate and let you all know what I come up with. Thanks for all of the pointers!


Jason...

 

Well turns out I needed to pay just a little more attention when installing the pistons/rods. Yes I can admit it in a public forum that I made a complete rookie mistake (but I guess I'm technically a rookie when it comes to these FEs). Turns out you can't just run the rods down the crank in order 1,2,3... "doh!" 1,5,2,6,3,7,4,8 seems to work much better :-). Anyway, I appreciate the help here at the very least it made me slow down and thoroughly investigate the whole crank/piston/rod relationship so I got it right and at most saved me from moving forward and finding out about it when the starter wouldn't turn it over. Cost me $100 bucks and some time for my mistake but live and learn...

Thanks all,

Jason...