Hi, new to the forum, I am rebuilding a 3.0 Ford v6 out of an 02 ranger and I noticed after I had it completely assembled that occasionally the motor would turn over pretty hard by hand, this is without the plugs installed. So I started disassembling it again and I was checking for resistance as I removed parts. I had the motor torn down to the rotating assembly and it still turned over hard. I had the connecting rods checked for any bends and they were all good (number 3 rod had a very small twist or bend according to the machinist but it was so small of a deformity he thought that would not cause any issues). So I reassembled the engine with just the pistons and crank (no rings on pistons) and it spun pretty freely, it was only when I put the rings on the pistons that the engine turned over hard by hand. Out of round of the cylinder and taper did not go above 2 thou across all the cylinders and according to my book that was within spec. Pistons are new standard size the clearances would have been too tight with the piston coating so I scuffed some of it off with a red scotch brite. Ring end gap was pretty close to being in spec, the only thing out of spec was the second compression ring across some cylinders but that was because the end gap was around 5 ten thou to big not to small, so I really don't know what is going on and the machinist and retired mechanic I talked to don't really know either. I noticed some cylinder scoring had come back to when I previously got rid of it with a dingle berry hone. You can't even feel the scoring (if you even call it scoring) but you can see it, the machinist said it was just the ends of the rings causing that and was no big deal, but the scoring is spread out in several lines about an inch in width and I have a hard time understanding how rings could move around that much just turning it over by hand but I wouldn't know for sure. I don't have a lot of experience building engines as this is only my second one. Any help would be much appreciated.

 

Pretty sure its the rings. After I initially checked end gap with the rings I kept track of which rings go to which cylinder. When I put the rings from cylinder 6 onto piston number 5 (and cylinder 5 was the one that caused the engine to turn over hard) the engine turned over with some resistance but it was not super hard like before. When I put cylinder 5 rings back onto piston 5 the engine started to turn over really hard again. I also double checked end gap of cyl 5 rings and the end gap was fine, so I am pretty sure the rings are faulty, probably pretty unusual. I'll keep the thread updated as I assemble the motor with different rings just for the sake of anyone in the future who might have the same problem looking for answers.

 

You mentioned it was difficult in a specific spot, right?
You may have some rings with a really tight gap, but I would also suspect a cylinder wall that is wonky.
Sounds like the bore diameter may vary in spots.

 

Did you have the black bored, or just honed, if either, I'd be taking it back and have the cylinders checked.

 

I think I was kind of chasing my tail on this one, the whole time I was turning it over by the harmonic balancer by hand and when I put a torque wrench on it, it was like butter and would not even register 10 ft(lb) of torque turning it over. Kind of dumb on my part. I knew it would turn over harder just grabbing the harmonic balancer to turn it over but I did not think it would be as big of a difference in force as it was compared to using a torque wrench to turn it over. While I was still trying to figure out what was wrong I took an expo marker and drew vertical lines about a half inch apart all the way around the cylinder and when I turned it over it wiped all the lines, so it must be sealing pretty well. I don't think there is anything wrong with it after taking a torque wrench to it. Stupid mistake. I'll be checking the rest of the cylinders with the marker tomorrow, but I don't think there is going to be any issues.