Technical Crank Won't Turn - New bearings/pistons/rings

Hi all,

So I have a problem with my current Ford 300 build: the crank won't turn. Here's where I'm currently at (head is off, just working with a bare block here):

- mic'd all the crank journals, and they all mic'd within spec;

- assembled crank bearings (dry), plastigauged them. Clearances were about .003;

- lube + reassemble everything. Torqued main bearings and rotate assembly. It mostly rotates freely - needs about two fingers of firm pressure to rotate (note: Camshaft and timing gears are installed, so might be a bit of extra resistance from this.)

- install new pistons and rings. Didn't break any rings (yay!)

- install rod bearings and caps (dry). Plastigauge bearings. Clearances show about .0008 to .0015-ish, which is within spec;

- Lube everything and reassemble. Torque to spec (40ft/lbs);

At this stage, nothing will rotate. I have a 1/2" drive ratchet on the block, and it won't move at all. If I loosen off the rod bolts a little bit, things will turn with the "usual" effort on the ratchet.

Has anyone seen this before? As far as I know, all the caps are on correctly, and the bearings are non-directional. But the last thing I want to assume is that because everything mic's/plastigauges within spec, I can just go ahead and fire things up. Not being able to turn the rotating assembly by hand is freaky.

 

Take the rod cap's back off. Replace and torque them one at a time ,rotate crank after you do each rod cap.

 

Did you dip the pistons in oil or oil the pistons and cylinder bores?

 

What he said and try to go backwards to the last one you torqued before it stopped turning. (did I say that right).

Pat

 

Check the thrust clearance, and the side clearance on the rods.

 

Any chance one of the rod caps is on backwards ?

 

As mentioned above. Make sure pistons/rings/bores are well oiled and then do one rod at a time till you find the issue. Could be something as simple as a rod cap on backwards or that rod could be well out of spec on the big end. Don't rule out wrong over/undersize bearings. Can always swap them to another rod to confirm before you order replacements.

 

You mean "on the crank", right? You would have been turning the crank while installing pistons/rods, was it getting tighter to turn as you installed them? Or did it just lock up with the last set?

 

I always install one piston at a time, and torque the rod nuts, then turn the crank a few revolutions, and get it in position to install the next rod/piston. If you do this, then you can see how it feels each time you add a part.

As for the rod bearings being "directional", the rods and caps are matched, the bearings have a tang, the rods and caps have notches for the tangs. The tangs and notches are supposed to be on the same side. And the rod/piston assembly should have a "front" side, although on an inline it's not as critical as on most V8s.

But yeah, take it apart, put it together slowly, see what the problem is.

 

You sure need to start again with the rods. Bearings and bores need to be lubricated. As has been said, you need to turn the crank after each rod is assembled. Bearings are directional. Rod caps are matched and directional. .0008 to .0015 may be within specs but is tighter than I'd want things.
Pete

 

Ring end gap?
What did you use for lube?

 

Bent crank?

 

I don't see how that would be possible. Normally, one would install the crank and bearings, check the end play, torque the mains, and then spin the crank to check that step, and then turn it for each piston and rod assembly.

 

Unlikely if he was able to turn it over with two fingers of firm pressure.

Pat

 

I found out a long time ago that it is prudent to do just as Jim says he does in that install 1 piston, toque the rod bolts, rotate the crank a couple or few times, get the rod journal on the next piston to be installed at the bottom of the stroke and go again. It lets you know if you have a problem then and there.
You keep saying that you put this that and another together "dry" did you pull the crank clear back out after you plastigauged the mains and lube all of the bearing? Did you lube both halves of the rod bearings after you plastigauged them ? Did you lube the pistons/rings before installing them as someone else asked?

 

i've seen tight rings do it. a friend had file fit rings and was gapping them on the tight side.

but that wouldn't explain why it will turn after loosening a few caps.

 

As already said go back and do one thing at a time.

If the crank was turned sometimes the journal radius will interfere with the rod & bearing chamfer

 

No rod is bent? Otherwise Jim's one at a time, and test.

 

I have a dumb question . I had a guy bring me a motor one time that he rebuilt and told me it would not turn over . I said did you use assembly lube and he looked me straight in the eye and said yes I did , both sides. He had put assembly lube on both sides of the bearings taking all the clearance out.
Took it apart and cleaned the backside of the bearings and the caps and it turned over just like it should. You didn't do that ,did you?

 

Are you sure you didn't switch caps from one rod to another?

 

Don't think it's pistons will turn with loose rod caps. If caps on backwards it would still plastigauge ok but would be tight at the parting lines. The non-directional bearing thing makes me wonder.

 

Did you protect the rod "Bolts" when you installed the rods and pistons? The only time I ever had this problem was the first time I built a motor. I didn't know that you needed to slip a protector over the rod bolts. When I installed the rods one bolt barely and I mean barely nicked the crank. There was no way to turn that crank. I pulled it apart and could not believe that little tiny nick was the problem, but it was...

 

Believe it or not, I am in the process of writing up a failure analysis report of a Cat C27 (V12 diesel engine) that had spun 2 connecting rod bearings. The engine was rebuilt about 5000 hours ago (about 2.5 years). This is a short time for one of these engines. Depending on the extent of the rebuild you would hope to achieve at least 10,000 hrs. Analysis of the bearings shows that something was applied to the backs of the rod bearings, creating a tight spot on the bearings, which is evident on several of the remaining bearings. My best guess is that it is oil or assembly lube. It also could have been some kind of retaining compound, but I'm betting it was oil.

 

ROD OFFSETS?
I would double and triple check that right bank rods are in the correct orientation frontfacing/rearfacing, and that all left bank rods are also on the correct side and facing correctly.
A simple act of putting a right bank rod on the left, or confusing front/rear facing can lock up a bearing by simply being slightly cocked.
A simple error such as "do the stamped numbers all face the cam, or all numbers face outward?" or all face to the right? can make all the difference.

WHY BE ORDINARY ?

 

300 six? or is it really a V8?

 

you're right. I didn't notice "head" singular.
I would still verify numbers facing right or left, just in case.
I would also note the tiny weep-hole locations on the rod big ends.
If there is one oil weep hole facing a different way compared to the other rods, that is a dead give away that one rod is facing wrong, or the wrong rod grabbed from the parts pile. Or a replacement rod used in the place of a bad rod in the past. Easy to overlook during hurried assembly.

WHY BE ORDINARY ?

 

I`m still trying to believe a 300-6 actually wore out and needed a re-build.

 

I think sitting around for years and years is harder on those engines than running them for the same amount of time. I've found some rough ones at swap meets that I rebuilt instead of trying to clean and run.

 

By torquing rods one at a time you'll figure out which one (or more) are causing the issue. When you find one that does it, loosen it back up and continue to check any remaining, as you could have a problem with more than the first rod that shows a problem.

.0008 is the absolute minimum acceptable clearance. Any error in measuring, or a rod journal slightly out of round at this minimum clearance, will cause a nasty bind.

 

You know guys, is this one of those post were a Poster asked a question everyone gets busy trying to figure a solution to "HIS" problem and we never hear from the cat again. I mean 30 post's and no response from him---Give me a break.