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As I'm adding more parts to the engine I'm rebuilding, and reading its Haynes and other manuals, I get more confused with those parts that should let the crankshaft "free spinning", as said in the manuals. For instance, when applying torque to the crankshaft or conrod bearings, they say "be sure everything spins free" or "assure yourself the crankshaft spins freely".

When I installed the crankshaft, and after some back and forth with the conrod bearings, I can turn it with bare hands and if I break the inertia good enough it would spin itself for 1/4 of turn or little less. When I installed the conrods, they were quite stiff...massaging the rings and the bearings made me now possible to turn the crankshaft by hand but it is not really really loose, it needs some little effort. It does turns, if I attach a wrench to the pulley bolt. If I put one piston, without rings, and torque its conrod bearing, I can (now :-) ) turn the crankshaft but it won't spin by itself like the crankshaft alone. Reading the bearings' oil/metal residue I can see no high spots, no line scratches and quite uniform oil layer.

So question would be: "Spin (the crankshaft, with conrod installed for instance) freely" means "effortlessly spin by bare hand" or would "spin by little force of a wrench" be just right?

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This is essentially looking for binding. It has nothing to do with how long it will spin on its own inertia.

As you progress thru the assembly, it should turn with little effort to ensure there is no binding. Some instructions will even give you torque specs for each piston added.

For example;

enter image description here

If it does not turn easily, then something may be installed wrong. This could be caused by wrong size bearings, main caps installed wrong, rod caps installed wrong, or even block improperly machined. That is why it is important to check after each stage. You don't want to assemble the entire engine only to find it got bound up somewhere along the way.

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  • This is great...it means that crankshaft installed, only 1 piston in place should need 5.4 lbs to spin the thing? Piston with rings?
    – Aram Alvarez
    May 17, 2017 at 15:23
  • As stated, this is an example. You need to use the specs for your specific build.
    – CharlieRB
    May 17, 2017 at 17:24
  • Well, before reading your comment, I put piston 1 without rings with its bearings not "adjusted" and it needed about 16 ft/lbs to spin...let me see when I massage the bearings next.
    – Aram Alvarez
    May 17, 2017 at 20:25
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After a full rebuild, with every part lubed as it should be I would not expect to be able to spin any 4+ cylinder engine over freely by hand.

If say you we're turning it at the flywheel, or the engine only had the crank installed then yes you should be able to turn it over quite easily.. but with pistons installed and trying to spin it say via the crank with a couple of bolts inserted... you would require a slight bit of leverage.

As you add parts like main bearings, big ends then pistons etc they all add to overall friction. Then as you mention you'll get a sticking point, this has to be overcome initially before the engine will turn over easier.

Little by little... The more friction surfaces you add the harder it gets to turn over, then once you add compression to the equation.. Well I reckon you know the rest. If though it seems too hard to turn over start checking that bearings etc are correct, not too tight or perhaps have grit etc trapped between surfaces.

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  • I had to sand the conrod bearings to make the crankshaft able to spin. The crankshaft alone was spinning smoothly by hand, but when adding conrods all of them seized the spin, so one by one, I adjusted their bearings so I'm sure they are not seizing the crankshaft...and with one of them at a time, I can spin by hand, a bit of effort by pulling the other conrod journals in the shaft, but turns ok. I don't have the flywheel there yet, so to spin this I need then to use the pulley bolt and a wrench, not much effort, but not totally soft as if no conrods are installed.
    – Aram Alvarez
    May 17, 2017 at 3:41
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    "I had to sand the conrod bearings" - what do you mean? How much material did you remove? Where these new bearing shells matched to the crankshaft? Had the crankshaft been re-ground and new shells supplied? If the shells were matched, then you may now have excessive clearance which may reduce the life or cause it to fail rapidly. Have you checked the clearance, using "plastigauge" or similar (a plastic that deforms, comes in small rods that you assemble in the bearing then remove and measure the thickness : giving the clearance)?
    – Solar Mike
    May 17, 2017 at 5:22
  • Here were I live...no plastigauge, no loctite, no "fancy" stuff :) So...to "adjust" the bearings, as we say, we sand the bearings by hand and check their oil fingerprint in the crankshaft, by torque steps. When 3/4 torque is reached and the bearing is almost free, then we use finer grits for the rest. I will post the procedure in my log at chat.stackexchange.com/rooms/55921/skoda-120-restoration-log
    – Aram Alvarez
    May 17, 2017 at 15:21

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