Motor build up, should the rotating assembly be hard to turn?
 

I'm building up my new 350 right now, as of now i have the crank in, and all 8 pistons. I put assembly lube everywhere...and not sparingly. I just want to be sure that it's normal for it to be difficult to turn the rotating assembly by hand. i don't feel any binding or anything, it just turns hard. I also coated the cylinder walls with light oil before i dropped each piston in.

Little nervous....first engine build up....

Eric

Yes thats normal. As long as your clearances, rod, main bearing, piston-wall, are all in spec, and there is no binding you should be okay. If it makes you feel better I just finished a 250 I-6 for a customer and even with the crank socket from Jegs, and a 2 1/2' 3/4" ratchet it was a little tough. Started fine, all is well. Clearances, and no sticking, or binding is what you need to pay most attention to.

As mentioned as long as it turns and everything is assembled correctly and machined properly you shouldent have any problems. Its still better to be on the safe side and recheck tq on the main bolts and rod bolts.

i 2nd and 3rd that! nothing would ever piss you off more then trowing a rod as soon as you start it

so what happens if i can't turn mine at all (and i am a BIG guy) w/ a 3' breaker bar?...is that bad?


jk...i siezed up the rotating assembly when i was putting mine together. it was a used long block and i didn't think to pull the heads or the pan:doh:

that's what happens when you don't listen to your dad on your first motor buildup.

well thats good news....i feel much better now. and btw, i've rechecked torque specs like 3 times now....all tight and good to go

Eric

this seems to come up a lot and i keep saying i'm going to check with a torque wrench what the pre load is on a fresh rebuild and never do. i'd guess in the 30 ft/lbs range is common.

Did the crank spin freely after it was torque down? It should have the correct endplay too, was that checked? Then after each rod and piston is installed I turn the engine over a few times, it should get progressively tighter when each piston assembly is installed, it should also not have any tight spots. It's been several years since I built one but I don't remember it being very hard to turn over as long as the heads are not on it making it develop compression.

put a torque wrench on the crank bolt. It should be able to turn with less than 20lbs on the torque setting. Much over 20 and its probably related to rod side clearance. especially if the rods are new.

Is this a rebuild or a build-up with all new parts?

If it's a rebuild, you're supposed to keep all of your rod caps together with their respective rods, and each rod to its respective cylinder. It's possible, then, that you could have swapped some rod caps, in which case torque specifications would tell you nothing.

That's what I accidently did on my first (and only) rebuild. What clued me in to it was not that the crank was "hard" to turn, but that it wasn't consistiently hard to turn throughout a full rotation (i.e. it was easier to turn in some degrees of rotation than in others). I took it to my machanist, and he found that I swapped two rod caps. When I looked at the bearings for those caps, I could see that they were very inconsistiently worn (i.e. one side of the cap was worn while the other side didn't even look like it was touching).

Just something you might want to be aware of if it's a rebuild... I don't guess that's an issue if it's a new build. :)

I'd agree with ede's approximation. I measured one once, and it seems like it was anywhere between about 25 and about 32 ft-lbs at various points in the rotation. It seemed to depend mostly on where the pistons were in the bore, which determines how fast they're trying to move.

to answer a few questions...with no pistons the crank spun relatively easily and it got progressively harder. There doesn't seem to be and hard spots in the rotation....all new parts are being used except the crank which was ground under, all clearances have been checked.

I'm gonna slide a bolt in the crank snout and turn it with the torque wrench to see how much it takes...


Eric

eric:

be careful how much you try to turn the engine over by the crank bolt. if you can get a nut or socket for the crank, get one.

while trying to run the valves during the 305 rebuild last year, i tried using the crank bolt to turn the engine over, and ended up stripping out the crank.

luckily, a friend was able to tap the threads out to the next larger size. saved me a major headache.

When I was a kid, this old drag racer down the street used to build engines. He did a lot of real smart things. After getting the parts from the machine shop he would re-clean everything. When he assembled anything with a bearing he would plastigauge it first. When he put the crank in, he would rotate it as he torqued each main to see if it had a tight spot. Same with the piston/rod assemblies, after each one was installed he rotated the engine to check the drag. That way if the motor tightened up, he knew it was the last assembly he installed. the rear mains were 2piece so instead of installing them flat like the factory, he would rotate each one so the main seal wouldn't line up with the parting line of the rear main. He would also dissasemble the oil pump to check for any trash in the new one (he marked the gears for re-assembly), and would then oil the pump so it would prime right away. When he primed the engine he would rotate it in order to see that all of the rockers would lube. This guy would use a small oil can and pump up each lifter by hand on a bench. He would also rock the crank back and forth to line up the thrust bearing, and do the same thing to the rods to check for side clearance. there's a ton more that I can't even think of, but this guy was an artist, everything had to be perfect, Hope some of these ideas help you out.

Re: Motor build up, should the rotating assembly be hard to turn?
 

With turning the crank, with only the piston rings as resistance (no timing on, and heads off/plugs out), should be from 25-45 ftlbs of resistance depending if you have a 2 piece seal which is the higher side.

The dude with the breaker bar, omg, I hope you just have very good compression, because that is not good otherwise.