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Crank shaft hard to turn
Topic Started: Nov 18 2011, 08:44 PM (3,615 Views)
Spidermoore
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I am putting my engine back together after doing the rings and getting a head rebuild from 3tech.

With the timing belt off (so no CAM load), and the spark plugs still removed (so no compression), how much effort should it take to turn the crank/pistons. The starter can only turn it rather slowly and I can turn it by hand with a wrench only with considerable effort.

With a torque wrench on the crank bolt it took about 45ft. lbs to rotate the crank around.

I had over torqued the piston cap nuts at the time mistaking the cap bolt torque (40lb ft.) for the cap nut torque (26ft. lbs.)

I loosened and retorqued the cap nuts to proper torque (26) and the amount of effort to turn the crank is now down to 27ft. lbs. the starter doesn't turn this too fast so I am not sure I have fixed the problem.

How easy should it be for me to manually turn the crank shaft when there only the pistons and oil pump connected to it? How quickly should the starter be able to rotate that?
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Spidermoore
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I'm wondering if I did something wrong with the re-ring and the pistons are too tight now.
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Spidermoore
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Here is a video of the crank turning over (I think folks should be able to see this even if not on FB)

https://www.facebook.com/video/video.php?v=10150470719500336

This is only with the 3 pistons and the oil pump. No compression and no CAM.
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Memphis metro


Has the battery run down while you were rebuilding it? Put the cam in and the timing belt on. It will turn over easier with the cam in than with it out.
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Spidermoore
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Battery is okay I think... although it did sound like it was running itself down in that video. I've got a charger on it (again) tonight but I do not believe the battery is the problem.

Since putting the head back on, I have not seen the bottom end (or entire engine when I had timing belt on) turn any faster than in this video and have seen it turn even slower.
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undgsx-R
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Do you have the right sized bearings in it? Did you use assembly lube when you put the bottom end together? Did you oil the pistons before you put them in?
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Spidermoore
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I reused the same bearings. I did use some lube (just oil though) when I put the pistons in but the engine sat for a long time at that stage before I got back at it.
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Spidermoore
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enginedoctorgeo
Nov 18 2011, 09:40 PM
Has the battery run down while you were rebuilding it? Put the cam in and the timing belt on. It will turn over easier with the cam in than with it out.
Forgive my ignorance, but why would it rotate easier with the timing belt on? I don't have any spark plugs in so there is no compression issue. Wouldn't I just be adding friction by doing that?
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undgsx-R
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Hmm might be normal, I do not remember how hard mine was to turn over when I rebuilt it. I know that the current Isuzu that I am rebuilding, I cant just grab the nut and turn it over, have to use a socket and ratchet, but it is smooth. Does yours turn over smoothly or does it hang up in any spots?
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Memphis metro


You would be adding friction as well as compression but you would also be adding air and exhaust. If you truly want it to spin over the max, remove the head. Your best option to find the answers you want is to charge battery fully, put on timing belt and cam and perform a compression test with a gauge with the throttle wide open. This will give you numbers you can rely on.
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Spidermoore
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It does seem harder in some parts than others.
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Memphis metro


Actually, you are still getting compression thru your spark plug hole with the cam off. With the engine spinning over fast enough, the amount of air within the cylinder would not escape thru the plug hole completely before piston was at tdc, therefore providing a slight compression resistance. Technicaly I do not know what would be the best scenario, cam in, belt on, or cam off. I know this though, an engine with cam in and timing belt on and plugs out will spin over real nice with a steady engine noise.
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billy508
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billy508

Everybody has their own system but here is what I do. 99% of the time I have the engine on a stand. I build one cylinder at a time. Before I connect any rod bearings I make sure the crank turns free in the block with the mains torqued down. Then I build one piston assembly, install it and turn the crank to see how smooth and how much torque it takes to turn it. Doing it this way you can tell when something is not right. I have found mis boxed rings, wrong sized bearings and machine shop mistakes by doing it this way. I use the Moly assembly lube now but I have built many a engine using 1/2 STP oil treatment and 30 weight oil. Take Care and good luck :banana :banana :banana
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JellyBeanDriver


That's a good idea Billy - I'll have to remember that.
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Spidermoore
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Billy, did you have a chance to look at the video? If so, does that look too slow of a turnover? It does to me, but I have no frame of reference.
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