engine rebuild
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Joined: Jan 2009
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engine rebuild
I have rebuilt the lower end on my 350. Everything has been torqued and retorqued to spec. When I put a wrench to the crankshaft bolt and rotate the engine, I have to put some muscle into it in order to rotate the assmebly (heads are off). Is is supposed to rotate this hard or am I missing something?
Burning Brakes
Joined: Jul 2009
Posts: 1,132
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From: A town SC
Put a torque wrench on the snout of the crank and tell us how many foot lbs it takes to start movement of the assembly. A click wrench will work but in this case I would use a needle type. Its hard to tell your muscle to my feels normal.You know what I mean?? Give me the ftlbs and ill get my torque wrench out and compare to give you and I an idea.
Melting Slicks
Joined: Apr 2007
Posts: 3,189
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From: Tolland CT
Are the main caps labeled as to position and orientation on a small block chevy? Don't recall. I've seen people get into trouble with other motors when they interchanged caps.
Did you check clearances when you replace the bearings? Plastigage them? Been a long time since I've worked on a bottom end.
Did you check clearances when you replace the bearings? Plastigage them? Been a long time since I've worked on a bottom end.
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I am pretty sure that I did not mix up the caps. All new main bearing and rod bearings. Did not use plastic guage but probably should have. Assembly lube was used on everything. Takes about 46 ft lbs on the torque wrendh to rotate.
Instructor
Joined: Jun 2010
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Did not use plastic guage but probably should have.
also did you buy over sized bearing. and possibly the crank did not need them.
Is this a new crank or the old that was gound and polished or just the one that was already in it?
Burning Brakes
Joined: Jul 2009
Posts: 1,132
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From: A town SC
Assuming that your torque wrench is correct this seems normal to me, maybe a little tighter clearances with your engine than mine, I took a needle type wrench to check a motor I just assembled, mine took 38ftlbs to get started to turn, .030 over 350 standard crank everything else stock. hope this helps. I would run it. If your sceptical tear it down, you and only you can satisfy your worries.
PS... no heads no cam...
PS... no heads no cam...
Last edited by forvicjr; Jul 28, 2010 at 12:57 AM. Reason: Add
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Pro
Joined: Apr 2008
Posts: 596
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From: Irving Texas
I remember doing my first two short blocks..........then realizing the machine shop will build the short block for $200.......thereby eliminating me having to redo it over and over checking clearances. Well worth the cost.
In your case, the only thing you are overcoming (without heads) is the friction of the rings to the cylinder walls......bottom line, I bet the crank or cam bearing clearances are off.
In your case, the only thing you are overcoming (without heads) is the friction of the rings to the cylinder walls......bottom line, I bet the crank or cam bearing clearances are off.
Instructor
Joined: Jun 2010
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ok did the person that ground the crank tell you bearing specs that you should of got(stock,+.10,+.20,+.30) i still would remove those caps and plastigauge them to be sure. also are your rings gapped right. and the piston not binding up in the cylinder. were the wrist pins loose? 46lbs is sounding like a lot to turn a bare block over.
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Machine shop that ground and polished the crank told me what oversized bearings and rings that I needed. Pistons had rings pre installed. I can probably just look it up but does anybody know the clearance for the mains and connecting rods? Motor is NOM, casting number 8970014.
Burning Brakes
Joined: Jul 2009
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From: A town SC
Machine shop that ground and polished the crank told me what oversized bearings and rings that I needed. Pistons had rings pre installed. I can probably just look it up but does anybody know the clearance for the mains and connecting rods? Motor is NOM, casting number 8970014.
Rods---.002/.0025
mains---.002/.0025---rear main---.0035
This is narrower min/max than chev recommends but its what I generally use.
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
With a 4-bolt cast iron block, the correct main bearing bolt torques are...
Inner: 70 ft-lb Molykote lubricant
Outer: 65 ft-lb Molykote lubricant
With a 2-bolt, 70 ft-lb with Molykote lubricant
Inner: 70 ft-lb Molykote lubricant
Outer: 65 ft-lb Molykote lubricant
With a 2-bolt, 70 ft-lb with Molykote lubricant
Instructor
Joined: Jun 2010
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larry thats if its a pre 1976 block everything after 77 went higher not sure when that block casting was used that could be checked
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
Sorry to disagree, but according to my 1978 Chevrolet Shop manual, and according to the GM's Chevrolet Power book, published in 1994, these sources use 70 ft-lb for 2-bolt mains, and 70 ft-lb inner & 65 ft-lb outer for the 4-bolt blocks.
Please recheck your sources and see if they might be referring to studs or aftermarket blocks.
Please recheck your sources and see if they might be referring to studs or aftermarket blocks.
Last edited by larrywalk; Jul 30, 2010 at 06:45 PM.