Torque to Spin Shortblock? - ClassicOldsmobile.com


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Old June 18th, 2017, 05:10 PM   #1
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Torque to Spin Shortblock?

I'm putting together a 455 and after putting in the first of the pistons, it seems to have more drag to rotate it than I anticipated. I can spin it over by hand with one hand turning the balancer, but it just feels more than I'm used to, particularly in the middle of the bore.

It's just a refresh of a 68 455. Same pistons, rods, and crank. Crank spins freely. Rod and main bearing clearances are right on the money. PTW clearance is in spec. Rings are ductile iron, and if anything the ring gap is on the larger side. Cylinders were less than 0.001" out of round, and I just ran a three stone 220 grit hone through them to clean them up. The piston went into the bore with a light tap. Cylinder was lubed with SAE 30 oil and bearings with assembly lube. Only thing I can think is something ring related got messed up pushing them in. I did not get a torque value on how much it took. I'll have to recheck that, and hopefully it's in the 25-35 ft-lb range.

Does anyone have a good feel for how much torque the typical BBO stock-ish rebuild takes to spin? I'll admit this is my first BBO so I may not have a good concept. It just felt like all the small blocks I've done were significantly easier, though I may be skewed. The last engine I built turned over effortlessly, but it was an all aluminum race motor with a lot more clearance and much thinner rings.
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Old June 19th, 2017, 06:02 AM   #2
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Ring gap doesn't determine drag if you have any at all. Oil ring tension is normally the most influential. I've assembled big blocks that have had as little as 13ftlbs, or as much as 27.
Find out what oil ring is in the ring set you have and go from there.
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Old June 19th, 2017, 06:36 AM   #3
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My 403 was a bear to turn over with everything fresh. I told the machinist, and he said wait til the rings seat. Now, its no big deal, but before I started it for the first time, it took some oomph.
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Old June 19th, 2017, 07:03 AM   #4
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Originally Posted by cutlassefi View Post
Ring gap doesn't determine drag if you have any at all. Oil ring tension is normally the most influential. I've assembled big blocks that have had as little as 13ftlbs, or as much as 27.
Find out what oil ring is in the ring set you have and go from there.

I just mentioned ring gap to make it clear it was checked and they aren't butting.


The oil ring pack is a stock replacement 3-piece, 3/16" standard tension.

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My 403 was a bear to turn over with everything fresh. I told the machinist, and he said wait til the rings seat. Now, its no big deal, but before I started it for the first time, it took some oomph.


That is good to hear. I did even think to myself when I was pushing the rings into the bore to gap them that there was a lot of drag.
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Old June 19th, 2017, 10:06 AM   #5
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What brand is the ring sent?
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Old June 19th, 2017, 12:05 PM   #6
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Rings are from Enginetech.
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Old June 19th, 2017, 02:11 PM   #7
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Rings are from Enginetech.
That's to be expected then. Moly top ring? If so then 220 isn't the right grit. You need at least 280.
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Old June 19th, 2017, 04:27 PM   #8
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Really? I had seen 180-240 grit was pretty typical for plain cast rings.

Also it seems I may have just been on the paranoid side. Turns out I had a metric socket that fit the crank bolt. I threw my torque wrench on it, and even at the lowest setting of 20 ft-lb it didn't click throughout the whole rotation. I might pull it out anyway to recheck and make sure nothing in the ringpack got messed up, but it seems like it's on the right track anyway. All those mod motors since the last time I worked on old iron must have thrown off my perception.
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Old June 20th, 2017, 04:42 AM   #9
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Really? I had seen 180-240 grit was pretty typical for plain cast rings.

Also it seems I may have just been on the paranoid side. Turns out I had a metric socket that fit the crank bolt. I threw my torque wrench on it, and even at the lowest setting of 20 ft-lb it didn't click throughout the whole rotation. I might pull it out anyway to recheck and make sure nothing in the ringpack got messed up, but it seems like it's on the right track anyway. All those mod motors since the last time I worked on old iron must have thrown off my perception.
Not sure what the socket would have to do with it.
I mentioned at least 280 grit IF it's a moly faced top ring. If it's not moly faced then the 220 is fine.
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Old June 20th, 2017, 05:06 AM   #10
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Not sure what the socket would have to do with it.

Finding the socket let me actually put my torque wrench on it to measure the torque. Before I was just going by the feel of turning the damper by hand.


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I mentioned at least 280 grit IF it's a moly faced top ring. If it's not moly faced then the 220 is fine.


Ok that makes much more sense. And nope, plain old ductile iron; no coating.


I'll update with what the final value ends up being once I get all 8 slugs in place.
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Old Yesterday, 05:01 PM   #11
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Final verdict: 37 ft-lbs to start it moving with all 8 cylinders, plus cam and fuel pump. On the high side but fingers crossed it will seat and work.
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