Small Block Cranking Torque

[bschubarg]

I am building a 318, actually rebuilding with cast pistons and chrome moly rings.

I understand that after putting in all the pistons in the bore with rings w/o the heads, there is a rating or specification about what it takes to rotate the assembly using a torque wrench.

With all the bearings in and caps tightened to spec. if you use a torque wrench to rotate the assembly, that torque spec will help you dtermine if the build is too tight or too loose.

So my question is, what torque would it take to turn my 0.030 over 318?

I hope I described what it is that I am talking about. If not, then I will just go back to my Johnny Walker Black......

 

[bschubarg]

You mean to tell me that no one here knows the spin torque is on a small block build?

I must be dreamin......

 

[340mopar]

There is no spec for what you are asking. There are to many variables like, ring tension, bore finish, what oil was used to assemble motor, etc. to have a spec.

If all of your clearances like, rod, main, piston to bore, ring gaps, etc are correct then there will be no problems with tightness or looseness.


Chuck

 

[bschubarg]

Thanks Chuck,

I just heard several times about this so called value and wanted to know if such a thing existed.

I do plan on doing all the measurements and checking clearances. This is my firsts build and thought that the first thing I could do to determine of measurements are incorrect is spin it with a torque wrench and get a value.

Thanks again.

 

[pagilman]

:salute: If you use the rope type seal you should use a torque wrench and the approximate torque is in most rebuild books. If you use the neoprene seal you should be able to turn by hand. I have several books on this and if no one else answers your question by sunday I will take the time to look it up for you. You should use plastigauge $7.00 at parts store. Use it on each main first before putting in the piston. as was said earlier the rings and alot of variables are involved after the pistons are installed. The torque figure is just for the crank with the rope seal with no pistons installed, neoprene seal should turn by hand or you have a problem. Thats my 2 cents and hope I didn't lie to you as I am in the middle of a 340 build and have did some reading on it. Your mopar brother Walt :salute:

 

[pagilman]

:salute: OK I looked it up. Chiltens and haynes books don't mention it, but "HP rebuilding small block mopars" states on page 119, to torque all caps ( rear main first) to 85 lbs.in increments and just leave the center saddle finger tight. this is the larger thrust bearing. pry the crank back and forth several times with a large screw driver and hold it forward and torque thrust cap. If you used a rope rear main seal install the washer and damper bolt on the crank and turn a few revolutions with a torque wrench and it should spin at 15 lbs. If more than that you have a problem. Then you can check end play, it should be between .002 to .007. if less than .002 or more than .010 at an absolute maximun you have a problem. If less than .002 you must remove the crank and have the thrust bearings thinned. If more than .010 it doesn't say what the hell to do. I strongly suggest getting a set of books as I have 4 different and they are cheap on ebay and all give you something that the other don't. The more advise the better. Hope this was helpful. "Your mopar brother walt" :toothy7:

 

[moper]

I will add, if you can turn it by hand, you didnt install the piston rings. And a rotating torque wrench is not the same as a torque wrench. So 15 lbs feet is on a rotating torque wrench. Similar to what you would use to check a rear axle build...

 

[ramcharger]

I will add, if you can turn it by hand, you didnt install the piston rings. And a rotating torque wrench is not the same as a torque wrench. So 15 lbs feet is on a rotating torque wrench. Similar to what you would use to check a rear axle build...

Agreed, if can turn the crank over by hand, you forgot something! I was a professional mechanic for 12 years and never heard of such a spec. Far too many variables.

 

[340mopar]

The last two posts is why I said what I said about the variables. I assembled my 340 with a line honed block and low tension 1/16" compression rings and I could rotate my complete short block by hand with the balancer with not much effort. Granted this style motor is an exception and not the rule but it is why there is no spec, this type of race motor would fail the spec. So use the measurement method, check your block for main straightness, check your crank for straightness, check your rod and main bearing clearances, check your rod side clearances, check your piston to bore clearance and check your ring gaps. You do this and you are good to go.

Chuck

 

[cavemanmoron]

plastiguage the bearings??

I never bothered on my 318, build.

I was lucky, the machine shop just had to polish the crank,
and rigid hone the block, I reused the pistons, with new stock bore
rings, and stock Clevite bearings.

Don't forget the oil galley plugs.

There is a large one that got left out of my 340 engine years ago.

I had to remove one of the threaded external plugs to get to the internal one. One side of the cam plug.....

 

[340mopar]

You got real lucky, since you are using std bearings and you didn't know how much came off the crank when the shop polished it. I'm guessing your bearing clearances are a little larger than normal but the pumps in mopars are pretty good making up the difference in clearance.

Chuck

 

[perfacar]

hi, bearing clearances always should be measured. as for a rotational torque value, there isn't any hard numbers. however, when assembling a motor, I measure it with a beam torque wrench. if a moly ring was installed, and a smooth wall finish, most require about, 25# to 30 # rotational torque. this is usually about average. low tension rings and ring width will show lower values.
on a race motor, like to see 8 #to 10 # rotatioal torque. another factor that will influence this, is whether the main caps were torqued when block was bored, also whether a deck plate was used. lots of variables.

 

[pagilman]

The 15 pounds is with a rope seal and no pistons. the neoprene seal should rotate by hand.

 

[moper]

The 15 pounds is with a rope seal and no pistons. the neoprene seal should rotate by hand.

Just re-reading...You mean crank only int he block..correct? You're right there. The crank should spin very easy by hand with both typews of seals in place. I was thinking at first you meant with pistons and rings.

 

[D-mailman]

Guys what he is refering to is called 'brake away' torque. The torque required to brake the friction of the resting crank into motion. Yes should be able to turn easily by hand with regular rubber type seal. I measure all the engines I build for this. The Corvette engine I put together for my brother, (he is very lucky I even let that piece of crapp into my shop), LOL. It measured 3 ft. lbs. to turn over (no pistons). Very important I feel. Good luck, Terry.

 

[340mopar]

Guys what he is refering to is called 'brake away' torque. The torque required to brake the friction of the resting crank into motion. Yes should be able to turn easily by hand with regular rubber type seal. I measure all the engines I build for this. The Corvette engine I put together for my brother, (he is very lucky I even let that piece of crapp into my shop), LOL. It measured 3 ft. lbs. to turn over (no pistons). Very important I feel. Good luck, Terry.

If the block and crank are checked for straightness and are OK and the main bearings are checked for clearance and OK there is nothing else to check and will be OK. With this break away torque method, what oil or grease do you use? what temperature should the oil or grease or block and crank be? All of these things are variables that could cause a crank to fail the break away torque test even if all of the clearances are OK. If when you test a motor with this method and it fails because it took to much torque do you open up the clearances even past the design limit so it passes? I am very interested in how you found out about this method and were from.

Also he asked what the rating is with the piston in the block. Not just the crank.

Chuck

 

[chrisII]

i was tought to check the crank without pistons, end play, and to observe how much more it took to spin the motor as i bolted up each rod. it shuld turn a little bit harder each piston thats added.

 

[bschubarg]

Guys what he is refering to is called 'brake away' torque. The torque required to brake the friction of the resting crank into motion. Very important I feel. Good luck, Terry.

Yes, that is what I was referring to. Brake away torque. I didn't realize that only included the crank and not the pistons with rings.

340mopar brings up a good point that this variable is just that. A variable. With other things to work into the equation(tempeture, grease, etc), this variable change change.

So having read all the posts(Thanks Pagilman, Chuck, Terry, and Dave), I went to ebay and bought me a set of Mitutoyo Vernier Calipers, 0-1, 2-3, 2-3" Mitutoyo Outside Micrometers(0.001 increments) and a set of 0-8" inside mics. I will do the necessary measurements like Dave and "My Mopar Brother" suggest instead of just relying on the brake away torque.

As far as crank staightness, I don't have the tools to measure that, but when I get the crank turned and polished at the machine shop, I will ask to get that checked.

 

[moper]

One small note on tools and parts...when you measure the parts, they need to be at the same temp, and 70° is possible. I measured a crank for a stroker when the material was 53° by the digital temp gun, and my tools were 70°. The crank mic'd on the small side by about .0002". Not a big deal but when you are aiming for .002 and its. .001 "and change" you start to question yourself...lol. As for turning torque with no pistons, after it's all measured, I drop the crank in with a mix of straight 30W oil and white lube, and I give it a spin by hand. If it turns smooth and easy, it's fine.

 

[D-mailman]

Very good point Moper. I never check clearences or assemble anything untill all parts are same temp. I try to keep the shop 68 to 72 degrees year round. Yes this is important. Terry.

 

[moper]

I now keep my parts and tools in the same place. It's heated.