How much to turn? [Archive] - Racingjunk Forums

cervidog

01-16-2014, 07:56 AM

I am building a 400 sbc.I remember a long time ago a engine builder Iknew said it should take just so much torque to turn a short block assembly.I was just wondering if anyone has heard of this,and just what it should take to turn one? Using my torque wrench on crank snout it takes between 18 / 20 ft lbs.

curtisreed

01-16-2014, 11:18 AM

Is that the break away torque or the turning torque? Every engine is different based on ring tension, ring thickness, cylinder diameter, assembly lube used, double or single lip seals. You see my point. It's not always just a straight forward number to cover them all.

That said if that is your break away torque it is probably just fine for a street / bracket type engine. JMO

Curtis

cervidog

01-17-2014, 05:37 AM

Yea I guess it would be break away torque. I see your point last time it was a 355 different bores,rings,ect. Thanks

hammertime

01-17-2014, 06:00 AM

markdunlap

01-18-2014, 09:28 PM

BBC short block only turning torque around 25-30 with std. tension 1/16 rings.

hink

01-22-2014, 08:02 PM

Cylinder finish plays a key role in both break away and turning torque.

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roadkill2

01-25-2014, 08:09 AM

What's the point? All the engine builders that I considered as "good ones' advocate turning the crankshaft assembly through several rotations so that the rings (in completely dry cylinders) will begin to seat.

Most modern racing engine builders will tell you that after about 5 revolutions, if you honed the cylinders correctly and they're straight, 75% of the "break in" or seating of the rings will be accomplished. The last 25% requires heat and compression to finish the job . .

But that's what I've been told over the years and some of you may have different ideas or mentors . .

And once you have turned your crank assembly four or five revolutions the torque readings will (or should) change . . even the breakaway will be affected . . The numbers? Whatever you end up with, but it certainly shouldn't require MORE torque to any degree . .

And without the full assembly, the crank should spin by just twisting the rear crank flywheel flange with your fingers . . If it doesn't, your bearing clearances are too tight!

TheYellaBrick

01-26-2014, 09:46 AM

And without the full assembly, the crank should spin by just twisting the rear crank flywheel flange with your fingers . . If it doesn't, your bearing clearances are too tight!

Unless it's damn cold in the clean room and your assembly lube is the consistency of grease ((((( :shock: )))))

roadkill2

01-27-2014, 12:19 PM

Well, Yeah . . !

heh, heh, back in the day, I had a buddy who built 392's for a couple of the T/F FEDs in the area and he assembled them with 50 weight. On a cold day you couldn't turn the damned things over with a 6' cheater pipe on your breaker bar . . First time he used white lubriplate on one he went back and took it apart to recheck the bearing clearances. . he said , at first he thought he had left the bearings out of it . . .

When I think of all the dumbassed stuff we used to do, because some hot shoe told us that's what he did, I wonder how I kept from either shooting myself for being so damned stupid or grenading everything I ever touched . . . Very flat learning curve . . heheheheheh

TheYellaBrick

01-27-2014, 09:58 PM

I learned later $$$$$ in life not to believe EVERYthing another 'racer' told you. They'd lead you up the wrong stream and laugh their a$$e$ off at your expen$e . Funny now but shor weren't then ! :roll: :oops: :oops: :oops:

roadkill2

01-28-2014, 05:38 AM

Back when I was in high school (the stone age), most of the older guys would tell you pretty much what did what, and if you heeded their advice and they thought you had promise they would help you out now and then.

Then once I started getting serious and wanted to make something build real horsepower, you had to leave flyover land to get the stuff you needed. If you called the Prunepickers on the phone, they'd sell you crap they couldn't give away on the coast, "but some hot shoe that was in last month's HRM was using it so it'll work for you, bunkie".

Then, in Fjasted's SPE Chassis shop, when we were picking up the new car, this local Jr. Fueler pilot gave us a line of sh*t that would have filled a 100 car tank train . . and you heard stuff in all the shops out there that you didn't know whether to take with a grain of salt or punch out the guy who said it.

We took some of it to heart. And some of it worked and some of it was disastrious!

Learned one thing. Know how YOUR stuff works, and then learn what's available to make it work even better. Analyze it all yourself, and in our case with the Camaro, fully discuss the pros and cons with each other. In some cases, 100 idiots can't be wrong if they all say the same thing . . but for the most part, you're gonna end up being the guy to blame if it's your car . .

So, if I offer advice, take it with a grain of salt because whatever you have, the chances of it being the same as mine or ours, not very good . . That probably goes for everybody up here!

zipper06

01-28-2014, 02:52 PM

Fortunately i had a lot of good help when i built my first super charged car, I was a neighbor to the ONO bros Top Fuel in Chgo. first cousins to Kenny Herrita of Herrita and Hobbs top fuel. Kenny ordered all my parts for the blown sm/blk chevy, i bought one of his blowers and hilborn 2 port injrection, and i never looked back, because all the parts matched the setup. That was in 1964, and i was already running pretty good NA at the time. I ran that first build engine for 5 yrs without breaking parts, but i did have to change the bearing every 15/20 passes. But today i look back i left a lot on the table because the build was so safe.

Zip.