We had a bit of a "friendly discussion" over on the Ford Barn about storing flathead crankshafts on their side. I had one stored on it's side for over 20 years, and it had less than .003 run-out. This was of no consequence, because the mains had to be ground .010 under anyway. Things got a bit heated about what is acceptable run-out, but nobody seems to know. I looked all over the internet, and the only thing I was able to find was on a Snowmobile forum where they seemed to think anything under .003 was OK. Does anyone here have a an authoritative number for flathead crankshaft run-out? Or for any automotive crank? Something from Ford specs or maybe even an old Motor Manual; I've already had enough personal opinions and "that's what my dad told me" responses.
I wouldn't have a problem with .003 on a long crank shaft. I like my motor cycle crankshafts to be closer then that but they are not very long. A long crank like a 4 cylinder automotive (or V-8) is going to flex more then that. I don't have numbers in a book close at hand though so someone with actual numbers should probably chime in here.
Any crankshaft runout should be addressed, and .003" would be enough to turn it, in my wallet's opinion. BMWs are nitride hardened only if they are within .002" I had a crank (4" Merc) that I had turned .010" - .010". Advertised it on Fordbarn, also that it had been shot peened and blasted, prior to being turned; Radii were held to max. size. I also had it indexed, (as it was being turned anyway) Some silly old Fordbarn duck raised hell about it being indexed, crying how unnecessary it was, and on and on. I had to retort that as long as it was designed with the rod journals 'evenly spaced', and was slightly scored, it made perfect sense to perform a 'free lunch' operation that would net a 'blueprint spec' in crankshaft spacing in one op... Heck, make it as good as you can! This old fart ranted some more, and a nice gent stepped up with $700.00 plus shipping. (the buyer was a machinist, so he understood. The 'duck' was some old curmudgeon that 'must have known everything', because of his age.) Wisdom from age is worse than youthful arrogance.
Porsche and the boys probably have a spec of 0.001" or so TIR. Chevy used to say something like 0.006" was acceptable on tufftrided V8 crankshaft. I'd expect such a crank to turn freely when installed in a block with all the main bearings installed and oiled, and a decently straight and sized mainline, and I'd have a hard time worrying much about it. That criteria was often quoted in magazine articles of the 60s and 70's. Certainly the opposite ( hard to turn or with tight spots ) would NOT be a good sign, requiring investigation and correction.
The amount of angle/index adjustment possible when grinding a 3.48" stroke crank 0.010" undersize (0.005" centerline offset) is less than 0.2 degrees. I always wondered how out-of-index people really found cranks to be.
I have certainly align bored blocks that were .010 spectrum easy and they were not virgin blocks. They'll run like that and evidently no one at the factory cared.
I would be the first to admit that I sent my machinist's kids to better schools than my own by paying for near perfection on racing engines but for low RPM street engines I wouldn't sweat .006" runout. Now, when you measure runout are you chucking the crank between centers on a lathe and using a dial indicater on the center main? If so you are not getting the real dimensions. You have to support the center and then check the front and rear main journal. The weight of the cranckshaft will sag without support.
Big Block Chevy nitrided steel 454 cranks were consistantly .006-.007" runout back in the early seventies.. Sent a few back to Berger Chevrolet for better exchange..
I used to take my new bent big block cranks to Henry Valasco and he would straighten them to about .001 - .0015 Then they would turn very free and not stiff like out of the box, as a stiff turning crank in a racing engine just did not seem right to me so Henry would fix me right up Plus chamfer the oil holes and a lite micro polish and you were on your way and a hell of a deal for 20 bucks
Youthful arrogance will be remembered longer than wisdom from age. Respect your elders and stuff that curmudgeon ******** - unless it is some 'insider' joke that I don't get.
Center Bearing Run-Out ( total indicator reading ) When Supported at Front and Rear Main Bearing .002 Taken from an old time spec sheet for the 241- 270 Dodge hemi. I always store cranks standing up but keep the grandkids away!
A buddy's older brother and his pal re-built his Lotus Super 7 DOHC engine in the garage. When starting "difficulties" arose they tried to tow it to start it. "New" engines are tight, you know. The rear wheels locked when the clutch was released. Turns out they'd flipped a few main caps. I guess they didn't do a test rotation every now and then during the ***embly.
Main bearing clearance comes into play. Radial Clearance ( desired ) .00 05 to .0015 again from the ancient Mopar scripts. It is again from the Chrysler specs. Kind of tight and hence the .002 run-out. Porkand****** and aaggie might well have been running more clearance (a common high performance practice). More bearing clearance = more run-out acceptable.
When we're line boring/line honing the main bores in a block, we're holding the dimensions to within .0005" and then gonna put in a crank with .010" runout? As previously mentioned, if it's a precision/performance build, anything more than .002" runout should be straightened. If one has paid for a precision grind, the crank grinder should have measured the runout and done the straightening before grinding. For the street engines with .006" runout, they'll live, but that can be felt when the bearings are torqued down. It will require more torque to turn the crank. Yes, No, Maybe on an old Pontiac straight eight. We don't find measurable sag on most 5-main OHV8 crankshafts. Agree, not between centers on a Y-drive grinder or in a lathe. Most grinders do their runout in chucks on the machine and if it's less than .005" most will just start grinding. The most precise method is to put the front and rear main on nylon/delrin V-blocks, measure first with a micrometer to determine if any main journals have gone egg-shaped, cause there's no point in chasing the last couple of thou runout on a out-of-round journal. Then, put the dial indicator on each journal. If one doesn't have nylon v-blocks, just leave the old front and rear bearing shells in the block, lay the crank in and put the dial indicator on the pan rail. jack vines
It's starting to look like .002 is the number for an automotive V8. As I said, I'm having the crank turned so it's not really a problem for me, but it's good to know and kinda' surprising it was so hard to ferret out. I would think that a 241/270 Dodge and a 239/255 Ford/Merc are similar enough in size that the Mopar specs would be appropriate for the FOMOCO's as well. Again, thanks for the solid data.
The Jalopy Journal
