anyone ever had a crank straigtined machine shop says its out 25 tho? and its toast. I remember hereing about cranks getting trued up. my inframe has turned into a tear out because the cylinders were way to far gone for 3 ring pistons so its getting bored 40 over, I definatly don't wanna buy 1,500 dollar crank
My machine shop straightens them all the time, with a BFH. The one I'm working on now was bent 30 thou. None have been a 3208 though. I've never had a problem with them.
Big Foolin Hammer?
Pop the liners buy a new crank I've learned a poor man pays twice.
Don't buy the crank... a GOOD machine shop can straighten it.... I sent one out of a 3304 to an automotive shop,,, they said it was toast,,, got ahold of my Cat dealer and asked them who straightened their's. They gave me his number and the rest is history. IS AS good as new.
Throw the crank I've tried this b4 forget it it not last
I"m with Gramps on this one. There is an official Caterpillar procedure to measure and straighten bent crankshafts and more importantly IT WORKS if properly carried out. Our Central Repair shop had cranks straightened all the time. I actually have a copy in my hard drive ..............
I just wonder if this is a big issue or not ? 0.025 seems like allot of run out but how long has the engine ran like this ? Main bearings show abnormal wear on them ? If not I don't know if I would worry about it as long as you could reach up & spin the crank freely after torqueing down the main caps with new bearings in them . Wonder if a brand new 3204 crank is perfectly strait ?
Where do they measure it? I had a Cat 3160 that measured .005 at the flywheel end. It kept breaking the center out of the outer clutch disk and coming out of high gear. It ran for years that way. Used a bungee to keep it in high for long runs. Hired two so called mechanics and it cost me allot of money for them to not figure it out. One said he checked and it was straight. It took 5 minutes for me to see that it was off.
Maximum permitted TIR (Total Indicator Runout) of any individual main bearing journal with respect to the adjacent main bearing journal on a new or reground crankshaft should be no more than 0.005". Obviously it doesn't help that we don't exactly know how the figure of 0.025" as posted by the OP was measured by his machine shop. There is a very tightly-written set of guidelines indicating exactly how the crankmust be supported and how the measurements should be done so that the TIR measurements that are obtained are actually relevant.
They'll put 'em in an oven first (without ruining the hardness) and then onto a crank press... then the BFH .
Oh no, not the BFH .............. But yes, you're absolutely right. They do heat them up before straightening.
Our local machine shop in Little Rock Arkansas Hilcrest Camshaft Service does it all the time for Our Cat Dealer.Straighten if needed then any machine work.
stumper120, I'd be more worried about turning the crank undersize more than 20 thou if you don't know for sure of the actual machine hours. I am leery of it because of the total operational hours that a crank has under its belt. It could have been run 16000 hrs on original bearings, overhauled and ran another 12000 hrs on 10 thou undersize bearings, and then sold to you. That'd be a lot of hours of twisting and flexing, especially in the higher HP engines that are common today. I have seen them break and it'll take out a lot more stuff than what a new crank would cost. It is a very common occurrence to have a crank straightened, especially in a diesel. Something else to think about...
That's a good point Nige . Normally on an in frame overhaul I don't bother checking run out on the crank . However when the scraper engine locked up on me I was concerned about the crank being twisted or warped in some way from the sudden stop . What I did was pull down all the center mains & upper bearing shells and left the front & rear main torqued down . Then set up a dial indicator on the center main journal . Gave the crank a full 360 degree roll and noted a movement of 0.008 on the dial . So the way I looked at it the crank was sprung / bent 0.004 of an inch . I was surprised it was that close after what the old Detroit had been through I rolled the new bearings in and torqued it all down . Was pretty happy to reach up & spin the crank with ease . HeavyEquipmentForums
Your crank may have been closer than you think. Note the comment "one main brg wrt the 2 immediately adjacent mains. By only leaving the extreme end mains supporting the crank in all probability the crank was incorrectly supported and would be sagging in the centre. You have to set up the crank on 2 main bearings then measure the one in between. So for example if you have a 6-cyl engine with 7 main bearings you would make 7 individual measurements. Set it on V-blocks on #3 and #5 to measure the run out on #4. To measure #5 you'd set it up on #4 and #6, etc, etc. I'm sure you get the idea.
Ok I can admitt when I'm wrong lets fix the crank and c what happens I hope I stand corrected. But don't b upset when it all goes to hell.
Well put Nige & thanks for the details on the procedure :thumbsup At the time we weren't looking for exact precision on the repair working out in the dirt on the job site. I was happy the crank was still in one piece . Funny thing is everyone says these Detroit's are obsolete and not worth anything ......... Ahhhh....... When you go look for a remanufactured 8 V 71 they want close to $20,000.00 for an engine . I was sure glad it all worked out with the rebuild kit and we got back to making noise & moving dirt
Yair . . . A little off topic here but we are talking about crankshafts. On large engines bearing/crankshaft condition is monitored monthly and recorded in "The Book". Readings are taken with a dial gauge across the webs. The indicator is located in dimples established for the purpose and readings are compared to base line values established when the engine was commissioned or last over hauled. I once walked into a power house in a little country town and nearly had conniptions when I noticed movement in the generator mounting of the on line English Electric where it bolts down to the bed . . . the generator shaft is in effect an extension of the crankshaft and is aligned to the crankshaft with machined to size blocks or a Babbitt metal pour. In later years we used an epoxy goop called Chock Fast and after that the mounts are drilled and reamed and located with tapered pins. The "engine driver" got a little narky when I suggested he shut it down. And speaking of crankshafts get a load of this one. . .
I pulled the crank from the automotive machine shop who said it was toast and dropped it off a a machine shop who specialized in cranks, fingers crossed he can get it fixed up. I believe the machine only has 4,300 original hours but who knows, they bored it 40 over and it cleaned up fine. also it seems a wrist pin bearing began to come apart and put some metal in the middle main jurnal. I caught it just in time I guess. it wasent even wrapping yet
$20,000. Holy crap, I have a 8V-71 in my log loader truck with only 1,200 miles on it. I never start it in the woods, only when roading the loader from site to site. Going to upgrade truck soon. Maybe there is a market for the engine.
Ask the second shop what procedure they are going to use to straighten it. If they tell you they are planning to heat it slowly in an oven to X degrees and then straighten it while still hot I would proceed with confidence. If they try to tell you they can straighten it cold I would be a little suspicious.
I know that crank would be expensive, but how much more would that lathe set you back? Prolly a large charge for each finished product.
I had the same reaction old-iron-habit . My buddy had just installed a remanufactured 8-V-71 in a bus and his cost on the engine was $ 18,000 and that was with a good return core . They would not have taken my old engine in as a "good core" with a hole in the block . My saving grace was that the crank was still good , was able to patch the block and the rebuild kit was pretty reasonable in price . Could be a market for your engine . Hey... 10 or 15 years ago I didn't have to go far to find a Detroit powered truck setting in the weeds or in a farmers shed . Today most of that stuff is long gone due to scrap price .