[polarisripper28]

what do professionals use to do bearings on a crank. how come i cant mark everything carefully and split the crank and do bearings myself? if everything lines up again i would think it would work just fine, no?

 

[polaris1man]

Do you have a press with dye to hold the crank while pressing the bearings on and off?

 

[polarisripper28]

i have a press and a bearing puller and a socket to put them on?

 

[shreddy]

I believe a crank shop will also true and balance when they reassemble it

 

[Bobinwi]

yes most crank shops true and balance the crank when they do it. if you are off a MM can throw your whole motor out of balance and keep eating crank bearings. unless you have a full machine shop for doing cranks take it in and pay to have it done correctly

 

[Austin1351]

If nothing else, split the crank and replace the bearings yourself. Then send to a shop to assemble and index / true the crank. Labor for this is $75 - $150 (depending on the shop). Cheaper than a new crank and anything else it takes out.

 

[heshtesh]

When you go to put it back togeather you will need v blocks and dial indicators to get the ballance perfect,have to make the crank throws zero to each other then ballance is perfect.

 

[mr_green]

here is a great little clip discussing truing of the crank.

http://www.slednutz.com/images/user_upload/allcool.wmv

 

[polarisripper28]

cool. so was that do it yourselfer or a profesional. i have all those tools. i feel as if i score everything and get everything line back up it will work. how would a professional tear it down and do it?

 

[mr_green]

I don't have that answer. I have often wondered about attempting some of this precision machine work, but I have not had a part that I could risk wrecking while learning on. I am sure that somebody on this board has more information on the subject, but as of yet nobody has come forth.

 

[polarisripper28]

ya, heres how im lookin at it, i have this old sled that needs bearings. it will cost alot of money to get it rebuilt. i got a crank off ebay for 30 bucks that wouldnt work with my engine cuz its not built for points, it has good bearings. i say i have only 30 to lose. to try and take the one with bad bearings apart. if taking it apart goes good, ill take the other apart. that video you showed me makes sense. i just need more people input from other people at this point.

i mean whats the worst that could happen?

 

[Luke]

here is a great little clip discussing truing of the crank.

http://www.slednutz.com/images/user_upload/allcool.wmv

Im a little skeptical about his methods in the video. I have split the crank from an old TX 340 and it took 10 tons with a hydraulic press to remove one of the pins. Im guessing that theres probably .001"-.002" interfenence between the pins and holes. Once that pin is in the hole, shrunk in or pressed, its where its supposed to be, there aint no changing it. Hes talking about BENDING the crank webbing. This does not fix the problem if your crank is out of true. If you apply his method to a crank and it reads true on a straight diameter, then you move your indicator to the taper, I guarantee your taper will not run concentric with the diameter you were indicating off of when you "trued your crank with a chisel". The misalignment that hes attempting to compensate for I think is from the webbings on both sides of a connecting rod pin not being alinged properly with each other about the con rod pin. This will cause the centerliine of the crank to be skewed, and all your crank bearing will not rotate about the same axis. Even a degree of misalignment at the con rod pin will cause several thousandths of misalignment at ends of the crank. You cannot fix this with a chisel or a vise.

I have never rebuilt a crank, but I do build high speed rotating machinery for a living. I build and run prototype machinery that spins up to 120,000 rpm, and sometimes higher, with tolerances of .0001"-.0002". And I make most of the rotating parts myself. Im sure the guy in the vid is not properly truing that crank. My $.02.