rebuilding crank yourself

[georgieboy]

Okee guys, here it comes.
Splitting the cases, putting in new bearings, do a topend etc i have done that but now i want to move on to take a higher step on that stairway.
The time has come for my bottom-end to be freshed up.
I want to rebuild my bottomend with a nice new rod.
i have got the tools to do it.
But the big question is, is it worth the risk and or joy.
I have done some homework, read some threads on the forum, and i have the feeling i can do this.
So, anyone who have already done this himself, pls throw me a line with helpfull hints or maybe talk me out of this.
Both ways i will appreciate yr input.

 

[GKKarns]

Have done many crankshafts myself,for my self and others to include Honda
cranks. The more you do the easier it gets. Must have access to a 10-15 ton
hydraulic press, surface plate, vblocks,bench centers,.0005 indicators or
better and understand exactly what it is that you are checking before making
an adjustment. I built my own jig for rebuilding my own and others. I don't do this for a living nor do I want to. I can tell you this though Your presses ability to push straight and not deflect is just as IMPORTANT as the jig that
you can buy or build. I can now reliably put cranks together at .0004-.0015
alot of it depends on how good your parts are that you are assembling. I
did a kx60 for a friend that once split apart the bigend holes were off
location .0015 from the same centerline. without ****ing the holes and starting over you could never make this crank perfect. but asembled
it fell within the factory specs.You see some good ones and you see some bad
ones. Always check your work. If you use a jig do not rely on it Ckeck and
double check.

 

[georgieboy]

GKKarns, pls tell me something about the jig. Can you do without?
The tools i have are a press, measuring equipment and V blocks. And a chisel for trueing and a blowdead-hammer(i hope my english is sufficient)

 

[Ol'89r]

georgieboy.

The tips GKKarns gave you are very good. I would recommend watching someone rebuild a crank before attempting one yourself. Also, be sure to use white lead on the crank pin to prevent galling. Instead of a deadblow hammer, you might want to use a lead hammer. They are hard to find and you may have to make yourself one.

It can be done without the fixtures that GKKarns mentioned, but, it is a lot easier if you use them.

Just my $ .02

Ol'89r

 

[georgieboy]

Is the heating/freezer method something to consider?

 

[GKKarns]

Hi georgiaboy, Yes you can do it without the jigs, but you had better have
a press that pushes straight and does not deflect. You can try the pin in
the freezer method but the shrinkage of the hardened pin is hardly measurable. Most of thes interferance fits are2.4 thous. 2.5 thous.I tried
liguid nitrogen tho shrink the pin. according to the machinist hand book
it should have shrunk 2.8 thou. 3 tenths of a thou is all I got. yes I did actually measure the temp of the pin the grain structure is so fine and these pins are so dense that they are not affected by temp. the coeffiecients
in the handbook are for mild unhardened steel. you would have better luck
heating the crank halves. I have done this also. Works quite well I personally
wouldn't heat over 350 degrees do one half at a time and then let it cool before doing the other half. do not forget a lubricant. I prefer an EP oil
but the grease that was suggested should work quite well also.The jig that I built is very similiar to the one that rce engineering sells but the bottom plate on mine has 4 independent jaws so that I can dial the halves into one another
I can tell you that it works very well, but I can't tell you that it works better
because i have never used the RCE jig. Remember that all of your measure
ments have to be referenced to the bearing journals on the crank halves.
That is what is IMPORTANT. The outside diameters tend to be 1.5 thous. out
of round 1-1.5 thous. off of the centerline of the bearing journals. Incidently
I f you check the halves individually between centers they are usually 1 thous. eccentric also. If you are really going for precision how does one check it once it is assembled I check off of the bearing journal clamp vertically
on one side (another fixture that I made) and indicate on the other sag has
no influence that I can measure with my equipment. I use interapid .0001
indicators. I'm telling you this because it is possible to have centers in
great shape assemble the crank check it in bench centers that you know
are good indicate perfect and be JUNK. I know I 've done it. and it took a while to find where the error came from ( the crank lasted another season in
my sons 80 but the bik always vibrated. I found it and fixed it last winter.
It was a wonderful learning experience. don't let this discourge you. Always
remember that you can screw it up as well as anybody else can and you don't
have to pay for it. most of the time If you are a decent careful methodical
thinker/mechanic you will come out with a good job and satisfaction. now I'm
building a press for pulling the cranks a part and a dynamic balancing machine
for cranks. Good Luck I hope it all works well for you.

 

[georgieboy]

GKKarns, thank you for sharing this with me and probably the rest out there.
And you are right about the scewing up thing. I rather screw it up myself than let a bikeshop do it for you. Than at least I have learned some other thing. Happy biking . bibi

 

[70 marlin]

pick up a used crank from the salvage yard.

get a old crank to practies on. be for you do your important one?:think

 

[georgieboy]

70 marlin, are you a mind reader??
Today i thought about that possibility. I shall pick up a few and press the hell out of them. bye

 

[Tapkawiman]

Would like to know if anyone has any links to crank rebuilding information, and maybe some pictures of these jigs you guys are talking about. There is no one around here that can rebuild a crank within 200 miles and get tired of waiting on the turnaround when I send it out.
Thanks TAP

 

[70 marlin]

no, just a old mechanic

who's learned the hard way! when I was a pup. I had a old mechanic show me how he did cranks rebuilds. he had a old work bench with two hole's in it a couple steel peg's, great big copper hammer a set of v-block, dial indicaters and some feeler guages and a huge press. it was a very crude method! but the mic's alway's showed true. :think

 

[georgieboy]

it was a very crude method! but the mic's alway's showed true. [/QUOTE]
70 Marlin, give me a mic like that LOL
and the world wld be a better place.;)

 

[Ol'89r]

TAP.

Crank pots or fixtures are simply peices of heavy wall pipe slightly bigger in the ID than the flywheels of your crank. They have a slot cut a few inches down one side for the rod to stick out.

All they do is roughly align the flywheels when you press them together. Final alignment is done with a soft hammer. You can use a straight edge on the OD of the flywheels when you press them together also, but, a crank pot is a lot easier. Sorry, no photos.

You can use 'V' blocks or if you have acess to a lathe, just put the crank between centers.

Oh yea, elk, if you are reading this, I said 'crank pot' not 'crack pot'. For some reason, I already know what your thinkin.;)

 

[jmics19067]

if you have access to a press , dial calipers ,vblocks, and atleast two dial indicators I am assuming you know how to use them then it is easy really just time consuming getting everything true and in spec. Can be frustating though. Seen a machinist do one without even a press just a big vise and squeezed the halves together. Definately not for a honda

 

[GKKarns]

A very good assembly jig can be seen at rce-racingor rceracing.com
the idea behind it is to be done rebuilding the crank once assembled
to the proper width. Notice how each half pilots off of the bearing
journals of the crank,in theory this brings themm into coincidence
with each other while also holding the the faces of the fly wheels
parrellel and perpindicular to the axis of rotation. This type of jig
works very well and there is very little to be doneonce the crank comes
out. This style of jig was designed for honda cranks that are wrapped
with sheet metal aka tin cans, because you cannot strike the cans
to align the crank after assembly. Ive done two cr250's this way
and wasn't happy with what they checked so I made some more tooling to nudge them into alignment. They were are collars that are split clamp onto
the cans of the flywheels. then when you strike these collars there is no damage to the cans. wall thickness is 1 inch collars are two inches in diameter
larger than the crank flywheels. Honda cranks are so cheap right now(to buy)
it's hardly worth doing them. Oh if you do buy new crank check them out
with the gauges some are good some need to be worked on out of the box.

 

[jmics19067]

yes check out new cranks definately!!!!!! I had the flywheel end of my crank all buggerred up from trying to remove an obscenely frozen flywheel. So instead of buying a crank half and a rod kit I went for the complete crank<20$difference> When the crank was delivered half of it was hanging out of the box and was 0.020 " out!!!!!

white bros. has crank jigs for sale head to your local dealer and ask if you can thumb thru the catalog if you want to see what one looks like.900$ for the single cylinder jig!!!!!!

How I made my truing stand is to take a piece of channel and cut slots in the web two pieces of angle iron each drilled on the flats so that one bolt will ride up and down the slot of the channel. The other holding your center points to place in the ends of the crank. too make my center points I took a couple of 3/8ths bolts chucked them in a drill press on a medium fast speed and used a grinder to shape it too a point completely low buck and homemade. And at first I ddint trust it but wanted to play so I tried it out rebuilt and trued a crank then took it too a machine shop to double check . I thought I was 0.003" out but the shop said I was 0.002" so I must be +/- 0.001" off in my setup and just take that into consideration when i rebuild. The bikes I have owned and rebuilt all had .004" as a runout limit so I am safe so far

I will see if I can take a picture of this homamade thing and post it to help try and understand how I made it. But it will only work on cranks that have good ends on it

 

[jmics19067]

Ok i got the picture on my computer but how do you post an image?

 

[georgieboy]

jmics, just buy stamps and send us by snail mail;)

 

[jmics19067]

the picture or the truing stand?:o

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  hmmm I just read the directions on how to post an image and I really dont think I am going to get it too soon