Technical Drawing of 175 crank

[Baron]

I am looking for a technical drawing of a 175 crank showing factory dimensions.  Any suggestions on where I could get one.
Thanks for your help
Baron 

[dcr]

I recall this question being asked previously. I don't think anyone offered up anything. Makes me think no one has such an item.

[dcr]

Has anyone out there rebuilt their own crank? Or more specifically, pressed out and replaced the center bearing and seal?

I have a local machinist evaluating one that I have. He is currently creating a jig to be able to reassemble the 2 halves and maintain the 180 degree offset.

[bsracer]

I've had several 175 cranks rebuilt over the years. Question is, do you have a new center seal? Bearings are available. I just used my last NOS crank in October for Barber. I have used Scott Clough Racing and a local guy. On occasion the cranks needed tweaking to fit properly in the cases. Mostly needed to be pressed together with tighter tolerances to fit within the locating pins/clips. There are some people out there that can rebuild a twin crank if they have the rebuild parts. Someone once gave me a quote of $600 plus the cost of rebuild parts (bearings, rods, etc). There are NOS ones out there for less than that.

paul

p.s. dcr, i'd be interested to know what the local machinist is making as a tool. There are some complicated tools for aligning the center halves to ensure 180 deg. I will be having some cranks done over the next few months that address the fact that they break under the stresses of racing.

[dcr]

I have a couple seals and center bearings that I was fortunate enough to obtain recently.

He is building a jig which will align and hold the center halves to assure a 180 degree offset while pressing them back together. I have no idea what it looks like, but will hopefully grab a photo and be able to post it once he has that part done. At that point, he will be open for business, so to speak, in the Bridgestone 175 crank rebuild business.

Dan

[craig641]

Paul - who is doing your crank work?  What are they doing?  I sent a crankshaft off to England because I couldn't find anybody in the states that seemed like they wanted to do the work.  I assume you're talking about getting the center pin made bigger to remove the step.
Craig

[bsracer]

Hey Craig,

I'm talking to Phil at Crank Works.  It seems he was off the radar for a while and now he's back. I plan on having a straight 20mm pin made for the center and not sure if I'll modify BS rods or use something else. I'm hoping to get a sample rod this week to see if that's what I want to use and then I'll send off some stuff to Phil to get some cranks done. I took on a project of building three race motors for next year. I need to get going so they will be ready for racing in April. I just got back from tearing down about 7 motors over the weekend in NM. I'm hoping to get 5 cranks built (two for me three for the project). 

paul

[OldSwartout]

I have a fixture that I made to assemble 175/200 cranks to get them at 180 deg.  I could assemble cranks, but don't have a supply of replacement parts.

[dcr]

Id love to see a picture of it.

[OldSwartout]

Here's three photos that I hope make sense.  There are two spring-loaded pieces that wedge the crankpin into a V.  These two are placed in between two plates in opposite directions, which hold the crankpins 180 deg. apart while the inner crank halves are pressed together. It's simple, but has worked well.  I've checked assembled cranks with a degree wheel and they're within less than 1/2 deg.

[slawsonb]

Yet another cool bit of Karl engineering. Nice!
...bert

[dcr]

Thanks for the pictures Karl.

Have you (or anyone else) ever measured a factory crank to see if it is exactly 180? My question would be, what is an acceptable tolerance from 180 degrees?

[OldSwartout]

I would guess that the practical limiting factor would be the amount of adjustment available in setting the ignition timing. Without actually measuring it, I'd think 2º could be accommodated.  Without some high end simulation and analysis software, I wouldn't even venture a guess on what would happen to the torsional dynamics of the crankshaft.