Most bent crankshafts from a crash can be straightened, at least that is my experience.
I get a kick out of repairing things, rather than just replacing them, or buying new parts.

I learned how to true and straighten cranks from the Pro's back in the 70's....I'm very
good at it.....I've been doing it for 35 years, professionally. Send me your bent crank,
and I will straighten it for free.....no problem.

Flyboy Dave.

I too hate buying new parts when the old parts can be resurrected . Why not describe for us your method to straighten a bent crank. Don't be afraid to use technical jargon, and assume we have access to the same machines and equipment that you do.

i think Dave's technique is very self describing in the picture................see the Big Hammer

Wow, that's a generous offer. I admire your approach to repairing parts instead of tossing them. It's a lot more gratifying and impressive, too.

Now, we just need someone to offer free conrod re-bushing! Or, at least I need it.

David

LOL Big Hammer

I will be sending Dave a very bent LA40 crankshaft as soon as I work off this evening (3-11) shift, prally Thursday

I will try and get a before and after pic, unless Dave wants to as He is doing the job.

Will you straight out a million of the bent crankshaft without time to fun with model airplane[sm=lol.gif][sm=lol.gif][sm=lol.gif]

.

Craig....send the case and the crank, so I can check it like this....

Craig is my first customer.....[sm=thumbup.gif]

FBD.

To the naysayers out there. Not naming names but rhymes w8ye and breeze.
It's obvious that FBD is using the pictured engine housing as a mount to run the shaft in. No problems with how he has it fixed to his surface plate as a method of holding things in place.
To really simplify the straightening proceedure. A whack put it in and a whack will take it out. No hitting shall take place on a surface plate...ever.

I appreciate what he is doing, just would not do it with my engines

First, I'm not doubting Dave's expertise in any way. But, I do have a question: How do we know that the mounting flanges on every case are perfectly square, true and in an exact parallel plane to the crankshaft?

David.

You're a good man, Flyboy Dave.


Ed Cregger

RD, the flanges have nothing to do with run-out, there is not a concern about alignment in this situation. This would work even if the shaft were a taper, the trick is finding the point where the bend originates from and working from there.

I don't mean to hijack Dave's thread, I also have some experience in this area.

.

It might be more in the spirit of helpfulness and in line with RCU's policy of not embarassing individuals if you were to ask your questions. Or state the way you do your bent shafts maybe even offer to join FBD in his efforts to be helpful instead of your tongue in cheek assult on his abilities.

Also Steel plate is hot rolled, pickled, and oiled. Not cold rolled. The cold rolling process is for bar product.

Vic

Sorry I got so far behind here, I have a S'T' carb thingy that's driving me nuts.

My pictures are rather at random, and don't show everything perfectly at all times. Firstly,
crankshafts are trued in the real World by bumping them with a BFBH....that's brass. Heavy
and soft. The hammer we had at the M/C shop 4" wide on the face and weighed about 8 pounds.
It was brass on both ends. After the crank haves are pressed together (with news parts in the middle)
using special alignment jigs, the assembled crank is checked in a truing stand.

Every now and then you get one that's perfect, but 95% of the time you have to true-up the crank.
You whack it with the BFBH. The whole thing about being an m/c mechanic (and we used to laugh
about this) is "knowing where to hit it, and how hard". You hold one flywheel in one hand, and whack
the other one. The flywheels will (believe it or not) turn ever so slightly on the crank pins if you strike
it correctly. You can move it about a thousandth of an inch or more with the correct blow.

Once you get it trued up to about .001 your in business. Sometimes you can get them perfect, but
sometimes the tolerance on the parts themselves do not allow perfection, because they are off a little.

Now if you have a twin, you assemble and true both cranks separately....then "block them up" with metal
wedges so they don't move....and press both cranks together with new bearings and seals in between.
Then back to the truing stand to check and true the assembly. The multi cylinder assemblies are trued
in a hydraulic press. These procedures are done by the old timers at the shop....trust me on that. I've
done hundreds and hundred of cranks during my last 15 years at the shop.

These little aero-model cranks are childs play really....I could true them in my sleep.

1. a single cylinder
2. a triple
3. a mechanic spot welding the pins on a racing crank after he has it perfect.

FBD.

Hey Dave, the next time I get the chance to go out flyin', I'll make sure I crash one, so I can send ya the bent crank...

We're snowed in over here...so it might be a while...

This is off topic from the intention of the OP but

It might be a little more in the spirit of the transfer of correct knowledge to our many readers in the forum if you did a little reading to garner a better knowledge about steel.

http://www.key-to-steel.com/Articles/Art26.htm

Thanks, Vic. [sm=thumbup.gif]

Awhile back I had a used S.T. 3000 with a bad vibration. I decided to tear it down and check the crank.
I had two other as well, all 3000's, I tore them all down. They were all used, and all three of them had
bent cranks....one of them .020 [:@].

Here's how they came out....it took awhile....me and my little brass hammer.

1. zeroed dial indicator
2. crank #1....less then .00025
3. crank #2....a needle width
4. crank #3....DEAD NUTS.

I shared this with Bill Robison at the time....he gave me a "damn good work, Dave" over the phone.
He said he couldn't have done better himself.

Off topic indeed.
Quite a comprehensive site. However if you follow your own advice you will notice there is not a spec there for "cold rolled plate" at least not in carbon steel. I am sure this is what you meant since the idea you posted was to make use of the mag base. "Cold rolled plate" only refers to austenitic stainless steel. If you are interested in further explanations and definitions of steel products I welcome you to start a thread and offer to post my experience there.

Notice again you choose to embarass someone going against the spirit of RCU policy by insuting my inteligence this time. [&o] Feel free to use the report button.

Dave, if you ever need an indicator with a finer scale you know who to call

Dave;

I will be sending the case along with the crank but I suspect the crank is A:really bent bad or B: the case is warped also, as the crank does not turn in the case freely. I think it must be the crank tho, as other LA40 cranks will spin like a top in the case.

This crank & case is from a parts motor that the P.O. gave up on.

For all to know, this is a very generous offer for Dave to take his time to even try and fix a piece of scrap into a useable part. And I for one give him KUDOS for doing it, no matter what the outcome. [8D]

If this thread doesn't turn friendly quickly it will be locked up.

Just to set the record straight ( Ive herd that somewhere before)[:-] you can get cold rolled steel sheet, Ive used it for years as a sheetmetalworker cheersthe pope