straighten bent crankshaft

[SAJ]

I bought a 1931 Tudor for my wife that has not been registered since 1996. It has been started and run a few times since then and I drove it briefly to assess it before having it delivered on a trailer to my workshop. On dismantling the motor I found corrosion in the bores and on the middle main bearing. The Babbit looked solid but a bit scored. Mainly from corrosion and the fact that there are no oil wells at the part lines or grooves in the mains caps. The block babbit has poorly formed axial grooves from the oil holes, scored in badly with a blunt chisel, but no oil path to the caps.
I set the crank in a lathe and dialed in the centres, and found the middle main runs out .0045 inches (total indicator reading)when rotated. All journals are perfectly round and unworn at 1.6120 Can one straighten a bent shaft safely by pressing?
I mounted the crank in V blocks in a press, confirmed the centre main ran out .0045 again, and pressed the high spot , increasing the force until I got to 3.5 mm bend (0.136 inch). But it sprung back to exactly .0045 inch again. My fear is that when I reach yield, the size of bend necessary will result in a huge permanent set – far greater than the .002 I need for straightness.
I have heard of cranks being straightened with a hammer and blunt bullnose bronze chisel on the fillets, but don’t like the sound of this.
Could I grind to be concentric with the end journals and remove shims (I have .012 in each side) and this would take out the corrosion pits too.
Advice please – I have heard that new cranks are often straightened after heat treating. Correct? Are my fears of a sudden yield to a large re-set justified?
I see the crank specs call for run out of .0005 to .001 inch max.
What would experts do?
SAJ in NZ

 

[James Rogers]

Your bearings look bad. They are grooved incorrectly where they are at all. The groove should be a spiral and there should be a well on each side for oil distribution. The grooves should never extend to the front or rear of the bearing and especially NEVER down the thrust of the bearing. This is a recipe for disaster and a massive oil leak.
This is what happens when the bearings are done like yours. As you can see, these are done without grooves or wells.

 

[Joe K]

And cranks ARE straightened almost exactly as you have done.

I had my rebuild block done by one firm, and the crank done by another. Seems the crank people were "enthusiastic" about their grinding efforts (they had some kid doing the work who wanted to get it done fast) and the crank ended up resurfaced, but the center off about 3 thousandth just as yours a bit more.

I was irate - where was I going to get another crank - especially since the block had already been done to match this crank?

Back to the grinding shop where I had an audience with the manager/owner.

"We've seen this before" he says. "Those 'A' cranks are 'sensitive. You even leave them standing up in a corner and they bend. We can straighten this out pronto. I'll even have the same technician do the straightening so it will teach him to be more careful."

My heart was in my throat.

Tech put the crank on the press and started in with the indicator. Bend - bend - bend. Indicate. Bend - bend - bend - indicate. Bend - bend - flip - bend. Indicate.

It took about 5 minutes of him fussing with it. But lo and behold it now indicates as "right on" on the center main. Well, a little flutter on the indicator out near the radiuses, but less than 2 ten thousandths.

I've had this crank in my block for 25 years. Most of it driven in the first five years. No problems.

But straightening a crank is a heart rending process as it is seen done. You almost think the crank is going to bend double in the process.

Kid did seem to know what he was doing. He'd done it before. Maybe a LOT?

He should be more careful and patient.

Joe K

 

[J and M Machine]

SAJ: just by bending the crankshaft you aren't going to eliminate the bend.
If anything it's going to show up in front or on the back main.
The chisel method with tip radiused to match your crank radii is the best way as it removes the bend rather than displacing it somewhere else.

Sounds like you're set up to accomplish this however it's a bit tedious if you've never done it before. Like trying to straighten a spring is best example.

I have pictures above that show the crank in a straightening press we use for crankshafts.

After identifiying the bend we'd bring the high side towards the hydraulic piston and by supporting both ends firmly create prssure to the bent area.

By doing so at a minimal 200lbs I peen the area of question to relive the induced stress"bend".
Peening is using the chisel I mentioned at the radius area on either corner of the journals of main and also at rods journal closest to the bent main.

However by doing this and it becomes straight you'll need to check front crank snout and also rear flange to make sure they didn't change.

The question is did they grind the crank bent or did it get bent by a poor babbitting job.?

Your babbitt work is terrible seems that rear groove on the thrust surface is a common misconception. Let oil to the rear to reduce oil on the ground.
I have included a picture so you can see a proper job.

 

[oldwoodsman]

My grandpa told me a story about a model T he had back in 1929, that would wear the center main bearing he put it in a press, but it would spring back to were it was until he put it in the press and wacked it with a large hammer. He put it back in the T and drove it 2400 miles to Montana and back without any problems. I don't remember the details as to his set up as that story was told about 55 yrs ago to me as 10 year old but the basics of the story stuck.

 

[hardtimes]

Hey JandM,
Thanks for your input/pics , as very informative in answering original Q !
Also germane to my present situation, as I just (nervously) took my drilled C crank to this engine shop. I saw their 'room' just used for crank work. Looked impressive with all the crank work equipment. Looks similar , in ways, to your pics ! As they also do 1k hp drag engines..hope all will be well.

Can not even imagine a guy picking up a BFH/chisel and (gulp) 'working' on that crank

 

[J and M Machine]

Hey JandM,
Thanks for your input/pics , as very informative in answering original Q !
Also germane to my present situation, as I just (nervously) took my drilled C crank to this engine shop. I saw their 'room' just used for crank work. Looked impressive with all the crank work equipment. Looks similar , in ways, to your pics ! As they also do 1k hp drag engines..hope all will be well.

Can not even imagine a guy picking up a BFH/chisel and (gulp) 'working' on that crank

Thank you for the comment. We are trying to educate/inform/Ford people and novices.
Ask them to show you how it's done. Remember, just because they build funny car drag engines doesn't give the right to work on yours.

We have many race shops here and lots of bad work comes out of those places.

Quote" An Educated Consumer is Our Best Customer" Sy Syms.

 

[700rpm]

A reputable "A" rebuilder in our area hangs his spare cranks frontside down, which seems better than standing them on the floor.

 

[James Rogers]

I have 2 engines that were brought to me for mains and the owner wanted them done without wells or grooves. I told him to take them elsewhere or let me do my work the way it is supposed to be done. I don't want his customer complaining about a failure and me getting the blame. He left them and I did them the right way. Do it right or send them to someone who will bend to financial pressure and cobble up the work! I don't need money as much as I need a good name in my profession.

 

[SAJ]

Thank you so much for great help. I got the crank to TIR <.0004 with a flutter of .0016 where it fell into the corrosion pit. I hope this will be OK. The pit is small but will nevertheless disturb the oil wedge each time it passes.
I could not find my Beryllium-copper non-sparking chisel to try out the J &M method properly, so I deflected the crank by increasing amounts as per the Joe K method until at 3.75 mm deflection it yielded and stayed at .0004. I did hit it a bit with a sissies hammer, in case that help internal stress, so I am not sure how much that contributed. It was a scary process for someone who has straightened lots of round things before, but not a complicated crankshaft. I was so nervous I did not look at the pressure gauge to see what 3.75 mm deflection took. I checked afterwards and its 5000 lbs. If I had looked I would have gone to the J&M method and bought a new chisel!
Re the babbit, I would like to block up the leak to the rear, which is about the width of a knife cut. I have no babbit to experiment with but wonder if a 50/50 mix of molybdenum Disulphide powder and epoxy would do it? If it came loose it would do no harm and should stay put in the end of the groove. Would a touch of tinmans solder right at the end work instead?
The problem is there are very few in NZ who can pour white metal well and I know of problems with many of the recent jobs.
There was a first post by Kevin in NJ last night which is now gone. He mentioned any movement shown up by oil squish is bad and will result in cracked babbit. The babbit I have will squish out oil when pressed at the ends (one needs an eyepiece magnifier to see the squish- very slight movement), but not where the cast holding "lugs" are, so it seems pretty tight. Plus the rear main babbit is thick and well constrained when the cap is on, so I hope it will be OK. Any comments?
It was so good to get answers from people who do this kind of thing professionally. I am not a machinist or auto engineer - I just collect interesting machine tools and play with them, so there are many methods I have read but never attempted personally.
I will groove the babbit with a dremel as shown in these and other previous pics from J&M, James and Herman Khonke. The rods all look nice, with X grooves and wells in them, and have .0015 with plastigauge.
Thanks again
SAJ in NZ

 

[Tom Wesenberg]

I would use solder on the end slit, rather than an epoxy.

 

[SAJ]

Thanks Tom. Solder is easier too, though I think James Rodgers said Don't attack babbit with a soldering iron because you will regret it. Have you soldered babitt? Does it tin easily with lead-based solder? I know lead can perfuse into tin-based babbit and ruin it if you tin with lead solder before pouring babbit.
The epoxy I would use would be many steps ahead of JB weld, since I have a selection of about 30 different hardeners and resins to choose from at my factory.
SAJ in NZ

 

[Tom Wesenberg]

I haven't soldered babbit, but to fill in that tiny slice seems very doable. If it's clean and dry it should attach well.

 

[hardtimes]

J&M,
Your read my mind, as I had intended to ask shop owner (and friend) to watch , unobtrusively...how this work is done. Alas , life gets in the way often, if seems ! Just had some 'work' on my back. They will have to carry on without the student,eh. BTW, this shop has some talented people and they have A and B blocks being worked most times. They build parts for engines of all kinds. They even have a full dyno setup. Nice people too !

Your input and teaching here is noticed and much appreciated. The work that you show/share looks amazing. Thanks from all of us neophytes !