Crankshaft questions

Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration
Model T Ford Forum: Forum 2014: Crankshaft questions
Top of pagePrevious messageNext messageBottom of page Link to this message  By Dean Yoder on Tuesday, January 21, 2014 - 08:01 pm:

Cg
I am looking for crankshaft straightening articles.
How much do crankshafts bend when not in a block?
How fast do they bend?
How much bend is acceptable?


Top of pagePrevious messageNext messageBottom of page Link to this message  By keith g barrier on Tuesday, January 21, 2014 - 09:41 pm:

Dean, I straightened the one in my 24 6 years ago on my shop press. Made some hard wood V blocks to set it up, trial and error, must have worked cause it's still running after over 40k. I was surprised how much I had to spring it past straight to get it to spring back where I wanted it but don't remember the figures. Probably not recommended by some on this forum but it worked. funny what you can make work on a budget! KGB


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kerry van Ekeren (Australia) on Tuesday, January 21, 2014 - 10:33 pm:

I assume Dean you are referring to a T shaft?
A shaft that is not stored properly will bend, how long? don't know, store standing vertical.
Cast steel will not stand as much bending as a forged shaft.
T shaft sprung less than .012" can be straightened, .001" would be good limit of runout

In saying that, I have rejected 2 fresh re-ground shafts given to me for re-babbit jobs, .005" out on 1 and the owner had it straigtened within .0015", that I fitted and runs great, heavy dodge rods still and it's a very strong pulling T.
The other one not so lucky, Owner got it back to me with 0 runout, great, after all the work of the babbiting and boring, I found a crack in it, crankshaft machine shop thinks that happened with the pressing.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Justin in South Africa on Wednesday, January 22, 2014 - 12:58 am:

Hi Dean,

I had 0.019" or about 0.5mm run out on my crank. Only between 2nd and 3rd main.

A very gifted Scotsman came up with a plan to straighten it and machined two half blocks that fitted in the 2nd main. He then bent it from 2nd main to 3rd.

The result is 0.004" or 0.1mm run out... But he should me on the dial gauge how weak a T crank is. He could get the dial gauge to spin with just a light press of his finger...

I'm getting it crack tested now... maybe should have done it before... But the ring test was promising enough... oh and I trust my Scotsman!

We will see.

Justin
South Africa


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting on Wednesday, January 22, 2014 - 05:35 pm:

In saying that, I have rejected 2 fresh re-ground shafts given to me for re-babbit jobs, .005" out on 1 and the owner had it straigtened within .0015", that I fitted and runs great, heavy dodge rods still and it's a very strong pulling T."END QUOTE"

An out of round shaft pushes the oil pool a head of the crank journal, wiping the bearing wall of any oil that normally would support the shaft in the bearing, and the pressure from the out of round journal puts undo stress on the babbitt wall of the bearing and will enlarge the bearing hole as the center of the crank is whipping with a out of line journal. Running strong or not.

That crank should have been ground at best.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kerry van Ekeren (Australia) on Wednesday, January 22, 2014 - 06:09 pm:

Herm, not talking about out of round journal but bent shafts, but if we check Fords specs for a journal, it can have up to .0015" out of round and still be a serviceable shaft. and if the whole shaft is out by the .0015" that's carried over the 3 mains as Ford explains in service letters.
And as you have stated, out of round shaft pushes the oil pool a head of the crank journal, is a good thing to maintain hydraulic pressure, remember, this is all with in Ford specs, any more of cause will do as you describe.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting on Wednesday, January 22, 2014 - 06:31 pm:

Boy, you have got a lot to learn, Kerry!!!!!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kerry van Ekeren (Australia) on Wednesday, January 22, 2014 - 06:41 pm:

I can admit that Herm, but can you??


Top of pagePrevious messageNext messageBottom of page Link to this message  By Allan Richard Bennett on Wednesday, January 22, 2014 - 06:59 pm:

Just a couple of rambling thoughts for your consideration. If straightening a crankshaft which has bent over the last 80-100 years, how likely is it to develop 'memory' and later revert to it's bent shape? Would stresses induced in the straightening be relieved in subsequent grinding, and thus have it more likely to relax back to that bent state. Would it be better to grind the shaft to true, rather than bend it back?

Most crankshafts I have had to deal with also were twisted. This wind-up has meant that at least .010" was needed in the grind to bring the rod journals back into line. I consider this to be acceptable and see no need to attempt to take the twist out of a shaft.

I would appreciate your input gentlemen.

Allan from down under.


Top of pagePrevious messageNext messageBottom of page Link to this message  By J and M Machine Co Inc on Wednesday, January 22, 2014 - 07:09 pm:

Hello:
There's very little if any written on the subject of straightening crankshafts.

By bending the crank in the opposite direction isn't going to straighten it as the steel has a memory and you have to erase it, so to speak.

In the machine shop, typically anyone who has a crank grinder has a straightening press to cure the bends before grinding.

The one I have was made by Storm Vulcan but there are others out there and accomplish the same thing. making the crank straight is the key before grinding.

Once you know via magnafluxing"crack checking" that the crank is good then you would proceed to straighten it.

Seen in the picture I am straightening a Model A crank.

Model A or T typically they are bent in the middle from the center main blowing out.

I will clamp both ends and there is a v block if you notice under the center journal that is attached to a hydraulic cylinder.

I first indicate the crank finding high and low of the bend. With the low side up and clamped, I put pressure on the center of the crank bending it upward.

The second picture, a chisel I have ground a radius that matches the crank radii.

With the crank under pressure I will peen spots I believe to hold the bend on the rod journals and other places.

By doing so it will relieve the memory of the crank.

Then loosening crank from the press I'll check it and keep doing so till it's in limit to grind.

Then I also have to check either end as by making the center straight now the ends are bent.
I also have to make sure those are true.

There's alot of labor that goes into making one right.
http://www.jandm-machine.com/crankshaftGrinding.html



Top of pagePrevious messageNext messageBottom of page Link to this message  By Kerry van Ekeren (Australia) on Wednesday, January 22, 2014 - 07:32 pm:

Allan, just a snippet out of Repco's Digest


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Garrison_Rice Minnesota on Wednesday, January 22, 2014 - 08:05 pm:

My God how complicated can you make such a simple thing. First show a Camshaft, call it a crankshaft. Understand what geometric specifications you're talking about. There are so many that can apply to a crankshaft. Runout, total runout, roundness, cylindricity, straightness and concentricity. Throw size and twist into the mix and you start to understand how nomenclature and making things harder than they need to be can cause ulcers. When you start with a used crankshaft, check it for cracks using magnetic particle inspection (magna-flux) before you even start. There's no reason to piss away time on a cracked crank so know up front what you're starting with. Then straighten it and check for cracks from straightening using mag particle inspection again. Keep in mind it's possible to think you're straightening it first but in reality you're checking 3 different features (main bearing journals) to each other for runout. If you've got out of round on your journals it comes into play and can make a straight crank appear to not run true between the mains. Support your crank on the 1st and 3rd mains and check the center main back to them. Pray to god there's not some kind of weird twist in the shaft. Once the mains are ground to size, display a reasonable amount of roundness and check close to each other within a specified runout tolerance there's a chance you're crank mains will be as good as you can reasonably get it without spending excessive amounts of money on inspection equipment. And now that you've got your mains ready you've still got 4 rod journals to consider.

Be aware of stresses caused by grinding and straightening. They may cause cracks by stress "relieving" over time. Sharp radii can cause stress points that can cause a grinding "check" to propagate into a crack. Another thought is to be aware of the fact no-one can tell if a crank is cracked by ringing it. You might think you can but it takes one hell of a crack to get a "dull" sound when ringing a chunk of steel. It's not like a grinding wheel where it actually works to ring it for cracks.

Over-bending can take some of the "memory out of steel" and keep it from "springing" back to where it was.

It's probably not a good idea to think that, if someone "straightened" a crankshaft on a press, didn't grind it and ran it 40k miles, it'll happen on the next one. A single trial of one is never a reasonable sample to base success on.


Top of pagePrevious messageNext messageBottom of page Link to this message  By J and M Machine Co Inc on Wednesday, January 22, 2014 - 08:16 pm:

Quote"My God how complicated can you make such a simple thing."


Glad you understand; there's a lot of work that goes into one to make it right.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kerry van Ekeren (Australia) on Wednesday, January 22, 2014 - 08:24 pm:

Mike, 'first show a cam shaft, call it a crankshaft'
I hope you are not referring to Deans photo?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting on Wednesday, January 22, 2014 - 08:27 pm:

I can admit that Herm, but can you?? "END QUOTE"

Yes Kerry, I can admit you have a lot to learn.


Kerry, see where your add says to grind out any remaining misalignment."END QUOTE"

It doesn't say straighten to .001-50 thousandths, and then use a bent shaft with New Babbitt, a waste of money for sure, and a cobble job in my opinion!!!!

Thanks for your article, and also your post Mr. J.& M.!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Garrison_Rice Minnesota on Wednesday, January 22, 2014 - 08:35 pm:

Quote"My God how complicated can you make such a simple thing."


Glad you understand; there's a lot of work that goes into one to make it right."

You caught my lousy attempt at sarcasm. What people have to understand is you're not just talking about a crankshaft. You're talking about a whole bunch of geometric features that have to work in unison in order for the machine it goes into to run it's best. If some of the features weren't going to inherently be correct by mere design it would be impossible to make it work. I thing the only thing more nightmarish than a crankshaft is a helical gear. I don't envy anyone who has to make a diet of working on this stuff and having been a machinist for over 40 years I spent my time playing with it. I hope I've forgotten enough of it to ward off nightmares and enjoy my retirement.

Kerry, you have to admit, that photo of Dean's looks an awful lot like it was taken of a camshaft. I suppose I missed something somewhere and now I'll find out what. Ready...... Go!!!!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kerry van Ekeren (Australia) on Wednesday, January 22, 2014 - 08:40 pm:

Herm, your opinion is like the old saying, (you no doubt know how that go's,) I on the other hand, am happy to use and stay within the wisdom of the Ford service specs.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Garrison_Rice Minnesota on Wednesday, January 22, 2014 - 08:48 pm:

Herm, regardless, I'll take you and your years of working knowledge over somebody's suggested specs. A lot of "engineers" who write specs never have an opportunity to put a wrench on as much as a prototype.


Top of pagePrevious messageNext messageBottom of page Link to this message  By J and M Machine Co Inc on Wednesday, January 22, 2014 - 08:49 pm:

Mike:
Being a machinist you get it.
What I've written down for an explanation; no one can understand the time that goes into it.



The sarcasm is much needed to make the day go faster.

Yes the ringing crank ....


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Garrison_Rice Minnesota on Wednesday, January 22, 2014 - 09:05 pm:

Hey, a cracked crank will still work for a dinner bell.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting on Wednesday, January 22, 2014 - 09:18 pm:

Herm, your opinion is like the old saying, (you no doubt know how that go's,) I on the other hand, am happy to use and stay within the wisdom of the Ford service specs."END QUOTE"

Well, as normal for you Kerry on 1920's Machine Shop Practises, you read the information wrong again!

Your Ford Manual says that if the shaft is more then .012 thousandths out, get a new shaft.

If less then .012 thousandths out, then straighten until OK!!!

It does NOT say!!! ".001" would be good limit of runout."END QUOTE" That is you, Ad-Libbing!!!!

What it does say, about the .001 thousandths figure is if the shaft is worn on the mains more then a .001, a NEW SHAFT should be installed!

So, read your Ford Service some more, I think you need the practice!


Top of pagePrevious messageNext messageBottom of page Link to this message  By keith g barrier on Wednesday, January 22, 2014 - 09:21 pm:

On this forum, it matters not about what has been done and whether or not it worked(not everyone has a huge budget) but why it will not work(even tho it has) I do not say that my way was "the correct way" but it was the only way to afford to having a running model T which I have enjoyed for many miles. I drive my car 30 to 35 which takes most of the strain off 90 year old parts. I never try and mislead anyone with my limited "shade tree experience". I think back in the day, people had to do what they had to do with. If I listened to a lot of what was posted here as a newbie, I think I would be greatly discouraged at times especially if on a limited budget. Have a great day everyone. KGB


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Garrison_Rice Minnesota on Wednesday, January 22, 2014 - 09:34 pm:

Keith, I hear ya. I've spent a lot of time crossing my fingers and praying it would hold up. I've shimmed rod bearings in a flathead and had to put JB Weld where I never stood a chance of having it work but it did. My exhaust on my '26 sedan is still being held up with baling wire. Hopefully I'll have that fixed before the years over. I was out of line inferring that your intention was to say your way was the correct way. When in reality it was the only way until you could make it better. Please forgive me. I'm actually struggling along trying to be civil tonight and again it's not working the best. But give me credit I'm trying. Usually by now Steve's chimed in and backed me down but he must be on hiatus tonight.
Mike
Mike.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Clayton Swanson on Wednesday, January 22, 2014 - 09:46 pm:

dean, are you writing this all down?


Top of pagePrevious messageNext messageBottom of page Link to this message  By keith g barrier on Wednesday, January 22, 2014 - 10:06 pm:

No problem Mike, I am incorrect regarding lots of things!:-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kerry van Ekeren (Australia) on Wednesday, January 22, 2014 - 10:16 pm:

Herm, your right, that service book doesn't give the minimum, but the Ford Power Plant Checking Standards does.
'Crank Shaft Alignment' Ideal .001" Allowable .003". Replace if over .012"


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kerry van Ekeren (Australia) on Wednesday, January 22, 2014 - 10:54 pm:

And of cause Herm, as usual, I will excuse your MANNERISM and accept your APOLOGY when and if you are brave enough to admit and post!!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting on Wednesday, January 22, 2014 - 11:52 pm:

Herm, your right, that service book doesn't give the minimum, but the Ford Power Plant Checking Standards does.
'Crank Shaft Alignment' Ideal .001" Allowable .003". Replace if over .012""END QUOTE"

No doubt written by some one with the same lack of knowledge of engines as you Kerry, because that makes no sense at all.

From the figures he used, it looks like he Misinterpreted the same information out of the service Manual as you did!!!


Tell me again how you don't have to check the alignment of the rods you machined on your mill, as the mill machines them straight!!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kerry van Ekeren (Australia) on Thursday, January 23, 2014 - 12:50 am:

Good onya Herm, your Mannerism shines again, I've got know idea why you think that engines have no tolerances, even modern engine tech specs will give you .001" on a crank and as for 'Tell me again' on your attempt to thread drift, that alone should be a new Thread on it's own to list some of the stuff you try to make us believe over the years!!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dean Yoder on Thursday, January 23, 2014 - 03:38 pm:

ChY
Sorry for the bad photo.
My computer and good camera are dead trying to cope with my I phone.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Thursday, January 23, 2014 - 04:39 pm:

On a related note. A few years back a guy brought his block and crank to me to help him put his engine together. Something just didn't feel right as the crank would bind and then turn and then bind as you rotated it. Turned out the crank was bent about .015". I had another crank in stock that needed grinding. So we had it ground to fit his babbitt. It wouldn't fit in properly. It turned out that the previous line bore job done by some guy I didn't know was off about .015" on the centre main. So we re did the babbitt and line bore job. His old crank had now been standing on end for about 6 weeks (we weren't in a big hurry). Just for the heck of it we decided to lay his old crank into the new babbitt job. It fit quite well, not perfect but not too bad either. Turned out is was now almost straight (only about .002-.003" out). So we laid it in the block and let it sit for another month. Now it was perfectly straight.

I would try some low deflection long time straightening. Probably only over correct about the amount it is bent. Leave it for a few weeks. You might be very pleased with the results!!! and you will reduce the risk of causing cracks.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kerry van Ekeren (Australia) on Friday, January 24, 2014 - 04:01 pm:

Dean, Just check your shaft on V blocks to see if you are getting different readings.


Posting is currently disabled in this topic. Contact your discussion moderator for more information.
Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration