"Fitting the crank shaft by SCRAPING the bearings"

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Model T Ford Forum: Forum 2010: "Fitting the crank shaft by SCRAPING the bearings"
Top of pagePrevious messageNext messageBottom of page Link to this message  By James J. Lyons on Tuesday, August 31, 2010 - 12:57 pm:

So by now, everyone knows I'm in the depths of an engine re-build and I'm trying to do it the way it would have been done (for the most part) in 1925.

I'm dealing right now with a bent crank shaft and there is another thread (called Bent Crank Shaft) were we are discussing this.

But I also pulled anther crank out of a spare engine I have and it is nice and straight and am considering using it. So I'm thinking about checking it for cracks, polishing the journals, and using it. Part of that will include fitting the bearings the "OLD FASHION" way by scraping the bearing surfaces. Now I am well aware that to properly fit the bearings, you must not stress the crank shaft or it may break.

The straight crank I have measures the following:
Front Journal - 1.247
center Journal - 1.247
Rear Journal - 1.245

So the rear journal is .002" in diameter smaller.

Considering the babbit in my good block is true to the same diameter on all three journal surfaces, this tells me that if I lay my crank in the block, the front and center journal will lay flush on the bearings but there will be a .001" air gap between the rear bearing and crank journal. Removing a shim from the rear journal bearing to close up the tolerance will result in bending the rear of the crank out of center line.

Therefore, my plan is to scrape the front and center journal which should drop the crank centerline in line with the rear journal, and then remove a shim from the rear journal cap to take up the space. I realize I may also have to scrape the front and rear journal caps also.

Any input will be appreciated.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Doug Money on Tuesday, August 31, 2010 - 01:23 pm:

I would at least plastigage the journals, Prussian blue the journals and that will see where you are at so to speak.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James J. Lyons on Tuesday, August 31, 2010 - 02:04 pm:

Doug - Yes, I am going to do that, but the process I'm using for fitting will be scraping only.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ted Dumas on Tuesday, August 31, 2010 - 02:19 pm:

You need to test your new crank and see if it is straight and not warped. You also need to have it magnafluxed top be sure its not cracked. What did your old crank main journals measure? Scraping the crank journals in is tedious and takes time, but if carefully done should produce good results. You will need both plastigage and prussian blue to check your fit.

On my 24, I scraped in the caps on mains 1 and 3 with good results. However, I did not have the crank magnafluxed, and about 4 years later it broke at 40+ mph and annihilated the block as well.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Patrick - (2) '26's - Bartow, FL on Tuesday, August 31, 2010 - 03:00 pm:

In 1971 at 16, in the midst of a complete Model T rebuild, I had the engine all apart and the crankshaft out. The deteriorating babbit was soft and grey and powdery and obviously needed to be re-poured, but with no money and no idea back in 1971 who could do it even if I had the money, I took a nice flat razor blade and gently scraped each bearing with the same number of strokes (count as you go) applying the same amount of pressure, until it was no longer powdery and I was down to solid shiney babbit. I then secured emery cloth around each bearing surface of the crakshaft and secured it in with the bearing caps slightly tightening it until I felt resistance. I turned the crank until there was no reistance and I tightened the caps some more, repeating the process and changing out the emery cloth several times until all three bearings were smooth and uniform. I then smoothed the babbit with 400, then 600 carbide wet/dry sandpaper. I then shimmed each bearing individually until I felt resitance then added a shim. I was surprised at how well it turned out.

I don't recommend doing this if you have the money to have it re-babbited, but if you are poor and it is the only way, then you might want to give it a try. I was lucky and must have done something right, because it ran great for 35 years this way until I had it rebabbited in 2005. Jim Patrick


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson on Tuesday, August 31, 2010 - 03:18 pm:

Timesaver has been around since at least the 40's, so it can be considered a time tested method. It will give you a better result faster than by scraping only. http://www.newmantools.com/lapping/time.htm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Wayne Sheldon on Tuesday, August 31, 2010 - 04:15 pm:

I have blued and scraped bearings for years and am getting ready to do three more engines that way. Take your time, go slow, and remember that you want as much smooth contact as you can get. You want at least 2/3 full contact with most of the rest of it so close that you know it is right there. And the most important area to have proper contact is the up and down center area (middle 2/3). If you have contact on the sides and not the middle (bottom), the crank is over-sized to an under-sized block or cap.
When bluing, I prefer the method of spreading a thin coating of Prussian blue onto the crank journals (don't leave any gobs). Carefully set the crank in place. Bolt the cap on with desired shims, and remove shims till almost snug. Give it a slow spin or two. Remove caps. (You can work the caps at the same time, but keep a sharp eye onto keeping the block line straight.) Lift out the crank, as straight as possible. It takes a little practice to read the transferred blue. No transfer, is a low spot. Don't cut or sand, but keep track of it in your mind and watch for it to get better in future transfers. Smooth, clean blue, is nice contact. A shiny spot with a dark transfer alongside is your high spot. Cut only slightly and carefully. (I then clean the bluing off and smooth it with fine sandpaper.) Do not sand the area of your low spot. The sanding evens the cut and lowers the good contact slightly and hopefully enough that you won't have to cut the good contact area to meet your low area.
There is a product out now, which I have not tried, that I understand is supposed to make fitting bearings easier. A trick I do use, is to smooth the Babbitt with fine sandpaper. EXTREME CAUTION! Do not leave any abrasive grit in or near the bearings or in any part of the engine. Babbitt is soft. Grit can embed into the Babbitt and held there, cut into the crankshaft as the engine runs damaging the crank. Damage to the crank can then damage the Babbitt. It probably could not cut enough to weaken the crank, but you don't want to risk that either.
Take it slow. It is quicker than undoing over-cuts. If the bearings are fairly good, you should be able to reach your goal in about two hours. (Several evenings if you're fitting miss-matched caps like I often do.)
Remember. The block holds the crank straight and aims it out the back. But most of the running is actually on the caps. (Three of the four strokes push the rods and crank down.) Their fit actually is the most critical.
.001 out of straight is within what many people would consider spec. But I am with you, make it right on.
Do you have bearing scrapers? I have done it with a pocket knife. But proper scrapers are much easier to work with.
Good luck, and have fun. and welcome to the world of archaic technology.
W2


Top of pagePrevious messageNext messageBottom of page Link to this message  By Richard Gould on Tuesday, August 31, 2010 - 07:55 pm:

One very important thing you need to know. What you often see in old T engines is the center main upper bearing has worn more than the first and third. Very common.
If you are going to get things straight, you need to scrape the first and third bearing in the block so all three are in alignment before proceeding to the caps. But now the problem is the crankshaft will be too close to the camshaft because by removing the babbitt in the first main,you have reduced the distance between the cam gears. You risk not being able to fit the cam gears.
This is nothing new by the way. KR Wilson wrote about this years ago.
Some folks are not aware of this and simply get the upper surfaces smooth with scraping or
Timesaver. Then they fit the caps to get the proper clearance without undertstanding they are binding and bending the crank when they bolt things up.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James J. Lyons on Tuesday, August 31, 2010 - 08:43 pm:

This is GREAT info! But it raises a question..... How much of a difference in diameters can be tolerated between the crank journal diameter and the bearing diameter? In other words..... If I had a crank that was 1.247 on all journals but was bent and I found a crank that was clean and straight but was only 1.240, can I still use this crank by fitting the crank to the existing babbit?? I can pull out the shims and set the clearance at the upper and lower 2/3'rds, but the sides where the two halves of the bearings come together will have gaps of about .004". Will this be a probelm?


Top of pagePrevious messageNext messageBottom of page Link to this message  By keith g barrier on Tuesday, August 31, 2010 - 08:59 pm:

Time saver, you cannot over do with it and you don't have to worry about getting every little bit out of the engine.I think the time saver has been around since about 1919. Have fun, KB


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Tuesday, August 31, 2010 - 09:49 pm:

James
Having read what you are planning, I would just refit the bent crank (without trying to straighten it) back into the engine it came out of. The modest amount of bend you have will not cause you any problems in my opinion. Much better chance of getting a good running engine that what you are proposing.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Larry Smith on Tuesday, August 31, 2010 - 10:07 pm:

The good crank you have is great. You usually don't find used cranks, with a rear main that size. You are lucky. Don't forget to magnaflux it. You don't want to install a cracked crank in your block!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Richard Gould on Wednesday, September 01, 2010 - 10:56 am:

Les, I am surprised you saying .009" run out is a modest bend. Didn't Ford advise discarding a crank with more than .012" and straightening them if less? I worry if I have more than .003" run out. Seems to me that if you have that amount of whip (.009) your mains will loose clearance.

James, I think if the main saddles have the same depth, use the newer straight crankshaft combined with minimal scraping and Timesaver and you'll get a better result.
I don't know the answer to your last question re using a crank with smaller diameter journals and sanding the caps so you get the correct clearance top and bottom but still have excessive clearance side to side. I would be tempted to do it if the diameters were as you say (.007) , but not if the difference was much greater.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Faccin on Wednesday, September 01, 2010 - 11:09 am:

They don't give that Timesaver away. Pricey!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Hal Davis on Wednesday, September 01, 2010 - 11:29 am:

Unless you're in the business, one jar will last for YEARS!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Wednesday, September 01, 2010 - 11:42 am:

Richard
Lets look at this; If I understand correctly his engine was running, but needed some "freshening up". So obviously it has been running with that bend in the crank. Probably the bend was caused by a sprung/bent crankcase/pan. To push the crank to straight when installed in the engine (I am not saying to straighten it) is not going to put much load on the bearings.

To straighten the crank he will need to push it a LOT more than .009, probably a 1/4 to 1/2" or more so it actually stays straight and it will take quite a bit of force.
Actually his crank is likely only bent .0045" as I am guessing what he is getting is .009 reading on a dial indicator, double the actual bend.

The odds are the babbitt in the block is straight (the main bearing are all in line). So if he refits the caps (which will take very little work, probably pull a shim or two). The crank will be pushed into line and impose very little extra force on the bearings.

Now if he finds that he has to pull a LOT of shims from the centre main then he should use a accurate straight edge to be sure that the babbitt in the block is not worn. If all the wear is in the cap (which is typical) then he can carry on. If the babbitt is badly worn in the block then a new babbitt job is called for and use his other crank (or straighten his bent one)

If he now ensures that the pan is straight (check it and straighten it as required) the 4th main will also be in line. I would suggest putting a dial indicator on the output shaft prior to installing the 4th main to be sure that he has no undue wobble at the back end because maybe the flywheel flange is bent and contributed to the bent crank issue. Assuming that the output shaft is running true with in a couple of thou then button it up.
It is well known that a slightly bent shaft subjected to vibration and held straight will relax the stresses in fairly short order and become straight again (it is called stress relieving). Heat accelerates this. If he starts the car and drives it conservatively for a 20 miles I would expect the crank to now be straight if he wanted to go to all the work of taking it apart again.

So to sum up; He needs to ensure that all three mains are fitting properly (about .001-.0015"). He will now have no "whip" when he puts it together.

He also should magniflux the crank to ensure that it does not have a big crack that is causing the bend, but he should do that with any crank he is going to use. If that service is not readily available a "poor mans" way is to soak it in solvent for awhile, takes it out and wipe it off quickly and then look for any solvent "bleeding" from any cracks. In industry this is used on non ferrous metals using special solvents and a type of paint referred to as "developer". Magniflux is better and faster, but if it isn't available the other way will work.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Richard Gould on Wednesday, September 01, 2010 - 12:15 pm:

Les we have a friendly disagreement here. While I agree with most of what you say, my bet is with a crank bent .009, the center main saddle will be worn. Either that or all three will have worn to accomodate a wobbling crankshaft.
Personally I would straighten the crank and true the flange if I were to use it. If the main saddles can be aligned by minimal scraping and Timesaver, I'd do that, otherwise a rebabbitt is in order. That's my opinion.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Paul Vitko on Wednesday, September 01, 2010 - 02:28 pm:

Wonder how you could check the center main for out of align with one and three unless you had a reasonably straight crank?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Pat Punter on Wednesday, September 01, 2010 - 03:21 pm:

A couple years ago I bought a used crankshaft from a well respected and honnest Model T shop. The crankshaft was standard (1.247-1.248 on all journals) free of rust and the timing gear was like new, but it has been returned to them by previous owner because of cracks. Seller didn't want to sell it but I insisted and he said OK fine, $25, no return, sold as is.

So I brought the "beast" to my local machine shop to have it tested. It was passed through an electromagnet under a black light with a liquid stuff applied on it. I learned that some cracks are the result of the forging and machining process and others are fractures. Some are dangerous others are not. No problematic crack was found and the little crankshaft was put back in service. 5K miles so far and still going strong.

I beleive that many serviceable crankshafts have been discarded by incompetent magnafluxer.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Richard Gould on Wednesday, September 01, 2010 - 04:38 pm:

Paul, one method, and I am sure there are others, is to bolt flat stock on the saddles then use a bore gage to mic the openings. This assumes the mating surfaces where the caps bolt on are all uniform.
Another would be to obtain or make 1.250 diam round stock and lay it in the three saddles using Prussian Blue.
I had a 10 block without babbitt in the saddles and was concerned about the amount of wear. I used the first techicque to determine whether I wanted to have them bored for babbitt. I was able to get good measurements.
BTW there was little wear except in the first main where the bore was tapered toward the cam gear. Understandable.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Faccin on Wednesday, September 01, 2010 - 04:47 pm:

Richard,

What procedure do you use to true the flange on a T crank?


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Faccin on Wednesday, September 01, 2010 - 04:49 pm:

Hal,

Since Timesaver comes in a one pound can at 65.00 I guess it would last a hobbyist about 500 years! :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Paul Vitko on Wednesday, September 01, 2010 - 05:02 pm:

With my limited machining experience and tools it would be tricky if the three mains were worn round but say from 2 to 8 thou under front to back.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson on Wednesday, September 01, 2010 - 06:27 pm:

Timesaver can be bought in a test kit with four 3 oz cans for $30: http://ws2coating.thomasnet.com/item/timesaver-lapping-compound-2/yellow-label-t imesaver-lapping-compound/item-1054
Or just one 3 oz can for $10: http://www.modeltford.com/item/TIMESAV-Y.aspx


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Faccin on Wednesday, September 01, 2010 - 06:38 pm:

Roger,

Thanks, thats more affordable.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Richard Gould on Wednesday, September 01, 2010 - 08:44 pm:

John, I place the front of the crank in a set tru chuck and set for zero run out. A four jaw would be fine. The flange end I place in a live center. Then I turn just enough off the flange to true it. Since most cranks are recessed in the flange area, you only need to true up the outer part before the recess.
If the center in the flange is messed up, I first cut it deeper by placing the OD of the flange in a steady rest.
Its not hard you just need to be careful, go slow and make sure everything is set up correctly. Last thing you want to do is mess up a perfectly good crank. Last one I did I had forgotten to do until the crank was installed in the block with rods and cam. After all that work, I was really nervous about doing it for fear I would screw it up, but it came out fine. Maybe I got lucky, aye?


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Faccin on Wednesday, September 01, 2010 - 08:53 pm:

Richard,

Thanks, EH


Top of pagePrevious messageNext messageBottom of page Link to this message  By James J. Lyons on Thursday, September 02, 2010 - 11:00 am:

Well, after all this good discussion, I'm back to the drawing board......The machine shop just called and said the center journal is cracked so bad they are suprised it didn't fall in half. So, I'm now on the hunt for a good crank that is close to standard....


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem on Thursday, September 02, 2010 - 03:02 pm:

James,

You asked, hypothetically, if you could fit a 1.240 crank where a 1.247 crank had previously been. Not really. Scraping is a slow tedious process that is meant for fine tuning a bearing fit and correcting small misalignments. It would be poor practice and take weeks to fit a crank so much different from the existing babbit bores. You would also begin to affect the spacing between the crankshaft & camshaft which may make your timing gears fit too closely.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Richard Gould on Thursday, September 02, 2010 - 05:05 pm:

BTW, Erik Barrett made a tool where you can cut the crankshaft flange after the crank is bolted in the block. I was very impressed. Perhaps he'll post here and describe it and maybe even upload a photo or two. Hey Erik, you out there?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Thursday, September 02, 2010 - 07:07 pm:

So now we no why the crank was bent. I encountered similar before, a fine looking crank that was bent a bit, sure enough it had a big crack too.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Thursday, September 02, 2010 - 07:44 pm:

James

You say that your other crank is 1.247 and is a reasonable fit in the front and centre main. You imply that the babbitt in your block is in good condition and I assume that you still had some shims in each of the bearings.

If all this is true a option to consider is to get the rear main only hard chromed back to standard. Where you live I believe is in a industrial area (coal mining) so there may well be a shop locally that does HARD CHROME. What they will do is grind the rear main lightly and then chrome it up and then grind it to size. The net .005 in diameter or so that you need is not very much for them to put back on to your crankshaft

Hard Chrome is not bumper chrome but is used extensively in industry for repair work and on good hydraulic cylinder shafts for long life.

If your babbitt is otherwise good and still has shims and if the front 2 bearings are a reasonable fit I would sure check this out. You may find it to be a economical solution and the hard chrome will out wear the the other 2 bearings.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James J. Lyons on Thursday, September 02, 2010 - 08:13 pm:

Les, Jerry and Richard....Thanks for the info. I'm going to search for a while to try and find a crank that is the same diameter as the broken one I have. Besides, the other crank I have that is good, but has a slightly smaller rear crank journal is out of a different engine and I don't want to break it up. So, I'll see what time turns up.
Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Erik Barrett on Friday, September 03, 2010 - 01:46 am:

I am here. I check every crank flange after I fit the crank to the block. If it has more than .001" lateral runout, I dress the flange with a tool I built out of a magneto coil ring and some steel and machine work. Basically, the tool amounts to a carriage with a pneumatic die grinder which slides over the mag ring fitted with slide tracks perfectly perpendicular to the crank centerline. I turn the crankshaft with the same equipment that drives my boring bar. I then feed the die grinder stone and slide the carriage across the crank flange
and clean it up to zero runout. About one of three cranks need this treatment. I will set the rig up and take photos if
there is interest. Alignment is crucial to T reliability. I have spent a stack of money on my KRW pan jig and also time
building the flange grinder so I can assure my main bearings will last.
Erik


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Faccin on Friday, September 03, 2010 - 02:57 am:

Erik,

Please post pictures, We are interested.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Erik Barrett on Saturday, September 04, 2010 - 12:40 am:

I am away from home at present but will get home and learn to post pix to the forum. It will be my first attempt. Bear with me.
Fordially, Erik


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Stroud on Saturday, September 04, 2010 - 04:14 am:

This a bit off topic, but a very good friend of mine took a crankshaft for a 312 Ford Y block to get it ground at a local machine shop in the early seventies. He had it in the back of his pickup, when he got to the shop, it was in two pieces. It rang like a bell when he left. Dave


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Saturday, September 04, 2010 - 11:16 am:

Erik
Yes I too want to see what you have done. Where do you live? I would like to visit sometime if it works out.
Thx


Top of pagePrevious messageNext messageBottom of page Link to this message  By Erik Barrett on Thursday, September 09, 2010 - 12:05 am:

I will get photos up a soon as possible. I can email pix and will learn to post them here.
Erik


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