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Keeping It Straight
By Paul Savadin
Dialing in an Older Crankshaft Grinding Machine for Taper and Alignment
Many machine shop owners who own crankshaft grinding machines have asked me why their machines do not grind true. The most common complaints regard taper in the grind and grinding out of round. However, most machine owners or operators don’t have a clue as to why they are having these problems.
Taper on a journal happens when a journal is being ground to a specified size and one side of the journal is larger or smaller in diameter than the other side.
Most American engine bearing specifications have at least .001˝ tolerance between the high and low side of the bearing size. For example, the rod bearing size for a 350 small block Chevy is 2.099˝ to 2.100˝. This means that the journal should not be ground to a size any lower than 2.089˝ nor left any higher than 2.090˝. This is on a shaft ground to .010˝ under the standard size.
If ground larger than the high side, the bearing will not have enough clearance, which may result in damage to the bearing and crankshaft; the final result will be engine failure. If the journal is ground below the low side of the tolerance, the result will be low oil pressure when the engine reaches operating temperature.
If a crankshaft grinding machine grinds with a little taper, the .001˝ tolerance between the high and low side is enough to hit within the bearing manufacturer’s bearing specifications. But, in most later model engines, such as the four cylinders and V6s, the tolerance between the high and low side is cut in half to .0005.˝ Now instead of hitting between the allowable size, if your machine is grinding with .0005˝ taper, some areas on the journal will be either too tight or too loose. This can be a big problem and cause many engine failures.
In the ideal grind, all rod journals should measure exactly the same when checked for size at any place on the journal. The main journals should also be the same size, with no variation in size, or any taper.
Occasionally, the bearing manufacturer will specify that one of the main bearings be ground slightly under the rest. An example of this would be the Chevy 350 V8, which calls for the rear main to be ground .0005˝ lower than the other four mains.
Both taper in a grind, and the problem of grinding out of round can be corrected by making sure that the head and tail stock on your machine are properly aligned.
Taper and grinding problems do not usually happen overnight but are gradual problems caused by wear. Sometimes moving a machine will also cause alignment problems. It is very important that a machine be properly set-up and leveled after it has been relocated. It should also be checked for level periodically in case the foundation of the building moves. After all, crankshaft grinding machines weigh several tons.
I know from experience that there is nothing worse than a grinder having to fight his machine every step of the way to complete grinding a shaft. My first machine was a 400 Van Norman that I purchased used in 1982, and I had problems with this grinder the first few years of operation. I shared my concerns with equipment dealer Howard Purvis of San Antonio, TX. When Howard asked me if I had aligned the head stock with the tail stock, my answer was "Alignment? What is that? I didn’t know they needed alignment!"
Before performing the alignment procedure on my grinder, I had to move the taper adjustment on my tail stock several times to complete one shaft. After aligning my machine, I ground for 14 years without ever touching the taper adjustment. However, the wheel must be dressed in the same manner every time it is dressed or taper will occur. If larger cuts than .002˝ are taken on each pass on the wheel, the diamond will heat up and expand, taking more off the wheel at the end of the dressing process. Never take more than a .002˝ each pass across the grinding wheel, and use plenty of coolant to prevent the diamond from heating up.
It is important to understand why your machine is not grinding right. The problem with most machines is that through years of service, things wear out. This is compounded when operators do not use oil or use the wrong quality oils. As a grinder, this machine is very hard on all its surfaces and parts. Instead of producing metal chips like a lathe or milling machine, the grinder produces some very abrasive grit.
On a crankshaft grinding machine, the most abused area is the table on which the tail stock is moved back and forth. The tail stock should never be moved without first wiping the table clean. The majority of the grit is in front of the tail stock. I usually move the tail stock back about three inches to be sure I get all the grit, then I oil the table before moving it forward.
My 400 machine had a very small amount of wear when I purchased it, and after almost 19 years of use, it still shows very little wear on the table. My machines stay spotless, but I have found that when an operator of a machine does not own it, he does not always take very good care of it.
At a shop owned by a close friend of mine, the machine operator wore an area close to 1/8˝ deep in the table from moving the tail stock without cleaning or using oil. It cost several thousand dollars to have the table machined.
Besides wear on the flat portion of the table, the front lip of the table and the bottom of the tail stock may also receive wear. The head stock does not wear much on most grinders; although it can be moved, it very seldom is.
One of the easiest ways to tell if a grinder is out of alignment is to chuck a crankshaft in the machine and engage the drive to let it rotate. After about five minutes of rotation, stop and try to put the index pins back in the head and tail stock. If the alignment is off, the pins will not fit, as the crankshaft will have slipped in the chucks. Before I performed the alignment on my 400, I couldn’t figure out why the shaft always slipped just a little in the chucks while I was grinding. After the alignment, the chucks never slipped again, and the index pins always fit perfectly. Here, then, is the proper way to line up a crankshaft grinding machine.
Be warned, though – this is certainly not a simple procedure and takes about four to six hours to do the first time. After that, you’ll get faster.
You will need two pieces of round steel stock, each approximately nine inches long. They should be about 1-1/2 inches in diameter. It is best to use material with a smooth surface – such as cold roll steel – because the dial indicator will have to move up and down the surface.
Begin by chucking one inch of the bar in the head stock. Take the second piece and chuck one inch in the tail stock. You will now have eight inches of round stock sticking out of each chuck. The machine is in perfect alignment if both shafts are perfectly aligned with each other; your task is to make sure they end up exactly that way. To get them lined up will require placing shims in certain positions on both the head and tail stock.
Shimming The Head Stock
Since the head stock has the least amount of wear, we will begin by checking it for alignment. Start by grinding a spot one inch out from the chuck .020˝ deep using the feed stop on the machine. Let it spark out, and be sure it is grinding true. Then move out six inches on the bar and grind a second spot to the same place on the feed stop. Remember, you are not grinding to a specific size on your sec
Now it is time to check your first alignment. Place a magnetic dial indicator on the first ground area one inch from the chuck. The indicator must be placed in a spot on the machine to allow moving the table without disturbing the indicator. Zero the indicator, then move your table, sliding the indicator along the bar until you make contact with the second spot, ground six inches from the chuck.
If the indicator reads zero in both spots, then you are >in line. However, if the indicator, for example, reads +.010˝, this means the head stock is .010˝ pointed out toward you; if it reads -.010˝, this means it is tilted toward the wheel housing or away from you.
You must check in one more plane before beginning the shimming process. The head stock can be misaligned horizontally, but it can also be off by being tilted up or down. To check the up and down alignment, place the indicator so it makes contact with the bottom of the first spot one inch out from the chuck. Move the table over six inches to the second ground spot. Whatever the difference between the indicator at the two points is, is how far the alignment is off on the vertical plane.
The task now is to place shims of the correct thickness in the appropriate areas under the head stock until you come up with 0˝ difference on both the side and bottom plane. I recommend purchasing several feeler gauge sets and using a pair of tin snips to cut them to the size you need. This shimming procedure can take from a few minutes to more than an hour, but the main thing is to go for precision. This alignment should be within at least .0005˝.
Because the head stock is seldom moved, there is no problem keeping the shims in place. Once the head stock is in the right position, tighten the bolts that hold it in place and go to the tail stock. Be sure not to disturb the bar in the head stock chuck as it will be necessary to travel from the tail stock bar to the head stock bar for final alignment.
For the tail stock, follow the same procedure as on the head stock. The one problem you’ll face is the fact that the tail stock has no power to rotate to allow the two spots to be ground, so it must be rotated by hand in order to grind the two spots. This is where you will need to get an assistant to rotate the tail stock in order to grind the bar. Once the two spots have been ground in the bar in the tail stock, use the same procedure used on the head stock to align it.
All grinders are not built the same, and the machines on which I have used this procedure are Van Norman machines. The shimming procedure may vary a little from one brand of machine to another, but it can be applied to any machine. The Van Norman machine has a cross slide on the tail stock to adjust taper. Shims can be placed in the cross slide in four corners to align it.
The tail stock often needs to be moved out, away from the wheel housing, from the wear encountered from sliding the unit back and forward so many times. This worn area is a lip on front of the table that keeps the tail stock from sliding off the rear of the table. My 400 machine needed to be moved out .014˝ to get it in perfect alignment with the head stock.
How far the tail stock needs to be moved out can be determined by running the indicator from the tail stock bar all the way over to the head stock bar once the tail stock alignment has been completed.
I used a .014˝ feeler gauge in both the front and rear of my tail stock, attaching it with a 10-32 screw to the base of the tail stock. That way, it can be shimmed yet moved without the shim falling out when the stock is moved for crankshafts of various sizes. Should more wear occur in the future, the shim can be removed and replaced with thicker ones. When the alignment is completed, the head and tail stock will be perfectly in line.
This should be the end of most problems causing taper and grinding out of round. A final adjustment must be made by placing a crankshaft that you know to be straight in the machine, and grind a spot on the main until it is round and running true. Place the grinding gauge on the extreme right of the grind, then the extreme left. If it reads the same on both sides, you are right on. If it is off, use the taper adjustment on your machine to adjust out the taper and redress and try again, This may take several adjustments to get it perfect. Once you complete this last operation of adjusting the taper, your machine should grind true for many years to come.
Remember, though, when dressing your wheel, cut only .002˝ with each cut and use plenty of coolant on the diamond. If you dress your wheel the same way every time, there will be no taper in your grind. If you vary your style of dress you will get taper. Always dress in one direction, preferably from the tail stock to the head stock, or right to left. Do not worry about getting wet or making a mess. Always cover the head and tail stock with a cloth when you are dressing your wheel to keep grit from getting into any sliding or rotating areas. And always clamp your dresser in the same spot on the table.
We did an alignment on a 438 Van Norman last year. Before the alignment, a crankshaft would walk out of the chucks in just a few minutes of rotation. After the alignment, there were no more problems. The 438 was manufactured in the 1960s; my 400 Van Norman was manufactured in 1957.
These are old machines but they still do a great job of grinding – with the proper set up. Even the newer machines should be checked every few years to correct any problems that may pop up. Usually, if there is a problem, you are the first to know as the machine will produce a poor grind.
If you are having problems with taper in your grind, grinding out of round or your crankshaft is moving in your chucks, it may be time to do an alignment on your machine. I am glad Howard Purvis was kind enough to share his alignment procedure with me. It made my life as a crankshaft grinding specialist much easier through the years and for many years to come.