Crankshaft Straightening: An Easier Way!

| July/August 2001

During the winter months here in the East, the weather is not severe, but usually just uncomfortably raw and wet with an occasional short-lived snow for excitement. We are very fortunate to have as a friend and member of the Rockville Field Day Of The Past, Bill Hoitt, who hosts an informal workshop in one of his warehouses in Richmond during the winter months to keep us acquainted and tinkering with our engines. Some of us bring project engines along, those that have been unusually difficult to figure out or ones that just have too much compression to roll over and adjust by ourselves at home. Having the group of guys together makes it more of an event to get an engine going anyway. Many folks come to watch or just to eat and talk engines. We all pitch in a couple dollars and Bill sends out for food, and some how there is always a surprise cake or pie that appears on the table, too. Our children often come along as well, to sit on their adopted grandpa's knee for the day and enjoy antics of teasing with Ernie and Ralph Unterzuber.

On one of these special occasions, I brought along my project, a 2 HP Domestic engine with a bent shaft on one side that caused the flywheel to wobble in and out at least a quarter of an inch. This wobble was awfully distracting at a show! Well, if you are fortunate enough to have met Leo Korb at some of the eastern shows, you know well he enjoys a challenge and can't stand to see an engine that doesn't run — or worse yet one running poorly! I phoned Leo the night before to see if he was willing to look at my problem and he wasted no time gathering jacks and dial indicators needed the next day for this new challenge. Leo has done this before, so for him it was old hat, I'm sure.

The next day, Saturday, we all met at Bill Hoitt's building, and everyone gathered around for the new crankshaft lesson. We first took the engine off the wagon and set it on the concrete floor beneath the loading dock door. A flat steel plate was placed on top of the bearing and a four-by-four timber was cut and driven tight between the flat plate on the bearing and the concrete lintel over the door. Everything was locked in place now.

Next, the dial indicator was attached to its magnetic base and stuck on the side of the water hopper. Now with the indicator tip touching the inside edge of the flywheel, the wheel was rolled around and the location where the wheel was deflected in the most was identified and marked with chalk on the face and outside. This chalk mark was then rolled down to the floor, a six-ton jack was placed under the end of the crankshaft, and jacking began.

Leo encouraged us to take it slowly at this point, as I tend most often to get in a hurry to fix things. So, we had to jack the shaft until the wheel appeared vertically straight, and then jack just a bit more. The shaft would spring back some anyway. Next, we released the jack pressure, rolled the wheel around and checked the indicator again to see how much more we needed to jack.

By jacking and rechecking the indicator we were able to bring the shaft back in alignment within several thousandths, certainly acceptable by the naked eye when running. I think my shaft was brought to within eight thousandths and we left it there.

Mark Vaughan
4/5/2012 9:07:33 AM

It's not good practice to straighten 'cast' cranks in a press, this upsets the crystaline structure of the steel creating stresses and weakens the crank. You then often find the crankwill bend again with the normal temperature cycling of the engine. The professional way is to use a hamer man who with experience will know how hard to hit the crank and with one blow will coreect the bend after which it is stress free and remains straight. I'm not sure though how the cranks in hit n miss engines were constructed, they may not be cast.


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