Crankshaft Grinding

I was actually starting a series on cylinder head recondition as I had just written the overview but I was challenged by a colleague to come up with a step by step guide to crank grinding. I try never to back down from positive challenges so here is my take on grinding. I will be going back cylinder heads in detail in by next article. I have tried to be as comprehensive as possible but any machinist will tell you that some of the steps can be skipped depending on the type and condition of the crankshaft.

Sequence of operation

• Tidy workstation, observe safety precautions and check accuracy of measuring instruments.
• Check the thrust collars with a t-gauge and outside micrometer.
• Check journal size with an outside micrometer.
• Determine size to be ground to and availability of bearings.
• Check for bow and twist with a dial test indicator (DTI) on a magnetic base and the crankshaft on 'V' blocks.
• Crack test with a magnaflux machine.
• Stress relieve for two hours at 150 degrees Celsius. Most, including me, believe this step is not necessary.
• Mount a balanced grinding wheel on the crankshaft grinding machine. True the wheel and dress it to the correct corner radius.
• Lock the machine Chucks in position 'A'.
• Set cross slides and outboard counterweights to zero.
• Secure the crankshaft in the chucks and make sure it rotates in the same direction as it would in the engine. The crank nose normally goes into the left chuck.
• Set the front and rear journals true with a DTI.
• Set the continuous measuring gauge.
• Turn the machine on and plunge grind a journal leaving 0.03mm from finish size (Do this with a continuous supply of coolant).
• Traverse grind the journal to finish size.
• Repeat for other main journals.
• when the main journals are complete Lock the chucks in position 'A'.
• Set a plane of big-ends journals parallel to the bed using a munk.
• Move cross slide simultaneously to give the correct throw on vernier slides.
• Set outboard counterweights to balance the crankshaft.
• Complete setting the big-end journal plane using a DTI and a stoke indicator gauge.
• Balance the shaft again using counterweights.
• Set continues measuring gauge.
• Grind to size as with mains.
• Repeat for other journals in the same plane.
• Rotate index plane to the next plane.
• Set plane as with previous journals and grind accordingly.
• Repeat grinding procedure for all planes. The common four cylinder inline shaft normally has two big-end planes only.
• Dry the journal with a cloth and polish with a super-finnisher tape.
• Oil shaft and remove from the machine.
• Dynamic balance the crankshaft.

If a component is not going to be used immediately, a coat of rust inhibitor on the machined surfaces is always a good idea.

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