Crankshaft grinding
Crankshaft grinding in Sydney is precise work, done to fine limits. The crankshaft turns the up and down movement of the pistons into rotation. It spins on smooth, round surfaces called journals. The main journals sit in the block. The big end journals, or crankpins, carry the conrods. Bearings sit between each journal and its housing, on a thin film of oil.
Crankshaft grinding: the process
- Clean and inspect. The crankshaft is cleaned and checked for cracks, hardness, bend and damage to threads, keyways, seal faces and the flange.
- Measure. Each journal is measured to decide the undersize to grind to.
- Grind the big end journals, then the main journals, with the crank set up to turn the right way.
- Finish. The oil holes are chamfered. The journals are polished to the right finish. The flange and seal areas are faced.
- Check. The journals are measured again. The crank is checked for straightness in V blocks with a dial indicator.
Read the full crankshaft grinding guide
What is crankshaft grinding?
Grinding takes a small, even amount of metal off each worn journal. The aim is a journal that is round, straight and smooth again. Because the journal is now smaller, it gets a matching new bearing, called an undersize bearing.
The work follows set steps:
- Clean and inspect. The crankshaft is cleaned and checked for cracks, hardness, bend and damage to threads, keyways, seal faces and the flange.
- Measure. Each journal is measured to decide the undersize to grind to.
- Grind the big end journals, then the main journals, with the crank set up to turn the right way.
- Finish. The oil holes are chamfered. The journals are polished to the right finish. The flange and seal areas are faced.
- Check. The journals are measured again. The crank is checked for straightness in V blocks with a dial indicator.
The finish matters. Bearing makers ask for a very smooth finish, and smoother again for diesel and racing engines. Journals are ground against the direction the engine turns, then polished with it. This removes tiny burrs that would wear a new bearing.
When do you need it?
- Worn journals. A journal can wear tapered, or into an hourglass or barrel shape. That loads the bearing unevenly, and the bearing wears out fast.
- Scored journals. Dirt in the oil is the biggest single cause of early bearing failure. It can score the journals as well as the bearing.
- A failed bearing. The journal under it may need grinding too.
- During a full rebuild. The crankshaft is measured as part of every engine reconditioning.
How we do it at Reco
We grind crankshafts at our Auburn machine shop. When you call, tell us the engine code and what happened to the engine. If a bearing failed, tell us that too.
What it costs
The price depends on the crankshaft and how worn it is.
Questions
Do I need new bearings after a crankshaft grind?
Yes. A ground journal is smaller than before, so it needs new undersize bearings to match. Old bearings will not fit the new size.
Is polishing a crankshaft the same as grinding it?
No. Grinding brings a worn journal back to a true, round shape. Polishing only removes a tiny amount to leave a smooth finish. Polishing cannot fix a journal that is out of shape.
Can every crankshaft be ground?
Not always. A crankshaft is checked for cracks and straightness before it is ground.
Related services
More answers are on our FAQs page.
Who it is for
- Worn journals. A journal can wear tapered, or into an hourglass or barrel shape. That loads the bearing unevenly, and the bearing wears out fast.
- Scored journals. Dirt in the oil is the biggest single cause of early bearing failure. It can score the journals as well as the bearing.
- A failed bearing. The journal under it may need grinding too.
- During a full rebuild. The crankshaft is measured as part of every engine reconditioning.
Price guide
The price depends on the crankshaft and how worn it is.
Crankshaft grinding FAQs
Do I need new bearings after a crankshaft grind?
Yes. A ground journal is smaller than before, so it needs new undersize bearings to match. Old bearings will not fit the new size.
Is polishing a crankshaft the same as grinding it?
No. Grinding brings a worn journal back to a true, round shape. Polishing only removes a tiny amount to leave a smooth finish. Polishing cannot fix a journal that is out of shape.
Can every crankshaft be ground?
Not always. A crankshaft is checked for cracks and straightness before it is ground.
Everything done under one roof
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