What does oversize piston mean?
Pistons don’t get oversized by themselves. After the cylinders have been bored oversize, they are chosen to be oversized and installed by whoever builds the engine. The word “oversize” means larger than original factory specifications.
How much should I bore my engine?
How do you determine if the block can be bored? Measure it! Most engines will have a limit as to how much they can be bored – typically something like +40 thou (thousandths of an inch).
What should the oversize be on a boring engine?
The oversize will depend on the thickness of the casting, how much boring it can safely handle without the cylinder walls getting too thin, and the amount of wear in the cylinders.
Why are the cylinders on a rebuilt engine always oversize?
Cylinders on rebuilt engines are almost always bored slightly oversize to remove any irregularities from the cylider wall. This is almost always done on used engine blocks, as cylinders can become slightly egg shaped after years of use. Without removing these irregularities, standard bore pistons wont hold compression and you’ll consume excess oil.
What should the bore be on a cylinder?
If your cylinders are out of round, a machine shop will need to bore the cylinders out .020 or .040 which is typically enough to bring the bore back to a perfect circle. The same holds true for engines that have seen piston failure in the past, as you’ll need to remove cylinder wall scratches by overboring.
Why do you have to bore overbore Pistons?
In rare cases, you’ll have to get a custom sized piston to achieve a specific piston-to-wall clearance, but in most cases this clearance can be matched with slightly overbore pistons. The last reason a machine shop will bore oversize is to increase the displacement of the engine.
How to bore and hone motorcycle cylinders to oversize and?
In this how to video, I show the proper method to bore and hone motorcycle cylinders and then fit oversized piston . Boring removes cylinder scores, pits and ridges and is done in oversize increments. The honing de-glazes and provides a cross-hatched surface for proper ring wear-in and performance.
The oversize will depend on the thickness of the casting, how much boring it can safely handle without the cylinder walls getting too thin, and the amount of wear in the cylinders.
Cylinders on rebuilt engines are almost always bored slightly oversize to remove any irregularities from the cylider wall. This is almost always done on used engine blocks, as cylinders can become slightly egg shaped after years of use. Without removing these irregularities, standard bore pistons wont hold compression and you’ll consume excess oil.
In rare cases, you’ll have to get a custom sized piston to achieve a specific piston-to-wall clearance, but in most cases this clearance can be matched with slightly overbore pistons. The last reason a machine shop will bore oversize is to increase the displacement of the engine.