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While reading this question about a motorcycle cylinder and piston, the question comes to mind basically for the same thing, only for an automobile engine. With this in mind, my questions are:

  • When should you bore a block during a rebuild?
  • How do you determine if the block should be bored?
  • How do you determine if the block can be bored?
  • How do you deal with sleeved blocks?
  • Any pitfalls or things you should look out for?
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I've nothing to cite for this, but I'd say the following:

When should you bore a block during a rebuild?

Only if necessary - if the bores are damaged, scored or heavily pitted.

How do you determine if the block should be bored?

Check the bores - if one or more are damaged, scored or heavily pitted, then it will need boring. light scratches and surface rust can be dealt with by honing, without the need for a full rebore.

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). It helps if you know the history - has the block been rebored before? If you bore it too far, the cylinder walls will become too thin. If it has been bored to the limit, it might be possible to sleeve it. You may also be restricted by piston availability - off-the-shelf pistons usually only come in a few sizes, typically +10, +20, +30 and +40 thou.

How do you deal with sleeved blocks?

Measure the thickness of the sleeve - again, there will be a limit as to how much they can then be bored before the sleeve becomes too thin (I'm not sure if sleeves can be removed and replaced with new, I'd assume they can...)

Any pitfalls or things you should look out for?

Wet-lined engines - common in aluminium-block engines, these are effectively already sleeved, with an oil jacket on the outside of the sleeve, but often the liners themselves can be replaced, in the same way as re-sleeving a normal block. Beware when dismantling a wetlined engine, as the liners can often stick to the head and become dislodged, requiring them to be properly reseated before reassembly...

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    I would add "out-of-round" to your list of reasons / when to bore. Because vehicular engines typically don't have a crosshead bearing, the piston exerts sideways forces on the cylinder when not at TDC / BDC (ie most of the time). With time, this will wear the cylinders "oblong." More than 0.010" variance between diameters = poor, uneven seal on the rings. In which case, bore the cylinder if possible. – Meower68 Oct 21 '16 at 18:59
  • Can you give more of an answer from a technical perspective? This information is good, but how would you go about doing any of this? What tools would you use? What would be good/bad when taking those measurements? When I was asking about "pitfalls", I was looking for overall pitfalls, not just those associated with sleeved engines (though that's not clear in the question). – Pᴀᴜʟsᴛᴇʀ2 Oct 22 '16 at 14:13
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When should you bore a block during a rebuild? When the bore has severe scratches, when the bore is out of round, or when the bore has excessive bore diameter out of tolerances between the top and bottom of bore, or when you want to increase the displacement. How do you determine if the block should be bored? see above. How do you determine if the block can be bored? Most manufactures or reputable machinist will tell you if the block can be bored and can give you the maximum safe bore diameter. How do you deal with sleeved blocks? Again a reputable machinist can determine if a sleeved block can be bored or if you can remove and install new sleeves. Any pitfalls or things you should look out for? Yes Boring and or re sleeving can be expensive. Compare the cost of the machining to the cost of a new block at the bore you want before you make your decision.

  • If I'm in the process of doing my own rebuild, why would I want to take it to a shop and have them do anything beyond the machine work if needed? What does a person need to do to come to the conclusion to see if machine work is needed? What steps should a person do to come to the conclusion? What tools would I be using to accomplish the tasks at hand? – Pᴀᴜʟsᴛᴇʀ2 Oct 22 '16 at 14:11

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