what cylinder clearance to rebore?

[downer]

i've got my 4.0 torn down to bare block, it's getting new pistons. i've got a set of keith black pistons, but i'm not sure if i need to get it bored. what's an acceptable clearance from cylinder to new hypereutectic piston? .005 or so??

 

[alwaysFlOoReD]

Any knowledge I have is very out of date. But I can suggest contacting the piston manufacturer.

Richard

 

[Dune Runner]

You need to ask the company that made the pistons. They all recommend different clearances. You should have checked to see if it needed boring before you bought the pistons though. You can't used STD size pistons in a block that has been bored. You might get away with honing if you are lucky.

 

[downer]

yes i realize i will need new pistons if it's bored.. $60 for a set of 6 pistons is not gonna break the bank. they will be resold if necessary. anyways, apologies for giant image.

i am not going to be at 3.9527. these have a skirt diameter of 3.9514
that would mean a clearance of .0013

how much beyond that is acceptable?

 

[lvwill]

Any time you are rebuilding an Engine the first thing you should do is get all machine work done then you will know exactly what parts to get for reassembly.

 

[drsvox]

how much beyond that is acceptable?

As mentioned, tolerable clearance will depend on alloy and application and you should be able to get those numbers from whomever supplied the KBs. You could also probably google search for the information.

However, as also previously mentioned, take the block in to a machine shop. Shouldn't cost more than a couple hundred to have it cleaned, checked for cracks, mic'd for bore taper and roundness, over-bored (if needed) and honed...you will feel so much better about new pistons going into a block w/ a clean bill of health

 

[downer]

good points, i should just take it in to the shop and do it right. thanks to all

 

[aspevacek]

Any time you are rebuilding an Engine the first thing you should do is get all machine work done then you will know exactly what parts to get for reassembly.

Actually get your pistons first and get your block punched to match the pistons. You should also have rings on hand if you decide to go with non standard rings as they may require a different final hone on the block. I used Total Seal low tensions and they run an extremely fine final hone. The machine shop thought I was joking when I gave them my numbers. I will say the machine shop I used in Germany did a killer job as they punched each cylinder to match each piston then numbered the pistons to the bore for me.