for example, If I bought a b20 block and want to put new pistons in it, If I get the block honed, should I get the 84mm pistons, or 84.5mm?

 

if the cylinder walls are ok and just need honing, then no; honing only takes a little bit off.make sure you give the machine shop the pistons so that they dont overhone.Sometimes is better to go overbore pistons just in case they mess up.

 

Best off sleeving the B20.. cause it will crack stock. Honing is like deglazing the cyl.walls, boring is making it bigger.

 

money is an issue here, so I dont think resleeving is an option for me.

As far as oversized pistons, yes, I have my choice of 84 or 84.5, so would it be smart to just buy the 84.5 and give the block and pistons to the shop?

Will they charge more to take it to 84.5mm, instead of honing the stock 84mm?

 

yes

 

can they just hone it to 84.5mm? or do they have to bore it first?

 

they bore, then hone

 

most places will just hone unless youre going .030 over or more. if you buy stock piston they can not hone. however there is one option if you want to use stock pistons, run a glaze breaker and knurl the pistons. a glaze breaker only takes about 5 tenths out of the hole and knurling and compensate for that.

 

The sleeve will crack and you will do it all over again with new pistons.That will cost more. it happen to me. Try it for yourself and remember some one told you to resleeve it....

 

i took my pistons out (b18a1) and honed the cyclinders, then put new rings in.... runs like a champ.... honing doesn't do much except scrap up the walls so the rings will seat

 

All of you that think honing does not remove material must be on crack!
Most real machine shops will hone a block to size rather than stick it in a boring bar, The Sunnen CK machines that just about everybody uses will hone a cylinder to size faster than they can get it setup in the boring bar machine... I have seen as much as .060" be taken out in under 2 minutes just by honing it!
Now, if your going a long way oversize, they will usually bore, because it saves their expensive stones that the honing machine uses.

First thing you need to do to decide what pistons to use is measure your bore and see where your at now and see how much taper the cylinders have... If you had stock pistons before you can get away with the same size bore on most cases (if its not completly worn out) by going to a forged piston that requires more piston to wall clearance anyway. In this case you would just have the machine shop very lightly hone it to the correct piston to wall clearance that will depend on your piston, but usually between .0025" and .0035"... stock is .001", so you can see that you have a tiny bit here to play with. If your already at this limit, its time to go to the next size piston if your sleeves permit it.

 

Honestly, there is a reason for the advice most people are giving you about sleeving. I've read of too many instances where properly assembled B20's have cracked the stock sleeves. If money is tight, skip the B20 block altogether, and have your current block sleeved and bored instead. It will most likely result in fewer headaches later on.