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2010 FXT Auto4
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409 Posts
Discussion Starter #1
I am confussed about having my short block rebuilt.The repair shop that rebuilding the block is going one size over(99.7)with stock pistons. Another engine builder said you should never bore or hone Subaru blocks, he just buy a stock block from Subaru. Anybody have any problems with oversize and will this effect the durability? Opinions welcome. Thanks Jeff
 

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99 UK S-turbo
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8,590 Posts
When you say stock pistons, I assume you mean replacement oversize?

Subaru blocks can be succesfully bored and honed, many in the UK are to create the 2.3 litre (2.5 stroke and overbored 2.0 block) that is the budget capacity option (stronger than 2.5 without spending out on the bits needed to make the 2.5 as strong) HOWEVER the honing pattern needed is different to most I4/V6/V8 engines due to the horizontal cylinders so make sure that whoever is doing the honing knows that and what to do.

Simon
 

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2008 Forester X Premium 5MT
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8,073 Posts
No real issues with boring them until you get past the 100mm point, then you may want to look at sleeving the block. For 100mm and down don't worry about it, what you are looking at is just a clean up pass to straighten out the cylinder wall wear.

bored 100mm
Stock 99.5mm
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.2mm or about .008"

which equals roughly .004" of material per side of the cylinder being removed, about the thickness of a sheet of paper. No worries.
 

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2004 Subaru FXT MT
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1,853 Posts
Yeah, I haven't understood some engine builders that say you can't bore and hone a subaru block. I mean, come on, we are talking .5mm. That's .020". That's nothing.

I have heard some of them talk about heat transfer issues and things like that. Frankly, .5mm isn't going to change those sorts of things a bit.

You are going to want to get new pistons of course. Even if you go .010 over you would want new pistons.
 
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