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how to know if a engine needs bored?

nyhillbilly

Full Member
Joined
Sep 22, 2006
Messages
173
Loc.
Canton, MI
when i disassemble my engine, and look at the bores, and see no obvious defects, how do i know if it needs a bore? its got blow by right now, which could be a ring or bore wore out. So how much wear is out of limits ? .005" ? less more? or is it really a question of being out of round? I don't have money to blow on a full rebuild at the moment.
 

Viperwolf1

Contributor
electron whisperer
Joined
Aug 23, 2007
Messages
24,316
X2. You cannot tell by looking at the bore. It needs to be measured at several different points.
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,835
If you have an engine apart a quick check is to use an old ring. Put the ring in the bore and square it up (the old piston works well). Measure the gap in the ring with a feeler gauge at the top of the bore and a couple times as you go down the bore to the very bottom. The very bottom of the boregenerally has very minimal wear. Take the largest number (should be at the top) and subtract it from the lowest number (should be at the bottom) and divide by 3. You now have a rough idea on the cylinder taper. Compare to allowable specs and you will know if the cylinder needs an overbore to square up the hole.

The other thing is to look at the scratches in the wall. The deeper they are, the more you will need an overbore and not just a hone. And it isn't super cut and dry either. if the taper is just in spec but has deep scratches, by the time you get the scratches out by honing you will have too big of a hole and need to overbore.
 

bmc69

Contributor
Bronco Guru
Joined
Jun 11, 2004
Messages
11,852
A real simple test..just insert a ring in the cylinder near the very top..the 'ridge' that is called, where the bore has not seen any wear. Measure the ring end gap.

Move the same ring down about an inch or so in to the cyliner and measure again. If you get a difference approaching 10 thousandths of an inch, the bore is beyond honing to clean it up.
 
OP
OP
nyhillbilly

nyhillbilly

Full Member
Joined
Sep 22, 2006
Messages
173
Loc.
Canton, MI
If you are short on funds the least expensive fix is a good used engine. JMO

im looking at that option also. if my engine is truly junk it wont hurt to tear it down and take a look, i am hoping that is a cracked ring or something else minor that does not require a bore job, if it is a bore then i will probably get a used motor. I hate used though because you never really know what your getting.
 
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