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how do you bore an engine?

405 views 5 replies 3 participants last post by  dave 
G
#1 ·
What does it mean when somebody "bores" the engine? Does it just mean that they drill out the cylinders to increase their diameter? I need someone to explain this.

Blake
93 YJ/4.0L/33x12.50s/3" Rough Country suspension/1.25" shackles
 
#2 ·
Im no expert, but I think I can help you a little on this..

yes basically enlarge hte cylinder diameter.
a good shop used to use a sunnen CK10, ( I think thats the right name) they were the machine for a awhile

enlarge the cylinders enough to overcome all taper and wear grooves that are present, a very badly worn cylinder might need to be sleeved, they insert a steel sleeve in, glue it with some high heat stuff, and then bore that.

it isnt cost effective to sleeve more than one cylinder ( $100 per cylinder usually) most blocks are just cheaper to replace.

after a bore job, you need a nice cross hatch pattern, and then some oversized pistions, with new rings with the proper end gap.

its actually pretty involved, more so than simply drilling the cylinders larger, but basically thats the deal

OzarkJeep

I love the U.S.A.
 
G
#3 ·
From what I understand that is exactly what it is. I think the smallest is 0.10 over all the way up to 0.90 I think. Some people do it for a little more power also it is common when rebuilding to have a clean smooth cylinder wall. As for your topic question I think you have to have some pretty precise tools so I think most people take it to a machine shop.

 
G
#5 ·
Drive it only on the highway, and at approximately the same RPM the whole time/wwwthreads_images/icons/wink.gif.
Actually, boring is like drilling the cylinders. But the cutter that is used is not a drill bit. Boring usually has to be done when an engine is worn beyond tolerance for a certain size piston. Lets say that a stock piston is exactly 4" in diameter, and the normal bore for that piston is 4.020" (these figures are for illustration only and do not represent any type of actual data). As the engine runs the bore wears and increases in diameter. Due to the movement of the piston the cylinders actually wear a little oval. So lets say an engine has gone for 300,000 miles and the cylinder is now 4.060" in diameter, and probably worn a little oval. The cylinder must be bored to make it true again, and a new larger piston must be used. I always hear people talking about the huge cubic inch gains they get from boring an engine, don't believe it. Boring an engine typically adds very few cubic inches (the cylinder walls are not thick enough to be able to bore big enough to make big displacement gains). The real way to gain cubes is by stroking the engine. Which means that the crank has been changed so the travel of the piston is increased. I am sure that there are others who can explain it better, but that is it in a nutshell. There you see, while I typed, all sorts of people responded. I need to type faster.

Cage Up, Wheels Down
Jeepfiend
All my Jeeps are in pieces! Except for one!!
 
#6 ·
Yes, in easy to explain terms, boring an engine cylinder is like drilling the cylinder holes to a larger diameter. There are a couple different machines / methods to bore an engine cylinder. The common oversizes to bore an engine cylinder are +.020", +.030", +.040", and +.060". When an engine cylinder is bored to a larger diameter, the new pistons will need to be matched to the new larger diameter as well.
dave

 
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