What exactly is a engine bore?

[Forgotten Ways]

I am looking at a FJ60 and hey have done an engine bore on it at 180,000 miles. Could some one explain why this is done and what benefits it has? Does it extend the life of the engine? Help HP, help MPG?? I just don't know. Thanks guys. learning lots every day.

 

[srogers]

When an engine is rebuilt, an engine bore is essentially resurfacing the face of the block where the pistons operate. Pretty common on a full rebuild, question should be what size pistons were installed (how far over) as well as confirming that the block was bored and not sleeved.

Also, ask if they had it professionally done and have receipts; how many miles are on the engine since the rebuild, any problems, warranty from the machine shop that rebuilt the engine, etc.

 

[klinetime574]

They either did it because

1. The PO wanted it that way.

or

2. They had to.

If the surfaces of your cylinder walls were roughed up, and the crosshatching was gone, then they would bore the cylinders. Only a small increment in thousandths of an inch. This restores the cylinder walls and then your crosshatching is all better. This crosshatching helps with oil lubrication of the cylinders by sort of "holding" the oil on the cylinder walls.

It will likely have no effect on gas mileage, unless the engine was running really badly because of the cylinder walls being messed up. In that case you might get .5 mpg difference

And with it being in effect a "new engine" it should definitely extend the the life.

Cars are fun.

 

[cjhollenshead]

"engine bore" can reffer to two things, as mentioned above it can be the cylinder being bored or what they call an allign bore. An align bore is were the surface that the crank shaft rides in including bearing caps are machined so each is exactly the same size and they are perfectly in-line.

 

[Spike Strip]

An Engine Bore is someone who knows all-about engines and will constantly tell you so.

 

[IH8Wood]

A club member who knows a lot about engines and not much else.

 

[Pighead]

You engine cylinders will oval out over time. Boring restores them to round. Routine part of an engine rebuild.

 

[Forgotten Ways]

An Engine Bore is someone who knows all-about engines and will constantly tell you so.

ha!! That's great.

 

[Gumby]

Frequently referred to as a positive thing by people who don't know any better. If the cylinders are scored, tapered or out-of-round they have to be put back right during a rebuild. The only way to make them perfectly finished, perfect cylinder shaped cylinders is to bore them oversized and put oversized pistons in them.

Engines generally have three or more sizes they can be bored over safely, usually in increments of .010" or .5mm. That means a minimum clean up can be done three or more times, but a bad one can go right out to max oversize in one shot.

Saying it's been bored over means one or more of those rebuilds is no longer possible. It does have more displacement, but not enough to make any kind of difference.

I love it when I hear "It's been bored sixty over". Great. So it's about junk then?

 

[Spike Strip]

Saying it's been bored over means one or more of those rebuilds is no longer possible. It does have more displacement, but not enough to make any kind of difference.

I love it when I hear "It's been bored sixty over". Great. So it's about junk then?

Pfffffftt! My 4.42 L 2F (forty over) can beat your 4.2L anytime !!

 

[Pighead]

Fifty over here...