Measuring engine bore

[FreeBeeTony]

Think I can accurately measure the engine bore of a SBC with vernier calipers to determine if it's been bored-out already?

ALso, what is the diameter of a std piston?........this maybe more easily measured.

Don't want to hump this thing into my basement if it's already been bored-out.

 

[Maclin]

Re: Measuring engine bore

If you are going to take the block apart before you lug it down there then just look at and measure a piston. If not then there will be a ridge at the top of the cylinder, measure there for the bore. If you measure down a ways you will get what the piston rings have hogged it out to. But that may not be a bad thing anyway, it may be able to be bored out again, there are tolerances for that kind of thing. You have to measure along the whole cylinder from top to bottom (with no piston in there obviously) to check the taper to see if there is enough meat to go again.

 

[erikgreen]

Re: Measuring engine bore

What he said.

And, I personally wouldn't use a vernier caliper for this unless you're pretty practiced with it... too easy to make mistakes, and digital calipers are cheap now.

 

[Mischief Managed]

Re: Measuring engine bore

Usually, oversize pistons will have the over bore size (typically .030) stamped into the top.

 

[MikDee]

Re: Measuring engine bore

If you are going to take the block apart before you lug it down there then just look at and measure a piston. If not then there will be a ridge at the top of the cylinder, measure there for the bore. If you measure down a ways you will get what the piston rings have hogged it out to. But that may not be a bad thing anyway, it may be able to be bored out again, there are tolerances for that kind of thing. You have to measure along the whole cylinder from top to bottom (with no piston in there obviously) to check the taper to see if there is enough meat to go again.

I believe they call this "mushrooming" it is how engines normally wear, i was told under .006 is the max allowable before a rebore is necessary. I found this out from a machinist when rebuilding a 74' Chevy Nova SS 350 motor, that I finally had bored out .030 over.

 

[JustJason]

Re: Measuring engine bore

No you cannot measure a bore with a verneer.
You have to have a MIC and a dial bore gauge set.
You also need to measure it in 6 spots.
Top, middle and bottom
X and Y axis
TOR and taper are just as important(if not probably more so) as the diameter of the bore....

 

[FreeBeeTony]

Re: Measuring engine bore

Judging from a quick measurement it looks like it's already been bored out....

Numbers on the piston

H423 NCP 040
353-00-16A

I googled the numbers and didn't come up with anything.

Anyone know if these are P/N's for a piston?

EDIT:

re-googled........looks like it's 040 over........

How far can a SBC be overbored safely? Can I go 060?

 

[Coors]

Re: Measuring engine bore

060 is pushing it; casting sand sometimes shifted. Ain't worth investing the $.
imho.

 

[John_S]

Re: Measuring engine bore

Tony,
That opens a wider aperature on what might have caused your lifter problem. Just about anything can get screwed-up on a rebuild, if not done right.

 

[FreeBeeTony]

Re: Measuring engine bore

Don't understand John?.......do you mean that because it was 040 over already might have had something to do with it?

 

[Coors]

Re: Measuring engine bore

I used to work for a Chevy dealer, saw a guy honing the lifter bores, during a rebuild. Not good.

 

[FreeBeeTony]

Re: Measuring engine bore

So the lifter bores should NOT be honed?

 

[John_S]

Re: Measuring engine bore

Only that it was rebuilt and a number of things could have been done wrong, and could be as simple as not cleaning oil passages. I remember that you were agonizing over the possibility of it being something that you had done.

 

[FreeBeeTony]

Re: Measuring engine bore

Yes John.........I am thinking it may have had something to do with cloged oil passages in the lifter valley.

Note: I didn't do the rebuild on that engine, just replaced the heads.

What about going 060 over? Not a good idea?

I was really looking to use this block and make a project out of building a stroker...i have another set of vortec heads I was going to heve redone, etc...

 

[John_S]

Re: Measuring engine bore

Note: I didn't do the rebuild on that engine, just replaced the heads.

What about going 060 over? Not a good idea?

I was really looking to use this block and make a project out of building a stroker...i have another set of vortec heads I was going to heve redone, etc...

Yea, I remember lifter/heads/valve discussions. Back then, I think the assumption was it was stock, and not already had a rebuild done.

No, I wouldn't think 060 over is good in a marine engine. Most people seem to think 030 is about as far to go with maine. Also, if there has been something done to the lifter bore that might mean scrapping anyway. Part it out and get that jinx away from you.

Start a stroker project with a good block. Lots of 350 blocks around.

 

[Coors]

Re: Measuring engine bore

Never hone a lifter bore, only use scotchbrite; .060 is too far over for auto.
Unless block x-rayed. and we can't afford that, only racers can.

 

[FreeBeeTony]

Re: Measuring engine bore

OK........this block is done........