I've been talking with my machine shop and I was planning on buying a dial bore guage and some micrometers to check their machine work before the engine was assembled.

The owner said that to do it right his zeroing machine for his dial bore gauge was $1200 and that with snap gauges it's very unlikely that you can get as close of readings.
He offered to let me watch him verify the readings but said he has several thousand in his measuring tools and that I probably wouldn't be able to duplicate his measurements to his close tolerances.

Does this sound right?

Thanks

 

yes and no.

Go watch, what's it going to hurt. It's true you do need the right tools and the knowledge to know how to use them. That's most of it. A dial bore gauge is going to be pretty dam close (within .00005) if you use it right without a zeroing machine.

I vote go watch him, see what he get's. Might as well have him measure your rod/main bearing clearances while you are there too.

Bret

 

If you can't trust your machinist, who can you trust?

Seriously, he sounds like the kind of guy I'd use. I agree with Bret.

Just because you have precision measuring equipment doesn't mean you'll get proper readings. There is some technique to be learned, and measuring a 4 inch holes 6 inches long accurately isn't easy.

If you watch, see if he checks for taper by measuring near the top, middle and bottom, and a few places around the bore. This should all be done with the torque plates still in place, of course.

Ask him to measure the surface finish of the bores. A top notch shop will have a profilometer, or gage that measures surface finish. He should be able to give you "Ra" and "Rz" readings.

Think of the Ra as average roughness (or smoothness), and Rz as the depth of the deeper "trenches". We are talking millionths of an inch here, so "trenches" is a relative term. Not every shop has this instrument, but if the correct honing stones were used in the correct sequence, the bore surface should be correct for the chosen rings. The profilometer just verifies it.

 

The main reason I wanted to be able to check the machine shops work is because I have heard of guys not checking the work and then having big problems due to poor machine work.

I did get a couple references on the shop. However, there are a lot of stories on here about poor work from even the bigger shops.
I figured no reason to take chances on a 10k motor

So you think a dial bore gauge would be very accurate even without the zeroing machine?

 

You can set a dial bore gage with micrometers, the same one you use to check the piston, but it's trickier. I believe folks like Sunnen have an easy to use dial bore gage and setting fixture that's extremely acurate. We use their equipment.

Trust is important here. If the guy who did the work has ownership of the business, and is willing to let you watch his measurements, that's a very good sign.

Has the work been done yet?