How is this done properly. I'm assuming that you zero the indicator on the deck of the block and then move the indicator over to the piston. I guess my question is how do you move the indicator without changing the height of the base. I've got a magnetic base and the only way I can see is to release the magnetic base and swivel it over so that the dial indicator is now over the flat part of the piston. From what I can see there isn't a way to swivel the dial over to the piston without rotating the whole base. If I release the clamp on the base the dial indicator will move on the indicator rod.

Any good books that would show me proper use of a dial indicator.

Thx.

 

I assume you're using a mag base and a dial indicator?

Once you "zero" the indicator on the deck surface you're good to go. Turn the mag base switch to the "off" position to release the base, move it over to the piston and turn it back on. You can either do that or just swivel the base around. Grab the base & rotate it, don't touch the indicator.

If you do the release and reset method, try it on the deck surface a few times to insure repeatibility to "zero". Of course everything has to be clean like a medical lab. At least that's the way I like to work when doing this stuff.

Any questions?

-Mindgame

 

That's pretty much what I've been doing. It just seemed to me that moving the base would throw off the measurement. The magnet almost makes it harder because if I'm not careful it will "lock" into position without being perfectly flush on the block deck. Thanks alot.

Mark.

 

What you attempting to do is use your mag/indicator as a 'surface gage'. A non magnetic base/extension rod/indicator assembly. What you are attempting is diffcult, as the base of the mag is not of adequate area to perform well, although not impossible. Can you get your hands on a 'depth mic' that has an appropriately large/long base? That would be the simplist.

 

No I don't currently. I've seen the "bridge" type of fitting that looks like it would work best. Is that the type of micrometer fixture that you're talking about?

 

No, I was referring to an actual 'depth mic'. The special purpose bridge setup, usually has a dial indicator attached to it, in lieu of a mic thimble/barrel assembly. The bridge/indicator setup would be the ideal first choice, as it is function specific, I.E., made for that purpose, but I figured that would be even harder to get ahold of, however, unless you bought one.

In a pinch, the mag base/indicator setup could work, if it was placed on a bigger plate instead on directly on the block deck surface. That way you could slide it (you would not be using the mag) over an area that would otherwise be the bore opening. Using an indicator of some sort, WOULD have an advantage over a depth mic, as it would allow easier access to more area of the piston crown, especially the center.

 

Here is a depth mic.

http://img346.imageshack.us/img346/6389/depthmic4nm.jpg

 

I guess I'm not understanding the difficulty in this procedure. I have never had a problem with getting the "zero" to repeat, nor have I had any problems getting a good magnetic hold in those areas between cylinders (top or bottom).

Perhaps the problem is a weak magnet?

I use a Noga mag base that came highly recommended by a tool & die maker friend of mine. Has about 175 lbs of pull when "on" (or so they claim). Either way, I can't break the darn thing loose without turning it off.

The mag-base/indicator also allows you to find TDC easily, check piston rock, etc., etc.. A must have tool for any half way serious engine guy.

-Mindgame

 

that's the way I do it....

Bret

 

I never had a problem with repeatability using MG's method. It works great.

Steve

 

I've had difficulty doing it that way, myself. I guess it depends on how good the base is that the dial indicator is sitting on. Mine's not so good once you go moving things around.

These days I have a depth mic, but back many moons I just used a straight edge and feeler gagues on a go/no-go basis.

 

Thanks for all the input guys. I really didn't have a problem measuring, I just wondered how accurate the measurement would be because of having to move the base. I was watching the dial indicator and the dial would move a couple of thousandths by putting pressure on the fixture anywhere. The magnetic base that I have is pretty strong, I can pull it off with it "locked" down, but not very easily. I might go for a bridge fixture which looks like it would make things really easy, and they aren't very expensive, about 40 bucks for a proform from Summit.

 

To add on...

Using the dial indiactor to find TDC then a depth mic to measure the deck height is a easy way to do it. Or just put a degree wheel on it and find TDC with a dead stop like you would when you degree the cam.

Bret

 

Sort off topic, but since it was mentioned:

Do any of you find that using a dial to find TDC is just as accurate (if not better)
than using a wheel?

My degree wheel is about 12" in diameter. I find the dial quicker and more accurate.

Any downsides for this method?

I've also used the dial to check piston to deck height. With the armature and
dial set screws tight, I simply roate the base (with the magnet off) so that
the needle swings off the deck onto the piston crown.

Very repeatable in any case.

 

I think a dial to find the top of piston travel is fine, But using a dial only to establish crank TDC would probably induce some error. A degree of crank rotation at TDC won't generate any piston motion. To find crank TDC you should use a piston stop and use the "split the difference" method.

Steve