Merry Xmas to me; I got a Mitutoyo 1" dial indicator, "Precise" (no-name) dial-indicator stand, and "Precise" metric/standard 6" dial calipers from my girlfriend. Looks like I'm moving further along the way to rebuilding my engine!

I know it's not the best idea, but could the calipers be used to measure the journals of the crank? Or should I save up the $$ for a set of mics?

Also, I still need to buy some telescoping gauges... but I'd need to measure 'em somehow. Is this another thing to save for the micrometer, or would the calipers be fine?

I'd rather not "try" using calipers if it turns out Plastigage will be more accurate but a set of large external mic's is pretty costly. Hm, Ebay, maybe?

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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
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[This message has been edited by TomP (edited January 09, 2001).]

 

Calipers are good for lots of stuff. However, when dealing with crankshaft journals, you are measuring down to the "tenths" or 1/10000 of an inch for absolute precision. Realistically you are measuring to the 1/1000 of an inch and micrometers measure this precisely. Calipers measure to the 1/1000 also but since the mandrel is so thin it is easy to not be quite so precise. When trying to be precise about a .005" clearance, you don't much room for error and calipers can give you that error if not used correctly. However it is my experience working with precision measuring tools for over 20 years that even the best micrometer is useless in the hands of someone who doesn't have the "feel" and the auto stop function on some mic's is not really used by pro's looking for the most precise measurement.

All that being said, I would think you could just use your calipers. Here is how I would do it: put the caliper on the journal, and slightly squeeze the jaws together with your fingers and then read the dial. Take multiple measurements around the journals in at lesat 4 places doing it this way. Always reading the dial with the jaws still on the journal. Pulling the caliper away to read it can move the jaws open, even when locking the caliper. Too much moment arm due to the length of a caliper.



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FORMULA 350 TK
Southern California 3rd Generation F-Body Organization©

 

It depends on the calipers. If their jawas are long enough to reach around the journal, and they have sufficient precision, they're fine. I have a set of digital calipers that I use for that, that are accurate to .0005".

The telescoping gauges mostly use either calipers or a "C"-frame mic - you put them in the bore or whatever, let them snap out, lock them in place, take them out and measure them with the other tool.

Tom K's technique is much the same as how I use my slide caliper to measure journals. Some of what he says applies either to a slide or a C-frame caliper, like check several places and read the instrument while it's on the work.

I prefer calipers to Plastigage. That is a simple and effective tool for someone without the tools, but the tools IMHO are better, though Plastigage makes a good check for correct assembly.

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"So many Mustangs, so little time..."

 

Thanks for the replies, guys! I'll have to check my calipers tonight to see how accurate they are. Would you recommend a "normal" micrometer over one with interchangeable anvils? Maybe I'll check out one of the flea markets nearby; they usually have guys selling tools.

Also, TomK, (er, well, both of you seem to agree) you say that I should lightly hold the calipers closed over the journal to take measurements. I never thought about that, but yeah, I guess I couldn't "compress" the calipers onto the surface get a funny reading, right? It's not like I'm measuring wood or plastic; the journals won't compress. (Of course the caliper jaws might... I take it that's why I should press them lightly closed?)

But would I do that same procedure with a micrometer? Would I spin the micrometer medium-strength against the journal and read my measurement?

And RB83L69, thanks for that idea on using Plastigage "anyway" for a back-up measurement... I didn't think of that.

Thanks!

Oh hell one more question.. think I should bother to hunt down larger micrometers? (My dad has an old 1" Starrett, but that won't get me far past valvestem thickness.) I'm trying not to spend a ton of money on this 2.8; but then again, I see myself using these tools again in the future... 'course I can always buy 'em later. The 2.8 will be a stock rebuild; right now it seems my redline is 6,000 (well, I've never gone past that).


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

i have several sets of dial calipers and would never use them for a crank. i use my mikes, if you're planning on doing engines very often buy a good set of mikes (starret). i've saw lots at swap meets and flea markets, but it's hard to tell if they're accurate or not.

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ICON Motorsports
1st & 3rd

 

Aren't there places that check/fix the accuracy of micrometers?

And the way I'm guessing, there'd be just two sizes I should hunt down (since I have a 1" one already)- one large enough for the crank journals, and one large enough for the pistons/bores. Sound good?

Hm, there's always that JC Whitney set of 6 micrometers for $120


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!