Nick in crank journal, machine shop or??

[Big_John]

Had some practice using the micrometer, not confident this is correct, but the crank rod journals is coming out to .3760 thousandths. Something still doesn't sound right, doing a bit more measuring to confirm whether this is correct or not.

Measured another crank journal and it's coming out to .3768.

Either my calculations are wrong or this crank is oblong/warped.
Homework time.

Assuming there's a "2" in front of that measurement, that measurement doesn't sound correct. Crankshafts don't get larger as they wear. LOL.

Did your micrometer come with a 2" standard to check the mic? That's the first thing to check. I've taught a lot of people to read micrometers, but trying to describe the "feel" is tough to do. It's an "over the shoulder" type training thing.

As far as the crank being out of round, if you are getting consistent readings (even if the number is incorrect), it's not surprising that the journal is out of round. That's why we have crankshafts reground.

 

[Sir Dodge alot]

Assuming there's a "2" in front of that measurement, that measurement doesn't sound correct. Crankshafts don't get larger as they wear. LOL.

Did your micrometer come with a 2" standard to check the mic? That's the first thing to check. I've taught a lot of people to read micrometers, but trying to describe the "feel" is tough to do. It's an "over the shoulder" type training thing.

As far as the crank being out of round, if you are getting consistent readings (even if the number is incorrect), it's not surprising that the journal is out of round. That's why we have crankshafts reground.

Yes sir, I knew something was off.
2" standard? Is it this long piece of stock that was marked with "2" on it?

Going to see if I can remove the crankshaft from the block, measuring the journals with it in the block is a bit awkward, least to say.
But having the crank sitting in the block was quite an effective jig.

 

[Big_John]

2" standard? Is it this long piece of stock that was marked with "2" on it?

Yep! You use that to check your mics.

 

[Sir Dodge alot]

I didn't get around to removing the crankshaft from the block today, I was studying on getting my new found micrometer measuring skills a bit more polished up.

Should be good to go now.

 

[Sir Dodge alot]

Thought I have listed the updated measurements on the journals, guess not.

Here are the updated measurements of the journals, both crank end cap and connecting rod area's of the journals on the crankshaft.

The left/right readings of the crank journals are measurements from different parts of the crank on the same journal.

The crank connecting rod journals readings were quite consistent, so I didn't bother listing those.

All measurements have been taken with the micrometer.

Crankshaft has passed the ringing test on the counterweights, will look more closely for cracks regardless of the ringing test.

 

[Big_John]

I'll bet you are off .025" on the second sheet.

BTW, .025" is a common mistake that I've seen guys with decades of experience make. Myself included. One turn of the micrometer.

 

[Sir Dodge alot]

I'll bet you are off .025" on the second sheet.

BTW, .025" is a common mistake that I've seen guys with decades of experience make. Myself included. One turn of the micrometer.

Hello sir,

Got it, will remeasure and record new readings.

 

[Sir Dodge alot]

Here's the new measurements but without including the barrel scale numbers, but including the vernier scale number in the end, this made alot more sense to what I'm seeing.

 

[Big_John]

OK grasshopper, you aren't ready to snatch the pebble out of the master's hand yet, but it's time for a short lesson.

In the metrology world, there is something often referred to as a "sanity check". That needs to happen when you are not sure of your measurement. Like you look at the nominal specs, and you see your measurement doesn't really jive with it. In this case, you were .025" larger than nominal.

Now, we know that this crankshaft journal is going to wear and not get larger. Kind of a hard fact.

So, this is where a "sanity check" comes in. You want to make sure you are measuring it correctly.

So, there's a couple ways to do this. If you had the luxury of another person there, with another pair of mics, you would have them remeasure a couple points to see if they agreed. The other, more usual method is to grab something else to do a quick measurement.

With .025" in question, the easy way to check this is to bust out the dial calipers and measure the journal in question. Yes, I know.... I told you the dial calipers aren't accurate enough. But a decent pair is +/- .001" and you are seeing if your measurement might be off .025".

It works with other stuff too. Let's say you measured something with that dial caliper and it's .250" off nominal. You grab your 6" ruler that's accurate to about .015" and lay it against what you're are measuring.

Usual human errors in measurement for a mic is .025" or one turn of the thimble. Typical human errors for dial calipers is .100", again, one turn of the dial. Then there's errors in the measuring tools themselves. A dropped mic could be anything, but it usually means the anvils aren't parallel any more. Crap in the gear rack of a dial caliper might cause the internal gears to "jump" .025" or some multiple of .025". Then there is wear but that's a subject for another day.

And for those wondering about it, metrology is the science of measurement. I used to use the grasshopper/pebble reference, but younger guys didn't get it, so I'd tell them to Google it.

Hopefully you understand this. I think it's the first time I haven't given this lesson in person, but if I had a nickel for every time I have taught this to someone, I'd have a whole bunch of nickels.

 

[Sir Dodge alot]

OK grasshopper, you aren't ready to snatch the pebble out of the master's hand yet, but it's time for a short lesson.

In the metrology world, there is something often referred to as a "sanity check". That needs to happen when you are not sure of your measurement. Like you look at the nominal specs, and you see your measurement doesn't really jive with it. In this case, you were .025" larger than nominal.

Now, we know that this crankshaft journal is going to wear and not get larger. Kind of a hard fact.

So, this is where a "sanity check" comes in. You want to make sure you are measuring it correctly.

So, there's a couple ways to do this. If you had the luxury of another person there, with another pair of mics, you would have them remeasure a couple points to see if they agreed. The other, more usual method is to grab something else to do a quick measurement.

With .025" in question, the easy way to check this is to bust out the dial calipers and measure the journal in question. Yes, I know.... I told you the dial calipers aren't accurate enough. But a decent pair is +/- .001" and you are seeing if your measurement might be off .025".

It works with other stuff too. Let's say you measured something with that dial caliper and it's .250" off nominal. You grab your 6" ruler that's accurate to about .015" and lay it against what you're are measuring.

Usual human errors in measurement for a mic is .025" or one turn of the thimble. Typical human errors for dial calipers is .100", again, one turn of the dial. Then there's errors in the measuring tools themselves. A dropped mic could be anything, but it usually means the anvils aren't parallel any more. Crap in the gear rack of a dial caliper might cause the internal gears to "jump" .025" or some multiple of .025". Then there is wear but that's a subject for another day.

And for those wondering about it, metrology is the science of measurement. I used to use the grasshopper/pebble reference, but younger guys didn't get it, so I'd tell them to Google it.

Hopefully you understand this. I think it's the first time I haven't given this lesson in person, but if I had a nickel for every time I have taught this to someone, I'd have a whole bunch of nickels.

Hello sir.

Appreciate the lecture, will compare and affirm my readings with other measuring devices, and to also scrutinize & recheck my methods.

 

[Big_John]

Hello sir.

Appreciate the lecture, will compare and affirm my readings with other measuring devices, and to also scrutinize & recheck my methods.

I wouldn't call it a "lecture". That always seems to me like talking down to someone.

I prefer to think of it as trying to share some of my knowledge and experience to someone that wants to learn and is willing to listen to me try to explain in words what I used to do in person. It's a learning experience for me to do that, believe it or not.

 

[Sir Dodge alot]

I wouldn't call it a "lecture". That always seems to me like talking down to someone.

I prefer to think of it as trying to share some of my knowledge and experience to someone that wants to learn and is willing to listen to me try to explain in words what I used to do in person. It's a learning experience for me to do that, believe it or not.

Hello sir,

Oh no sir, I didn't think of the previous message as a lecture as talking down on someone, not at all.
I have taken some of the advice you have given me and am now attempting to put into practice.

Some of the points you mentioned reminded me of my automotive professors I had a few years back. But they did not mention anything about Metrology, which I think was a missed opportunity to teach.
Thanks.