Inside Micrometer

[Wolverine]

I am getting ready to install my 351C crankshaft...just waiting of the engine paint to dry.

I was just going to check it with plastigage, as I did for my first rebuild. But then the 385 forum guys kind of scared me into thinking I should get a guage.

So I looked for a gauge and went ARE YOU KIDDING ME????

Anyone have a good source for an accurate inside micrometer good to 3.5"?

Thanks.

 

[sm3570]

How did the paint come out? Did it dry correctly this time?

 

[marks73]

Accuracy costs.

 

[Tnfastbk]

You building a big block?

 

[caspianwendell]

Plastiguage will work...if your worried about egging, check all around the journal.

check pawn shops and flea markets...I have seen some for a good price there.

Too bad your in a third world county as I have a great inside set you could use

 

[c9zx]

With practice this may be an alternative, if you have outside micrometers or dial caliper. http://www.sears.com/hft-telescopic-engine-cylinder-inside-bore-gauge-0.315-quot/p-SPM6110881001?prdNo=21&blockNo=21&blockType=G21

 

[chompz]

this should work

http://www1.mscdirect.com/eCommerce/NavigationServlet/Measuring-Inspecting/Dimensional-Measuring-Tools-Instruments/Inside-Diameter-Measurement-Gages/Bore-Gages-Accessories/Dial-Bore-Gages/_/N-77dcz?refinement=4294949659&searchandizedOk=N

 

[VegasFastback]

I found a good set on Amazon.com. I also found a dial indicator and a cam bearing removal tool.

 

[marks73]

Inside mic good to 3.5 inch Just what exactly are you trying to measure?

 

[Wolverine]

Inside mic good to 3.5 inch Just what exactly are you trying to measure?

I am getting ready to install my 351C crankshaft...so the inside bearing diameter.

I have looked on eBay, but I need accuracy to .0001. Almost bought one without looking very close...got into lots of trouble in my younger years that way.

Inside mic good to 3.5 inch Just what exactly are you trying to measure?

I am getting ready to install my 351C crankshaft...so the inside bearing diameter.

I believe that is

Crankshaft= 2.75" less the .0010 taken off the crank

Crankshaft fine= 2.74" (I have a mic for this)

With .0015 to .0025 journal clearance= 2.7385 to 2.7375.

I have looked on eBay, but I need accuracy to .0001. Almost bought one without looking very close...got into lots of trouble in my younger years looking at girls that way.

 

[droptop73]

Do you mean you want ACCURACY within .0001" or do you want a tenths scale. You will need a climate controlled lab if you want to measure accurately to .0001". The cost goes way up with that kind of accuracy.

For my dollar you cannot beat Scherr-Tumico. (http://www.lighttoolsupply.com/catalog/Manufacturers/Scherr-Tumico/SCHERR-TUMICO-INSIDE-MICROMETER--0001--GRADUATION-ROD-TYPE?productID=4972) Good accuracy at reasonable prices. I have also bought and used Mitutoyo, Starrett, Brown & Sharpe and Lufkin. Those brands have the accuracy you are looking for whrther you want inside or outside mics.

 

[Wolverine]

Do you mean you want ACCURACY within .0001" or do you want a tenths scale.

Maybe I need an education. My understanding is I need .0015 to .0025 clearance. How am I going to determine the +/- .0005 tolerance with a .001 gauge? If I have a .001 gauge with a tenths dial, I guess that works.

You will need a climate controlled lab if you want to measure accurately to .0001". The cost goes way up with that kind of accuracy.

Again, I can use some educating regarding the temp. But I thought this was not pertinent to my application.

For my specific application, my understanding is as long as the crank and bearings are the same temp, and let's say both are within 2 degrees of each other, 65-75 degrees, and measured within minutes of each other, I can rely on the reading.

Although my crankshaft did caliper out at 2.740(if I remember correctly), if the temperature causes it to be 2.735, as long as the bearing are 2.735 +/-.0015 to +/-.0025 I am good...

I am not mic'ing dozens of items over a long time period for comparison later. In that case, I can see why temperature would make a difference. I am just measuring the crankshaft diameter and bearing inside diameter for clearance.

This all got started due to the 385 forum saying plastigage is not accurate at all, and a Car Craft magazine demonstrating such.

Side Note: I did not like the way Car Craft measured the crank. They did not use a feeler gauge between the crank and caliper or the bearing and micrometer to protect the surfaces from scratches when measuring with a carbide tipped micrometer/caliper. Just seems like common sense to me.

 

[VegasFastback]

Do you mean you want ACCURACY within .0001" or do you want a tenths scale.

Maybe I need an education. My understanding is I need .0015 to .0025 clearance. How am I going to determine the +/- .0005 tolerance with a .001 gauge? If I have a .001 gauge with a tenths dial, I guess that works.

You will need a climate controlled lab if you want to measure accurately to .0001". The cost goes way up with that kind of accuracy.

Again, I can use some educating regarding the temp. But I thought this was not pertinent to my application.

For my specific application, my understanding is as long as the crank and bearings are the same temp, and let's say both are within 2 degrees of each other, 65-75 degrees, and measured within minutes of each other, I can rely on the reading.

Although my crankshaft did caliper out at 2.740(if I remember correctly), if the temperature causes it to be 2.735, as long as the bearing are 2.735 +/-.0015 to +/-.0025 I am good...

I am not mic'ing dozens of items over a long time period for comparison later. In that case, I can see why temperature would make a difference. I am just measuring the crankshaft diameter and bearing inside diameter for clearance.

This all got started due to the 385 forum saying plastigage is not accurate at all, and a Car Craft magazine demonstrating such.

Side Note: I did not like the way Car Craft measured the crank. They did not use a feeler gauge between the crank and caliper or the bearing and micrometer to protect the surfaces from scratches when measuring with a carbide tipped micrometer/caliper. Just seems like common sense to me.

First of all I believe your way overthinking this. That being said if you were trying to blueprint this engine to the tick temperature would play a role because different metals expand at different rates. So if you were building a race engine you would need a controlled environment with a specific temperature to ensure everything would turn out as intended.

For you though a good mirometer, not a caliper, will have the accuracy you want and go to .0001. As long as you calibrate the micrometer every time you use it the temp won't matter.

I bought a three micro set of Amazon for less than $100 and it worked great for ensuring proper clearances on my mains. I used it in tandem with a dial indicator I used to measure the bearings. I also have a caliper but like you said they're only accurate to .001".

As for the car craft thing my micrometer doesn't accually close tight enough to grip what its measuring so it doesn't leave any marks on the crank. It will click like a torque wrench to tell you to stop tightening.

 

[Wolverine]

Thanks for all the help.

 

[Darkhorse71]

You definitely need a dial bore gauge to .0001 to accurately measure your bearings. When I built my 408w, I compared the plastigauge to my mitutoyo and the accuracy of the plastigauge wasn't close. While you want the crank and bearings to be of similar temperatures when your measure, it isn't going to be that drastic, especially considering they will get to 200+ degrees while your motor is running. I was able to accurately measure them to the point of going to one step up over size crank bearings. Mine are .0030-.0035 on my mains (351w based).

I fought for weeks avoiding to buy the .0001 Mitutoyo. I eventually found one locally in a craigslist for $200 used! But it's something I'll keep for the rest of my life now. Dial bore gauge to .001 is worthless for checking rod/crank bearings. Great for cylinder bore however..

It's like buying the tools to build the motor has to be factored in the build as well. I bought piston ring filer, piston/deck bridge checker, micrometers, pushrod checker, dial bore gauge (.0001), 8 inch caliper, piston ring compressor, nice valve spring compressor, head CC kit.. I'm sure there is more but that's just what I could think of off top of my head I had to buy just for accurate motor building. Not to mention all the basic tools that most already have, like pullers, engine load balancer/hoist, stands, torque wrenches, etc.

Chaz

 

[Wolverine]

You definitely need a dial bore gauge to .0001 to accurately measure your bearings. When I built my 408w, I compared the plastigauge to my mitutoyo and the accuracy of the plastigauge wasn't close.

That is why I am wondering why it was the "standard" for us schmucks for so many years.

It's like buying the tools to build the motor has to be factored in the build as well. I bought piston ring filer, piston/deck bridge checker, micrometers, pushrod checker, dial bore gauge (.0001), 8 inch caliper, piston ring compressor, nice valve spring compressor, head CC kit.. I'm sure there is more but that's just what I could think of off top of my head I had to buy just for accurate motor building. Not to mention all the basic tools that most already have, like pullers, engine load balancer/hoist, stands, torque wrenches, etc.

Chaz

I think I have started a tool kit list for engine rebuilding. This plastigage inaccuracy is a little irritating.

 

[marks73]

It's like anything else if you want it right. Measure twice wrench once.

 

[c9zx]

You definitely need a dial bore gauge to .0001 to accurately measure your bearings. When I built my 408w, I compared the plastigauge to my mitutoyo and the accuracy of the plastigauge wasn't close.

That is why I am wondering why it was the "standard" for us schmucks for so many years.

It's like buying the tools to build the motor has to be factored in the build as well. I bought piston ring filer, piston/deck bridge checker, micrometers, pushrod checker, dial bore gauge (.0001), 8 inch caliper, piston ring compressor, nice valve spring compressor, head CC kit.. I'm sure there is more but that's just what I could think of off top of my head I had to buy just for accurate motor building. Not to mention all the basic tools that most already have, like pullers, engine load balancer/hoist, stands, torque wrenches, etc.

Chaz

I think I have started a tool kit list for engine rebuilding. This plastigage inaccuracy is a little irritating.

James, Please read the linked document. It will help you understand all the bearing tolerances to be concerned about as well as a few bits of information that may be new to you. I hope it helps. Chuck

http://www.kingbearings.com/files/Geometry_and_Dimensional_Tolerances_of_Engine_Bearings.pdf

 

[Wolverine]

1. Great article....especially liked the part on the crushing of the crankshaft bearing.

2. Makes me wonder why, on a previous 351W build, I remember checking the crankshaft bearing/journal clearance with plastigauge, but don't remember checking the piston rod/journal clearance.

3. And, I didn't know King Engine Bearing made their own bearings...It thought they were just a reseller, unless I am thinking of a different King Engine Bearing.

4. Again, schmucks like me are stuck trusting our engine shops because if we check all of those tolerances, as I think we should, we are going to spend more time checking and less time assembling...and more money on gauges and such then on HP.