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Dial Bore Gage Specs

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Sitting on Blocks Racing

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#1
I picked up a Fowler 52-646-400 bore gage to help check clearance on an engine I'm building.

Specs
.0005 Graduations
.0009 Total Error
.0004 Repeatability
.00025 Self Centering Error

I should probably have gotten the .0001 resolution since I'm trying to measure .0004 taper and out of round specs as well as bearing clearances at .0025.

I am having alot of variability between reading on different days .0005 on a bearing clearance reading between yesterday and today. The block was approximately the same temp.

I assume that is due to the error specs on the gage? Does anyone have a clear definition to the above specs or what I should look into for a replacement .0001 resolution gage

For comparison I looked up a Shars gage for a possible replacement.
303-3117
Product description
  • Measuring Range:0-1"
  • Graduations: 0.0001"
  • Accuracy (1st 2.5 Rev): +/- 0.0001"
  • Accuracy (Overall): +/- 0.0004"
Is Total Error the error over the complete range of the dial .0009 on the Fowler vs .0004 on the Shars for instance?
 

JimDawson

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#4
Unless you are line boring/honing the mains, Plastigage would be my choice for bearing clearance measurements.

But I would expect repeatable readings on the gage. Part of that error could be technique, it takes some practice to get consistent readings. But with only 0.0004 repeatability, your readings seem to be in the range of allowed error in the tool. For engine work I would want to read to 0.0001. If it were me, I would buy a Sunnen DBG, a much higher quality gage and reads to 0.0001 There are quite a few on ebay. A few master setting rings might be in order also.
 

Sitting on Blocks Racing

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#5
The bore gage has a 1.4" to 6" range with interchangeable anvils. There are no included ring gages. I've been setting with a micrometer.

I started by plastic gaging the mains and all 5 came in all at .002. Straight with no taper and on the high side of the spec which is what I want for a higher boost 4 cylinder.

The problem came with plastic gaging the rods, I could not keep them from rotating while torqueing the rod bolts. So I assume there was some smearing of the plastic gage.

I used the big end of the Manley rod as a sort of ring gage. I got the spec for the bearing end at 1.89" without the bearing. I would assume that the quality of a $700 set of rods would be pretty consistent. I checked them with a pair of Starrett dial caliper and a cheaper set of digital caliper and they both read 1.89" on the bore. I then set the bore gage with a set of micrometer to 1.89. When I put the bore gage in the rod end, it read .001 under. Hmmm, something in my setting technique may be off.

Hopefully that make sense.
 

JimDawson

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#6
The problem came with plastic gaging the rods, I could not keep them from rotating while torqueing the rod bolts. So I assume there was some smearing of the plastic gage.
That is possible. Are you doing this with the crank on the bench? When setting clearance out of the engine, I normally put the rod in the vice (soft jaws) and torque to spec. Then measure the bore at 3 positions. Then measure the crank at 3 positions. Average the readings and subtract the difference.

I used the big end of the Manley rod as a sort of ring gage. I got the spec for the bearing end at 1.89" without the bearing. I would assume that the quality of a $700 set of rods would be pretty consistent. I checked them with a pair of Starrett dial caliper and a cheaper set of digital caliper and they both read 1.89" on the bore. I then set the bore gage with a set of micrometer to 1.89. When I put the bore gage in the rod end, it read .001 under. Hmmm, something in my setting technique may be off.
That is proabaly a safe way to do it, since it's what you have to work with. Rather than setting with a mic, I would just use the rod bore as a ring gage and set directly to that. I would confirm the rod bore with a snap gage and a mic. That really requires some practice to get good readings, but a skill well worth learning. With some practice, you should be able to measure to 0.0001 consistently. Make sure your mic is calibrated correctly.
 

Sitting on Blocks Racing

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#7
That is possible. Are you doing this with the crank on the bench? When setting clearance out of the engine, I normally put the rod in the vice (soft jaws) and torque to spec. Then measure the bore at 3 positions. Then measure the crank at 3 positions. Average the readings and subtract the difference..
I measured the crank with a micrometer, zero'd the bore gage with that mic and then read the clearance directly
 

Tony Wells

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#8
Some mics, particularly those with lever style locks, will move when you lock them and not be accurate. Also, if the mics are not carbide faced, there easily could be dishing on the anvil and or spindle and this will throw your setting off. IOW, it's a bit tricky to set a bore gage with an OD mic. If you have a suitable lathe, you can make a set ring as close as possible to your zero size (although it really doesn't have to hit it you just need to know what size it is), and measure it as many ways as you can, even to going to a friend's and using different instruments (and people) and get a very close actual size. That's about the best you can do short of sending it to a metrology lab for calibration. Make the ID as smooth as you can without adding taper, barrel or hourglass shape. It will last longer. And no, don't use aluminum. Make it as thick walled as you can and keep everything at the same temperature.

Another way is to use part of a high end gage block set. One accessory that comes with a really full set is a device to allow a gage block stack to be held and a longer precision block clamped against each end of the stack that forms 2 parallel surfaces a precise distance apart. You might find one on ebay, or it's certainly something you could make.
 

rgray

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#9
I'll second that thought from tony on the gage block stacker.
I have also used a mic to set a bore gage and it is nothing but a finicky thing. If you have a heavy mic holder it helps.
I've been gonna build a gage block stack holder but have not gotten around to it yet.
 

Sitting on Blocks Racing

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#11
So I got my ring gages. I also brought everything in the house to bring the part temps up to 70 degrees.

Please check my math and reasoning
I got a 45mm XX Edmunds gage = 1.7716"
Set the Dial bore to 0 with the ring Gage. Measured the rod bearing size got .0022 larger (yes I had to interpolate the .0002) so the bearing bore 1.7716+.0022= 1.7738'
Crank measured 1.7708

Clearance 1.7738-1.7708=.003 clearance
 

JimDawson

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So I got my ring gages. I also brought everything in the house to bring the part temps up to 70 degrees.

Please check my math and reasoning
I got a 45mm XX Edmunds gage = 1.7716"
Set the Dial bore to 0 with the ring Gage. Measured the rod bearing size got .0022 larger (yes I had to interpolate the .0002) so the bearing bore 1.7716+.0022= 1.7738'
Crank measured 1.7708

Clearance 1.7738-1.7708=.003 clearance
Your math looks correct.
 

Wreck™Wreck

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#13
Set a micrometer with blocks, ring gauges are far easier to use however you will need thousands of them to cover the bore gauge range in tenths.
 

Wreck™Wreck

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#15
Actually there is no special holder needed, set micrometer with blocks, a mic stand is nice but a vice works fine I often use large toolpost blocks for this. Set bore gauge and have at it.

What is a "dial gauge holder"?
 

Tony Wells

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#16
There is a small but important caveat to setting a bore gage with either a micrometer or gage blocks, or any flat surface method. Bore gages have, in general, some mechanism to center themselves in the bore. There are a few different way this is accomplished, but with wear, they often fail to do a perfect job of centering the measuring contacts. The result is that the measuring contacts, which should touch the bore only at the true diameter line, geometrically described as a straight line across the bore that contains the center point of the bore, are pushed off to one side, off the diameter line, resulting in a false reading. It will always read smaller than the actual bore size because of this. That's the main reason gage rings are superior to any other means of setting bore gage. Just something to bear in mind.
 

Sitting on Blocks Racing

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#17

royesses

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