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TomSimon
Samba Member
Joined: January 13, 2004
Posts: 751
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 Posted: Fri Nov 22, 2019 11:30 am Post subject: Re: Plastigauge, torque specs, mock-up questions |
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| jpaull wrote: |
| Please don't anyone buy that bore gauge that Tom linked to from SUMMIT. I have that exact one, and the spring pressure is too much for bearings... |
I just looked that particular one up quickly, I bought my Chinese dial bore gauge 20yrs ago.
If you found one you'd recommend, Paul, post up a link 
I also wanted to add that if you go the automotive machinist route, he can also fix, 'tighten' up a loose rod to crank clearance, also by resizing the big end of the rod. He has to grind the interface of the cap, where it clamps to the beam half of the rod face, remove maybe .001". The hole now becomes (American) football shaped. Then he just hones it round again to the new correct inside diameter.
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67 Sunroof
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Joined: February 22, 2014
Posts: 1836
Location: Salisbury, MD
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| Posted: Fri Nov 22, 2019 11:31 am Post subject: Re: Plastigauge, torque specs, mock-up questions |
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Tom-
Thanks for the time you took and the information you provided. I will have to digest it later as I am work but thanks for the thorough explanation on what tools are necessary.
I appreciate it very much!! |
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jpaull
Samba Member
Joined: February 22, 2005
Posts: 3466
Location: Paradise, Ca
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| Posted: Fri Nov 22, 2019 11:33 am Post subject: Re: Plastigauge, torque specs, mock-up questions |
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| Brian_e wrote: |
I have a china bore gauge set from Ebay bought years ago. It will put a mark on the bearing coating, but it won"t scratch it. Cant feel it with a finger nail, and it will polish right off.
Wonder if you could pull yours apart and snip a coil off the spring?
Brian |
Thats a good idea! |
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raygreenwood
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Joined: November 24, 2008
Posts: 21519
Location: Oklahoma City
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| Posted: Fri Nov 22, 2019 1:38 pm Post subject: Re: Plastigauge, torque specs, mock-up questions |
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| jpaull wrote: |
Please don't anyone buy that bore gauge that Tom linked to from SUMMIT. I have that exact one, and the spring pressure is too much for bearings. Its perfect for cast iron cylinder bores though. My guess is that a different brand would have a lighter spring for the tension, and could be used for rod bearings. If that spring pressure is adjustable, or if someone else has that summit model and had success, speak up. For the sake of others, I would love if mine is the only one, but just in case, I wouldn't rush out and order that model for the purpose of rod bearings or any other soft bearings.
Snap gauges can mess up bearings too as Tom mentioned, but if your careful they work just fine.
Tom is correct, dial bore gauge is THE way to go. Just get one that has a light spring pressure or can be adjusted so the pressure is not so heavy. |
I have that gauge...and it DOES have the problem you list....far too much spring pressure.
However....that takes less than a minute to fix. Remove the gauge, unscrew the bottom tool section and pull out the "transmission" rod. Remove the spring. You can always put it back.
The tool itself is actually quite good. However...even the dial gauge that comes with it has a little too much spring pressure for my tastes. If you happen to already own a good standard diameter dial gauge....you can put that one right into this tool after you unscrew the foot.
I use this exact tool with my Starret .0001 dial gauge and it holds its own with a couple of Sunnen gauges I have played with as well.
As you note....low spring pressure is the key to not screwing up bearings. Ray |
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chrisflstf
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Joined: February 10, 2004
Posts: 3444
Location: San Diego
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| Posted: Fri Nov 22, 2019 2:23 pm Post subject: Re: Plastigauge, torque specs, mock-up questions |
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These are what I use. The bore gauge set I bought on ebay for just over $200.
The pics are upside down, sorry bout that
Last edited by chrisflstf on Fri Nov 22, 2019 4:22 pm; edited 1 time in total |
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rugblaster
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Joined: March 31, 2016
Posts: 1171
Location: San Angelo, Texas
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| Posted: Fri Nov 22, 2019 3:11 pm Post subject: Re: Plastigauge, torque specs, mock-up questions |
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If you get complaints about to much pressure put a little lube (oil) on the tip of your hard shaft or plunger, if you will.
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65calvw
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Joined: January 17, 2012
Posts: 19
Location: San Diego
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| Posted: Fri Nov 22, 2019 3:11 pm Post subject: Re: Plastigauge, torque specs, mock-up questions |
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I'm curious how accurate Plastigauge is compared to a micrometer. Only an idiot would let a rod or crank ROTATE before taking a measurement of the Plastigauge. I wouldn't trust that person to use a micrometer either. I just want to be clear when we talk about using calipers, micrometers, etc., we use them properly. Sure, I've used the edge of a putty knife to twist out a screw but I'm not returning it to Home Depot because I (some idiot) bent it.
Last edited by 65calvw on Fri Nov 22, 2019 3:32 pm; edited 1 time in total |
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Glenn 
Mr. 010
Joined: December 25, 2001
Posts: 76938
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| Posted: Fri Nov 22, 2019 3:24 pm Post subject: Re: Plastigauge, torque specs, mock-up questions |
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| 65calvw wrote: |
| Only an idiot would let a rod or crank ROTATE before taking a measurement of the Plastigauge. I wouldn't trust that person to use a micrometer either. |
If you've installed and torqued a rod to a crank, you'd know how hard it is to keep the rod from rotating when you remove the rod bolts and split the cap from the rod.
In a V8 the small end is held by the piston, the crank is in the block and the rod cap and bolts are accessed from the bottom where the oil pan would be.
Try not moving the rod on a vw.
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TomSimon
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Joined: January 13, 2004
Posts: 751
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| Posted: Fri Nov 22, 2019 5:14 pm Post subject: Re: Plastigauge, torque specs, mock-up questions |
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^^^^^^^^ This ^^^^^^^
| Glenn wrote: |
If you've installed and torqued a rod to a crank, you'd know how hard it is to keep the rod from rotating when you remove the rod bolts and split the cap from the rod.
In a V8 the small end is held by the piston, the crank is in the block and the rod cap and bolts are accessed from the bottom where the oil pan would be.
Try not moving the rod on a vw.
] |
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Brian
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| Posted: Sat Nov 23, 2019 3:04 am Post subject: Re: Plastigauge, torque specs, mock-up questions |
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That makes much more sense.
So, assume a jig that held the crank and rods in place: then plastigauge would be accurate?
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FreeBug
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Joined: March 12, 2012
Posts: 4278
Location: deepest, darkest Switzerland
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| Posted: Sat Nov 23, 2019 3:15 am Post subject: Re: Plastigauge, torque specs, mock-up questions |
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| chrisflstf wrote: |
These are what I use. The bore gauge set I bought on ebay for just over $200.
The pics are upside down, sorry bout that |
I have the same Mitutoyo bore gauge. 54$ on Ebay. Somedays you get really lucky. There were lots of other guys on it, but somehow, it worked out.
That's a nice set of calipers, all-in-one.I had to get mine one at a time. And I'm super lazy, so I got the ones with the mechanical-digital readouts. I still have one to find, the 50-75mm. And the 0-25 is Etalon, a local brand, very good. |
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TomSimon
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Posts: 751
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| Posted: Sat Nov 23, 2019 7:48 am Post subject: Re: Plastigauge, torque specs, mock-up questions |
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| FreeBug wrote: |
| And the 0-25 is Etalon, a local brand, very good. |
Etalon is definitely tool room quality, some inovative designs on some of their very high accuracy products.
you're very fortunate to have them nearby, maybe they have an occasional 'scratch and dent' Saturday parking lot sale?
At the end of the day, a tool is just a tool, hopefully my example of using mid-grade mics and a mid grade dial bore gauge resonates with the inexperienced, that you aren't looking for an 'absolute' diameter numbers, but a comparison when it comes to bearing clearance.
I'm headed to a friend's house this morning, loading up my cheap tubing notcher and hole saws, Harbor Freight die grinder, we will cobble together a chassis jig before we back-half his drag car chassis. If the wheel base comes out 94", 95", we really don't care, so long as the left wheel base and the right wheel base are within 3/32" or better, and our diagonal measurements are within 3/16" of one another with the trans squared up in the frame horns.
You'd be amazed at what you can get away with if you are careful, and consider the foundations of geometry and really, metrology, when taking on a task you don't do very often.
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FreeBug
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Posts: 4278
Location: deepest, darkest Switzerland
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| Posted: Sat Nov 23, 2019 9:02 am Post subject: Re: Plastigauge, torque specs, mock-up questions |
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| TomSimon wrote: |
| FreeBug wrote: |
| And the 0-25 is Etalon, a local brand, very good. |
Etalon is definitely tool room quality, some inovative designs on some of their very high accuracy products.
you're very fortunate to have them nearby, maybe they have an occasional 'scratch and dent' Saturday parking lot sale?
At the end of the day, a tool is just a tool, hopefully my example of using mid-grade mics and a mid grade dial bore gauge resonates with the inexperienced, that you aren't looking for an 'absolute' diameter numbers, but a comparison when it comes to bearing clearance.
I'm headed to a friend's house this morning, loading up my cheap tubing notcher and hole saws, Harbor Freight die grinder, we will cobble together a chassis jig before we back-half his drag car chassis. If the wheel base comes out 94", 95", we really don't care, so long as the left wheel base and the right wheel base are within 3/32" or better, and our diagonal measurements are within 3/16" of one another with the trans squared up in the frame horns.
You'd be amazed at what you can get away with if you are careful, and consider the foundations of geometry and really, metrology, when taking on a task you don't do very often. |
Sadly, Etalon was in Rolle, about 25 miles away...but they were baught up by Tesa. But, yeah, you occasionally find good tools in garage sales, lots of machinists and watchmakers closed down... |
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Zundfolge1432
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Joined: June 13, 2004
Posts: 12467
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| Posted: Sat Nov 23, 2019 6:07 pm Post subject: Re: Plastigauge, torque specs, mock-up questions |
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| chrisflstf wrote: |
These are what I use. The bore gauge set I bought on ebay for just over $200.
The pics are upside down, sorry bout that |
Unless you are high then they look great 👍 I like em. |
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raygreenwood
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Posts: 21519
Location: Oklahoma City
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| Posted: Sat Nov 23, 2019 7:58 pm Post subject: Re: Plastigauge, torque specs, mock-up questions |
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| Brian wrote: |
That makes much more sense.
So, assume a jig that held the crank and rods in place: then plastigauge would be accurate? |
Yes....and its not actually that hard to do. I have a sturdy wioden cradle I made for the current sloooow build Im doing now. It holds the crank horizontally by two main journals. I lock it where I need it with the flyhweel on one end. The rods hang down and Iock the one I am working in a small flat machine vise with brass plates on the jaws that bolted to the base.
Its just not that hard to devise a holding device if you want to backstop check your dial bore gauge.
I made this...precisely because I was swapping around between several sets of rod bearings....and repeated chdcking with the two dial bore gauges I have was lightly scratching the surface. I later fixed that by removing the spring and using a dial gauge in the hand piece that had lower spring pressure.
How accurate is plastigage?.....its accurate enough ....or more precisely....its repeatahle enough (if it was well stored and not mangled) but the real question is what is its tolerance?
I have found the tolerance to be about a +/- of .0005". Thats a spread of .001" ish.....on the Green plastigage. If the temperature tolerance alone is "somewhat" linear like with most plastics...the thicker the material....the wider the tolerance. So the red is less accurate.
This is the problem with plastigage. Humidity, temperature, working time and poswibly eveb incompatible oils used on the journal.....can cause variation.
But it works ok for a quick backstop check. Ray |
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jpaull
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Joined: February 22, 2005
Posts: 3466
Location: Paradise, Ca
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| Posted: Sun Nov 24, 2019 11:56 am Post subject: Re: Plastigauge, torque specs, mock-up questions |
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| raygreenwood wrote: |
| jpaull wrote: |
Please don't anyone buy that bore gauge that Tom linked to from SUMMIT. I have that exact one, and the spring pressure is too much for bearings. Its perfect for cast iron cylinder bores though. My guess is that a different brand would have a lighter spring for the tension, and could be used for rod bearings. If that spring pressure is adjustable, or if someone else has that summit model and had success, speak up. For the sake of others, I would love if mine is the only one, but just in case, I wouldn't rush out and order that model for the purpose of rod bearings or any other soft bearings.
Snap gauges can mess up bearings too as Tom mentioned, but if your careful they work just fine.
Tom is correct, dial bore gauge is THE way to go. Just get one that has a light spring pressure or can be adjusted so the pressure is not so heavy. |
I have that gauge...and it DOES have the problem you list....far too much spring pressure.
However....that takes less than a minute to fix. Remove the gauge, unscrew the bottom tool section and pull out the "transmission" rod. Remove the spring. You can always put it back.
The tool itself is actually quite good. However...even the dial gauge that comes with it has a little too much spring pressure for my tastes. If you happen to already own a good standard diameter dial gauge....you can put that one right into this tool after you unscrew the foot.
I use this exact tool with my Starret .0001 dial gauge and it holds its own with a couple of Sunnen gauges I have played with as well.
As you note....low spring pressure is the key to not screwing up bearings. Ray |
Great tip! |
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