entropy
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posted August 07, 2005 09:34 AM
 Edited By: entropy on 8 Aug 2005 03:28
measuring the mains - part II
OK, all the talk of plastigauge vs direct measurement got me wondering, and as i am waiting on pistons, i did an experiment.
(this IS my senior science fair project, afterall  )
1. measured the mains (blues), journals & bearings, with micrometer & bore gauge. Measurements were consistently .0001-2 higher than when i did it last week, but resulting clearances were almost identical (.0019-.0023).
2. I then plastigauged em:
- WTF???? way tighter; like .0013-.0018
- so i cleaned the oil from the back of the shells, and plastigauged em dry. loosened em up some, but still 4-6 tenths tighter than direct measurement.
- so i put the blacks in and plastigauged em again. Predictably, they were .0005 looser, but still the plastigauge indicated 4-tenths tighter than the direct measurement i did on the blacks last week.
conclusion:
1. my plastigauge showed measurements about .0005 tighter than direct measurement.
2. both methods were within spec (.0012 -.0025)
This is pretty fun, but i am starting to run out of experiments; pistons coming next week.
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gunner
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posted August 07, 2005 12:05 PM
I have always felt that platigauge smears a little and gives an indication of tighter clearances. Just my own idea of what happens with this stuff. Being a tool maker by trade
(even though I don't do that anymore) I like direct measure with a Dial Bore gauge and a non molested set of mics.
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osti33
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posted August 07, 2005 12:17 PM
quote:
I like direct measure with a Dial Bore gauge and a non molested set of mics.
Me too.
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entropy
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posted August 08, 2005 04:28 AM
the question is, why should the plastigauge method indicate clearances 4-6+/- tenths LESS than direct measurement??????
This may be "mike-ing a brick" (pun intended), but I am curious.
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gunner
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posted August 08, 2005 06:30 AM
quote:
the question is, why should the plastigauge method indicate clearances 4-6+/- tenths LESS than direct measurement??????
This may be "mike-ing a brick" (pun intended), but I am curious.
Smearing is my guess.
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psycho1122
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posted August 08, 2005 07:09 AM
entropy;
Did you "wedge" feeler guages between the rods and crank throws??
This will keep the rod from "twisting" when torque is applied, thus preventing the "smearing" effect.
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entropy
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posted August 08, 2005 09:20 AM
nope, no smearing apparent.
This is on MAINS, not rods. the plastigauge "string" was carefully placed at 12 o'clock of all 5 main journals, then the lower case was c-a-r-e-f-u-l-l-y placed on its dowels, and bolted down.
my 1st results were so different (and consistently so) from my direct measurements, I did it a 2nd time with the blues, then changed all shells, and did it a 3rd time with blacks.
hmmmmmmmm???????????
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VincentHill
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posted August 08, 2005 12:29 PM
When you say 12 Oclock, (Top Center? Straight across?) Being me, I lay mine diagonal across so that it can run in the groves caused by the rotating crank.
Also, did you switch the tight and lose bearing and measure?
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dougmeyer
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posted August 08, 2005 03:35 PM
Plastigage= a smushed strip of plastic wherein the smushed width is expected to be consistent with the amount of smush regardless of the ambient temperature and the age ond/or hardness of the plastic and then said width is determined by eyeballing a printed strip of ink on a porous piece of paper...........
Micrometer and bore gauge= precision instruments certified to accuracy within .0001" or better when checked against a standard gauge certified by methods and standards used throughout the industrial world........
Mmmmm, I wonder.........
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VincentHill
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posted August 08, 2005 04:28 PM
GOOD to hear from the Real Doctor Using his tools.
Telescoping Bore depth Gauge read by another Micrometer. two tools I must use feel with. Between using my eyes or Hands which do I trust Mmmmm I wonder (Being Old and Eyes Gone and Hands lacking the Feel) (A :Few: things I can still feel  )
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entropy
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posted August 08, 2005 10:50 PM
quote:
When you say 12 Oclock, (Top Center? Straight across?) Being me, I lay mine diagonal across so that it can run in the groves caused by the rotating crank.
Also, did you switch the tight and lose bearing and measure?
VH
1. i don't know what grooves you are talking about
2. yes i did switch 1 & 5 bearings, no appreciable difference
also
"Telescoping Bore depth Gauge"
do you mean a bore gauge with dial indicator (good), or one o' those telescoping "T" things (not good)
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entropy
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posted August 08, 2005 10:55 PM
quote:
Plastigage= a smushed strip of plastic wherein the smushed width is expected to be consistent with the amount of smush regardless of the ambient temperature and the age ond/or hardness of the plastic and then said width is determined by eyeballing a printed strip of ink on a porous piece of paper...........
Micrometer and bore gauge= precision instruments certified to accuracy within .0001" or better when checked against a standard gauge certified by methods and standards used throughout the industrial world........
Mmmmm, I wonder.........
Bahahahahahahahahahahaha....
Doug, you gotta admit that at least my questions are slightly more educamated than they were 4 years ago
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VincentHill
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posted August 09, 2005 07:15 AM
No difference OK That was my real question.
And like you say without the Dial gauge "NO GOOD" with the Dial guage better. I first had the ones without he dial gauge for measuring the cylinder wear, Taper and out of round
SInce the crank rotatesit makes microscopic grooves in the Surface. Laying it straight across also has the disadvantage of the peaks and valleys the rotation causes. AKA Wear!
I am going to get the (a lot more) expensive tool and see what I see the next time the engine is apart.
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TedG
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posted August 11, 2005 01:19 PM
TEMPERATURE, TEMPERATURE, Temperature. Relative clearances are what are important.
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ninja12
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posted August 11, 2005 02:12 PM
Why are the "T" gages no good?
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scooter trash
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posted August 11, 2005 03:13 PM
quote:
No difference OK That was my real question.
And like you say without the Dial gauge "NO GOOD" with the Dial guage better. I first had the ones without he dial gauge for measuring the cylinder wear, Taper and out of round
SInce the crank rotatesit makes microscopic grooves in the Surface. Laying it straight across also has the disadvantage of the peaks and valleys the rotation causes. AKA Wear!
I am going to get the (a lot more) expensive tool and see what I see the next time the engine is apart.
Bypass Harbor Freight here. ;-)
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kram
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posted August 11, 2005 03:48 PM
I was so anal when I used plastigage, I would even put the cases together using silicon sealer cuz i thought it might make a wee bit difference when I torqued down the mains. Plastigage = good shit!
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entropy
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posted August 11, 2005 11:06 PM
Edited By: entropy on 12 Aug 2005 00:08
quote:
Why are the "T" gages no good?
ninja12,
It's not that the the T gauges are NO GOOD, its more that it is MUCH, MUCH easier to get consistent measurements with the bore gauge (& dig mike). Its a pure PITA to get reproducible numbers at the .0001" level.
I have a set of T's and a vernier micrometer but couldn't do it it consistently. Went to the bore gauge and a digital micrometer (accurate to .00005") and everything clicked.
As Ted and VH point out above, the temp of the piece being measured surely does change the dimensions day by day, but the relative clearance does not really change.
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ninja12
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posted August 12, 2005 10:54 AM
gotcha,
What do you recommend?
Do you like this one?
http://www.toolweb.com/itemdetail.cfm?partno=FOW74-646-401
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VincentHill
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posted August 12, 2005 12:02 PM
quote:
gotcha,
What do you recommend?
Do you like this one?
http://www.toolweb.com/itemdetail.cfm?partno=FOW74-646-401
Use [url] and [/url ] (with no spaces so that we can click on them) and not for you only.
Yes, that is the type of gauge
My explanation on what makes the "T" Not as good is, #1, your feel when using the "T" and then using the Mic on the "T" feel. Using this Dial removes one entire feeling process the reason for the Ratchet on the end of mics to keep the feeling the same (Like using SAE HP)
It is expensive to have good tools. It is even more expensive "NOT" To use good tools! The difference is, you only pay for the tool once, not using them you pay over and Over again!
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entropy
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posted August 12, 2005 12:10 PM
Edited By: entropy on 12 Aug 2005 13:12
ninja12,
I am not at all competant to recommend, but that Fowler is the one i have. The min bore it will go into is 1.4".
If you wanna fool with this process, you will need a good set of 1-2" micrometers. I 110% suggest you get a digital which has an resolution of .00005". About $200 but a VERY cool instrument.
I am not at all sure this stuff is needed, but it sure is FUN!
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