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Help with plastigage process/tolerances, please
- Thread starter 2wrench
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Banjo
Yoda
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Plasti-guage is simple. You take off the bearing cap, clean off the oil from the bearing and the journal , break of a length of plasti-guage and lay it across the journal. it should run across the face, not with the curve. then carefully replace the bearing cap, and torque it to spec. Then remove the bearing cap again (being careful not to let the crank rotate while all this is happening) and use the guage printed on the side of the paper packaging to measure how much the plasti-guage "squished". the wider it squished out, the tighter your tolerance.
you also want to varify that the "squish" is equal across the entire width of the journal. If not, that may indicate a tapered or otherwise unevenly worn journal.
Your specs vary a bit depending on which engine your working on.
I can't remember what you have. TR6?
you also want to varify that the "squish" is equal across the entire width of the journal. If not, that may indicate a tapered or otherwise unevenly worn journal.
Your specs vary a bit depending on which engine your working on.
I can't remember what you have. TR6?
poolboy
Yoda
Online
I can tell you how to use it and I'd be interested to know the tolerances myself.
The plastigage is made in specific diameters, when squashed between the journal and the bearing insert by the correct torque, it will flaten out to a measureable width. That width can be measured and compared to the illustration on the package. That will give you the annular space or clearance in question.
The plastigage is made in specific diameters, when squashed between the journal and the bearing insert by the correct torque, it will flaten out to a measureable width. That width can be measured and compared to the illustration on the package. That will give you the annular space or clearance in question.
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Most main & rod bearing clearances will run between 0.0015" & 0.0025". anything tighter or looser may cause problems.
D
D
OP
2wrench
Luke Skywalker
Offline
Sounds easy enough. I have two choices for use.
Red: .002 to .006
or
Green: .001 to .003
My car is a '74 TR6. Which do you recommend I try first?
Need to know for my car what the most acceptable spec
is. Knowing this could answer question above re
red or green.
Note further: Crank was renewed and bearings are
new. This is a double-check on machine work
recommended by the Forum. It was suggested I check the connecting rod bearings as well.
Thanks,
Red: .002 to .006
or
Green: .001 to .003
My car is a '74 TR6. Which do you recommend I try first?
Need to know for my car what the most acceptable spec
is. Knowing this could answer question above re
red or green.
Note further: Crank was renewed and bearings are
new. This is a double-check on machine work
recommended by the Forum. It was suggested I check the connecting rod bearings as well.
Thanks,
OP
2wrench
Luke Skywalker
Offline
DNK said:
Don: I would be willing to bet the machine shop did check this. Gordo
mentioned that, nonetheless, he had a situation where one of the journals
was machined so poorly, he had to correct the problem before installation --
actaully, maybe a couple different instances were mentioned.
I think it was recommended as not a bad idea to take a look at these
tolerances. Sounds like good advice to double-check things. Could be
considered cheap insurance.
OP
2wrench
Luke Skywalker
Offline
Hmmm, Paul. It has been recommended not to turn
the crank without lube. All lube is wiped off to do the
test.
I did read mention of turning the crank 30 degrees or
so after torquing caps down, then removing cap and
checking the squish/spread.
I know it's simple, but it is starting to sound a little
confusing. It is as if the crank has to be turned
maybe 30 degrees to facilitate the squish; and then
turning it again to check the next bearing?
I thought instruction was not to turn the crank at
all at one point. I'm a bit confused.
the crank without lube. All lube is wiped off to do the
test.
I did read mention of turning the crank 30 degrees or
so after torquing caps down, then removing cap and
checking the squish/spread.
I know it's simple, but it is starting to sound a little
confusing. It is as if the crank has to be turned
maybe 30 degrees to facilitate the squish; and then
turning it again to check the next bearing?
I thought instruction was not to turn the crank at
all at one point. I'm a bit confused.
Offline
Re: Help with plastigage process/tolerances, pleas
Use the green. If it's tighter than .001" or looser than .003", there are problems. It's ok to have a light film of oil on the parts. Keeps the plastic from sticking so tightly. As Paul said, DON'T turn the crankshaft while the plastic is in the bearing. It will just smear it & make it hard to accurately measure the squished width. After you have checked a bearing, remove the plastic & move on to the next one.
D
Use the green. If it's tighter than .001" or looser than .003", there are problems. It's ok to have a light film of oil on the parts. Keeps the plastic from sticking so tightly. As Paul said, DON'T turn the crankshaft while the plastic is in the bearing. It will just smear it & make it hard to accurately measure the squished width. After you have checked a bearing, remove the plastic & move on to the next one.
D
Brosky
Great Pumpkin
Offline
Re: Help with plastigage process/tolerances, pleas
2W,
Set the crank in place with plenty of oil on the journals. You can turn it a few times and it should turn freely with no rods connected. If it doesn't stop right there and correct any problems. Maybe you've already done this and have the rods connected. Even so, by removing the oil, we only mean to wipe it lightly with a clean rag, leaving just a very light film on the journal. Do NOT use brake clean or anything lik e that to remove the oil.
After you crush the plasti-gauge and complete your measurement, re-oil that journal and bearing and reassemble.
2W,
Set the crank in place with plenty of oil on the journals. You can turn it a few times and it should turn freely with no rods connected. If it doesn't stop right there and correct any problems. Maybe you've already done this and have the rods connected. Even so, by removing the oil, we only mean to wipe it lightly with a clean rag, leaving just a very light film on the journal. Do NOT use brake clean or anything lik e that to remove the oil.
After you crush the plasti-gauge and complete your measurement, re-oil that journal and bearing and reassemble.
Brosky
Great Pumpkin
Offline
Re: Help with plastigage process/tolerances, pleas
PB,
Squashed worked for me...I knew what you meant.
It's no fun doing any of this unless you're on your back, in the cold and working with oil dripping down into your eyes while you're trying to read a 1960's style torque wrench
PB,
Squashed worked for me...I knew what you meant.
It's no fun doing any of this unless you're on your back, in the cold and working with oil dripping down into your eyes while you're trying to read a 1960's style torque wrench
