Plastigauge
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Instructor
Joined: Jun 2005
Posts: 119
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From: Ringgold Georgia
Plastigauge
I am pulling my motor soon for a cam and cam bearing change. I want to check my rod and main bearing tolerances. I plan to use plastigauge. Has anyone used it? How does it work best? What should my main and rod tolerances be?
Racer
Joined: Jul 2005
Posts: 301
Likes: 0
From: Dallas/Spring Texas
1. Get new plastigauge from a parts store. (as stated above)
2. Get the motor on a stand and flip it over.
3. Install new main bearings in block and caps paying close attention to the markings on the bearings as they will read upper and lower and with the engine flipped over it's the opposite of the way it would normally be.
4. Make sure the surfaces of the crank and bearings are clean.
5. Lay the crank in the bearings and avoid turning the crank.
6. You'll get different opinions on this, but I like to torque them all down first and then remove them one at a time to check individually.
7. With the cap removed, cut a strip of pg almost the width of the bearing surface and lay it on the crank journal widthwise at the 12 o'clock position (or right on top, however you want to look at it).
8. Torque down the cap bolts as per specification (which I don't know right off the top of my head, but you should be using the green pg that is .001-.003 so it will be in that area).
9. Remove the cap bolts and cap and use the paper part of the pg to see what range the pg has spread out to. The width that the pg spreads out to is directly proportional to the amount of clearance between the bearing and journal. More clearance=thinner pg, less clearance=wider pg. You'll see what I'm talking about when you get the pg in your hand. After determining the clearances, use a lint-free towel with brake clean on it to remove the pg from the bearing and journal surfaces.
10. Repeat the procedure for all of the remaining caps and when completed remove all the caps and take the crank out and lubricate all of the main journal and bearing surfaces with assembly lube and reinstall the crank.
11. For the rods you want to do basically the same thing. Start by installing one rod and piston with the bearings. Pay close attention that it is installed in the correct position. I would start at #1 and work my way back one at a time.
12. Rotate the crank so that the rod journal is up and install the piston/rod combo until the rod contacts the journal.
13. Cut a strip of pg so that it goes almost across the rod journal widthwise and place it on the journal at 12 o'clock.
14. Torque down the rod bolts/nuts without turning the crank.
15. Remove the rod bolts/nuts and cap.
16. Check the clearance as above using the paper from the pg and compare it with specs. After the clearance has been determined, use brake cleaner on a clean lint-free towel to remove the pg that is on the bearing or journal.
17. Tap the piston/rod into the cylinder enough that you can lubricate the bearing surface with assembly lube and do so. Also lubricate the rod bearing in the cap and install the cap, torque to specs.
18. Repeat the procedure for the remaining rods/pistons.
19. Bathe in the glow of a properly assembled engine.
2. Get the motor on a stand and flip it over.
3. Install new main bearings in block and caps paying close attention to the markings on the bearings as they will read upper and lower and with the engine flipped over it's the opposite of the way it would normally be.
4. Make sure the surfaces of the crank and bearings are clean.
5. Lay the crank in the bearings and avoid turning the crank.
6. You'll get different opinions on this, but I like to torque them all down first and then remove them one at a time to check individually.
7. With the cap removed, cut a strip of pg almost the width of the bearing surface and lay it on the crank journal widthwise at the 12 o'clock position (or right on top, however you want to look at it).
8. Torque down the cap bolts as per specification (which I don't know right off the top of my head, but you should be using the green pg that is .001-.003 so it will be in that area).
9. Remove the cap bolts and cap and use the paper part of the pg to see what range the pg has spread out to. The width that the pg spreads out to is directly proportional to the amount of clearance between the bearing and journal. More clearance=thinner pg, less clearance=wider pg. You'll see what I'm talking about when you get the pg in your hand. After determining the clearances, use a lint-free towel with brake clean on it to remove the pg from the bearing and journal surfaces.
10. Repeat the procedure for all of the remaining caps and when completed remove all the caps and take the crank out and lubricate all of the main journal and bearing surfaces with assembly lube and reinstall the crank.
11. For the rods you want to do basically the same thing. Start by installing one rod and piston with the bearings. Pay close attention that it is installed in the correct position. I would start at #1 and work my way back one at a time.
12. Rotate the crank so that the rod journal is up and install the piston/rod combo until the rod contacts the journal.
13. Cut a strip of pg so that it goes almost across the rod journal widthwise and place it on the journal at 12 o'clock.
14. Torque down the rod bolts/nuts without turning the crank.
15. Remove the rod bolts/nuts and cap.
16. Check the clearance as above using the paper from the pg and compare it with specs. After the clearance has been determined, use brake cleaner on a clean lint-free towel to remove the pg that is on the bearing or journal.
17. Tap the piston/rod into the cylinder enough that you can lubricate the bearing surface with assembly lube and do so. Also lubricate the rod bearing in the cap and install the cap, torque to specs.
18. Repeat the procedure for the remaining rods/pistons.
19. Bathe in the glow of a properly assembled engine.
