Crankshaft replacement

Tiny
UNEAK82
  • MEMBER
  • 2001 JEEP CHEROKEE
  • 4.0L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 175,000 MILES
Cherokee Sport 4.0L i6. I have had a low oil pressure problem when vehicle is up to running temperature. PSI eventually drops to zero when idling after engine is at running temperature. My vehicle overheated a couple years back. The radiator/cooling system was replaced. Shortly thereafter came these problems with oil pressure. Eventually I discovered a crack in the 0331 tuppy head between cylinders 3 and 4. I have most recently replaced the cracked head with a brand new head from clear-water, but before the crack was discovered, the oil pump was replaced following the replacement of the oil sending unit. Now after all of that, we disassembled the lower engine to inspect crankshaft bearings. Thus far this is the result using SPG-1(green) for 0.001" TO 0.003" plastic gauge.

Connecting rod clearances(1-6)
[+/-.00001" for error]
1-less than or equal to 0.00175"
2- less than or equal to 0.002"
3-less than or equal to 0.00175"
4-less than or equal to 0.00175"
5-less than or equal to 0.002"
6-less than or equal to 0.002"

Main bearings(not fully completed)

1-
2-
3-
4-
5-
6- 0.00175" [(+/-) 0.00001" for error]

So I am wondering what the desired clearances should be along with the torque specs. Additionally, any suggestions or advice would be much appreciated, preferably from someone that has experienced this issue with the 2001 Cherokee Sport 4.0 i6. There has been a lot of forums with other people in my same situation. I hope to find the definite problem and equally importantly, the solution. Hopefully to minimize the chances someone else will have to deal with all of this issue.
Thank you,
Greg
Sunday, November 4th, 2018 AT 12:45 PM

6 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 43,665 POSTS
Hello,

Here are the tolerances and torque specs for the crankshaft and rod bearing with fitting guides below.

1. Tighten the bolts of main bearing caps # 1, 2, 4, 5, 6 and 7 in three steps.
- Step 1: 54 Nm (40 ft. lbs.)
- Step 2: 95 Nm (70 ft. lbs.)
- Step 3: 108 Nm (80 ft. lbs.)

2. Push the crankshaft forward and backward. Load the crankshaft front or rear and tighten main bearing cap bolt # 3 in three steps.
- Step 1: 54 Nm (40 ft. lbs.)
- Step 2: 95 Nm (70 ft. lbs.)
- Step 3: 108 Nm (80 ft. lbs.)

3. Install main bearing cap brace and tighten nuts to 47 Nm (35 ft. lbs.).

Here is how you use a torque wrench:

https://youtu.be/juOClONIWeY

Check out the diagrams (below). Please let us know if you need anything else to get the problem fixed.

Cheers, Ken
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Monday, November 5th, 2018 AT 4:03 PM
Tiny
MJ-AV8
  • MEMBER
  • 1 POST
  • 2001 JEEP CHEROKEE
Engine Mechanical problem
2001 Jeep Cherokee 6 cyl Four Wheel Drive Automatic

what causes the rankshaft not to turn on the # 6 cylinder when the rod bearings are torched down to specs? We have replaced the pistons because some have cracked and decided to replace the bearings also. Alll will rotate except 6 which stops the engine cold head is completly off
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Wednesday, November 7th, 2018 AT 9:22 AM (Merged)
Tiny
CJ MEDEVAC
  • MECHANIC
  • 11,004 POSTS
LOTS of possibilities. Torque specs correct. ROD CAP ON BACKWARDS
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Wednesday, November 7th, 2018 AT 9:22 AM (Merged)
Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
Hi there,

As Mr TD (strange name in deed) has mentioned there are a number of possibilities that could cause this, I would be checking that you have all the caps on the correct rods, did you number them? That No 6 is not reversed, that the bearing is clean as is the journal, did you do an oil clearance measurement with flexi gauge, this should be done as well, check these items and re post your findings.

Mark (mhpautos)
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Wednesday, November 7th, 2018 AT 9:22 AM (Merged)
Tiny
RED101803
  • MEMBER
  • 1 POST
  • 2001 JEEP CHEROKEE
  • 146,000 MILES
Looking for the specs on the crankshaft so I know if I need to polish or grind them plus I need to know what bearings to buy.010.020.030
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Wednesday, November 7th, 2018 AT 9:22 AM (Merged)
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
CRANKSHAFT End Play 0.0015 to 0.0065 in
Main Bearing Journal Diameter No. 1-6 2.4996 to 2.5001 in
No. 7 2.4980 to 2.4995 in
Main Bearing Journal Width No. 1 1.086 to 1.098 inch
No. 3 1.271 to 1.273 inch
No. 2-4-5-6-7 1.182 to 1.188 inch
Main Bearing Clearance 0.001 to 0.0025 in
Preferred 0.002 in
Connecting Rod Journal Diameter 2.0934 to 2.0955 in
Connecting Rod Journal Width 1.070 to 1.076 inch
Out-of-Round (MAX) 0.0005 in
Taper (MAX) 0.0005 in
Main Bearting Cap - Bolt 80 ft. Lb
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Wednesday, November 7th, 2018 AT 9:22 AM (Merged)

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