3.7L 02 vs 03 and Later Bedplate and Cylinder Head Bolt Tightening

[Shankster]

Hello everyone. I'm new to the forum and also to Jeeps. I bought a 02 Liberty Limited 4x4 3.7L with a spun rod bearing about a month ago. I just got everything back from the machine shop and I'm ready to reassemble the motor.

My apologies if this has been asked and answered before but I can't find an explanation here or anywhere else.

So here's my question. I've downloaded the 02 shop manual and also the 03 and 06 shop manuals. The bolt tightening method for both the bedplate and the cylinder heads are very different on the 02 when compared with the 03 and later model years. So is there something different about the 02 motor or did Chrysler see a problem and revise the specs? In other words, should I follow the 02 process or should I go with the later process?

 

[LibertyTC]

Welcome.
That is a very good question. Possibly the dealer only may know why the differences?
Considering you own a 2002 model year, I would use the recommended torque/sequence/ & specifications from the 2002 factory service manual.

 

[ltd02]

I did the bedplate (replaced Crankshaft) and heads (HG replacement) on my departed 02. I followed the 2002 FSM and had no issues. I would recommend doing the same.

 

[Shankster]

Thanks guys. I'm still not sure which way I should go but I'm actually leaning towards using the 2003+ procedure. After hours of searching I can't find any difference between the 2002 motor and the 2003 motor leading me to believe the only thing that changed was the procedure because there were problems with the 2002 manual's procedure. And I suspect there may not be anything technically wrong with that 2002 procedure but that it had the potential for larger error and repeatability issues than the newer method. After jumping between manuals trying to get a feel for what the end torque result of each method might be I decided to put them in a table to compare side by side:

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Disclaimer - nobody should use this as a guide to bolt stuff down - you need to read the manual since things need to be done in a specific order and there are other critical details provided in the manual.

For the bed plate, I'm betting Chrysler got feedback from dealer mechanics saying the 2002 process was just silly complicated and that the engineers need to come up with something simpler and more repeatable. I don't know what the difference in a couple of degrees might make but I don't have much confidence in myself to hit 32 degrees exactly for example - it's probably going to be somewhere in the 25 to 40 degree range - maybe that's significant? maybe not? I'll likely wait another day before I dive in and hopefully in the meantime someone comes up with some actual history to guide my decision - I have other stuff I can do but getting anxious seeing all those shiny parts lying around that need to be attached to one another.

For the cylinder heads, I now see that there was just a typo in the manual - I assumed there really were 14 bolts on each head when there are actually only 12 - I'm wondering if they just used the manual for the 4.7 V8 as a template and missed that detail? I'll use the 2003+ process.

 

[Shankster]

Sorry, I obviously don't know how to link to an image - will try to figure that out and include the table

 

[Shankster]

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[sleazy rider]

Torque wrenches are available for torque plus angle. I’d check one of the local auto parts places to see if they lend one. More than a few degrees variance does make a difference in my experience.

I’d also recommend following your year manual.

 

[Shankster]

Still haven't decided which way to go but getting really antsy - was going to call the dealer tomorrow (Monday) but not real confident they'll go to the trouble of cornering a mechanic (an old, experienced mechanic, if they even have one). Not sure if I can stand to twiddle my thumbs all day today with so much assembly work to do.

By the way, I got a response back from "Car And Truck Engines 4less" out of Hialeah Gardens, FL. His entire email response was:

"Hello
Use the later process"

These engines are one of their specialties and apparently they go with the 03+ process on 02s. I wish he had elaborated a bit more but this encourages me to go with my gut and use the 03+ process.

 

[Shankster]

Not sure if I'll ever figure out the whole story with the different methods but I went with my gut and used the later process. I doubt there is much difference in the end and I haven't lost any sleep over the last 3 days which is hopefully a good sign. I promise I'll report back if anything bad happens (or even if I get a slight oil leak).

Anyway, I appreciate everyone's input and opinions, even if I went a different direction.

Thanks
Robert