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-   -   2002 KJ 3.7L Engine Rebuild (http://www.jeepforum.com/forum/f19/2002-kj-3-7l-engine-rebuild-1498781/)

dhole 03-25-2013 10:13 AM

2 Attachment(s)
I am the lucky recipient of a dropped valve seat. Since I am having to replace the heads and pistons I figured I will go the extra step and do a complete rebuild. This is the first time I have messed with the 3.7L engine. Are there gotchas I should be aware of prior to going forward with my endeavors? Any help would be appreciated.

headlayoutman1 03-27-2013 03:05 PM

I have repaired the exact same failure on three 02'-03' Libertys that I have worked on in the past 10 months , this is pretty common failure on early 3.7s. #2 cylinder intake valve seat drops out of the head and holds the valve open , piston hits valve and destroys head , piston , or piston & cylinder wall . , I have been lucky on two of the repairs , no damage to the piston or cylinder walls , just had to replace two cylinder heads , got rebuilt heads from Odessa Cylinder Heads in Florida , both ran like new . On the I other had to pull the engine and replace or completely rebuild the engine , due to the #2 piston scoring cylinder wall after the valve seat and valve contacted the piston .
From the looks of your picks you will probably have a scored cylinder wall , but it might not be trashed and you might be able to hone that cylinder , and get buy with one new piston and ring set , a rebuilt head , and a gasket set .

dhole 03-27-2013 03:32 PM

I pulled the other head and some of the pieces must have traveled through the intake manifold because there is damage on two other pistons and the head. The cylinder walls weren't that bad. They are getting bored out. With that and the pistons being changed would you suggest getting the motor rebalanced?

headlayoutman1 03-27-2013 05:18 PM

Should not have to , if you are going to hang your connecting rods on new pistons and make sure that each rod goes back to its original cylinder . If your using a set of quality pistons & rings , check your ring end gap in each cylinder and make any corrections before installing the rings onto the pistons . I have replaced pistons without balancing and not had any problems . The thing to do is , - if your reusing your standard size crankshaft with new main bearings , make sure to use MOPAR main bearings , since the main bearings are "select fit" to the crankshaft , there is a four digit letter code on the rear side of the crankshaft tone wheel ( on one of the teeth ) each letter corresponds to each main bearing journal size , the code is read left to right and indicates mains 1 thru 4 ( 4 being the rear journal ) Have your crank polished and checked for straightness , and then check your main bearing clearances with plasti-gauge . If you decide to have your crank reground to nearest undersize you can get the appropriate generic brand main bearing set for your cranks new size .
If you use a standard size generic brand main bearing set on your standard size polished crank you may have clearance issues or low oil pressure , because they may not be matched to your "select fit" journal size(s) .
Rod bearings you can go either way just match your cranks size with a bearing set of your choice

dhole 03-27-2013 05:30 PM

Quote:

Originally Posted by headlayoutman1
Should not have to , if you are going to hang your connecting rods on new pistons and make sure that each rod goes back to its original cylinder . If your using a set of quality pistons & rings , check your ring end gap in each cylinder and make any corrections before installing the rings onto the pistons . I have replaced pistons without balancing and not had any problems . The thing to do is , - if your reusing your standard size crankshaft with new main bearings , make sure to use MOPAR main bearings , since the main bearings are "select fit" to the crankshaft , there is a four digit letter code on the rear side of the crankshaft tone wheel ( on one of the teeth ) each letter corresponds to each main bearing journal size , the code is read left to right and indicates mains 1 thru 4 ( 4 being the rear journal ) Have your crank polished and checked for straightness , and then check your main bearing clearances with plasti-gauge . If you decide to have your crank reground to nearest undersize you can get the appropriate generic brand main bearing set for your cranks new size .
If you use a standard size generic brand main bearing set on your standard size polished crank you may have clearance issues or low oil pressure , because they may not be matched to your "select fit" journal size(s) .
Rod bearings you can go either way just match your cranks size with a bearing set of your choice

Thanks that helps a lot.

headlayoutman1 03-27-2013 05:35 PM

Also get new connecting rod cap bolts . Don't reuse your rod cap bolts , they are "torque to yield" and should not be reused on final assembly .
But you may reuse your old bolts only to check your rod bearing clearances with plasti-gauge , Then install your new bolts on each rod and torque to spec. after it has been checked. Then move on to the next rod and repeat


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