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Unread 07-22-2010, 11:55 PM   #1
michla
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1989 XJ Cherokee 
 
Join Date: Nov 2008
Location: Wasilla, AK
Posts: 148
valve spring installed height and spring pressure

I know, I know ...call me a PERFECTIONIST !
I'm setting up 4.0 heads for my Cherokee engine rebuild, want to shim the new stock springs to affect the same cam nose pressure on all 12 springs. Even though the springs are new, all new valve springs will vary slightly as a normal manufacturing thing.

Problem is, manual says "Valve closed height is 1.625 @ 66-74 *lbf* which is foot-pounds. The manual shows using a beam torque wrench on an old-fashioned lever-arm spring tester. For example: 66-74 ft-pounds of lever-arm pressure could actually translate into something like 100 pounds on a inline direct-pressure tester...depending on the length of that lever-arm as displayed in the manual!

Therefore, does anybody know the INLINE spring pressure that should be @ 1.625" installed height in valve-closed position? I have a platform-type inline spring tester with a gauge showing actual pounds of pressure, intended to be used in a bench vise.

Yes I realize most folks just install the springs as is and call it good, but I like a real smooth-running engine with even cam nose pressure all the way across the valves. Yes I realize coil bind is the MOST important issue (too much shim).


Last edited by michla; 07-23-2010 at 12:22 AM..
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Unread 07-23-2010, 07:09 AM   #2
djb383
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1998 XJ Cherokee 
 
Join Date: Jan 2010
Location: The Republic of TEXAS
Posts: 2,201
I would say you're waisting your time on valve spring pressures. The biggest improvement to the 4.0 valve train would be installing "full roller" type rocker arms. The valve springs on a Jeep 4.0 have only a little more pressure than the spring in a click-type ball point pen. LOL As you have already mentioned, concentrate on spring height valve closed. Also, you can't beat doing a final valve polish/grind by hand. It takes time and effort to do this but even a 400 lb valve spring won't seal a valve that doesn't have a perfect sealing surface (face to seat). Make sure the block deck and head surface are dead flat and use the best head gasket you can find. Torque the head bolts in at least 4 passes. Pay close attention when setting the initial valve lash.
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Unread 07-23-2010, 08:27 AM   #3
michla
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1989 XJ Cherokee 
 
Join Date: Nov 2008
Location: Wasilla, AK
Posts: 148
Thanks for that good advice....I did find spring manufacturer specs for set-up online last night. LOL--you're so right about stock springs...the really don't last very long either (tension).

By the way, there is no lash adjust on these hydraulic tappets. Just using stock components--this is just a daily-driver/grocery-getter.
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Unread 07-23-2010, 08:40 AM   #4
90si
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1998 XJ Cherokee 
 
Join Date: Feb 2007
Location: Mission
Posts: 104
sbc springs and a change in rocker arm ratio smooths it out nice too ..even with a big cam
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Unread 07-23-2010, 10:05 AM   #5
djb383
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1998 XJ Cherokee 
 
Join Date: Jan 2010
Location: The Republic of TEXAS
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Quote:
Originally Posted by michla View Post
..........By the way, there is no lash adjust on these hydraulic tappets.........
Yes, there is an initial rocker arm adjustment/setting for hydraulic lifters, check the manual for the correct procedure. No feeler/thickness gauge is used and seldom does a hydraulic lifter/valve train need additional adjustment but it's not unheard of. Mechanical lifter/valve trains need frequent checking/adjustment.....at least they do in a push-rod motor.
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Unread 07-23-2010, 10:12 AM   #6
djb383
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1998 XJ Cherokee 
 
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Location: The Republic of TEXAS
Posts: 2,201
Quote:
Originally Posted by 90si View Post
sbc springs and a change in rocker arm ratio smooths it out nice too ..even with a big cam
Smooth and big cams usually don't go together and anyone will be well advised that they need to be really sharp/educated on valve train geometry when changing from stock...........that goes for any motor.
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