4.0 Conversion questions.

[Will]

I have been trying to wrap my head around a 4.0 conversion for some time now.  So far all I've come up with is questions.    Having a spare engine means I don't have to rush.  I just want to make sure all my ducks are in a row before I purchase a 4.0 head.  The eagle is an  83 SX4 with a three speed auto.  What I have so far on the wish list is as follows:  New head, headers, clifford intake, and a weber carb.

Some questions for anyone who knows. 

1) What are the proper rocker preload specs?
2) What push rods will I be using? 4.2 or 4.0
3) Are there any major (or minor) changes that will need to be made to the engine block or engine components to ensure a proper balance with the 4.0 head? 
4) Are there any engine rebuild spec changes that I should be aware of as of a 4.0 head swap?

Sorry all.  That was more then a few questions.

Best,

Will

[amc78concord]

Here is the best write-up you'll ever read for a 4.0L head swap from Tougeagle.

http://forums.amceaglenest.com/index.php?topic=31874.0

[thereverendbill]

I would just go with what tougeagle did and go 4.0 head and EFI.  He outlined everything really well and appears to be happy with the outcome

[shanebo]

Ill second that Bill....I have seen tougeagles Eagle in person and it is quite impressive to say the least. Im going that route on mine as well...loads more power...better fuel economy..and overall better reliability.

[Will]

I'm also thinking out of curiosity - Is there anything you can do your 4.2 head to bring it up to snuff, or is the conversion the the best way one should go in order to see significant head improvements?

[amc78concord]

I'm also thinking out of curiosity - Is there anything you can do your 4.2 head to bring it up to snuff, or is the conversion the the best way one should go in order to see significant head improvements?

4.0 head is the best way to go.  The 4.0 head has for one a better angle for the valves.  The 4.2 head takes a 90 degree turn for the fuel to travel, whereas the 4.0 head is a little angled for it to flow better

[Will]

Posted this question in another topic, but never got a response.  Guess i'll try this one. 

More posts then not never mention the 4.0 cam swap with the 4.0m head conversion.  Why is this?  Basically, why does it appear that most people are not switching their cams when doing the conversion? 

[amcinstaller]

probly preference. i dont have the two cam specs (or more if you want every style of 4.0 cam) in front of me to compare, but they do have slightly different profiles. but whatever cam you use, unless you get new lifters, use the lifters that were already on that cam, in the positions they were originally. cams and lifters dont find new mates very well.

[shanebo]

The 4.o cam has higher lobes. the stock 4.2 cam is rather whimpy in comparison. push rods and lifters should be replaced to compensate the higher lift of the cam. The stock cam will likely not provide enough lift to allow the 4.0's valves to function to they're full ability..also the 4.0 cam does not have the extra lobe that cranks the fuel pump...a block off plate will need to be installed to block off where the engine mounted fuel pump is and an electric fuel pump will need to be installed.

Im about to tackle this project too...Ill keep ya posted if I run across any issues.
good luck man!!
shane

[Will]

thanks so much shane.  keep me posted. 
best,

Will

[Will]

anyone know for certain the compression difference between the 4.2 and the 4.0?

[Whuntmore]

Here's another good write-up on that

http://www.jeepstrokers.com/forum/viewtopic.php?f=6&t=24

[shanebo]

I believe the 4.0 is running around 8.8 :1 compression  and if im not mistaken i think the 4.2 is running 9.2 :1 I could have the 2 reversed I had looked it up some time ago.

[Draekon]

I believe the 4.0 is running around 8.8 :1 compression  and if im not mistaken i think the 4.2 is running 9.2 :1 I could have the 2 reversed I had looked it up some time ago.

In 1981 the 4.2 was running 8.0:1 compression.  I think this figure increased somewhat over the years, but don't have the exact numbers

[shanebo]

Ya know I think your right...the 4.0 had the higher compression...I had them mixed up