2nd Rebuild, 1st Stroker

[goatbrother70]

ALCON,
First, thanks for reading,.....cuz I need the help. I rebuilt my 1990 4.2 a while back to get EFI on it, all is good, it runs like a champ. I want to put in a stroker motor (take out the 4.2 and replace with 4.0 block/head and 4.2 crank, etc), but am overwhelmed by the pure number of posts here. I have an idea of what I would like to do and would appreciate some "hand-offs" to other posts if my logic is just whacked. So here goes......

My plan is to get a 4.0 from the junkyard, then re-build and stroke for a one-for-one swap in my Jeep.
- I plan on no machine work on the head (other than magnaflux to make sure it's good and basic valve job/cleaning/ etc).
- I plan on a .030" overbore on the cylinders. Putting in Silv-O-Lite Hypereutectic Pistons 3242HC-030
- Planning to re-use the stock 4.0 connecting rods
- Ordering a refurbished 4.2 crank from Advance Auto
- Plan on the CompCams 68-231-4 206/214 for the cam
- Head Gasket of 0.043"
The above plan (computed in the Static/Dynamic Compression Ratio Calculator) brings me to a Dynamic Compression Ratio of 8.4........oh and I live at 2000 feet altitude.

My questions revolve around what is "reliable" and what needs replacement. I would like to know your opinions on:
- Valves - Do I really need to change them?
- Valve Springs - seen a few posts about upgrading to the performance Mopar ones, does it make a difference?
- What other things on this type of build would be "OK" to re-use?

I sincerely appreciate your help -- Ken

[RenoF250]

You cannot use those pistons with 4.0 rods, you need 4.2 rods or the IC944s. You will also need new bigger injectors.

[6TIME]

Your stock valve springs will not like the Comp 231. I would strongly recommend using the proper springs with that cam..

[Cheromaniac]

- I plan on a .030" overbore on the cylinders. Putting in Silv-O-Lite Hypereutectic Pistons 3242HC-030
- Planning to re-use the stock 4.0 connecting rods
- Ordering a refurbished 4.2 crank from Advance Auto
- Plan on the CompCams 68-231-4 206/214 for the cam

As RenoF250 said you cannot use the 4.0L connecting rod/Silvolite piston combination with the 4.2L crank in a 4.0L block. You'll either need to use the shorter 4.2L rods with the longer Silvolite pistons or the longer 4.0L rods with shorter Keith Black IC944 pistons. The latter is a better choice.
You'll need to use Mopar Performance #5249464 valve springs with #4452032 retainers & #4529218 keepers (assuming single groove stems).

[akadeutsch]

I agree that your stock valve springs will present problems if you use the 232 or 231 Comp cam. The lift is greater with the comp cam and I dont think the stock Valve springs are able to compress enough to open that far. But I am not sure.
Also, Keith Black now makes two piston choices that will work. The 944 is dished 21cc's while the other, 945 is dished out only 10.8ccs. the 945 will produce greater compression. But both will work with the stock 4.0 rods.