Just Picked Up A 4.2...

[Jr. Mechanic]

Found a complete running 4.2 for $150 out of a 1990 YJ. It seems to be in overall good shape however I haven't torn it down.

The 4.0 in my 1993 ZJ is at the point where the blow by is pushing oil out the dipstick tube, so the plan is to pull the engine and send the block over to be checked out and bored .060 over for a 4.7L along with having the crank ground and or polished with the rods resized with ARP bolts.

From what I've gathered, I can use stock .060 over pistons with the 4.2 rods and crank, correct? What will my CR be? Obviously I need to do all of these calculations before and during the build, but I just picked up the engine tonight and am looking to get on the right path.

I plan on adding a 99+ intake manifold as well as a header and I already have 703 injectors and will most likely add an adjustable FPR as well. I am undecided as to what cam I'm going with. Are any of the Comp kits compatible with the 4.0, more specifically the valve springs that are included?

My goal for the build is as much power as possible while staying on a budget. Somewhere around 250-275hp would be ideal. I don't mind running premium fuel either.

This is the overhaul kit I was looking at:

http://www.ebay.com/itm/JEEP-4-0-242-94 ... 2d&vxp=mtr

[ftpiercecracker1]

your piston and rod combo will work, so long as you dont deck the crap out of the Block or head.
For the cam i wouldnt stray to far from stock specs Stock cam, stock springs, stock pushrods, solid lifters , from everything i have read the one thing that seems to be plaguing strokers is cam failures. Not sure what your CR will be, shouldnt be too hard to calulate.

Port and polish the head, oversize valves if you can, some sort of valve angle grind. The gentleman who is building my motor has about 50 years of experience and always says the cylinder head is where your real power can be unleashed.

Since your adding the 99 intake it would be a good idea to find an oversized TB so that your engine make use of the better air flow. I am running Jeff Leigh's 62mm TB, $90. Good guy to work with, he also has the FPR you need and a MAP adjuster dont know if you need this.

You are doing a build thats pretty much a mirror image of mine, only difference is that i will be doing using the long rods and forged pistons.

[Cheromaniac]

From what I've gathered, I can use stock .060 over pistons with the 4.2 rods and crank, correct? What will my CR be?

Yes, you can use those pistons and the CR will be ~9.7:1 without milling the block deck/head surface.

I am undecided as to what cam I'm going with. Are any of the Comp kits compatible with the 4.0, more specifically the valve springs that are included?

The CompCams 68-231-4 cam/lifter package would be a good way to go, but use the Mopar Performance 5249464 valve springs with MP 4452032 retainers and MP 4529218 valve keepers. The CompCams springs are way too stiff.

[Jr. Mechanic]

your piston and rod combo will work, so long as you dont deck the crap out of the Block or head.
For the cam i wouldnt stray to far from stock specs Stock cam, stock springs, stock pushrods, solid lifters , from everything i have read the one thing that seems to be plaguing strokers is cam failures. Not sure what your CR will be, shouldnt be too hard to calulate.

Port and polish the head, oversize valves if you can, some sort of valve angle grind. The gentleman who is building my motor has about 50 years of experience and always says the cylinder head is where your real power can be unleashed.

Since your adding the 99 intake it would be a good idea to find an oversized TB so that your engine make use of the better air flow. I am running Jeff Leigh's 62mm TB, $90. Good guy to work with, he also has the FPR you need and a MAP adjuster dont know if you need this.

You are doing a build thats pretty much a mirror image of mine, only difference is that i will be doing using the long rods and forged pistons.

Most flat tappet cam failures are due to improper initial break in as well as using modern conventional oil with a low zinc content and/or an improper cam and spring combination. Break the cam in correctly with some Rotella and a bottle of ZDDP or break in oil designed for flat tappet cams and you'll rarely have an issue so long as your spring pressures are correct.

I'm fairly unfamiliar with names in the stroker world... Who is Jeff Leigh? $90 for a TB isn't bad at all, I already have the taper removed from mine so it's 60mm all the way through but for $90 I'd probably grab one.

Anyways, I tore down the 4.2 to a short block today. Overall, the engine is a beauty so I'm extremely optimistic about the crank and rods. The cross hatching is still in the cylinders, there was absolutely no carbon or sludge build up ANYWHERE, the pistons only had a slight film of carbon. No ridge in the cylinder to speak of. Hopefully the crank won't need ground and will be good to go with a polishing.

9.7:1 is exactly where I want to be (just under 10:1). I don't mind running premium and I'm more interested in short term reliability with maximum power. I've put 30,000 miles on this Jeep in the last four years, so there's no way I'll need another 200,000 out of it like the original motor. I'll probably just have the block surface ground and not decked.

As far as the head, I'm torn on what to do. It was just fully checked out and rebuilt 40,000 miles ago (my brother was the previous owner) so I know it's in good shape. My initial plan was to do a quick grind on the valves and replace the seals when I change out the springs. I would also spend some time opening up the ports and gasket matching the manifolds. However I'm well aware the stock valves will create a bottle neck and will greatly reduce the engine's potential which makes me want to pony up the money and do it right.

On the other hand, if I match the cam right I should get more than adequate results with the stock valves and a little bench time with the die grinder considering this is a budget build for a daily driver.

Thoughts?

[SilverXJ]

your piston and rod combo will work, so long as you dont deck the crap out of the Block or head.
For the cam i wouldnt stray to far from stock specs Stock cam, stock springs, stock pushrods, solid lifters ,

stock lifters were not solid.

oversize valves if you can,

I have never seen any proof that larger valves do any good

some sort of valve angle grind.

3 angle valve job maybe?

Most flat tappet cam failures are due to improper initial break in as well as using modern conventional oil with a low zinc content and/or an improper cam and spring combination. Break the cam in correctly with some Rotella and a bottle of ZDDP or break in oil designed for flat tappet cams and you'll rarely have an issue so long as your spring pressures are correct.

x2

I'm fairly unfamiliar with names in the stroker world... Who is Jeff Leigh?

http://www.strokedjeep.com/ good guy to deal with, good work.

[ftpiercecracker1]

Dont know why i put solid lifters, Ment to say stock. hydraulic right?

As for the Valves, i have seen/heard a LOT of guys using LS1 valves or the like, i figured that wouldnt be too bad of an idea, bigger valves let the head flow more air in and out with each cycle, right?

Performance valve grind, 3, 4, 5, whatever your hearts content. Although i am really not sure what it does, I have yet to hear of a single build that did not include this.

[Cheromaniac]

As for the Valves, i have seen/heard a LOT of guys using LS1 valves or the like, i figured that wouldnt be too bad of an idea, bigger valves let the head flow more air in and out with each cycle, right?

Paradoxically that doesn't appear to be the case with the 4.0 head. Bigger valves, especially the exhausts, cause more shrouding which hurts low lift flow. The port sizes also limit how far it's worth going with bigger valves so it's probably better to stick with stock sizes.

[SilverXJ]

As for the Valves, i have seen/heard a LOT of guys using LS1 valves or the like, i figured that wouldnt be too bad of an idea, bigger valves let the head flow more air in and out with each cycle, right?

as dino said, larger valves don't help. There are some LS1 valves that are near identical to stock dimensions. However, they are lighter and give you more spring, retainer and lock options. With out being larger (or too large). Hesco's aluminum head comes with stock sized valves a well.

Performance valve grind, 3, 4, 5, whatever your hearts content. Although i am really not sure what it does, I have yet to hear of a single build that did not include this.

Instead of throwing terms and words around it maybe a better idea to understand what you are saying.

[ftpiercecracker1]

Performance valve grind, 3, 4, 5, whatever your hearts content. Although i am really not sure what it does, I have yet to hear of a single build that did not include this.

Instead of throwing terms and words around it maybe a better idea to understand what you are saying.

Probably. So then go right ahead, esplain it tu meh.

But i will say this, at least i am not throwing out completely bogus and undocumented figures, Example: my head is going to recieve a 3 angle grind, part of his basic head rebuild. 4 and 5 angle vavle grinds are also fairly commonplace and have been proven beneficial.

[SilverXJ]

http://www.tomboracing.com/2011/02/comp ... explained/
http://www.enginebuildermag.com/Article ... _flow.aspx

Two good starts at reading up.

[Jr. Mechanic]

Back on topic:

After weeding through all the information out there, here's what I've come up with:

With the 4.2 rods and stock .060 over pistons, I will actually have a 9.9:1 CR. Now, this combination would net a quench of .073" using a Mopar Performance head gasket (.043" compressed thickness +.030" deck height). This is obviously a fairly high quench, and even if I had the block decked .010" that would still leave my quench at .63" and my CR would be up to 10.1:1.

What pistons will have the correct pin height to get my quench tighter?

On another note, I got the 4.2 completely torn down and the crank looks beautiful! Couple of pics:

[SilverXJ]

You can deck the block to get the deck clearance down. As far as pistons you can get a custom piston with the 4.2L rod, or KB 944 or Bulltear pistons with the 4.0L rod or a 4.0L rod with a custom piston.

I hope you get that crank checked out and at least polished before use. Some of those scratches don't look like will polish out.

[Jr. Mechanic]

You can deck the block to get the deck clearance down. As far as pistons you can get a custom piston with the 4.2L rod, or KB 944 or Bulltear pistons with the 4.0L rod or a 4.0L rod with a custom piston.

I hope you get that crank checked out and at least polished before use. Some of those scratches don't look like will polish out.

None of the scratches are deep, the pictures are deceiving. The crank is actually in amazing shape. I plan on having it checked however I am very confident all it needs is polished.

Decking the block will put my CR too high with the stock .060 pistons. What other pistons are available to use with the 4.2 rods?

[SilverXJ]

From the FAQ forum: http://www.jeepstrokers.com/forum/viewt ... ?f=34&t=67

[Jr. Mechanic]

From the FAQ forum: http://www.jeepstrokers.com/forum/viewt ... ?f=34&t=67

If I went with these:

http://www.summitracing.com/parts/slp-h ... /overview/

What would the 1.592 compression distance do compared to the stock pistons?

If I were to leave my deck height alone and go with the .073 quench, what would the negative effects be other than definitely requiring premium fuel? Is there a thinner head gasket available than .043?