Recomendations

[fedrusion]

Maybe I was a little nieve after I read the article here, http://www.ajeepthing.com/stroker-motor, which I'm sure everyone has seen and read many times. I originally thought I could simply swap all stock parts from a 4.2 and 4.0 into one engine install it throw in a cam and be able to run on low-mid grade pump gas.

I have since then realized that this may not be as easy as I first thought.

What I'm looking for is recomendations or ideas that will let me use as many stock components as posible since I am trying to build this on a tight budget.

I have a complete 88 4.2 and a complete 98 4.0 to start with. based on this selection of parts to start with I realize I have a couple directions. Any will use the 4.2 crank and 4.0 block.

If I use 4.2 rods and stock 4.0 pistons:
Can stock pistons be dished and how far? My concern with this is opening porosity in the castings and creating hot spots that will cause ping.

If I use the 4.0 rods and custom pistons:
What kind of performance diference positive or negative could be atributed to the use of these rods?
What should I look for in a custom piston?


I'm sure there are other things I should be considering and concerned with but cannot think of them now.

[1bolt]

Oh man there are SO many possible builds, each one has something to recommend it, I bet each person on here, whether they've built one or two or none; has a build he would like to try or a combination he wishes he could have done, a part he could afford or whatever.

The first question anyone is going to ask is undoubtedly: what will you use the engine for primarily? And depending on that answer How much can you spend, and how much can you do by yourself?

[Shark]

i am also interested in finding out how much the stock pistons can be dished.

[oletshot]

I dished my stock pistons to 23cc's. I found they were actually thicker than the silvolite 2229s that people machine to 26+ cc's. My pistons weren't the metric pistons as yours are. I would assume they are different castings. I haven't assembled my engine yet either, so I have no idea on reliability yet.

There are many benefits (as I'm sure you know) of custom forged pistons/4.0 rod combo:
1. Strength (forged vs cast/hyper).
2. Ability to set proper quench by setting the pistons at zero deck height at TDC (having the piston come closer to the surface of the head without hitting causes more air movement during compression stroke which has a cooling effect, reducing ping and allowing higher compression ratios without ping).
3. Custom dish allows you to set compression ratio to your builds requirements (especially important to forced induction).
4. The rod angle of the 4.0 rod vs 4.2 rod is less severe (less side load on the piston as it travels up and down in the bore, only a few degrees different though).
5. The 4.0 rod/piston will not come out of the bore as much as the 4.2 rod/off-the-shelf piston will at BDC (there is only about .050" difference, because the 4.0 rod/piston start out at zero deck, about .050" higher than the 4.2/piston depending on the off-the-shelf piston choosen).

Since this is in the Basics section, I tried to quickly give some explanation of the benefits.

One of the members here says you can buy custom forged pistons directly from Diamond pistons for $450 a set. It's unclear to me if they come with matched wrist pins, if they do this sets up an excellent situation. Apply the $$$ saved by not having to buy 4.2 rods to the custom pistons. This will make up some of the high cost of the custom pistons and may bring it as close as $100-$150 difference. A smll price to pay for all the benefits of the custom piston, IMHO. Since you already have your rods this doesn't apply, unless you sell them and apply that $$$ to the pistons.

As 1bolt stated, many combos, and even more opinions.

[fedrusion]

I totaly forgot to mention my goals for this engine, this will be going in my 99 Auto XJ which is my daily driver, I will ocasionally be wheeling it but it will primarily see street use so I am also shooting for it to run on 87-89 octane pump fuel. I'm hoping that if I shoot for low test and it pings I can step up a fuel grade to get by. As far as my budget??

I have not set a dollar figure but I want to spend only what I absolutely need to, ie minimal machining and as many stock parts as possible between the two engines that I have. So far between the 4.0 and 4.2 I am up to $150 total. Some of the machining needed I am sure I can have done at work. I have accepted that some extra $$ will need to be spent so I can run on lower grade fuel.

A couple more questions I have are:
With the 4.0 Rods and shallower angle will these produce more torque than the shorter and steeper 4.2 Rods?

With the 4.0 rods am I to understand that less machine work would be required on the block to achieve my quench height?

How much of a factor has piston size played into everyones builds? I would like to try to use stock sized 4.0 pistons if possible to help minimize the total machine work required since this is one thing I dont think I can have done at work.

Some info about the engines:
4.2 pulled from 88 YJ with approx 200K for a fresher motor. $50

4.0 Pulled from 98 XJ with 70-80K for a "performance built" motor. $100

Both were in running condition when pulled. So far I have disassembled the 4.2 and have left the 4.0 untouched.

Do you have any pictures of how the dished stock pistons turned out? Any recomendations on How to dish pistons properly?

What are the available head gasket thiknesses? Does anyone use a thicker gasket in order to maintain close to stock quench and CR?

[seanyb505]

I cant answer a few of those questions but here are the ones I can:

If you use stock 4.0 pistons you will not need to bore out your cylinders UNLESS there is damage to the walls. Even if you dont have them bored they should be honed.

It cost the same to deck the block .001 and .04. If you need to do anything any machining at all to achieve desired quench it will cost the same for 4.2 and 4.0 rods.

A good machine shop can dish out pistons properly.

There are several head gasket thicknesses: .052" .051"(Stock) .050" .043" .032". They effect CR and quench differently. A smaller than stock gasket will increase the CR (depending on what CR you are starting with this may not be a good thing), and will decrease the quench compared to stock which is good (stock quench is not that good, so decreasing quench is good). The Fel pro .052" gasket will result in a lower compression than if a stock or smaller gasket is used, but will increase quench (try not to do that). A good quench is around .040"-0.060". Since the Fel-pro is already .052", you will have to add that to how far down the hole your piston sits at TDC. If you have zero deck height, the best quench you can get with a .052" head gasket is .052". From what Ive read a good quench will help offset a high CR. I hope that helps..

[oletshot]

You and I are doing almost the same thing. Only difference is the year of our 4.0's. My plans are take running 4.0 and 4.2, and build a stroker. It will be '90 4.0 block with '88 4.2 crank and rods, '90 stock pistons dished to 23cc's, '94 HO head (junkyard) and intake, clevite 229-2174 cam and lifters, mopar perfomance pushrods (ebay).
The '90 block was donated from my rusting cherokee and the '88 4.2 was a $50 craigslist find. Top end of the 4.2 had just been rebuilt, unfortunately no use to me. Crank was in great shape so I'm not grinding it.
I tried to keep my numbers close to stock to keep from having pinging problems and still run 87-89 octane. The nice thing about reusing the stock pistons is the pin height, pistons are .008" lower in the hole than a stock 4.0. You can make up that .008" by using the .043" head gasket, so quench matches stock. I then machined the pistons to try to match the stock static compression ratio. I'm hoping for 30-40 more HP and more torque than stock 4.0. I'm a tool & die maker and I program and run a CNC mill all day long, so I was able to machine the pistons myself. I'll post pictures of the pistons later.

The top of the block and the head are flat, so no machining to be done. I honed the cylinders with a three stone hand drill hone, only a little practices to achieve a nice cross hatch. Pistons cleaned up well. I had planned on buying new ones and started messing around with the stock ones. They cleaned up so well, that I started checking dimensions for fit and machining dish. Dishing was not a problem, fitting the bore is a little out of tolerence, .003" clearance between piston and bore on 5 cylinders and .0035"-.004" on 1 cylinder. I bought cast rings as I hear the seat quicker than moly (beside if your going cheap might as well be consistent). Time will tell if slaps and smokes, I joke that if it does I'll put a CRD badge from a liberty on it.
Seems to me put custom pistons in a block that your trying to build with as little machining as possible is like putting a diamond on a polished turd, my opinion. It sounds nasty and I don't mean it that way at all, remember I'm polishing my turd also.

[fedrusion]

Those are the numbers I was trying to get using the calculator, I must have overlooked that gasket thickness, since I have pistons from both the 4.2 and 4.0 I will use the 4.2 pistons to play around with at work and test dishing them before I try to do the one I want to use.

I'm hoping that reliability will be as good as stock as long as I dont use any sub-stock quality parts.

[oletshot]

Here are the pictures of my pistons that you asked for. Sorry it took so long. I had go with my wife and get groceries. I did stop at Carquest and picked up my Victor Reinz head gasket, though.

[John]

Good looking work, What thickness did you have before and after cutting.
John

[oletshot]

Thanks, they were .250" thick at the thinnest area and up to .300" thick at the thickest area after machining. Before machining I measured from the top face of the piston (not dished area) to the inside face and got .480" thick. I wish I had documented this better, I would have better answers for you.

[John]

Thank you, I just keep too many notebooks with important things like this written down.
John

[fedrusion]

I was envisioning something more complicated for the shape of the dish, what you have there looks very easy to achieve. I will defenitly look at dooing that as soon as I asses the condition of the pistons I have.

That is one very green block.

[oletshot]

Yes it is. We wanted something unusual. As far as the shape, it's a copy of the stock dish only deeper.

[fedrusion]

How deep is the dish measured from the face of the piston?