cheap jeep stroker

[wolfesgreenxj]

I have 91 4.0 out of a auto yj. I also have a 4.2 out of a older standard yj. Im planing on building a stroker motor out of the two. My plan is to take the crank an rods out of the 4.2 an put in the 4.0 with the stock 4.0 pistons. Would i be able to do that and it work?

[SilverXJ]

Are you planning any machine work or just swapping?

[wolfesgreenxj]

Planing on just swaping. I took the 4.2 crank out today an it was in good shape an didnt have any grooves wore in it. I plan on doing a diy port an polish on the head but thats it.

[SilverXJ]

Bad idea. Just swapping parts with out machine work and proper checking will lead to an early death for the engine.

[wolfesgreenxj]

I got 3 laying around so i aint worried. The 91 4.0 im building only has 59,000 miles an runs like a top an the 4.2 has low miles an still ran. Im planing on buying new bearings an putting it together. Im not asking how long it will last. Im just asking if it will work?

[wolfesgreenxj]

The crank would have been balanced from the factory so i aint worried about it an i can balance the pistons an rods myself an i can check everything myself without paying a shop to do it for me. Im just not totally sure about the quench an all that.

[Cheromaniac]

Have a machine shop check the cylinder bores for roundness and taper. If they're within factory tolerances and there are no ridges at the top of the bores, just have them lightly rehoned and you'll be good to go with standard bore pistons.
If you're going to reuse your original pistons (with new rings of course), be careful not to damage the piston pins when separating them from the original rods as you'll need to use them again.
If you use the 4.2 crank/rods with OEM 4.0 pistons in a 4.0 block, the deck clearance will be ~0.030" and displacement will be 4516cc (4.5L). Add a Victor-Reinz 0.043" MLS head gasket and the quench will come in at 0.073" (same as a stock 4.0). However the CR will be much higher at ~9.8:1 so I recommend that you smooth/polish the combustion chambers/piston dishes to gain some volume and reduce the risk of detonation problems. You're going to need 91 octane fuel at a minimum anyway, possibly 93. Use colder Champion RC10LYC plugs.
The combination will work (especially since your 4.0 block is low mileage) but it's important that the cylinders are true and honed perfectly so you get good ring seal and avoid high oil consumption problems.

[akadeutsch]

Id like to know where you will be running this rig? Elevation can make a big difference in compression numbers.

[Cheromaniac]

Id like to know where you will be running this rig? Elevation can make a big difference in compression numbers.

At sea level he'd almost certainly need 93 octane. If it's not available in his location, it might be a good idea to carry a spare bottle of octane booster under the rear seat.

[wolfesgreenxj]

Thanks for the info. Ill be running it in ohio an it will only be used in a offroad rig so it wont see much road time. I might just go ahead and order the sealed power .30 over 677ap pistons an plan on doing a port an polish. Will it mater if the crank is out of a standard shift 4.2?

[Cheromaniac]

Will it mater if the crank is out of a standard shift 4.2?

No. If you're running an auto tranny, just simply leave the crank without a pilot bearing.

[darkcorp]

I am very interested in this "very poor man's stroker" configuration because here in Russia we got ruble devaluation and now everything from USA cost two+ times higher than before. For example those Keith Black UEM-IC944-030 pistons cost for me like $1000 + shipping.
Thanks god last year I got luck to buy my 258 crank here on forum. So I hope my stroker will be build finally.
I was going to buy Keith Black pistons and build 4.6L Modified "poor man's" stroker. But now I'm looking for cheaper way.
Maybe I can order to produse custom forged pistons here in Russia, but I need all dimentions and also need to find proper piston rings.
Another way - to find 4.2 rods and leave stock pistons as described here. My WJ has 280'000 kms but engine doesn't consume any oil and works ok. Maybe only to change piston rings.

Also is it better to buy all gasket set or order few nessesary gaskets? Complete gasket set is rather expensive.

[Cheromaniac]

Maybe I can order to produse custom forged pistons here in Russia, but I need all dimentions and also need to find proper piston rings.

if there's a company in Russia that can produce custom forged pistons, I'll help you out with the dimensions.

Another way - to find 4.2 rods and leave stock pistons as described here. My WJ has 280'000 kms but engine doesn't consume any oil and works ok. Maybe only to change piston rings.

Bad idea on such a high mileage engine. You'll need to have the cylinders rebored to make them round and true so you'll need oversize pistons if you're going to build the engine properly. Therefore you might as well buy a set of Bulltear custom pistons and reuse your 4.0L rods. A set of stock replacement 4.0L pistons plus 4.2L rods would probably end up costing about the same and the engine wouldn't perform as well.

Also is it better to buy all gasket set or order few nessesary gaskets? Complete gasket set is rather expensive.

It's better to buy complete upper & lower gasket sets.

[darkcorp]

Cheromaniac, thanks you so much.
Although for some reason bulltear's site doesn't open I found that their custom forged pistons aren't so much cheaper than Keith Black's.
So better way to produce set of pistons in my country. I know few firms that make custom forged pistons. But before I contact them I should prepare all the characteristics of pistons. So these will be close to IC944.
I have found in local shop +0.20" and +0.30 rings. Also I use LPG (propane) and ignition timing device for LPG, but I plan to travel the countries where fuel is bad quality.

[Cheromaniac]

But before I contact them I should prepare all the characteristics of pistons. So these will be close to IC944.
I have found in local shop +0.20" and +0.30 rings. Also I use LPG (propane) and ignition timing device for LPG, but I plan to travel the countries where fuel is bad quality.

If you're planning to build to this recipe, you'll find the piston specs in bold:

4.6L Modified "poor man's" stroker

Jeep 4.2L 3.895" stroke crank
Jeep 4.0L 6.125" rods
Custom forged +0.020" bore pistons, compression height 1.380", dish volume 26cc
9.25:1 CR
Stock 4.0 camshaft
Ported HO 1.91"/1.50" cylinder head
Mopar/Victor 0.043" head gasket
0.043" quench height
Ford 24lb/hr injectors for '87-'95 engines
248hp @ 4900rpm, 306lbft @ 3250rpm ('87-'95 camshaft)

The piston pin diameter will need to be the same as that of the stock pistons (0.931") with 5/64 in., 5/64 in., 3/16 in. ring grooves for standard size rings.