Project "Flying down a backroad"

[MJ H.O.]

Project "flying down a backroad" came about after some of life's challenges. In a way, the jeep brings me back in time and moves me forward. I like things simple and light weight. The truck is meant for loading up dirt bikes and hauling down a back road.

 

The truck differs from every jeep I have ever owned. It's two wheel drive. In the form of a 1991 Comanche short bed 4.0 ax15

[MJ H.O.]

 When I got the Comanche, the engine ran and you could drive it but it needed attention. Found there was no compression on cylinder number one. Pulling the head revealed a piece missing from the piston and a block beyond repair.

I put aside thoughts of an engine swap to a ford 2.3 turbo and a t5.

Pulled an engine from a 1996 Grand Cherokee with 220,000 miles. Moved over the flywheel and didn't bother to swap to an external slave. Just wanted to drive it. Installed an aluminum radiator and one later model Xj auxiliary cooling fan and wiring, ditched the mechanical fan. The hvac unit under the dash wouldn't work so it was pulled, then out came the air conditioning compressor and heater lines... the radio and speakers that didn't work - gone. Old Carpet and headliner- gone. Found a broken front swap bar link which meant swapping to thicker zj front swaybar 

Installed a new fuel tank and got the brakes freed up.

Replaced the MJ exhaust down pipe with the 96 zj pipe. Installed the exhaust mount from the MJ and installed the Cat and new muffler. Dumped the exhaust out in front of the right rear tire. Bought a set of Jeep 5.9 rims and bald tires off of a Toyota 4cyl pickup.

Finally it was road worthy

 

[MJ H.O.]

Made a short shifter using a spare ax15 shifter. Cut the ball off the end of one shifter and welded in an extension piece. Took one spare housing and cut it down to become a spacer. Installed longer bolts and two gaskets.The idea here is to lengthen the ball end and then move the pivot point higher. The travel between first gear and second was six inches and now is four inches. 

[MJ H.O.]

Swapped in a 96 brake booster and master. Installed the later 4.0 intake. 

Installed an aluminum driveshaft

Ditched as much weight as I coul including the jack, bumpers, spare tire and hoist then went to the track. 

Struggled to get the old tires to hookup in first gear. Took them down to 15 psi. Managed to run a 15 second quarter mile at 91 mph. 

[MJ H.O.]

Installed yellaterra 1.7 ratio roller rocker into the 1996 engine. I highly recommend the 96 cam and the 1.7 roller rockers. 

I ran this setup while sourcing an low mileage 4.0 engine and a 232 crankshaft. A 232 not a 258 crankshaft. 

If no ridge is present in the cylinder, a 232 crank can be installed into a 4.0 block using the 4.0 pistons and 4.0 rods

The quench height will be 0.030" using the thicker head gaskets available 0.050" compressed head gaskets not the 0.041" compressed gaskets some folks argue that 0.030" quench is too tight. A 232 crank is a great way to tighten quench and bump up compression. 

The static compression ratio will be 9.6-9.7:1 

Great torque and response out of the engine. The jeep is a blast to drive. I have got 8 months on the 232 crank engine. She gets 25-26 mpg with a dirt bike and gear loaded. Even loaded up she is quick. 

Continued weight removal currently at roughly 2620 lbs. A set of 255/50r16 bfg tires help a lot to regain traction. 

 

 

 

 

[87Warrior]

This sounds like a fun build. I am particularly interested in seeing how the motor build turns out. The quench is pretty tight, but I don't see why it won't work with a 4.0.

 

Do you have any current pictures of the truck with the 255/50r16 bfgs?

[HOrnbrod]

A 232 crank in a 4.0 makes it a mini stroker.    It's a bit lighter too so it supposedly spools up faster.  Good inexpensive mod...........

[MJ H.O.]

On 11/3/2017 at 11:16 AM, 87Warrior said:

This sounds like a fun build. I am particularly interested in seeing how the motor build turns out. The quench is pretty tight, but I don't see why it won't work with a 4.0.

 

Do you have any current pictures of the truck with the 255/50r16 bfgs?

 

I have been running the "mini" stroker engine for several months Now. Everytime I drive the truck I don't expect it to accelerate that quick. The power to weight is much different compared to my old lifted renix XJ, civic and lifted 05 Lj rubicon

I first had ran the 96+camshaft and 1.7 roller rockers for a couple months. More torque starting at idle and it would rev out stronger. Then located a $50 232 engine from a 1972 cj5 Next found a 80k mile Xj 4.0

Pulled the Xj engine out of a wrecked Jeep on a Saturday morning, checked the cylinder. Installed the 232 crank with new main and con rod bearings. Moved over my 1.7 roller rockers. Then pulled the mj high mileage engine and installed the mini stroker engine. Two long days but drove it to work on Monday

I feel that the 232 crank and 96+cam with 1.7 rockers are two great "bolt ons" for the 4.0

 

There are many ways to build a 4.0 but Quench is important. The 232 crank swap is an easy cheap way to tighten up the quench to 0.030" and raise the compression. Yes, there is a slight gain in displacement and slight gain in stroke (3.50" stroke verse stock 3.411" stroke) but I believe the gains are in the higher compression and tighter quench(piston to head clearance at TDC) You could get the same result using a 4.0 crank and longer eagle rods 6.150" to get the quench to 0.040"

Keep in mind stock quench is 0.076"  and milling material off the head does change quench. Thinner head gasket, longer strokes and taller pistons tighten quench. Some cases such as the longer 258 crank you might use the shorter 258 rods with stock pistons or 258 crank with longer 4.0 rods but use shorter pistons. 

 

Follow the link below and scroll down to the quench section

http://jeepm62superchargerkit.blogspot.com/p/misc-xj.html?m=1

 

Mine is the 3.50" crank with a quench height of 0.030-0.032" 

At top dead center, the pistons are 0.018" out of the block. The compressed head gasket is 0.050" thick. There is 0.030" quench clearance between the head and the piston. The top of the piston is in the head gasket area. 

 

It's counterintuitive but a build with tighter quench may be less likely to detonate and may allow you to run a lower octane. You get more velocity in the squish area as the piston comes in close contact with the flat area on the head forcing the mixture towards the center of the combustion chamber and heat is transferred from the head to piston during the close proximity. The piston is then being cooled by the oil beneath. But if your piston hits your head it could be bad. I have seen engines that have piston with evidence of kissing the head. High rpm can temporarily stretch connecting rods. There's debate on how tight is too tight for a given engine type and rpm range. We don't go that high on our jeeps. Quench at 0.030"-0.055" is better than building out at 0.080". Less than 0.025" on a 4.0 might be asking for trouble. It's a diminishing return so going 0.025" verse 0.035" would be slightly better but it's best to be below 0.055" 

I am running 0.030" quench and 9.7 static compression and 8.5 dynamic compression.

Regardless of crankshaft used, 4.0 232 or 258 be mindful of quench and can be run tighter than stock 0.076" 

 

You will need the 255/50r16 tires 

 

 

 

[MJ H.O.]

Been running the following suspension setup for the past year. Larger sway bar from a zj grand Cherokee, upper and lower control arms from a wj grand Cherokee, poly upper control arm bushings on the axle side and 2" blocks in the rear. 

[MJ H.O.]

Installed a set of Xj shackles which lowered the rear slightly. Took a set of jk rubicon front springs and cut off one full coil. This dropped the front 2 inches. The truck still has 3" of uptravel. Checked clearances at full compression with the rubber stops removed and there's barely any room. The axle is about 3/4" away from the oil pan. The right upper control arm is very close to the engine mount and somehow clears the oil pan. Here's two inches lower in the front. 

[HOrnbrod]

Lower the rear another inch and you'll have a good looking MJ gasser. 

[MJ H.O.]

Changed the rear suspension to fiberglass springs. These weigh 9 lbs each. Installed new shocks and a chevy blazer rear swaybar.