Renix to H.O

93bluebeast

New member
I have a 93 xj ish... driving to work the other day and my idle stared to get real rough, like holy hell thats a crazy cam rough. Got home did a compression test got 122-130 on cylinders 1-5 but on cylinder 6 I got thirty. Took a nifty syringe and tube thing I made (girlfriends a vet tech) and squirted some oil down in that cylinder and retested. Still about 30. So I thought ok great most likely valves. I’m not a mechanic by any means but I figured with the limited knowledge I have that makes the most sense to me. I proceeded to strip it down (manifolds, ps pump, ac bracket etc..) that’s when today I noticed some numbers painted on the side of the block. This got me a little worried so decided to do some quick casting number checking. On my head it’s stamped 2686 and on my block it’s 806mx 27. Now correct me if I’m wrong but I believe this is a 88 Renix motor that got swapped in. I still have the factory 93 ecm with wiring, heck even my injectors are from a 93. My question is what is the difference between the Renix and h.o? Is it just the head? If so I might just go pull one and rebuild it or get a rebuilt one and slap it on assuming that’s the issue with my low compression. Also since it is a 88 do u guys think my time/money would be better spent just pulling/finding a used h.o motor? I’m pretty broke so no freshly rebuilt crate motors for me.
 

Jim Malcolm

New member
The only difference is the head. The camshaft grind didn't change until '96 for more torque at lower rpm (225 ft-lb @ 3000 rpm vs at 4000 rpm). Getting a newer model head would give you back the 13hp you're losing out on by using the '88 motor compared to a stock '93 (177 vs 190 hp, torque is same)

If you're going to get a later model head, the 0331 is your best option. Stock torque went up 10 ft-lb (even while adding pre-cats right after the exhaust manifolds (in the manifold if you compare it against the earlier version). The only issue is lack of a hole at the back driver's side for the coolant temperature gauge sensor. It's not a big deal to drill and tap if you're so equipped (or willing to pay), but it's easier to add a hole to the thermostat housing and extend the wiring. There's a nice flat spot that make it easy.

I'd shop around to see what's available to you, For not much more than a junkyard motor, you can replace the rod and main bearings, lifters, timing set, oil pump, gaskets, etc and have a freshened up motor, or you can have another unknown. Granted, swapping a 4.0 can be done in a day if you're so inclined. Rebuilding-in-place, not so much. I'd have to drop the pan, inspect the crankshaft journals and decide if new rod and main bearings will get it good enough or whether the shaft needs polished/cut. Or you can just replace the head with a rebuilt newer model and then down the road when the bottom end goes out, the head will likely be reusable as-is. I'd take a rebuild head over a junkyard motor; same price around here ($400-$500). But if you find a low mile 99-01 XJ motor (TJ & WJ won't work) for a good price, it may be worth it to swap the motor given the known age of your '88 motor. Just make sure any 0331 head is a TUPY or aftermarket model. Turn and run as fast as you can from a stock head 99-01 XJ 4.0 unless you're planning to replace it.
 

lawsoncl

New member
I have a 93 xj ish... driving to work the other day and my idle stared to get real rough, like holy hell thats a crazy cam rough. Got home did a compression test got 122-130 on cylinders 1-5 but on cylinder 6 I got thirty. Took a nifty syringe and tube thing I made (girlfriends a vet tech) and squirted some oil down in that cylinder and retested. Still about 30. So I thought ok great most likely valves. I’m not a mechanic by any means but I figured with the limited knowledge I have that makes the most sense to me. I proceeded to strip it down (manifolds, ps pump, ac bracket etc..) that’s when today I noticed some numbers painted on the side of the block. This got me a little worried so decided to do some quick casting number checking. On my head it’s stamped 2686 and on my block it’s 806mx 27. Now correct me if I’m wrong but I believe this is a 88 Renix motor that got swapped in. I still have the factory 93 ecm with wiring, heck even my injectors are from a 93. My question is what is the difference between the Renix and h.o? Is it just the head? If so I might just go pull one and rebuild it or get a rebuilt one and slap it on assuming that’s the issue with my low compression. Also since it is a 88 do u guys think my time/money would be better spent just pulling/finding a used h.o motor? I’m pretty broke so no freshly rebuilt crate motors for me.

The option of rebuilding it depends on what's wrong. Badly gouged cylinder wall wouldn't be worth rebuilding. If this is needed as a daily driver, a newer engine would be faster and simpler.


I planned to rebuild mine until I came across someone parting out an XJ with an engine that had 25k on a rebuild for $300.
 

cruiser54

New member
4.0 Engine date codes

The date code is on the passenger side of the engine, on the block, just forward and up from the distributor on a machined flat surface.

The digits of the code identify:
 1st Digit-The year (8 = 1998).
 2nd & 3rd Digits-The month (01 - 12).
 4th & 5th Digits-The engine type/fuel system/compression ratio (MX = A 4.0 Liter (242 CID) 8.7:1 compression ratio engine with a multi-point fuel injection system).
 6th & 7th Digits-The day of engine build (01 - 31).
1. FOR EXAMPLE: Code * 801MX12 * identifies a 4.0 Liter (242 CID) engine with a multi-point fuel injection system, 8.7:1 compression ratio and built on January 12, 1998.

So, you have an 88 motor. No biggie. as long as someone used the intake gasket for the 93 and all it's other goodies you are fine.

I will attach a link to swapping from Renix to HO for informational purposes.

http://cruiser54.com/?p=100
 

cruiser54

New member
The only difference is the head. The camshaft grind didn't change until '96 for more torque at lower rpm (225 ft-lb @ 3000 rpm vs at 4000 rpm). Getting a newer model head would give you back the 13hp you're losing out on by using the '88 motor compared to a stock '93 (177 vs 190 hp, torque is same)

If you're going to get a later model head, the 0331 is your best option. Stock torque went up 10 ft-lb (even while adding pre-cats right after the exhaust manifolds (in the manifold if you compare it against the earlier version). The only issue is lack of a hole at the back driver's side for the coolant temperature gauge sensor. It's not a big deal to drill and tap if you're so equipped (or willing to pay), but it's easier to add a hole to the thermostat housing and extend the wiring. There's a nice flat spot that make it easy.

I'd shop around to see what's available to you, For not much more than a junkyard motor, you can replace the rod and main bearings, lifters, timing set, oil pump, gaskets, etc and have a freshened up motor, or you can have another unknown. Granted, swapping a 4.0 can be done in a day if you're so inclined. Rebuilding-in-place, not so much. I'd have to drop the pan, inspect the crankshaft journals and decide if new rod and main bearings will get it good enough or whether the shaft needs polished/cut. Or you can just replace the head with a rebuilt newer model and then down the road when the bottom end goes out, the head will likely be reusable as-is. I'd take a rebuild head over a junkyard motor; same price around here ($400-$500). But if you find a low mile 99-01 XJ motor (TJ & WJ won't work) for a good price, it may be worth it to swap the motor given the known age of your '88 motor. Just make sure any 0331 head is a TUPY or aftermarket model. Turn and run as fast as you can from a stock head 99-01 XJ 4.0 unless you're planning to replace it.
It's 2000 and 2001 that had the 0331 head. 1999 did not.

And, the ports on the 0331 head do not match with 1991 to 1999.
 

alexgalexg

New member
I believe the head you are looking for is an 0630. And you can order them remanufactured with or without the temp sensor hole. I'd take a look at what's going on. My guess is since that engine is so old and could have 800k on it for all you know that it could be buildup on the valves.

Seafoam and other engine cleansing products would be a good shot but since you have it already apart you may as well get a visual. Dont reuse gaskets!

Sent from my SM-G950U using Tapatalk
 

CJR

New member
93Bluebeast,

Squirting oil down a cylinder doesn't test if the rings are stuck in the piston grooves. Typically, lacquers are in gasoline and are NOT dissolved by gasoline. GumOut has two (2) solvents in it to dissolve lacquers which can lock rings in a closed position in the piston ring grooves and result in NO compression pressure. Before you rip your engine apart, I'd recommend you remove the spark plug, in the low compression cylinder, and spray a can of GumOut into that cylinder and it let it set a couple of hours or over night. Then compression test that cylinder again. You may simply have piston rings locked in a closed position in the piston grooves. Typically, what happens over time is the oil-control piston rings (in lower groove) start sticking and the oil flow drain-back to the crankcase (from the cylinder walls) slows down and accelerates the ring sticking for all the piston rings. This also happens on new cars that don't have properly sized oil drain holes or enough of them in the lower oil-control piston ring groove. A couple of years ago I refreshed my son's low mileage Mitsubishi V6 with better rings. When I pulled the pistons, three(3) pistons had rings stuck in the closed position. I then opened the drainback holes in the pistons to improve oil drain back to the crankcase. Try the GumOut. It may work for you.

Best regards,

CJR
 

Jim Malcolm

New member
And, the ports on the 0331 head do not match with 1991 to 1999.
Please elaborate. There's a picture floating around of a 0630 gasket (shown in red) over top of an 0331 head (shown in black). The 0630 completely covers the ports on the 0331, thus there should be no issue with a 91-99 intake and exhaust manifold sealing up against a 0331 head. What am I missing? While the intake manifold port being larger than that on the head is less than ideal. Swap on the 99+ intake, which is worth it for the belt tensioning aspect alone.
 

Jim Malcolm

New member
I still suggest an 0331 head for his '93, but any of them will work just fine. Biggest thing is the coolant temp sensor port. There are some stock 0630s with the port in place, but no such luck on the 0331.
 

cruiser54

New member
You may find this interesting.

HO myth buster


Renix in 90 made 182 HP. HO in 91 made 190 HP. That's 8 HP difference.

HO only made more HP than Renix at higher RPMs and not a bit more torque. HO had a 58 mm throttle body versus a 52 mm throttle body on a Renix. That’s 20% more air available through the HO throttle body. The HO also had a better design header. See where I'm going with this?

It’s only a 4% horsepower increase…..

The whole 8HP was not mostly from the head, but from the bigger TB and better exhaust manifold.

Put a 60mm TB from www.strokedjeep.com on your present manifold using the Renix head, eliminate the "crush" in your headpipe with proper re-routing, and go for it.

HO stands for Highly Overrated.
__________________
 

lazyxj

NAXJA Member #1310
NAXJA Member
. There's a picture floating around of a 0630 gasket (shown in red) over top of an 0331 head (shown in black). The 0630 completely covers the ports on the 0331, thus there should be no issue with a 91-99 intake and exhaust manifold sealing up against a 0331 head. .
If the stock exhaust manifolds do not fully cover the ports, an aftermarket header usually does.
I'm running a Pottenger 7120 head on my 2001, using a Banks header.
 

93bluebeast

New member
So decided to pull the head and do a visual, only one problem the damn head won’t come off! Tried mallets, hammers and a block of wood, 15 inch crescent in intake port and prying, finally grabbed the engine lift and started cranking. Still the damn thing won’t break free. I did snap a head bolt off so tried to lift straight up with the hoist but it didn’t do a thing. Any ideas? Hidden bolts? Got the two to the ac compressor bracket off
 

Jim Malcolm

New member
14 head bolts, two for the AC bracket and the intake/exhaust bolts are all I'm aware of. Disconnect the fuel pump by whatever means you choose and hit the starter quick like. Maybe have a bolt or two in loose to catch it :eyes:
 

93bluebeast

New member
Yup got all the bolts, been out here with a breaker bar and jack handle giving her hell and so far I’ve only managed to bend my handle. Think the starter thing might work? I’m getting pretty desperate at this point. Ready to pump some acetylene down the spark plug holes fire it up and blow the damn head off.
 

93bluebeast

New member
Finally got the head off, after driving in some flat head screwdrivers while keepin pressure on it with the hoist I managed to pop it free by jumping up and down on the front bumper 😂
 

93bluebeast

New member
Heads off finally, cylinder walls look good, new Ironman4x4 motor mounts installed (pita) valves on 6 are black and burnt so now it’s down to rebuilding a head. What are your guys’ thoughts? What year head with what year manifold? I have about 600 for the project, machine shop said they would tank/surface the head for 40. Have to get lifters and head bolts plus gaskets but other than that what do you guys think would be a smart buy for parts? Any money left over goes to finishing buying lift parts...
 

markw

web wheeler
NAXJA Member
I still suggest an 0331 head for his '93, but any of them will work just fine. Biggest thing is the coolant temp sensor port. There are some stock 0630s with the port in place, but no such luck on the 0331.
0331 is the head that cracks on everyone. It's a 93, so do a 91-95 put a 7120 (correct head) or 0630 (96-99). I would not recommend a 0331, unless it was a "Tupy" casting which corrects the problem with cracking, and then only if you have to match up to the pre-cat manifolds. Since you don't have the proper exhaust, stick with the 7120. Don't put the renix back on. 99+ manifold with the bracket for the ps pump and idler.

If you want more torque, you need to replace the crankshaft with a 4.2 and just build a stroker at that point. The 99+ intake is only a benefit if you've had other engine work done, but it will let you run a PSC overdrive pulley on your power steering pump for better low speed pressure.
 

93bluebeast

New member
Thanks for the info, so a 7120 head which I’m assuming will match up with my intake and exhaust manifold. Quick dumb questions, Is there a good head kit out there with valves, valve stem seals, head gaskets, bolts and lifters? Can’t afford to do a stroker, though it sounds nice. Quoted 40 for head work at a local machine shop plus another 40$ for the 91-95 head from a jy. I’m assuming I’m taking everything including rods from the new head?
 
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