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  #1  
Old October 16th, 2018, 14:38
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93bluebeast 93bluebeast is offline
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Renix to H.O

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. Iím 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..) thatís 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 itís stamped 2686 and on my block itís 806mx 27. Now correct me if Iím 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 thatís 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? Iím pretty broke so no freshly rebuilt crate motors for me.
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  #2  
Old October 16th, 2018, 19:42
Jim Malcolm Jim Malcolm is offline
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Re: Renix to H.O

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.
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  #3  
Old October 16th, 2018, 23:19
lawsoncl lawsoncl is offline
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Re: Renix to H.O

Quote:
Originally Posted by 93bluebeast View Post
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. Iím 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..) thatís 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 itís stamped 2686 and on my block itís 806mx 27. Now correct me if Iím 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 thatís 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? Iím 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.
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  #4  
Old October 17th, 2018, 06:15
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cruiser54 cruiser54 is offline
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Re: Renix to H.O

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
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  #5  
Old October 17th, 2018, 06:18
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cruiser54 cruiser54 is offline
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Re: Renix to H.O

Quote:
Originally Posted by Jim Malcolm View Post
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.
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  #6  
Old October 17th, 2018, 08:42
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alexgalexg alexgalexg is offline
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Renix to H.O

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
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  #7  
Old October 17th, 2018, 13:13
CJR CJR is offline
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Re: Renix to H.O

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
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  #8  
Old October 17th, 2018, 14:31
Jim Malcolm Jim Malcolm is offline
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Re: Renix to H.O

Quote:
Originally Posted by cruiser54 View Post
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.
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  #9  
Old October 17th, 2018, 14:37
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cruiser54 cruiser54 is offline
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Re: Renix to H.O

Here ya go.
https://jeepexhaustadapter.com/
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  #10  
Old October 17th, 2018, 14:53
Jim Malcolm Jim Malcolm is offline
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Re: Renix to H.O

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  #11  
Old October 17th, 2018, 14:58
Jim Malcolm Jim Malcolm is offline
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Re: Renix to H.O

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.
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  #12  
Old October 17th, 2018, 15:05
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cruiser54 cruiser54 is offline
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Re: Renix to H.O

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.
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  #13  
Old October 18th, 2018, 10:38
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Re: Renix to H.O

Quote:
Originally Posted by Jim Malcolm View Post
. 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.
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  #14  
Old October 18th, 2018, 14:43
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93bluebeast 93bluebeast is offline
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Re: Renix to H.O

So decided to pull the head and do a visual, only one problem the damn head wonít 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 wonít break free. I did snap a head bolt off so tried to lift straight up with the hoist but it didnít do a thing. Any ideas? Hidden bolts? Got the two to the ac compressor bracket off
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  #15  
Old October 19th, 2018, 12:18
Jim Malcolm Jim Malcolm is offline
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Re: Renix to H.O

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
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