Rebuild kits?

My current Renix 4.0 has unknown miles, iffy oil pressure and a slight knock when I take off so I’m looking at rebuild kits for the(hopefully decent) block in my parts Jeep. My questions are what rebuild kits have y’all used, and with it being a Renix can I put a better cam in it without running into issues with the fuel injection? I’m completely new to these 4.0s and jeeps in general so any help, tips, or tricks are welcome and appreciated. Thanks.

If that knocking is under the floor, check the trans mount and whether the exhaust is banging on the crossmember. Checked compression and verify the oil pressure with a mechanical gauge before deciding if it really needs a rebuild.

It sounds like it’s coming from the right front side of the engine bay. Maybe 4-5 knocks when I take of from a stop and sometimes it does it and sometimes it doesn’t. Does it hot or cold too.

Check here (view is from behind the xfercase looking forward). If the trans or motor mounts are bad, the exhaust will sag and start rattling against the cross member.

BurnettDow13 said:

It sounds like it’s coming from the right front side of the engine bay. Maybe 4-5 knocks when I take of from a stop and sometimes it does it and sometimes it doesn’t. Does it hot or cold too.

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I'd check the motor mounts, as suggested above. Also, how many miles? What is the oil pressure? Does the idiot light come on, or do you have gauges?

BurnettDow13,

Some tips on engine building:
1. Use ductile iron or stainless steel (if available) compression rings on the pistons. They don't break.
2. I only use forged aluminum pistons and not any cast pistons.
3. Pull the original OEM wide-lobe camshaft and inspect for wear, particularly the bearing surfaces. If in reasonable shape, send it to Competition Cams to find out what regrinds can be done to it. If the cam is bad or has too much lobe wear, Comp Cams will tell you it can't be reground. New cams have significantly narrower cam lobes than the original OEM wider cam lobes. If you decide to raise the "Static Compression Ratio" to say 11:1(i.e. using custom pistons), ask Comp Cams what cam grinds give a "Dynamic Compression Ratio" of about 8.4 to 8.7:1. Or you can buy some engine software (i.e. Performance Trends) and run the regrinds Comp Cams gives you to determine the actual "Dynamic Compression Ratios" for each regrind. Why do all this? Because it improves engine performance while burning regular gasoline.
4. Use one piece stainless steel valves rather than two piece welded together valves which can break. Chevy stainless steel one-piece valves will fit the 4.0L engine.
5, "Zero deck" the engine block, for the pistons you choose, so you can install the proper head gasket thickness to obtain the proper "Quench Height" of about 0,045".
6. Use ARP head bolts.
7. Lightly port the head.
8. Use quality rebuild gaskets.

This should get you started. Enjoy the rebuild! They're lots of fun to do.

Best regards,

CJR

75SV1 said:

I'd check the motor mounts, as suggested above. Also, how many miles? What is the oil pressure? Does the idiot light come on, or do you have gauges?

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Miles are at least 300-350k. The odometer doesn’t work but stopped at 283k in 2011. Oil pressure is 40 at cold idle and 5-10 hot.

I've tried before to post. ??? I would look at replacing the oil pump, if on a tight budget. Also, you could inspect the crankshaft bearings and journals. Also, check the rod bearings.

Ok, finally, got to post again. As far as a rebuild, I could find some kits for the RENIX. Cleggs, Titan and some on Ebay. I think most are Engine tech. I did see one on Ebay with Sealed power pistons. I see Engine Tech, Mahle and Sealed Power pistons on Rock Auto. It shows those cover from 87-95 for XJs. The ones for 96-2006 4.0L seemed to be Hyper-Eutectic, and a bit higher compression height.
I might look at piecing together the parts. Mainly for quality. Especially, for lifters. I'd get ones made in the US. Johnson Hylift are suppose to be VG. As for a camshaft, I'd try and get one with a split lift. A bit more lift on the exhuast cam lobe. Over .450 lift, you might need aftermarket springs. I am having Schneider's regrind some 99+ stock camshafts. .450 Intake, .452 exhuast and 252 duration.
Also, I am porting some heads. They will have Chevy valves. If I did it again, I'd check out Russ Pottengers Chevy LS valve kit. I think $300.