4.2 To 4.0 Swap Discussion

Greetings, all! I’ve got a problem that I’d like to open up for discussion. See, I’ve got a 4.2 out of (what I’m told) an ‘81 CJ. It was running strong so I decided to fuel inject it using a Howell based kit. Things were great!... until yesterday. Ever once in a while I’d start it and there would be a few seconds of a knock. I never stood next to it at start up so I never knew if it was in the head or if it was deeper. Yesterday the knock continued longer then usual... then it went away... then it came back at higher rpms. I definitely have a rod knock. Right now I’m working towards putting up a work shed so I’m thinking budget friendly but also a few other thoughts to justify things. Bear with me.

What are some opinions on 4.0 swap but retaining my Howell fuel injection? Everything is only a few weeks old and I’ve got an HEI distributor in it too. 4.0s are a slightly higher reving engine than the 4.2 so I think long term it’d have a happier life in front of my T14. The 4.0 engines are definitely easier to find in good used condition as well.

Looking around in internet land, there are a bunch of “4.0 with a carb” threads and they all have the same follow up questions concerning keeping the EFI over a carb. The 4.0 will run in a carb so it’ll definitely run on a Howell.

So... thoughts?

 

Yes, story is you can run the '81-up aluminum intake with the 4.0L HO exhaust manifold. You may need to get new or larger bridging washers between the manifolds. Not sure about what you can do with the earlier Renix engine.

Typically rod bearing failure is accompanied by loss of oil pressure, as the hammered bearing dumps oil freely. You should also be able to isolate the knocking cylinder by removing each plug wire until the knock goes away. I would not condemn the 258 until I saw the hammered bearing.

If you find a 4.0L HO donor, you may as well take the Mopar-Bosch MPI along with the engine and use that. Then sell off the Howell system as a unit. The MPI is a turnkey system, and if you buy the donor complete, it's more likely you'll find one with a bad head or such than to find problems with the MPI.

The other possibility is to find a pre-91 4.0L with the Renault/Bendix (Renix) MPI engine and use that. The Renix engine does not have the HO head, but makes almost as much power as the HO. I expect the main power boost comes from the increased compression, hotter cam and more favorable stroke ratio of the 4.0L.

Note that these MPI engines were designed with spark control and knock sensors, allowing the higher compression ratio. Your Howell system does not have this - it's basically an electronic carburetor. Spark control is a significant advantage. You can run the Renix engine with a Megasquirt - that's been done. I presume you could also make the GM computer that comes with the Howell work with the native spark control and knock sensor, but you'd need to burn a new chip and enable the spark control functionality that's been bypassed with the Howell system.

If you really want to get into this, I'd suggest you post on the swapology forum at www.jeepstrokers.com

The 4.0L has more power than the 258. the 258 torque comes on sooner, but I would not expect any benefit in T-14 longevity with the 4.0L swap compared to the 258.

 

Heading into the shop tomorrow. Diagnosing on Wednesday.

 

Crisis averted.

Apparently my connecting rods were panning for gold. The crank looks great though! Plastigage says I’m good to go with rolling on a set of standard bearings.



Timing chain must have minutes of hesitation though. Taking care of that along with a new oil pump and a slew of gaskets while it’s apart.

 

I would at least eyeball the cam and the top end if the bottom was dry the top was dry

 

Already did. At some point someone must’ve changed out the crank bearings and cam for sure. Not sure why they left the rods alone, but here we are.

 

Do you have a standard bearing set for the 258? I would buy an inexpensive micrometer and mic the crank. Plastigage is good to check your machinist's work, but a mic will tell you more.

This is a cast iron crank, and it's not much harder than the bearing material. With a cast crank, you typically lose as much crank material as is worn off the bearings. I would go with a crank kit ... but if I went with new bearings, I would not touch the crank with crocus cloth or whatever. If it's not polished bright now, trying to polish it could remove more crank material than you want. If it were a forged steel crank, I'd polish it.

 

Well, things went well today. I did end up putting a mic on the crank before anything. Obviously the crank is worn some and I was shocked with how close to spec it still was. The more I looked at the interternals the more surprised I was with its condition.

It was a day of a few surprises though! What I was told was that the engine was out of an ‘81. Nope. This thing has Chrysler stamps all over it! I went into the parts store and gave them the vehicle to search for parts as a ‘90 YJ. Everything worked out.

In the end, it got standard bearings, a timing chain, oil pump, valve cover gasket, thermostat, and belts. I plan to continue to look into a 4.0 swap but I’m in no hurry. This refreshed engine still runs super strong!... but I know I’m on borrowed time.