Do I Need Engine Rectification/rebuild?

Long time follower of the forum but this is my first post. Sorry for the details but I wanted to give as much information in case it is relevant to the problem.

Background:
I live in Turkey and own a 1977 CJ-5 with I6 232cu, 3-speed that has been highly played and modified thanks to previous owners. It even showed up in some off-road races as I hear. It runs on 33'' silverstone boggers, has power and disc brakes, hydraulic steering box, single piece axles with an LSD in the back that was harvested from an International Harvester Scout. This beast has also been modified to run on LPG (in addition to gasoline, which be managed through a switch) which was very common in Turkey due to high gasoline costs.
It has a 2 barrel carburetor, again modified to be used with LPG. There is also an HEI distributor.

History:
I had the jeep for more than a year and have been having problems running the engine with gasoline since then.
There were a couple instances where the engine did overheat and the problems (popping noises from the exhaust, misfire, low power, etc.) increased after that, but the engine was running fine with LPG. I changed the fuel pump, filter, return valve, etc. but it was never fully fixed. I assume the adjustments and specifications for the carb and spark plugs should be different for LPG and gasoline so maybe my jeep was tuned for LPG in the end.

Problem:
The 2nd cylinder seemed to have a problem producing any power as when I remove the cable from the spark plug I notice no change in engine sound or any shaking whatsoever, which was easily noticeable when I removed other cables.

Tests and observations:
Compression: I decided to do compression test and the readings are as follows: 105, 65, 120, 105, 110, 110 PSI. Test was done around 400ft altitude and around 50F weather with the engine cold. I read somewhere in the forum that the compression for my engine should be between 120-150 PSI and only the best cylinder reaches the lower threshold.
Spark plugs: noticed not all of them are the same brand and some (esp on cylinders 4,5,6) are extremely rusted on the body and the threads.
Visual observations: I checked the engine oil cap (removing it) as well as oil dipstick tube but no visible air pressure or smoke comes out.
Oil level: The oil level is decreasing but very slowly (unless the mechanic has been topping it without my knowledge). It fell below the line only after 1 year or so. It used to leak from the oil dipstick hole to allover the starter but that is fixed.
Coolant: Coolant fluid is a bit rusty but no signs of oil mixing there.
Air intake: when I clog the air intake with my hand, I don't see any change in engine sound or RPM when running in gasoline, however in LPG the engine stalls and comes to a stop. Suspect an air leak in the gasoline fuel system.

Recent fixes:
- Carb tuning
- Radiator cleaning and fluid change
- Exhaust manifold gasket change (incl. the pipe gasket to the manifold)

Question:
My mechanic told me that the engine needs rectification and I wanted to consult to the forum before jumping in a costly and risky process.
He also told me that the valves on 2nd cylinder was burnt but the engine needs a broader overhaul instead of just replacing the valves. LPG is known to cause burnt valves sooner anyways so I wasn't surprised. Also the overheat problems I faced earlier twice might have accelerated the process.
There is obviously a problem with the engine, though how severe I don't know. My practical question is, would you suggest an engine rectification? The alternative I can think about is trying something like Restore to increase the compression but I'm afraid to cause more damage to the engine in the process. I can also try to change the possibly burnt valve caps and then do the Restore way after that as well. However, in that option if it doesn't work I'll have to bear the labor cost of removing the engine twice.

Look forward to hearing your thoughts and suggestions.

 

In the USA, we’re not familiar with the term “recertification”, bur suspect you are referring to an overhaul or rebuild. The faults with your engine possibly indicate leaking valves. Regrinding/replacement of the valves, and replacing or resurfacing the seats in the head are what we refer to as a valve job. This can possibly restore your engine alone, of it may require crankshaft regrinding and bearing replacement, and cylinder boring and fresh pistons and rings.
You won’t know until you pull the head off and evaluate the rest of the engine’s condition.
I do know that LP gas conversions can sometimes cause a leak running condition that can burn the valves, especially if there are vacuum leaks.
-Donny

 

rec·ti·fy| verb - put right; correct:

 

Like Howard said I’d recommend a leak down test to see if you can narrow down the issue. Sounds like valve issues but it can help determine if there are ring issues or not as well.

 

Thank you Donny and others for the responses. I guess rectification is a loan word we use from French. Yes, I mean an overhaul/rebuild of the engine, exactly as you described.
I will ask for a leak down test as well. Couldn't check the oil pressure yet but not sure the gauge works fine either

 

I agree with the others. If it's not burning oil and the oil pressue is good, you may only need to do a valve job. A full rebuild won't hurt but probably isn't needed. It is also good to check the condition of the timing chain.

 

Another that believes a valve job will likely fix the issue. If it turns out you need a replacement head, apparently 4.0L heads will work on 232's as well as the 258's.

 

The old wisdom was that a new 'top end' valve job can stress a worn 'bottom end.' I would want to verify that the crankshaft and rod bearings are okay and have good oil pressure.

 

That is a good point PeteL. I will probably go with a complete overhaul of the engine including checking the cylinders, rods, pistons, rings, etc. I will post an update once I get the time to go ahead with it.