Serious engine sludge Clean it or lost cause

fourwheelinj1

Well-Known Member
Joined
Apr 11, 2011
Location
Raleigh
I bought a used YJ with 135k miles on it's 4.0 so I could swap the 4.0 into my cj. I have the 4.0 on my engine stand so I can freshen it up a little before installing in the cj. I had planned on having the head rebuilt, new oil pump, timing set and some gaskets. I pulled the valve cover last night to prepare for pulling the head and found major sludge build up. The rocker arms look pretty much the same. I scrapped about a full solo cup full of sludge out of the valve cover. So now I am concerned about the condition of this engine. It ran good and had good compression. I plan on pulling the oil pan to replace the oil pump and oil plan gasket. The head is going to be rebuilt so it will get hot tanked to clean it up. Is it reasonable to think that tanking the head, cleaning out the oil pan and replacing the oil pump will clean most of the gunk out. I am going to spend about $400-$500 for the head rebuild, oil pump, and timing set replacement. I can have a company called Poteat Engines do a full rebuild including those parts mentioned for about $1150. I would prefer to put that $700 towards something else if the sludge engine can be cleaned up, but if it can't I don't want to spend. $500 freshening this one up to have it crap out on me 10k-20k miles later. Thoughts?






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Clean what you can and run the piss out of it.
 
If there is no evidence of water contamination then I would clean it and run it, otherwise replace the rod bearings.
 
Yep, there won't be a lot left by the time you have the head cleaned/rebuilt. See if they will also clean the oil pan and pickup while you have the bottom end apart.
 
If your going to have the head rebuilt pull it and then fill the block with diesel fuel and let it sit for a few days, this will eat the sludge and make cleaning much easier when you drop the oil pan. I redid a 4.0 that way and when I pulled the valve cover the sludge was so thick it looked like a second valve cover. Rebuilt head new oil, water pumps and timing set, few gaskets and it runs like a top.
 
you've got an engine that already has 135k on it, there's a reason you want to build the head, you're already that far into it and making the top end tight, which will put more stress on the rings and bearings of the bottom end. You're concerned about the potential of having to dive back in in 10-20k miles. why not just do it, get it right, then you know it's clean, you know there isn't anything that will be nagging because " I shoulda done..." , then drive it for another 200k...

new or old, shit can happen, old increases that potential.

If you're gonna spend the money, do it once, do it right, move on to the next upgrade.

FWIW, blow by is one of the contributors to the slugging/coking you're seeing in the engine. worn rings/cyls are suspect in that. engine temps (cold and hot) and lack of maint are contributors as well.
 
i've rebuilt way worse and used/seen/bought way worse and never had an issue: soak it in Kerosene overnight or diesel fuel then pressure wash the hell out of it with oil pan and valve covers off and put the pressure washer on the straight nozzle from 3-4ft away and when you're done, the inside will look brand new. then put the stuff back on whatever you replace or reuse, put pans back on and put some real cheap oil in it or used oil for that matter and just turn the motor by hand several times, install it and use the starter to turn it for 20-30revolutions with good charger hooked up. this will get about 90%of any remaining moisture buildup from passages/bearings out and then ur good to run cheap cheap clean oil for an hour or so then change it to whatever you normally would. I've done this for years and works flawlessly...even on one engine with so much gunk that you couldn't see the oil pump screen/tube or bump and bottom of crank but when done, that motor ran like new with 81K original miles. (this is why nowadays i won't give much for a old low mileage 4.0 cause they are gurarnteed to look like this). have fun and enjoy!!
 
OHH YEAH, WEAR A RAINSUIT/COVER when pressure washing cause you will get that crap all over you even at 6-7ft away!! LOL
 
X2 on the kerosene and a rain suit.
i do this to all the engines i build before they go to the machine shop.
 
While cleaning the sludge may be easier than you think, I second the decision to send it to the shop and have the bottom end rebuilt as well. If there is nothing major wrong with it, adding rings and bearings will not add a huge amount of dollars to the project. If there is something bad enough to require machine work (and extra cost), you may have just saved yourself the headache of having to do it again later. At least ask your engine builder about that option.
 
The reason for the head rebuild is just because I am going to have it off to replace the head gasket. I think I got the engine a little too hot when I was idling it one day when it was apparently low on coolant due to a trashed water pump. The oil on the dipstick up to that point was clean, but shortly after that the tip of the dipstick had a white/yellow sludge on it so I think I have a small head gasket leak and possibly slightly warped head. I figured that since I had the head off and it was probably getting resurfaced I might as well have it rebuilt for $175 more. Like i said up until I pulled the engine the jeep ran good and had good compression numbers. Since this is a 4.0 which are known for 250k+ miles I was thinking that freshening it up and rebuilding the head should hopefully get me another 100k miles out of it.



Blkvoodoo said:
you've got an engine that already has 135k on it, there's a reason you want to build the head, you're already that far into it and making the top end tight, which will put more stress on the rings and bearings of the bottom end. You're concerned about the potential of having to dive back in in 10-20k miles. why not just do it, get it right, then you know it's clean, you know there isn't anything that will be nagging because " I shoulda done..." , then drive it for another 200k...

new or old, shit can happen, old increases that potential.

If you're gonna spend the money, do it once, do it right, move on to the next upgrade.

FWIW, blow by is one of the contributors to the slugging/coking you're seeing in the engine. worn rings/cyls are suspect in that. engine temps (cold and hot) and lack of maint are contributors as well.
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with that low mileage 4.0 man, clean the crap out of it and run it. she will run great for another 100K the way it is and keep 10w30 with 1QT of Lucas and it will love you for long time. Jeep motors with the infamous piston slap will still run forever with thicker oil so you are plenty fine with what you have. now some will disagree with this but in my 15years of pulling 4.0s apart, main bearings are hardly ever worn and rod bearings at 200k still look descent: piston skirts are the main issue on the newer 4.0s so clean it, flush it good, run good oil with high volume oil pump since you are there and it will serve you a good long time problem free.
 
Just Wana throw in there that I have got several engines from poteats and they have all been great just got a 22r from there a few months ago they will also give you a 2 year warranty on the motor for the money I would definitely get it rebiult
 
John Fuller said:
with that low mileage 4.0 man, clean the crap out of it and run it. she will run great for another 100K the way it is and keep 10w30 with 1QT of Lucas and it will love you for long time. Jeep motors with the infamous piston slap will still run forever with thicker oil so you are plenty fine with what you have. now some will disagree with this but in my 15years of pulling 4.0s apart, main bearings are hardly ever worn and rod bearings at 200k still look descent: piston skirts are the main issue on the newer 4.0s so clean it, flush it good, run good oil with high volume oil pump since you are there and it will serve you a good long time problem free.
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And Ive got pics on here of a 130k mile 4.0 with a rod hangin out the block
 
Wow seems like there is no clear consensus on this. Seems like almost as many people saying rebuild as those saying clean it and run it. I think I am going to wait and make my decision after I have the head and oil pan off. If the bottom end looks good and isn't too full of sludge I think I am just going to clean it and run it. It ran so good before that I hate to spend money on a rebuild that may not be needed. If the cj was my DD I would probably rebuild it no matter what, but since it is just a weekend toy that will see 8k miles or less a year I will try and clean it and save it if the bottom end looks decent.
 
Instead of guessing, do a simple check. Pull the rod caps and measure the diameter of the crank journals to see if they are within spec or out of tolerance. Measure the bore of a few cylinders to see if it is within spec. If everything measures within spec, then maybe just replace the rod bearings and you could hone the cylinders and install new rings, or just do nothing and put the head back on after having it freshened up.

Some years back I bought a 77 CJ5 from a coworker for a few hundred bucks that had a non-running engine. The original motor had a rod come through the block. They bought a motor from a junkyard, put it in, and never could get it running so gave up on it. I did a compression check and found two dead cylinders. I took the head off and found two melted pistons. I had the head redone like you are doing. I pulled the oil pan, and measured a few of the crank rod journals(they all measured within tolerance). I also measured the bore on a few cylinders (which was still within spec). I bought a re-ring and bearing kit, got a used set of pistons and rods from a friend, honed the cylinders and put it all back together. Within a minute or two of starting up, the water pump starting puking, so that was the reason the motor melted the pistons in the first place. I replaced the water pump, and it ran great.
 
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drkelly said:
Instead of guessing, do a simple check. Pull the rod caps and measure the diameter of the crank journals to see if they are within spec or out of tolerance. Measure the bore of a few cylinders to see if it is within spec. If everything measures within spec, then maybe just replace the rod bearings and you could hone the cylinders and install new rings, or just do nothing and put the head back on after having it freshened up..
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This. I have a "supposed to have been built" 4.3 on a stand now with an oil pan gasket laying across the top. When the time comes to put it in, we will flip it over, pull the pan, and make sure the bottom end is within spec.
 
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