Used OHV - what to look for

[Baddecision93]

Ok, so I am going to be putting a used 4.0 OHV into my truck but before I spend a couple hundred I'd really rather not buy an engine with the same issues mine has...So my question is, is there a way to really inspect an engine as it sits and determine if it's worth buying? I know this is a little bit of a complex engine and I realize that all used engines w/80,000+ are going to have slight leaks, issues, etc.

More info (if you're so inclined to read on):

Basically I understand that purchasing a used engine as opposed to a new or rebuilt is a gamble. However, my engine is slowly dying and I just want to get something to buy time. I'm not going complex; no 302 swap, I'm not even going to attempt messing with SOHC. I'm pretty green with this stuff so I want a straightforward what I've got to what I've got kinda thing.

What's wrong with mine is it eats through coolant...I have to completely refill the reservoir (not the radiator) once a week. I can smell some antifreeze in the oil and it's a little frothy and from reading around here I'm fairly certain it's a cracked head and that doing a head gasket replacement will be a waste of my time and money.
It seems like this is a fairly common flaw with these engines so I'd really rather not buy another engine with the same issues.

My plan is to do a "mild" refreshening of my old engine once it's out (new gaskets/seals, maybe a new camshaft, new intake and headers). However, I've never done any of this so I know I will need ample time to complete it. And I really don't want to buy a running engine and attempt this in case I run into serious issues. I don't want to disable a perfectly good engine just to have mine completely die.

My engine runs pretty darn strong as it is so I know I have time. Everything attached to it is new. If I get this used engine I'm just going to slowly buy the replacement parts I need and if mine is still going strong I might just start "rebuilding" the new (used) engine.

I just want to have one waiting in the wings in the meantime in case mine completely gives up.

Hopefully this isn't too confusing...I'm really looking forward to some help here. I'm finding all kinds of engines in the $200-$300 range and I have an engine stand so I'd really like to get on buying one so I have a backup just in case.

 

[safn1949]

If your engine runs good why not do the top end,get a set of heads,have them magnafluxed for cracks and the valves done.Then you will solve the 2 most common problems,head gasket and intake leaks.

R&R motor is a hell of a job for a beginner,you could have the head job done in a weekend easy,then if you want to pick up an engine and run thru it at your leisure.Just my 2 cents.

 

[Baddecision93]

If your engine runs good why not do the top end,get a set of heads,have them magnafluxed for cracks and the valves done.Then you will solve the 2 most common problems,head gasket and intake leaks.

R&R motor is a hell of a job for a beginner,you could have the head job done in a weekend easy,then if you want to pick up an engine and run thru it at your leisure.Just my 2 cents.

Do you really think I would be able to redo the top end in a weekend? That's really my concern...since this is a daily driver. I could borrow a car for about a week if need be so if I absolutely had to I would have evenings after work.
I was just worried about what all went into doing the top end. I don't want to just buy the heads and head gaskets just to discover more issues after it's tore apart.

My other concern was putting that kind of money into my current engine. Without a lot of background with engines I was worried if there can be anything internal wrong with it. I didn't want to put the new heads on and then have it blow in 6 months...from reading on here and from driving it I think that other than the heads it's in good shape but I'm not totally certain.

I guess my thoughts on getting a used one is if mine completely takes a crap I can throw the used running engine in and then I'll have all the time in the world to learn how to rebuild the one I would be taking out.

 

[safn1949]

My understanding is that these engines rarely blow,mine has 140,000 on it and purrs like a kitten,another choice is go buy a $500 beater,save the money to do the top end and then you have car #2 to drive if it takes longer then expected.

Always have a backup plan just in case,I usually have 2 or even 3 vehicles.

 

[Baddecision93]

My understanding is that these engines rarely blow,mine has 140,000 on it and purrs like a kitten,another choice is go buy a $500 beater,save the money to do the top end and then you have car #2 to drive if it takes longer then expected.

Always have a backup plan just in case,I usually have 2 or even 3 vehicles.

Lol, mine has 173,000. Literally the only thing left original (mechanically) at this point are the engine and axles.
I have heard they rarely out and out blow but I figure with the symptoms I've got mine has to be on the downhill slide.
Guess I can always just keep saving money and buying parts and wait for the inevitable death. A beater wouldn't be a terrible idea but I just don't know. A $500 car is going to have its own set of wonderful problems.

 

[FIND]

It is easy to swap heads out in a weekend if you have two full days of nice weather, even as a beginner. Just as long as you are prepared in advance and you hit a couple odds and ends with penetrating oil ahead of time.

As long as you have all the parts ahead of time, and all the tools you need (not that many tools honestly, 10, 13, 15, 17mm deep sockets, 3" & 6" extensions, ratchet, breaker bar (optional but handy), t-50 torx bit, 5/8", 11/16", & 3/4" wrench, 5/8" spark plug socket, flat tip screwdriver, 5/16" nutdriver, a pair of pliers, hammer (for gentle persuasion purposes only), and a shop vac. You will need to drain the radiator, remove the UIM, valve covers, LIM, Alternator, and move the AC compressor a little bit to get it out of the way. One can get it done in a day, faster if they are pretty experienced. A person taking their time, maybe not as experienced, or a novice mechanic should be able to get it done in a weekend no problem if they are fully prepared.

Engine R&R is pretty much the same tools, plus a couple extras, like a Cherry Picker and some metric wrenches. If you don't mess around, even a novice mechanic should be able to do an engine swap in a weekend.

If you do either project, start a thread ahead of time, and I'll try and check it when you are gonna be doing it to see if you post with any problems. I'm sure there will be a few others on here that will keep an eye out for you too as long as they know ahead of time what you are doing and when you are doing it.

 

[69Explorer69]

mine has 176,000 and she purrs and starts on the first crank of the engine...got it a little 7 months ago from PA for 600,came with no "ParK" in the trans,stuck a rebuilt one in,she was good to go..

 

[92exp4x4]

The bottom ends on these engines are pretty tough. I think you could get away with doing the top end for a long while until you either got another vehicle or rebuilt the engine completely later.

A next project of mine will be doing just that. Except I am getting new heads. The chance of finding good used heads is slim because they are so prone to cracking.

Like safn1949 said, get a set of heads and rebuild them and swap them out for now. Then you could even have the originals (if good) redone as spares or use them when you overhaul the whole engine later.

 

[Baddecision93]

Well mine starts first crank like a champ - hot, cold, she doesn't care. There doesn't seem to be a noticeable lack of compression either...

So the concensus here is don't really worry about getting a replacement and just rebuild the top end in a weekend when it finally does give up & won't make compression?


Even if that's what everyone thinks, for fun, does anyone have any good tips as to what you should look for when buying a used 4.0 OHV? Is there anything you can look for by just pulling a head off (beyond the condition of the head itself)?

 

[FIND]

If you are looking for a backup, by all means, pick up a used engine to rebuild in your spare time. It can be a fun project and a good hobby.

I usually won't use a used engine myself, I give them a quick rebuild, because it is good insurance, and guarantees me the engine will be good for another 100k or 200k miles at least.

When buying a used engine that you want to avoid rebuilding, pull the valve covers off to inspect the condition of the rockers and look for signs of excessive sludge, pull the pan to check for sludge and wear, and the yard selling you the engine should have checked compression of the engine, so you are looking for even compression across all 6 cylinders. Have a good look at the outside of the engine too, that way you can see any of the places where it may have been leaking. It is not a bad idea to change freeze plugs and flush out the coolant channels. If you have an air compressor (or even a small low pressure air pump), take out the thermostat, put the housing back on, then put air (low pressure so you don't blow out your freeze plugs) to the coolant lines while blocking off the rest so you can check for any coolant leaks. If you do all that, you can be fairly confident you have a good engine that will be trouble free after installing. Most salvage yards will also give you a 30 day warranty, so if you buy an engine and have to install it immediately, you can put it in, and if you have any problems, swap it.

 

[Baddecision93]

If you are looking for a backup, by all means, pick up a used engine to rebuild in your spare time. It can be a fun project and a good hobby.

I usually won't use a used engine myself, I give them a quick rebuild, because it is good insurance, and guarantees me the engine will be good for another 100k or 200k miles at least.

When buying a used engine that you want to avoid rebuilding, pull the valve covers off to inspect the condition of the rockers and look for signs of excessive sludge, pull the pan to check for sludge and wear, and the yard selling you the engine should have checked compression of the engine, so you are looking for even compression across all 6 cylinders. Have a good look at the outside of the engine too, that way you can see any of the places where it may have been leaking. It is not a bad idea to change freeze plugs and flush out the coolant channels. If you have an air compressor (or even a small low pressure air pump), take out the thermostat, put the housing back on, then put air (low pressure so you don't blow out your freeze plugs) to the coolant lines while blocking off the rest so you can check for any coolant leaks. If you do all that, you can be fairly confident you have a good engine that will be trouble free after installing. Most salvage yards will also give you a 30 day warranty, so if you buy an engine and have to install it immediately, you can put it in, and if you have any problems, swap it.

That's exactly the info I was looking for. A rebuild of a used engine might be in my future both to have something that will guarantee me 100k trouble-free miles and for the education of it.

Until then you guys have given me a little more confidence that I shouldn't worry too much about mine until it gives me a lot of reason to.

I'll just keep my eyes open for a super deal on a used engine and at least now I'll have a better idea of what to look for.

 

[FIND]

That's exactly the info I was looking for. A rebuild of a used engine might be in my future both to have something that will guarantee me 100k trouble-free miles and for the education of it.

Until then you guys have given me a little more confidence that I shouldn't worry too much about mine until it gives me a lot of reason to.

I'll just keep my eyes open for a super deal on a used engine and at least now I'll have a better idea of what to look for.

A good rebuild and regular maintenance on a 4.0 OHV shouldn't even leave you wondering if you are going to have any trouble under 200k miles. Heck, you should feel confident about that engine long after that even. My dad's explorer is on its second transmission since leaving the factory, We have had to replace most of the steering and front suspension components, it has a rebuilt alternator and starter, but with 240k miles, it runs almost as good as the day it was new (minor tick aside). Still gets 21-22 highway mpg on stock tires and 3.73 gears, and has almost every single bit of power it did new.

 

[gt fast]

i got a similar problem. my 92 has 180,000 on it. it runs good never had any problems and i changed my oil every 2 weeks seeing as i drive damn near 3000 miles in 2 weeks. my thing is that annoying lifter tick, is it a bad or ok idea to replace jsut one head?. im going to be doing it in my garage and just wanted to know ahead olf time what to expect on parts that gave others problems.

 

[Baddecision93]

A good rebuild and regular maintenance on a 4.0 OHV shouldn't even leave you wondering if you are going to have any trouble under 200k miles. Heck, you should feel confident about that engine long after that even. My dad's explorer is on its second transmission since leaving the factory, We have had to replace most of the steering and front suspension components, it has a rebuilt alternator and starter, but with 240k miles, it runs almost as good as the day it was new (minor tick aside). Still gets 21-22 highway mpg on stock tires and 3.73 gears, and has almost every single bit of power it did new.

Well good. I see a power steering pump in my future but the truck came with new starter, alternator, radiator & lines, & tranny (and that's just the drivetrain stuff) so hopefully that should buy me some time.

It would be nice to be able to save up and get all the rebuild parts at once so the only limit would be my learning curve. I feel a little better now about being able to get to that point with my current engine. I have some camping trips planned and I was a little on the fence about taking my truck distances but I guess as long as I keep up on it and keep a close watch on the fluids I should be good for now.

 

[FIND]

i got a similar problem. my 92 has 180,000 on it. it runs good never had any problems and i changed my oil every 2 weeks seeing as i drive damn near 3000 miles in 2 weeks. my thing is that annoying lifter tick, is it a bad or ok idea to replace jsut one head?. im going to be doing it in my garage and just wanted to know ahead olf time what to expect on parts that gave others problems.

Replacing oil every 3000 miles is extreme overkill, especially with the changes made in oil since the 70s and 80s, and the only thing it is doing is increasing the profit margin of an oil company. If you are putting on that many miles, I am assuming they are nearly all highway miles at constant speed. You should be fine going 7500-10000 mile intervals between oil changes, probably more. The best way to gauge what oil life should be would be to send out samples to a testing facility when you change your oil. They will be able to tell you what percentage your oil is worn.

The tick on these explorers is usually rockers/pushrods. Sometimes they are lifters. Rockers and pushrods only require taking the UIM and valve covers off. Lifters require taking the LIM and heads off as well. I wrote a thread for step by step disassembly down to the rockers and LIM. Just search for threads I started, it should be the most recent. Getting rid of lifter tick does not require replacing heads. You only need to replace heads if they are cracked or worn to the point they cannot be corrected easily through machining.

 

[safn1949]

I agree with Find,if you are just hwy driving long distance every day 5000+ on conventional oil and up to 25,000 with Amsoil and the right filter.Well worth the money for you.I only drive 3-4000 miles a year.

They also sell a postage paid oil analysis kit for around $35,I have one on the front seat of my 94 waiting for an oil change to make sure we got the mystery coolant leak fixed.The first kit showed tons of coolant in the oil.....about 5 days before the intake started leaking externally.