4.0 Head Gaskets and Exhaust Manifold - Ranger-Forums - The Ultimate Ford Ranger Resource


4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

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Old 04-29-2015
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4.0 Head Gaskets and Exhaust Manifold

HELP!! 1991 4.0 Ranger OHV. I need to replace head gaskets. I have it torn apart to the point I am ready to Loosen the head Bolts but....I cannot get
the exhaust pipes loose from the exhaust manifold. I have used penetrating oil and an electric impact gun with extension and socket from under the car.
They won't budge. I was thinking of trying heat..I have a MAP gas torch for soldering...what do you think?
Also the bolts from the exhaust manifold to the heads are impossible also (I was able to get 2 out)....so I decided to pull the heads with
the exhaust manifold still attached and deal with them off the engine...Do you see a problem doing it that way..and I can't try it until I get the exhaust pipes loose.
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Old 04-29-2015
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Yes, pulling the head(s) with exhaust manifold attached is not uncommon, those bolts get stuck pretty tight.

Crank up the torque on the impact and break the studs/bolts on the collector(exhaust pipe).
You will be pulling the stud part out with the manifold so can repair it when it is out.

Yes, heating up the manifold around the stud can break the rust loose enough to get the stud out, but be CAREFUL, metal transfers heat quite well you can burn up wires and parts INSIDE the cab via firewall heat transfer, heat rises.


Too late now but just as a heads up, when I know I will need to pull exhaust parts that haven't been touched in years, I drop vehicle off at a local muffler shop.
They will remove all the bolts/nuts then reinstall them, snug not tight, and replace any with stripped heads, threads or that broke.
Usually takes them about an hour shop time.
They know all the tricks and have all the tools, they do this every day, lol, and they have all the spare nuts and bolts on hand.

Most I ever paid was $60, to me it is worth it because of the time it takes and the frustration level of stuck hard to get at bolts, lol.
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Old 04-29-2015
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Quote:
Originally Posted by RonD View Post
Yes, pulling the head(s) with exhaust manifold attached is not uncommon, those bolts get stuck pretty tight.

Crank up the torque on the impact and break the bolts on the collector(exhaust pipe).
You will be pulling the stud part out with the manifold so can repair it when it is out.

Yes, heating up the manifold around the stud can break the rust loose enough to get the stud out, but be CAREFUL, metal transfers heat quite well you can burn up wires and parts INSIDE the cab via firewall heat transfer, heat rises.


Too late now but just as a heads up, when I know I will need to pull exhaust parts that haven't been touched in years, I drop vehicle off at a local muffler shop.
They will remove all the bolts/nuts then reinstall them, snug not tight, and replace any with stripped heads, threads or that broke.
Usually takes them about an hour shop time.
They know all the trick and have all the tools, they do this every day, lol, and they have all the spare nuts and bolts on hand.

Most I ever paid was $60, to me it is worth it because of the time it takes and the frustration level of stuck hard to get at bolts, lol.
Thanks Ron. Good idea about Muffler shop. I had the impact wrench to it's Max and nothing broke. I can try a dremmel to cut them. How would you remove the stud that will be left in the exhaust manifold??
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Old 04-30-2015
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Yes, if you can get a dremmel or metal saw blade in there to score the stud then an impact can often break it off.

Easiest method is to take exhaust manifold to muffler shop, lol, they will also reinstall new studs and give you new nuts.
As said they do this all the time so it is fast for them.

lots of methods out there, heating and cooling is usually what works the best.
heating up the area around the stud expands the metal then using compressed air to rapidly cool the stud(shrink it) can break the threads loose, but you still need enough of the stud showing to grip it with extractor or similar gripper.
When area is heated up use wax(candle), touch it to the threads and it will be sucked in to the threads, this will help loosen them.

Using a reverse drill bit in a reversible drill works as well, the vibration if drilling and the fact the drill is rotating in the direction to unscrew the broke stud/bolt is also a benefit.
And if it doesn't unscrew, you will still be left with a hole that an eze-out can be used on.
Heating and cooling, and wax, using the drill method is also needed, breaking the rusted threads free is the goal.

When drilling steel start off small, drill small pilot hole to a good depth, then go to larger drill bit, then larger.
This is usually faster than starting out large, so cost of 2 drill bits can speed up the time it takes, and also use oil on the bit, keeps it cool and cutting, hot drill bit = no cut

Last edited by RonD; 04-30-2015 at 11:05 AM.
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Old 04-30-2015
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Originally Posted by RonD View Post
Yes, if you can get a dremmel or metal saw blade in there to score the stud then an impact can often break it off.

Easiest method is to take exhaust manifold to muffler shop, lol, they will also reinstall new studs and give you new nuts.
As said they do this all the time so it is fast for them.

lots of methods out there, heating and cooling is usually what works the best.
heating up the area around the stud expands the metal then using compressed air to rapidly cool the stud(shrink it) can break the threads loose, but you still need enough of the stud showing to grip it with extractor or similar gripper.
When area is heated up use wax(candle), touch it to the threads and it will be sucked in to the threads, this will help loosen them.

Using a reverse drill bit in a reversible drill works as well, the vibration if drilling and the fact the drill is rotating in the direction to unscrew the broke stud/bolt is also a benefit.
And if it doesn't unscrew, you will still be left with a hole that an eze-out can be used on.
Heating and cooling, and wax, using the drill method is also needed, breaking the rusted threads free is the goal.

When drilling steel start off small, drill small pilot hole to a good depth, then go to larger drill bit, then larger.
This is usually faster than starting out large, so cost of 2 drill bits can speed up the time it takes, and also use oil on the bit, keeps it cool and cutting, hot drill bit = no cut
Thanks for the tips Ron..YAY...I finally got the exhaust pipes unscrewed from the heads. I tried a penetrating formula from BG and squirted it on and off for hours. Borrowed an air impact wrench that is stroner then my electric one and cranked the compressor to 135 LBS and using a few 1/2" extensions and a universal got them loose. Working on my back in the street is a bear, especially had knee surgery 2 weeks ago....but their out.

Now how to get the exhaust manifold unbolted from the head. There is no place for penetrating oil. Would you heat the heads of the bolts or just go for it with a breaker bar and a pipe?? any suggestions...?

I can see where the water was leaking into cylinder #1 ...the top of #1piston looks like it is brand new and shiny...But.. there is something strange. Looking at the 6 pair of valves of both heads where they seat. Some pairs have a blackish color where carbon has built up..but some of them have a tanish while color with no carbon. Any thoughts on that.....((#1 valves are fairly clean)
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Old 05-01-2015
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Heat up the head near the bolt, expands the metal, then breaker bar, and tight fitting socket.
Impact works best as it vibrates bolt.

4.0l OHV has a casting flaw, weak spot between valve seats, so look very carefully with good light at that area on all cylinder domes, it will look like a line, it is a crack.


Computer bases fuel mix on MAF sensor and O2 sensors.
MAF sensor tells it how much air there is coming in and computer then uses 14:1 air:fuel ratio.
O2 sensor reads the Oxygen in the exhaust, too much oxygen means Lean burn, to little oxygen means to rich.

When a cylinder misfires, even a little, all the oxygen isn't burned up and it is dumped into exhaust, O2 reads high oxygen computer adds more fuel to that bank.

Burning coolant can cause limited burn in that cylinder so high oxygen in exhaust.

Could be fuel injectors have dirty tips, so drip fuel instead of spraying fuel, this coats the inside of intake and eventually leaks into cylinders cause rich burns on start up which causes carbon build up.

loads of reasons, lol.
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Old 05-03-2015
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Need to replace heads

I can see a small crack in both heads between the intake and exhaust valve seats. I wonder if this can be superficial...but from what I have read it seems that is where the problem usually is. I started looking online for heads. I found kingcylinderheads.com that have new heads complete for 300 each, no cores. 2 year warranty. Ramscyl.com has 5 year warranty for remanufactured and cracked cores are ok 295 each. Cylinderheads.com remanufactured is 185 each cracked cores ok 2 year warranty. Has anyone purchased from these company's or can suggest a reliable source.
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Old 05-03-2015
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First have the heads pressure tested at a machine shop, that will decide IF they are cracked.
If they are or 1 is then ask the shop if they can get heads and how much.
If heads are good you still need them resurfaced in any case.

If you get the gasket set it will come with new valve guide seals, if you don't have a spring compressor or even if you do, lol, machine shop will often install them for free with cleaning and resurfacing, so bring them with you

Been a few years since I replaced one of mine but if memory serves machine shop got me a new head and swapped over my valves, for less than I could get a new head to my door.
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