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Inline 6 head is on the coffee table. Now what?

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Inline 6 head is on the coffee table. Now what?

 
Old 12-08-2018, 06:04 PM
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Default Inline 6 head is on the coffee table. Now what?

My beloved 1991 f150 with the 4.9l inline 6 needs help. I have driven this thing daily for 18 years and have tried to maintain it as best I could. It has amazingly stayed at 137K miles for that entire length of time but I would assume I'm working with something like 300K today. Last week it lost power, like a couple cylinders went out -- reminded me of when my 86 Ranger got a chip in the head. I checked the dip stick and it had rusty water all up and down it. Limped it a few blocks home, drained the oil -- looked pretty okay, maybe a little frothy; drained the coolant -- looked pretty nice and green, no rainbows. I went ahead and pulled the head. My plan is to put a rebuilt head back on with a new head gasket. Looking for advice on a few things:

Should I do more than climb in and look closely at the block with a flashlight before I bolt a new head on?

What should I do about the rods and rocker arms? I carefully kept track of them in a cardboard box with holes just like grandpa taught me. Should I reuse them or buy new ones?

I plan to replace a couple obvious things while the head is out, but is there anything in particular that I should consider doing while I'm in there?

Thanks for all the great advice on this forum.
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Old 12-09-2018, 09:05 AM
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You don't say anything about new rings on the pistons?
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Old 12-09-2018, 11:54 AM
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First, get that head off the coffee table before your wife comes home.

Look for broken spark plugs, burnt valves, busted rings. If you don't know the cause, a new head may just be lipstick.

At 300K wouldn't hurt to at least hone/break the cylinder glaze and install new rings.
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Old 12-09-2018, 12:35 PM
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I'm going to take a closer look at these things and check back.

The #6 (furthest aft) spark plug insulation was broken when I removed it to take a look at all the plugs. The "exterior" part of the ceramic (not the firing end) came out in pieces when I went to remove it, . The firing end looked identical to the other five (pretty much normal for the mileage on them.) I assumed I broke it with my socket as it is the most difficult one to access and I had an awkward extension/u-joint combination. Is that broken plug worth thinking about?
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Old 12-17-2018, 11:59 AM
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Update:
I put a rebuilt head back on. The block looked okay to me after a good cleaning of the surface, a 12" steel rule and a flashlight. I opted not to remove the block or do anything with rings. I didn't open the pushrod cover. Head went back on, then new rocker arm kits, re-used the pushrods. The rods rolled fine on glass and showed no obvious wear. I read about adjusting the valves to make sure I didn't need longer or shorter rods after the rebuild, but I couldn't find the tool and it seemed that they weren't too long, so I just went for it.

On my first test I had a fuel leak. Fuel pouring all over the exhaust manifold while it was running was a bit worrisome. I damaged a fuel injector o ring during reinstallation so I went back in and replaced all twelve injector o rings. Fuel leak resolved.

The AIR pipe was tricky. One of the six tubes was broken when I removed it. I might have done it. The junkyard had one but it had two tubes broken, so I kept mine. The six ferrules(?) need to be loosened a bit at a time so as not to break the pipe. I had the muffler guy weld the broken tube and drop some brazing metal in one that looked cracked. By the time I was reinstalling the pipe those were both broken again. I did unspeakable things to the pipe to try to get those ferrules to tighten up in the smog holes and not leak. I managed to thread them in. I think the tubes got in there okay. I used a high-heat resistant epoxy (the one that is the color of metal) on the joints between the main pipe and the two cracked tubes. I took a lot of care to get things clean and tight but I'm crossing my fingers on that.

I had trouble getting the thermostat housing back on right, but I eventually did. I ended up using a length of string to hold the thermostat in place while I bolted it up, then pulled the string through the outlet.

It runs now, but is overheating. I double checked the thermostat, looked at the weep hole on the water pump, and tried to get all of the air out of the cooling system. The fan clutch seems suspect (I can stop it with my finger when the engine is hot) so that is this morning's task. If I have to change it I will but I want to make sure it isn't a sensor thing first.
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Old 12-17-2018, 03:21 PM
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It sounds like you stopped the fan when it was running????? You have any fingers left?

The clutch fan that failed on my truck drove the temperature up only during idling. It free wheeled at higher temperatures. At cruising speed, you should have enough air crossing the radiator to keep the temperature down regardless of the fan.. Is the upper hose hot to indicate the thermostat is opening? Is the thermostat installed correctly??
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Old 12-17-2018, 04:01 PM
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You read that right. I didn't even break a nail with my finger in the fan. I went and got a replacement clutch then pulled mine out. Mine had so much crud -- road dirt, oil whatever on it that the thermocoil thing was completely filled and covered. The cake was so thick it looked like it would impede the coil from expanding/contracting, so I cleaned it up with Simple Green and the hose, and put it back in. The fan immediately started working and I wouldn't dare put my fingers in it now.

Temperature seems good now. The gauge stays pinned right to the "N" of "NORMAL" driving or idling. It usually runs a tad cooler but the computer might be relearning so it runs in a default mode.

For what it's worth, my fan clutch is regular right hand thread. It has a stamp that says "tighten" with an arrow indicating the thread direction. I don't know the size of the nut but it is bigger than 1 1/4", so I had to use big channel locks.

Now I'm on to replace the battery I think. Voltage looks good while I'm driving around; won't crank after I turn it off for a couple minutes.
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Old 12-20-2018, 02:34 AM
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Was a rebuilt 4.9 head reasonably priced?
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Old 12-20-2018, 10:33 AM
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Originally Posted by sdmartin65 View Post
Was a rebuilt 4.9 head reasonably priced?
I think so. I paid under $4oo with tax, with the core return. For a little more you could have yours rebuilt at a machine shop, which I probably would prefer. I went with the rebuilt one mainly for turn around time. I was able to get it in three days. I bought it from a chain auto parts store with a one year warranty. It's rebuilt in Mexico.
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Old 12-23-2018, 12:05 PM
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Update:

Still sounds like I have an exhaust leak, possibly at the EGR valve, and a little whistle from the EGR valve. The exhaust leak sound is only when the motor is under load, like when accelerating from a dead stop. The whistle seems to be the opposite -- when the load is eased, like when I let off the gas after accelerating and right when I turn the motor off with the key. The truck is running warm. Not really hot, but hotter than usual -- at the "N" of "Normal", which for this truck with this thermostat is hotter than normal. It also seems to be burning more fuel than normal, but as I don't have a working odometer, I don't have any hard data on that.

Recap of recent work:

Rebuilt head
New Rocker arm kits
Head Gasket
New ignition wires (cap and rotor looked good)
New plugs (gapped correctly)
New fuel injector o rings (all 12)
Replaced (junk yard) EGR crossover pipe. (had to destroy the original to remove manifolds)
Repaired AIR pipe (see post above)
New Thermostat (195F) and housing
New gaskets: head, combination manifold, upper intake manifold, throttle body, EGR Valve, thermostat
New heater hose (water outlet to heater core)
PCV valve and hose (from valve cover to upper intake)
New air filter
New oil and filter
New fan clutch (I think mine was fixed, but I replaced it anyway)

Repair notes:

I could not get the forward exhaust manifold to bolt up to the rebuilt head. The front and rear bolts would not both thread in at the same time, like the manifold bolt holes were about 1/16" closer together than the bolt holes on the head. After lots of trying I took the manifold out and drilled out one of the bolt holes a little bit (oversized by 1/32" or 1/16", can't remember now). It seemed to bolt up really good after that.

I stripped the threads on the upper intake manifold where the EGR valve bolts on. I may have over-tightened it. I tapped it and put a repair coil in and seems to be okay now. The gasket is new and seems okay.

I will probably throw a new EGR valve at it unless I can think of something else to try first.
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