Spark plug torque
11-01-2008, 09:50 PM
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Spark plug torque
Hello all,
I'm getting a range of recommendations. 1996 4.9L, how much torque on the spark plugs? Alldata says "for V8 engines, 7-15 ft-lb," and says nothing about the 4.9. Haynes says 17-22 (no units, which they say is ft-lb by default), and 72-120 in-lb for 7.5L.
So, 20 ft-lb for the 4.9L? A couple of sources say 0.044" for the gap.
Bill
I'm getting a range of recommendations. 1996 4.9L, how much torque on the spark plugs? Alldata says "for V8 engines, 7-15 ft-lb," and says nothing about the 4.9. Haynes says 17-22 (no units, which they say is ft-lb by default), and 72-120 in-lb for 7.5L.
So, 20 ft-lb for the 4.9L? A couple of sources say 0.044" for the gap.
Bill
11-01-2008, 10:06 PM
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I've always been told to hand-tighten, then take down another 1/4 turn. That's enough to seat the crush washer but not enough to screw things up.
There should be an emissions sticker on the underside of your hood - it'll list the plug gap for your truck - that's the only source that I would trust. I've been through the gap and install, remove, re-gap, reinstall bit before, because the guy at the parts store gave me incorrect info.
There should be an emissions sticker on the underside of your hood - it'll list the plug gap for your truck - that's the only source that I would trust. I've been through the gap and install, remove, re-gap, reinstall bit before, because the guy at the parts store gave me incorrect info.
11-02-2008, 05:05 PM
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As an aside, I hit a snag with my Craftsman air compressor. The drain valve has always been a pain (no good way to grab it), and I decided not to trust it until I replace it. Is that the kind of thing that needs an exact match, or would anybody's brass drain valve and some low-strength lock-tite take care of it?
I am using a seriously old and small compressor to blow dirt off of the head. I decided to start with the plugs and got two of them, working front to back. Both look more or less like what I understand a normal plug to look like, with gray deposits. The first wire runs under/around the power steering pump bracket, and has a sheath on it. It looks like it is probably the split conduit/sheath (not sure what to call it), but I am having trouble finding the split if that is the case. Any ideas? If it is not split, it seems unlikely that I would be able to transfer it??
The sticker said 42-46 for the gap.
As I work on the plugs and later the distributor, is there anything I should expect to remove to make room? So far, the throttle body gave me some trouble, but a flexible extension did the trick.
Re torque, the second plug felt great. It bottomed out clearly, and I gave it 1/4 turn past that. The first plug, I'm not as convinced, mostly because it did have such a clear bottom. I am torn between backing off and trying it again and leaving well enough alone.
I am not sure how much more work I will be able to do on it today as time is getting away from me. At least with two plugs replaced, it still runs
Bill
I am using a seriously old and small compressor to blow dirt off of the head. I decided to start with the plugs and got two of them, working front to back. Both look more or less like what I understand a normal plug to look like, with gray deposits. The first wire runs under/around the power steering pump bracket, and has a sheath on it. It looks like it is probably the split conduit/sheath (not sure what to call it), but I am having trouble finding the split if that is the case. Any ideas? If it is not split, it seems unlikely that I would be able to transfer it??
The sticker said 42-46 for the gap.
As I work on the plugs and later the distributor, is there anything I should expect to remove to make room? So far, the throttle body gave me some trouble, but a flexible extension did the trick.
Re torque, the second plug felt great. It bottomed out clearly, and I gave it 1/4 turn past that. The first plug, I'm not as convinced, mostly because it did have such a clear bottom. I am torn between backing off and trying it again and leaving well enough alone.
I am not sure how much more work I will be able to do on it today as time is getting away from me. At least with two plugs replaced, it still runs
Bill
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11-02-2008, 05:43 PM
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The sheath is just plastic with a split down the middle as you thought - they wrap them with electrical tape at the factory though. It's good stuff and seems to shrink wrap over time. Might be hard to find the split. If you got good heavy wires, you probably won't need the sheath anyway.
Gray deposits are good - probably normal wear.
Black oily stuff is bad.
Carbon coating would indicate a lack of combustion - pointing you toward the fuel injector for that cylinder.
Check the gap as you pull them. If one or more have a huge gap or build up almost closing the gap, that could be part of your issue too.
You mentioned distributor - did you get a cap and rotor kit too? If you have a distributor, you should replace those while you're at it.
The first plug might have had some junk in the threads - not a lot you can do about it. Get a feel for how that 1/4 turn feels, and try to get it about the same feel as the others.
Gray deposits are good - probably normal wear.
Black oily stuff is bad.
Carbon coating would indicate a lack of combustion - pointing you toward the fuel injector for that cylinder.
Check the gap as you pull them. If one or more have a huge gap or build up almost closing the gap, that could be part of your issue too.
You mentioned distributor - did you get a cap and rotor kit too? If you have a distributor, you should replace those while you're at it.
The first plug might have had some junk in the threads - not a lot you can do about it. Get a feel for how that 1/4 turn feels, and try to get it about the same feel as the others.
11-02-2008, 06:03 PM
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It's officially dark outside - can't stand time changes 
IMHO, we should move the clocks 30 minutes one time and be done with it, or, just change schedules by 30 minutes. IIRC AZ changes time zone to keep their clocks where they were, while the rest of the country either loses sleep or wonders why they're so hungry before lunch.
The changed plug count is up to four. The next two look rustier than the ones I have removed, and will probably be easier to reach - think. They are also fairly far back. I generally stand on a couple of cement blocks - better ideas welcome.
Plug 3 was enlightening. I was hand-tightening it with my $4 leather/polyester gloves and an extension, and ended up lightly gripping/slipping while I turned it. It is hard to describe, but the bottom line is that they plugs seem to want to trick me into thinking they are tight when they are in fact not all the way in. After a fair amount of that (all very low torque, but lots of little steps), it started threading easily and hit a clear bottom.
Do you really want a 1/4 turn after bottoming out? On a couple of them, I probably got to 1/8 turn and decided it was about done.
I became suspicious that the first plug tricked me, and it had. A little fiddling go it moving again, then it bottomed out properly and I nudged it some more to (hopefully) seat it. In particular, it should be easy to reach with a torque wrench as a check.
Let me know if anything sounds stupid. Do you want me to run the engine for a while and then re-check the plugs? If so, how long is a while? Any particular conditions?
It is definitely time to replace the wires. The instructions all say to pull on the boot, not the wire. One of the boots pulled off of the wire. Another clip or two is getting a little weak.
I have long known about the trick of changing one wire at a time. What about when changing the cap. Would I just move them from the old cap to the new one, one at a time, or should I label them and replace the cap that way?
Bill
IMHO, we should move the clocks 30 minutes one time and be done with it, or, just change schedules by 30 minutes. IIRC AZ changes time zone to keep their clocks where they were, while the rest of the country either loses sleep or wonders why they're so hungry before lunch.The changed plug count is up to four. The next two look rustier than the ones I have removed, and will probably be easier to reach - think. They are also fairly far back. I generally stand on a couple of cement blocks - better ideas welcome.
Plug 3 was enlightening. I was hand-tightening it with my $4 leather/polyester gloves and an extension, and ended up lightly gripping/slipping while I turned it. It is hard to describe, but the bottom line is that they plugs seem to want to trick me into thinking they are tight when they are in fact not all the way in. After a fair amount of that (all very low torque, but lots of little steps), it started threading easily and hit a clear bottom.
Do you really want a 1/4 turn after bottoming out? On a couple of them, I probably got to 1/8 turn and decided it was about done.
I became suspicious that the first plug tricked me, and it had. A little fiddling go it moving again, then it bottomed out properly and I nudged it some more to (hopefully) seat it. In particular, it should be easy to reach with a torque wrench as a check.
Let me know if anything sounds stupid. Do you want me to run the engine for a while and then re-check the plugs? If so, how long is a while? Any particular conditions?
It is definitely time to replace the wires. The instructions all say to pull on the boot, not the wire. One of the boots pulled off of the wire. Another clip or two is getting a little weak.
I have long known about the trick of changing one wire at a time. What about when changing the cap. Would I just move them from the old cap to the new one, one at a time, or should I label them and replace the cap that way?
Bill
11-02-2008, 06:24 PM
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The sheath is just plastic with a split down the middle as you thought - they wrap them with electrical tape at the factory though. It's good stuff and seems to shrink wrap over time. Might be hard to find the split. If you got good heavy wires, you probably won't need the sheath anyway.
Check the gap as you pull them. If one or more have a huge gap or build up almost closing the gap, that could be part of your issue too.
You mentioned distributor - did you get a cap and rotor kit too? If you have a distributor, you should replace those while you're at it.
You mentioned distributor - did you get a cap and rotor kit too? If you have a distributor, you should replace those while you're at it.
I did buy a cap and rotor. I just posted a question about how to best get the wires from the old cap to the new. One at a time until the old cap is free?
Call me nuts, but I ran it again with four plugs changed, and I think it's running better. Thanks for your help!!!
Bill