Quick question. When reviving my 4.9 in my F-150 after sitting for a decade, I noticed there was a dead skip in the motor at idle. Revving it up made it smooth out a little. My mechanic told me it was the smoothest miss he'd seen in a while - the only way you knew it wasn't running right was a slight shaking at idle speed and **** poor fuel economy.

First I threw a tune up kit at it (needed to anyway) and that didn't help. A compression test revealed #2 cylinder not having any compression. When we took the head off we found that #2 exhaust valve was recessed enough in the valve seat to let all the compression out. The valve sat slightly farther in the head than the others, and spraying liquid on it would cause it to leak past. I'm just curious what could have possibly caused this to happen? The truck had 170K on it when I pulled it out of the woods - I don't know why the truck was parked but it was a mess when I found it. After new seats and a valve job she runs like a top.

Anyone know what made the valve get messed up?

Evan

 

ethanol fuel
poor seat heat treat
lots of heavy throttle
bad previous valve job / guide repair
bad luck

 

My boss at the repair shop told me it was probably ethanol fuel - but the last time the truck was on the road was '05 so ethanol fuel wasn't a big deal back then right? When we fired it up it didn't seem to miss that badly (was running on local pump gas so probably ethanol gas) - but is it possible for ethanol to ruin a valve seat within a few weeks of running? The miss started out very slight but became a dead skip within less than a month.

However it could also be any of these other conditions as I never knew how the truck ran before or why it was parked in the first place.
Thanks for the explanation.

 

I ran ethanol fuel in my '81 for years and never had an issue. I wouldn't say it's directly that, or you'd see that all over the place.

It's difficult to say what happened in a situation like this. Maybe that valve was sitting completely closed for 12 years, and moisture/water collected in it and rusted it out? Then when you fired it up, it just chewed right through it.

Did you happen to get pictures of it?

Otherwise, it's honestly a best guess, and very difficult to say with certainty what caused it. Especially since that's a very rare occurrence (at least, this is the first time I've heard of it happening).

 

Yeah I figured it'd just be a guessing game. I think the missing link is that no one knows exactly WHY the truck was parked - this problem could have arose back in '05. The people who owned the truck moved out, left the truck, and a new family moved in, so there isn't even any way to contact the old owners. I did get a picture but I don't think it tells much. The exhaust valve on the middle cylinder (#2) is slightly farther in the head than the valves on #1 and #3. Unfortunately I didn't get a picture of it disassembled since we sent the head off to a machine shop for a valve job.

Is there any way that running the truck for maybe 20-30 seconds on starting fluid could have caused/contributed to this problem? Otherwise, the truck was cranked a good deal before it was fired up and ran - it built good oil pressure so it wasn't really a "dry" start.

At the end of the day, I suppose I'll never really know what caused this issue. I'm just looking for the best explanation someone could give me - up to that point valvetrains were a mystery to me. Thanks for the response!

 

I see what you mean in the picture. Not something you'd even notice at first glance unless you looked closely / measured.

Dry starts wouldn't matter on the valves since the valve seat mating surface isn't lubricated. Only the valve stems are, but that'd be more of an issue with the valve guides.

The only way I know of that starting fluid would cause damage is if you liberally sprayed (to the point of almost flooding the engine) and then starting it. It's a type of solvent, so it'd remove the lubricating oil from the cylinder walls in large doses. But that's a rare case and you'd almost have to do it on purpose. It also wouldn't affect the valves.

I'm thinking it was either a bad valve seat to start with, like the material was too soft, or something corroded/damaged it and then it chewed itself up. Either way, something like that seems like it would take some time for the damage to manifest.