Didn't the rev limiter kick in? I believe it's set for about 5400 rpm.

 

For acceleration yes, but I being really smart one day and decided to downshift to 2nd and forced it while doing like 60 or 70 mph while going down a hill, do the hill forced it past 5400 rpm. Probably 6000 rpm for all I know.

 

You must be mistaken. glc has already clearly established for us that no on can ever over-rev a 4.2.

 

The rev-limiter will work for when you floor it. When you are barreling down a hill, the force of the hill will make it go over the rev-limiter if you are dumb enough to drop it in 2nd at high speeds.

In the owners manual it even states this.

 

Clearly the guys who wrote that manual did not consult with glc first!

When I first brought up the possibility of over-rev in this thread, this was the exact situation I was thinking of.

One valve kisses a piston lightly. Over-rev seems like a possibility worth inquiring about to me. Especially if someone not familiar with the OP's truck may have borrowed it and caught 2nd or 3rd when they meant to grab 4th or 5th.

BTW, when the new valve gets put in, I would seriously recommend replacing the valve spring, or at least testing it to confirm it is within spec.

 

Well, let's be more specific. The limiter shuts off fuel and spark when you are accelerating, and with an automatic, it will not downshift when you pull the lever if it would put it over redline. However, if you can get a manual to shift, of course it will be over redline. You won't have spark or fuel, but it will be turning too fast. You didn't say that's what you did!

 

I've revved the hell out of my 4.2 and it is very possible to float the valves. It may take more than one time to float them, but repetitive over-revving of the engine will eventually cause one or more valves to float.

 

You calling glc a liar?

 

If you float the valves when accelerating before the limiter kicks in, something is not right (maybe the limiter has been removed by a tune?). I have NEVER hit the RPM limiter - just the speed limiter. The engine is making a LOT of racket before it hits the limiter, and the acceleration is dropping way off, so I don't see the need to try to hit it! I think the highest I've ever had it is about 5200.

 

Never said from accelerating. Never said I hit the rev limiter either. But you said it was not possible to float the valves. It's possible to float valves on any motor. I personally have neither hit the speed limiter(never had one), the rev limiter, or floated my valves. But it is entirely possible.

And just because I'm new to this board doesn't make my input any less reputable than glc's. I've been on the other V6 board for a while. =)

You glc's wife or something?

 

Lighten up, Francis.

Try this on for size: I was poking some fun at glc for seeming to say that you could not float the valves or over rev these motors.

Try re-reading my posts with that in mind. Then you should see that nobody was questioning you, or even aware of the fact that you are an insecure board newbie. But thanks for pointing that out.

 

You should probably clarify that before you think everyone can understand your sarcasm through text. Call me the board newbie because yes, I am a newbie to this board. Did it take you looking at all 22 posts of mine to realize that?

I apologize for not seeing the true intent on your comments but you gotta realize, its just text, I can't infer meaning or emotion from it.

EDIT: I didn't see your post up there about consulting GLC about writing the Owner's Manual first. My mistake. We all make them...but that is pretty funny now that I read it and actually understand your comment now.

 

x2. By 5,000 rpm, my motor is making only noise, not power. No reason not to shift by then. I think I took it up to 5200 rpm one time, when I first got the Superchip. Even then, it would accelerate quicker shifting much earlier.

I can't imagine intentionally taking it to 5,400 (the reported stock rev limiter).

I can imagine floating a 4.2 valve before 5400 rpm, especially on a high mileage motor that may have a tired valve spring.

FWIW, I've floated valves many times (never on a 4.2) but was lucky to get off with bent pushrods, or no damage at all. Once the valve gets out of control, the luck of the draw says occasionally it's going to be hanging out there long enough to kiss a piston.

For all we know, the OP's 17 year old son who is used to driving a high revving import borrowed his truck the day before the valve touched the piston.

Basically, short of some sort of random part failure, I'm having a hard time coming up with a scenario where rpm is not a factor when a valve touches a piston.

 

For all we know it could have not even been valve float. The world works in mysterious ways. Things happen that nobody can really explain. Could've just been the end of the life for a weakened valve.

 

Well in answer to somebodys question, I did say there was almost no carbon, it was very clean. I have also never had it near 5400 rpms. I got it all back together and it was running, but I had a miss, I suspected a plug or wire, it was only missing from idle to about 2500. So today I pulled all the plugs, checked for cracks in the porcelain, re-gapped them, a couple were a bit out of whack. Went to start it up, and it sounded just like it did the other day when all of this started. Which takes me back to this isnt a freak occurrence, something caused all of this, but what? I have the Valve on #4 stuck open this time, which means its probably bent, which makes me think maybe the timing chain is out of whack? The marks on the gears lined up perfectly, but could the tensioner be making up the slack and keep it in time, so to speak? I dont know, but what I do know is I am back to square one. what a piece. I know a lot of people love the 4.2, but I have been less than impressed since day one.