1968 Rocker Issue

[Mosesatm]

The Houston weather yesterday was amazing so it was a perfect day to take the Mustang to work. Since I left late the freeway was wide open and about 10 miles into my drive at 75-80mph I heard a noise coming from the truck next to me and thought, "Wow, he'd better get that fixed, whatever it is, it sounds terrible!"

But when I passed him the noise continued.

Uh oh!!!

I pulled off the freeway and into a gas station with the engine internals rapping the entire way, just waiting for the inevitable whoosh noise and cloud of blue smoke.

Towed it home and drove the truck to work. I was too busy at work to think about what the noise could be, other than a wrist pin. When I got home I started tearing the engine apart so I could pull it, but one of my neighbors came over to chat and by the time we were done talking I called it a night for the tear-down.

When I finally had some time to think about the noise and the work involved in removing the engine I thought it may be best to first see if something as simple as a failed lifter could be the problem.

The attached photo is what I found when I removed the driver's valve cover.

Any ideas on how the rocker can jump off the valve stem?

 

[franklinair]

My guess would be the lifter collapsed, relieving the pressure on the pushrod & clearance to the rocker arm, letting it flop off center.

Neil

 

[Mosesatm]

Would that more likely be a one-time freak event that just happens sometimes, or a faulty lifter?

Oops, never mind.
The valve spring is compressed without the rocker pushing on it so the valve is obviously stuck, which means there are probably some nice little dents on the top of the piston.

Oh well, pulling one head is still easier than removing the entire engine (if the piston is not damaged).

But now the big question is why did the valve stick open. Would a weak spring not close it fast enough, and the piston hit it?

 

[rvrtrash]

Which came first, the chicken or the egg? The valve stem might be bent because the rocker was pushing on the side of it. You could have a weak or broken valve spring, some foreign material stuck in the valve seat (have you lost any lock washers lately?), damaged or worn rocker arm. At this point, you need to take it apart and check all the parts very carefully. Does the rocker show signs of galling due to oiling problems? Could you have over-reved it and floated the valve?

Steve

 

[Midnight Special]

Which came first, the chicken or the egg? The valve stem might be bent because the rocker was pushing on the side of it. You could have a weak or broken valve spring, some foreign material stuck in the valve seat (have you lost any lock washers lately?), damaged or worn rocker arm. At this point, you need to take it apart and check all the parts very carefully. Does the rocker show signs of galling due to oiling problems? Could you have over-revved it and floated the valve?

Steve

+1. I'll bet you'll find that Steve nailed it! I was thinking "bent or galled" valve stem...

 

[Ruppstang]

Wow what a bad way to spoil a great day. I bet it was a long shift at work. Good thing it did not happen on one of your long trips. As said above I would pull the head and throughly inspect it if more than the one had problems I would pull the other head as well. I am sure you will have it back on road soon. Marty

 

[Mosesatm]

Here it is in all its glory.
For those of you who are not into engine internals this is what a stuck valve looks like.

Luckily it didn't damage the piston, but that carbon line sure scared me for a second!

 

[Midnight Special]

Here it is in all its glory.
For those of you who are not into engine internals ....
Luckily it didn't damage the piston, but that carbon line sure scared me for a second!

...Here's another view...
http://www.youtube.com/watch?v=UvmBLqjaZxY

 

[rvrtrash]

Here it is in all its glory.
For those of you who are not into engine internals this is what a stuck valve looks like.

Luckily it didn't damage the piston, but that carbon line sure scared me for a second!

It would me too, but everything else looks ok. I broke a keeper on one once (actually it was the ex because she didn't know she had to shift and just held the pedal down) and it broke the piston in half and punched a hole in the head. Yours will be much easier to fix.

Steve