Dropped valve seat?

[Mike Mulligan]

Is there any way to tell if you have a dropped valve seat before you remove the head? My car rather suddenly started making a valve-type tapping sound on the #3/#4 side.

I have not yet checked under the valve cover to see if one of the adjustment screws got loose or something, but I wondered if there was anything in particular that would tend to indicate to a dropped seat.

------------------
Mike
'73 914 2.0

[JP Noonan]

It could also be an exhaust leak. Or a loose valve lash adjuster.

To check for a dropped seat try a leak down test or at least a compression test. A dropped seat will cause an audible noise of leaking air out the exhaust or intake during the leak down test. It will cause a very low reading during a compresion test. Sometimes seats come loose and then go back in, but they still leak. Also looking uder the valve cover like you said helps.

[Conrad W Peden]

My motor ate a cam follower a couple of years ago. That sounded like a valve seat gone bad but not as loud, I've had that too. Not quite as bad as the article in the tech section but close, out the bottom instead. http://www.pelicanparts.com/techarticles/914_valve_blown/914_valve_blown.htm

Check to see if just one of your valves is way out of adjustment. Then make sure it isn't the adjusting screw and that you do have compression.

If you have compression chances are it isn't the valve seat. If the screw is tight and in good condition its probably not that either.

I've heard of rockers breaking but I doubt its that or you would definitly know by now.

The only way to know is to pull the follower out. That can be done with the motor in the car. Just take off the rockers pull out the push rods and tubes. Then stick you finger in the hole and pull the follower out with your finger tip. If you put a rag on your finger it helps grip. If you cant get the follower from the affected cylinder out, I would say its time to open the case(engine case,that is).

I would recommend cleaning the whole area first before you start taking stuff apart though.


Conrad Peden
72 L20E in rusto.
73 L20E in resto.



[This message has been edited by Conrad W Peden (edited 11-19-2000).]

[Dave at Pelican Parts]

You can also use a magnet to fish the follower out.

I replied to this one on the Rennlist and/or E-groups list, but I figure I might as well chime in here.

A dropped valve seat can be very loud. 1/4" of valve clearance sounds kind of like "THWACK!" over and over. You get 1/4" of clearance when the valve seat pops out and holds the valve open. It's very obvious when you pull the valve cover and look--one valve stem is definitely out of line with the others.

A dropped valve seat can also be very quiet. I had one that popped out and fell back in again, quite a number of times. It was in place, but didn't seal on the valve for squat. A compression test finally told me what was going on. (The sound from cranking the starter got me to actually do the compression test. RR-RR-RR--RR-RR-RR- One dead cylinder.) I checked the valve adjustment, and found it to be in spec.

Zero compression with the valves in spec means you have a problem inside the motor. I pulled the heads and looked. One of the intake valves (the one on the dead cylinder) had little "divots" around the valve seat. I could also see light around the valve. Yup, another dropped seat...

--DD