I still call it a dropped seat anyways.. . My reasoning is, "It had to drop out before being recessed back in".
Every recessed head I've torn down the seat just fell out when the valve was removed.
Best way to tell is if you cant obviously see the different spring/retainer heights: Take off the rockers arms (use nails/bolts in the holes to keep the assembly together temporarly). This will illiminate any cam interferance, and put a straight edge across the valves. It will become very apparent which seat is dropped or recessed. All the ones I've found were recessed also (valve higher(closer to v. cover) than the rest).
My G/f's van is just now starting to drop a seat it sounds like a progressive clatter.. Its really loud when you first fire (dry lifters) then after about 10 minutes it starts comming back (clack, clack clack). Thats the best way I can explain it.
Good luck and thats a great find (the vanagon)!
I was given an '80 vanagon that has some issues. First one for me. My experience has been with type 1 motors. I hear the achilles heel of my type 4 is overheating and as a result, dropped exhaust valves, right? not the intake valves.
New ignition, timing checked, a big, big vacuum leak fixed (the lid of the EGR valve I think, opened and held in place with a very brittle rubber band) and some other things. Valves checked and set with no lash as I recall. I've heard about noisy hydraulic lifters for a bit if the van has been sitting, but this thing is just clattery noisy, with no let-up.
No one has mentioned any oil-leaking issues related to a dropped valve, is that because it isn't generally a symptom? Maybe I have other issues because I have oil spewing from somewhere I haven't been able to pinpoint yet, I just know it's above the heater boxes and isn't my valve covers, but is profuse and smokes up a storm, billowing into the cab through the heating system, dripping mainly from the passenger side heater box.
I had hoped the vanagon would be my driver while I rebuilt the 1641 for my '70 bay, but it went the other way. I had to let the van sit 5 months and today got it move from in front of the PO's home. I had wanted to tow it, but had nowhere to tow it. Found a place finally, close enough that today I fired it up and drove it over. Same symptoms.
I have a question about this...
I had a dropped seat on an exhaust valve with my old bus... It made a tick tick tick, BANG.. then it ran and sounded like a machine gun for 10seconds and died.
I put new heads on it and everythin was fine... but
I had a 79 bus that dropped a seat. Most times it ran fine, other times it would miss at idle and loose power when the seat shited and the valve would not seat completely.
Really?? Is this possible??
You can drive one and just have it act like it's missing?
Yes...its possible. This thread has moved all over the place and it has summed nothing up.
(1)The valve seats sit on a rather thin ledge at the botton their bores. Serious and repeated overheating through the life of the engine can cause stress that crack this away...allowing the seat in effect...to drop into the intake or exhaust pocket area. That means that this particular valve stem will be higher than the rest. The head is toast without serious welding.
(2) The valve seat can simply become loose in its bore. Wether it starteddue to improper interference fit? who knows. Either way...it is propagated from repeated or gross overheating. This causes the aluminum to lose some of its flexible thermo-elasticity. In other words...it can begin not to contract as much after it expands. That can be resstored through re-heat treating. As Dave mentioned. This type of seat can fall out, @@@@ sideways and snap off a valve head....or keep popping in and out of its socket clacking. It will always eventually beat away the ledge and destroy the head. Ray
. My reasoning is, "It had to drop out before being recessed back in". 