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Home > Technical Articles > Rendezvous With a Dropped Valve Seat

Guest Technical Article

Rendezvous with a
Dropped Valve Seat

Frustration Level: 10

Frustration scale:
Having your 914-6 fan belt break is a 4
Getting a flat tire is a 2

Wayne R. Dempsey

exclaimation.JPG (2021 bytes) WARNING:  The following article contains pictures of a violent destructive nature, and should only be viewed by Porsche owners with very strong stomachs.


Figure 1: Top View of Hole in Engine Case

Figure 2: Top View of Engine Case Damage

Figure 3: Rod #3 on Top, Rod #1 on Bottom

Figure 4: Inside the Engine Case, Rods #1 & #3

Figure 5: Carnage from the Destruction

Figure 6: Remains of Piston #3

Figure 7: Looking Inside Combustion Chamber of Piston #3

Figure 8: #3 Exhaust Valve Missing From Cylinder Head

     Here are some photos of a recent 914 engine disaster.  Since a complete teardown has not been performed, there is no definitive method of determining the exact cause of the failure.  I am currently soliciting ideas on what happened here.  If you have any input or questions that may help figure out what went on here, please email me, and I will include it in this article.   Ok, here's the story.

     This engine was recently rebuilt, about 20K miles ago.  It frequently went on long trips back and forth from Lompoc to Los Angeles every weekend (about 150 miles).  It is a 1.7 engine with stock components, and stock fuel injection.  The owner of the car was driving north on a somewhat cool day a few weeks ago.  The car had been in the shop just that morning, for an oil leak problem.  The oil leak turned out to be a loose valve cover gasket that hadn't been replaced when the owner adjusted the valves one week prior.  The car was confirmed to have ample oil in it when it took off on it's journey north.

    After driving about half the distance (75 miles), the car began to make a rattling noise, but continued to hold oil pressure.  Shortly after that, the oil pressure dropped to zero, at which point the owner pulled the car over to the side of the road, lifted the engine lid, and saw many chunks of metal all over the engine compartment.  The car was towed the rest of the way home, where the owner and myself dropped the engine, and looked at what was there.

     Ok, here are the pictures and their gruesome descriptions:

Figure 1:  Here you can see the size of the hole smashed into the top of the case.  With quite a large hole in the case, you would image that only the rod could have done that amount of damage.  Strangely enough, the rods are intact.

Figure 2:  You can see the two rods (#3 and #1) intact within the case.  They didn't break off and go through the top of the case.

Figure 3: The crank is pretty banged up, but intact.  The Type IV motors have cranks that are pretty much bullet-proof.  You really have to mess up big to crack or break a crank.

Figure 4:  Here you can see the inside wall of the case, and another angle of the crank.  There's not even a serial number left.

Figure 5: Fall out from the carnage.  Check out the top of the case on the left, complete with ground post for the fuel injection.  The small piece of metal located to the upper right is a piece of what used to be #3 piston.  You can see the rings embedded in the melted metal.

Figure 6:   Looking at the remains of combustion chamber #3.  A small mound of metal still attached to the wrist pin is what remains of the piston.  Other remains can be seen along the cylinder walls.

Figure 7:   Looking down into the combustion chamber (isn't this camera great!).  It looks like something bounced around in there for a while before destroying the piston.

Figure 8: Number 3 exhaust valve has been broken off, and is presumably some place within the engine.   Looks like a dropped valve seat, maybe?  I can't really tell from the photo.

     My guess on what happened is that the #3 exhaust valve seat let go, and jammed the valve open which impacted the piston, broke it, and sent it flying around the case in the near vicinity.  A chunk of piston got caught between the crank and the rod on the upswing and blew a hole in the case.  Dropped seats usually only happen on 2.0L heads, not 1.7L though.  Also, dropped seats usually don't cause this much catastrophic damage.  Any thoughts?  We'd like to know...

John Harrell has the following to add:

This is the engine that was in the 914 pictured in my last e-mail. When I first saw this car the guy that I bought it from said that he was having trouble getting it started but that he was charging the battery and maybe that would be all that it needed. It didn't seem to help at all! But then since I had picked up an exhaust valve that was laying in the engine compartment I didn't think that it would.

Frazer McGuinness adds:

Hi Guys,

Just seen the pictures of carnage on your website - the 914 that dropped a valve.

Well you wanted to know if it had happened to anyone else and hey, it happened to me last year! I spent a fair bit of money on a blueprinted 2.0L CJ (type 4) short block for my ‘73 camper and bought a set of 1.7L heads to go with it (ported and bored out to 2.0L). 3 weeks later, late at night on the M25 (London - England) I’m 50 miles from home when I hear a rattling sound and oil smoke starts billowing out behind me. So I pull over and come off the motorway, no drop in oil pressure yet but when I pull over it drops to zero.

After getting towed home and dropping the engine out what do I find? Number 3 exhaust valve has sheared, chewed up the combustion chamber, gone straight through the piston (very little left), bashed around inside the crankcase, mashed up the underside of the opposite piston then smashed straight through the top of the crankcase.....ouch!!!

Anyways, the pictures looked exactly the same as the damage to my engine. I stripped the valves out from the head and guess what? - The seat was still there!!!! However, I reckon that the broken valve was due to excessive play of the valve shaft in its guide (the remaining inlet / outlet valves in the head were in a similar condition). So I guess the moral to this sad tale is if you re-build, recondition, or blueprint an engine, spend the extra bucks and get those heads set up with new springs, seats, guides and valves!!!!! I thought that my heads had had the full treatment but alas, didn’t check out the valves.....

Hope this helps...



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