Please tell me I dont need a rebuild.

BenI · 08-22-2000, 08:44 AM

I was taking my 914 across country for the 3rd time when, by Hays Kansas, I snapped a valve in half. I towed it the rest of the way to Boulder, CO, and have taken a head off now. The engine was 7000 miles old. The #4 cyl exhaust valve broke off at the top of the stem at the valve flare, rattled around digging up my head and punching a small hole through the piston, before becomming embedded into the piston. As soon as I heard the terrible sound, I was running about 3200 rpm and shut the engine off immediately. I then cranked it a few times to try to figure out what happened. All together I estimate the engine turned over about 20 times after the valve split. Of course I would like to be able to just replace the head and the piston. Does anyone have any experience with this? I know its hard to say, but what are your thoughts on the new head/piston vs. a complete rebuild. Any thoughts would be appreciated.

Joe Bob · Joe Bob's Garage

Have you looked at the oil? Metal parts or shavings is an indicator of a need to tear down and clean it up.....might not be such a bad idea....if everything is in good shape, you can get by with a gasket kit.

If the bottom end has parts of the handgrenaded head, then you needed to do it anyways....

Neal Colingham · 08-22-2000, 09:37 AM

I'm sorry to hear about your valve. I would
think you need to tear the engine down to get all the metal parts out of the longblock. If
it looks good then you could just replace the damaged parts. I am not a mechanic but it just makes sense to survey the damage by tearing down the engine.

Eddie Willers · 08-22-2000, 10:35 AM

Was it an OE sodium valve?
Or an aftermarket SS valve?

72porsche914 · 08-22-2000, 10:42 AM

What kind of sound did your car make? Mine is sitting in my driveway with what I believe is a blown motor. It gave no warning. At about cruising speed, it started sounding like a machine gun and it cut out. When you crank it, it sounds like a mess of clanking metal. Im guessing it spun a bearing. What kind of sound does it sound like if you brake a valve? I know a few days before this happened, my exhaust broke away from the head. I had to retap it and bolt it back up(drove a few days with off). I didnt realize that it was exhaust at first. I went through and checked the timing and replaced plugs, wires, condensor, points ect.. It was backfiring and never occured to me that it was exhaust. It was loud in the first place so it really didnt make a difference.

bowlsby · 08-22-2000, 11:09 AM

Lets see...

3200 revs per minute / 60 seconds per min = 53 revs per second. Given that the engine is slowing down after its turned off, if it toakes 1 second to come to a complete stop...you may be about right with the estimate of about 20 revs in the 1 secoind to turn the engine off...if you're fast at turning the key off.

BenI · 08-22-2000, 11:34 AM

The oil looked fine, I did find a lot of chewed up metal in the intake manifold.

I think they are SS valves.

The sound was a steady clanging. At first I assumed it was a dropped valve seat. Once I took the valve cover off I found one valve with too much clearence (the broken valve had mauled the seat so the intake wouldnt close all the way) and one valve with no clearence (the valve had broken off the stem so the spring had nothing stopping it). I have no idea of what the car ran like because I didnt drive it at all once the sound started.

You shouldve seen me, I almost turned that thing off before it made a sound-reflexes like a fox!

Well, Ive decided to try to patch it up with a new head and piston. I know it may be taking a chance, but its worth it to me right now to take it. Thanks for all the comments

Eddie Willers · 08-22-2000, 01:08 PM

That's what I figured.
SS valves are the most expensive mistake you can make in rebuilding a 914 engine.
Eddie

roadtrp204 · roadtrp204's Garage

Take the other head off and clear out any pieces that have traveled across the intake manifold. On every engine I have seen where something has scattered in the upper end, small amounts of pieces travel across the intake to the other cylinders. When you have the piston off, look around inside for any big pieces from the broken piston. The windage tray will keep them from settling in the bottom, but close to the cam.
Good Luck!
Chris