What are these parts?

sixgun · 05-02-2009, 03:14 PM

Hello fellow wrenches,
I am in the middle of tearing down my 83 911SC due to a broken cylinder stud and no compression in #5 cyl. This morning when I finally get the tower, head and cylinder off I discover this damage to the head and piston that had managed to bend both valves before exiting the cylinder. I have no idea where this came from as I have only changed plugs last summer and it ran fine after that. This had to have been dropped into the induction system from somewhere at some point. Any of you guys know what it was or where it might have come from?
I have had this car for about 8 years and it has given sterling performance in the time I have had it. I baby it, I will admit....... I don,t think I have ever had it over 70 MPH in all the driving I have done. It,s got 39,000 origional miles on it and I,m the 3rd owner with all the paper..........
I am a nuube to this forum and I love it! I manage to learn something from you guys every time I visit.
Hopefully one of you guys will have an answer for me, but this this little critter sure made a mess out of the head and top of the piston. The bent valves was what gave me the compression loss , not the broken stud! Go figure!
Thanking you guys in advance........... George

Aurel · Aurel's Garage

It looks like a screw went in there, now we have to figure out where it came from. The picture is very dark, it makes it hard to identify. Is the dark from carbon deposits, or the light from when you took the pic? A closeup picture with more light may help.

euro911sc · euro911sc's Garage

Looks like a stud was dropped in there when the engine was reassembled... Unless you have had that head cleaned post tear down? Usually, it is pretty hard to get a screw in there once the intake is on

Does not look like a whole lot of damage. You could probably smooth it out and be fine. What does the piston top look like?

Best regards,

Michael

lucittm · lucittm's Garage

It looks like a screw rather than a stud because there is not an unthreaded portion in the middle. It could have been lodged in the area around the spark plug and fallen down when you changed the plug. Inserting the plug would have pushed it right into the cylinder.

The other scenario is that it was dropped into the intake system during assembly. At startup, it rattled around a bit and then jammed a valve open. It ran that way for awhile and then fell out only to get caught in the other valve. During this process, both valves were bent.

Where exactly did you find the pieces, in the exhaust pipe? What size is the thread? It looks to be 5 or 6mm. That would help to identify the souce of the intrusion.

I would re-use the head after all the sharp points are dressed down. The impressions will quickly fill with carbon and you will be fine. I wonder what the valve seats look like...

Good post,

Mark

jcge · 05-03-2009, 07:25 PM

Suggest you also check your conrod and bearings, and (depending on what you find) beyond. The mechanical forces as the piston moves over TDC are huge. The threaded impressions in your chamber attest to this.

sixgun · 05-04-2009, 02:24 PM

Thanks for the reply,s guys, I should have taken a better photo of the screw and related parts with more light. Sorry.-It is about a 3mm as best I can tell after the trashing it got in there [as well as inflicted] and therein lies the mystery. I found it by shaking out the cat over the bench top and out they popped. All magnetic...The screen on the cat exit holds all that stuff from going into the muffler. It looks as tho it might have been attached to a caged nut when it got in there........
As far as the valve seats go, they are surprisingly good considering what they have been thru. I think I can run them again, tho I will lap the new valves into them when they arrive. The piston top looks much the same as the head, mostly superficial damage.
I,m going to smooth the parts out and put it all back together with new valves. I know I could straighten them in a lathe with an indicator but what if there is the start of a crack in one of them? I don,t care to chance it!.....2 New valves are cheap when you consider what a broken one could do!
Thanks for the help guys.
Best regards.... George