altarchsa

This is embarrassing, but I want to tell you a story that might keep one of you from making a similar mistake.

I bought a 109K mile, '89 C4 about 2 1/2 years ago. The seller owed an "exotic car" garage $11,300 for repairs that involved first a top end, and then a bottom end rebuild after they had mis-diagnosed the real problem. Lots of new parts, obviously, in an $11K+ bill. I thought I wouldn't have to work on the car for years.

After about 4 months, I experienced a catastrophic failure, dropping the intake valve in #2 cylinder. It was quite serious by the time I got it stopped, as you can see from the photo.

I had done 5 rebuilds on 70's era 911's, so I rebuilt the engine myself. I found that some valves were worn past spec, which the exotic garage missed and which apparently caused the first failure. I replaced worn parts and sourced a matched used piston/cylinder/head for #2. It ran great until I autox'd it in Dallas a few months later. After only 6 spirited runs, it developed a "tinny" sounding knock. I tore it down again and found a piece if metal that looked like half a pair of valve keepers lodged between the valve and seat in #5.

I could only guess that the "less than qualified" garage that had done the previous work (there were lots of other problems, in additon to not checking the valves in their rebuilds) had dropped the keeper down into the injection system and didn't notice (or take the time to look for it). I had meticulously accounted for all my parts in my repair.

I cleaned the lower injector tubes, put it back together and got it on the street and, again, it ran great until another autox in Dallas when it started knocking. This time a valve was bent and there was a lot of shrapnel in the cylinder. I thought it was from the rings lettting go and breaking through the top edge of the piston.

Lather, rinse, repeat, I put it back together, this time putting a lot of additional new parts in to replace anything that was even close to wear limits. I had invested so much of my time, I was sure it was going to last. This car was now going to run "like new".

And it did.......... for three days. You guessed it, another knocking noise.

This time it came on immediately after I restarted it after an hour-long drive. I shut it off immediately and there was no significant damage, again to the #2 cylinder, which had a small piece of metal jammed into the head of the piston.

I'm embarrassed to say that it took me 3 rebuilds to finally realize that there was another cause for the problems, other than parts letting go in the cylinders. I knew it had to be something from the injection system, as there was no other damage to the cylinder that could have generated the piece of metal jammed into the piston.

I tore the injection system down and found a remaining small pile of shrapnel, obviously from the original failure, mixed in an oily sludge in the bottom of the lower horizontal, large diameter tube. Apparently, the force of the piston in the original failure had pumped the oil and shrapnel up past the broken valve and into the injection system, where it coagulated when it cooled. With dilution of oil from fuel, and the vibration of harder driving, the shrapnel had continued to trickle down past the intake valves into various cylinders.

In a few days, it will be on the street, this time running like new for a LONG time. I'M SURE OF IT. Like I said, I'm embarrassed to tell you what a naive DIY mechanic I was, but maybe you can avoid an expensive rebuild, or two, if you have a catastrphic failure of an intake valve.

CLEAN OUT THAT INJECTION SYSTEM, thoroughly, while you have it down! Happy driving fellow Rennlisters.

DAVISRILEY

All I can say is ouch. Good to hear that you have finally gotten to the bottem of it, sorry it took 3 times to get there. Good luck.

941MXVET

Good advise, things like that can be humbling...
ask me how I know.

Anyhoo, glad to hear you got to the bottom of your issues.

BlueHeeler

Ugh that story makes me feel ill.

zunix

Oy vey. That's painful - but good advice. Thanks and best of luck.

911Jetta

Your post is the next step of the recovery process...

Ok, mistakes were made... but I envy the knowledge you have of these engines! One day I hope to summons the courage to change my old pressure sender...

I have to believe you've got it now. Like you said, time to enjoy the car. Plan a road trip to complete the circle!

ian89C4

Wow, it is from stories like those that I am glad I am paranoid about cleaing everything, even if I am not going to mess with it, while I have the engine out.

911Jetta,
The oil sender is quite easy, even removing the engine was pretty easy. If you need help ever I just live down by Ft. bragg. Shoot me a PM, I would be happy to help. I have just about enough knowledge to make me dangerous right now.

Rocket Rob

Its a lesson to all of us to double check everything when you work on your car. Back in the '80's, I was into hot rodding VW bugs. I had purchased a new 2110 cc engine and as I was installing it, I dropped one of the intake manifold nuts. I searched and searched and couldn't find it. I decided that it must be on the floor somewhere and proceeded to install a new nut. I was so happy when the engine fired up, it sounded great......for the first 30 seconds. Then clank - clunk. The engine would not turn over. I dropped the engine to find out what went wrong. I found the "missing" nut. It had fallen into the #2 cylinder. The nut was all banged up. I keep this nut above my workbench as a reminder to account for every part that you take off and reinstall.

aj986s

Unfortunately......it seems the best lessons are usually the most painful ones.

911Jetta

Hey Ian,
Thanks for the offer... when you first started posting I noticed you live in NC. Did a quick Google map from Raeford to CH... I was wishing we were two hour closer. Let me know if you ever swing by the area, I'd love to see everything you've done to your car. Have you been to VIR, they just released the 2010 spectator race schedule? I live right along the way.
Best,
Udo

Wachuko

+1

Wish I had your patience and mechanical skills... what a horror story.

DWS964

An expert is a person who has made all the mistakes that can be made in a very narrow field.
- Niels Bohr

Have Fun, Be Safe

hawk911

hmmm- there's a project 914 that would be fun to tackle, but I'd be remembering this story the entire time

frankvan

Just for clarification, when you say "injection tube" and "injection system" do you mean intake? AFAIK, injection is what the injectors do with fuel and the orifice of an injector is quite small for metal shrapnel to come out. Intake is what the air flows through to the cylinders. Want to make sure I'm not missing something.

crg53

Hi DWS964, where did you find that statement, so few people knows Niels Bohr, everybody knows Werner Von Braun?