1 Topic by sethrobot (edited by sethrobot 2023-11-03 03:04 PM)

  • Registered: 2023-02-14
  • Posts: 3

Topic: Help? Reviving a 1975 Porsche 911

So my wife was out of the country and my neighbor tells me he's got an old car in his garage on jacks that he started fixing an exhaust leak on about 25 years ago but he's starting to think he may never get around to finishing, and that he'd like to see it go to someone that would get it back together.

It's a 1975 Porsche 911 with wide body flares that's in pretty decent shape, but in a state of multiple simultaneous half-completed projects (dash, headlights, exhaust), so I of course buy it. I've done enough to get it back on the road and holy hell this car is fun when you open it up, but it still isn't running "great" around town or when cold, and it leaks some oil here and there.

I would love to get some advice from someone who's worked on these old magnesium air cooled engines before on where to start chasing down cold start issues and oil leaks. I'm doing the math on if I should try to keep chasing down one symptom at a time or just drop the motor and go through it end to end. Anyone gone down this path before and willing to advise?

Cheers,
Seth

  • From: Paraguay
  • Registered: 2019-11-21
  • Posts: 6

Re: Help? Reviving a 1975 Porsche 911

Congrats on the Porsche 911 find! For cold start issues and oil leaks, start with a thorough inspection. Check common leak sources and look into the fuel and ignition systems for the cold start problem.

  • Registered: 2023-02-14
  • Posts: 3

Re: Help? Reviving a 1975 Porsche 911

Thanks Cameron, good advice. I've ran through all the normal engine stuff (fuel + air + spark) but the WUR, thermotime switch, and general CIS setup are all foreign to me, so dialing that in is a bit of a black box having never worked on one of these systems before.

  • From: Aurora, IL
  • Registered: 2012-02-06
  • Posts: 910

Re: Help? Reviving a 1975 Porsche 911

sethrobot wrote:

Thanks Cameron, good advice. I've ran through all the normal engine stuff (fuel + air + spark) but the WUR, thermotime switch, and general CIS setup are all foreign to me, so dialing that in is a bit of a black box having never worked on one of these systems before.

Is it more important to you for the car to run well or have period correct engine management? Have you considered taking it to an air-cooled expert? How important is your money and your sanity to you?

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  • From: Tustin, CA
  • Registered: 2010-12-30
  • Posts: 3,275

Re: Help? Reviving a 1975 Porsche 911

Those midyear 911s had several problems common to all of them. 

1.  Heat exchangers rust out (i.e. guessing your exhaust leak)
2. Rust in bad places.  They were pre-galvanization or poor galvanization can't remember which.
3.  Broken head/cylinder studs.  They tended to run hot and broke studs.

If it's been sitting too long I wouldn't be surprised if the CIS distributor was gummed up.  Honestly, my advice would be that step one is to send out the fuel distributor to be refurbished.  Probably the injectors too.  Clean out the fuel tank and lines.  Buy multiple fuel filters and replace after the first and 2 month after it's going.  It's been many, many years since I messed with one but I seem to recall having to use a long allen wrench through the fan shroud and an exhaust sniffer to adjust mixture.  In any case, I'm sure adjustment instructions are available through Mr Google.  I would plan on doing the turbo chain tensioner upgrade.  Another failure point on those were the tensioners and it's an interference engine.   For what is essentially a mass produced exotic, the engines are surprisingly stout.  I would resist pulling it unless it exhibits some serious symptom.  The bottom ends on those are bulletproof and really shouldn't need work unless it's really high mileage or poorly maintained/run out of oil.  If the compression varies by more than, I don't know, 20lbs? I might have the heads redone but I'd resist splitting the case until I had to.


The midyear cars were kind of the red-headed stepchild of 911s.  I remember looking at a 76 911 25 years ago with bad heat exchangers.  The replacements cost more than what the car retailed for.  Since the ones from before then and after then have risen in value the midyear cars have come up too.

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  • From: Tustin, CA
  • Registered: 2010-12-30
  • Posts: 3,275

Re: Help? Reviving a 1975 Porsche 911

Wait, I just remembered.  The chain tensioner fix dealio was actually a little donut that clamped onto the tensioner shaft.  It kept the tensioner from fully collapsing and allowing the chain to skip teeth.

1990 RX7 "Mazdarita"  1964 Sunbeam Imp (IOE 2013 Sears Pointless) 2002 Jaguar x-type (Winner C-Class 2021 Sears Pointless)
Gone bye-bye
1994 Jaguar XJ12 (Winner C-Class 2013 Sears Pointless)  1980 Rover SD1 (I Got Screwed 2014 Return of Lemonites)
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Re: Help? Reviving a 1975 Porsche 911

CIS injection is easy. If the fuel distributor is clean and the diaphragm is intact, and the fuel pressure is to spec, they run fine. Rebuilt the FD in 6 or 7 Benzes and 2 Audis,  no issues. Cheseroo is right about the mixture adjustment being a 3 mm Allen,  but that only pertains to idle mixture.

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Re: Help? Reviving a 1975 Porsche 911

CIS injection is easy. If the fuel distributor is clean and the diaphragm is intact, and the fuel pressure is to spec, they run fine. Rebuilt the FD in 6 or 7 Benzes and 2 Audis,  no issues. Cheseroo is right about the mixture adjustment being a 3 mm Allen,  but that only pertains to idle mixture.

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9 Reply by ukemike (edited by ukemike 2023-12-17 10:23 AM)

  • Registered: 2014-11-11
  • Posts: 148

Re: Help? Reviving a 1975 Porsche 911

I used to have a 1976. I'm so jealous.

1 join to the forums at pelicanparts dot com.  That is THE 911 forum, or at least it was when I had one 20 years ago.
2 1975 should have a galvanized body but not fenders, hood, or doors, those were galvanized starting in 76. 
3 the proper chain tensioner upgrade is to replace the spring loaded tensioner with the carrera style hydraulic tensioner. This has almost certainly been done by now.
4 valves need to be adjusted periodically on these. It's super had to do on the valves deepest in the engine bay with the engine in the car.  A good mechanic who knows his way around these can drop the engine out, do that, address most leaks and get it back in easily enough.  Find a good mechanic.  Ask on pelicanparts for local recommendations.
5 A badly maintained porsche is a nightmare. A well maintained porsche is a joy. Find that good mechanic and get all the maintenance tasks done and then restart the clock on all of them and do them as recommended by the factory.
6 Don't ever sell it or wreck it. If you do you'll regret it for the rest of your life.