1979 911SC Where to start???

[J Saunders]

Hi all!
I picked up a 79 911SC 59k Black Metallic with Cork interior. 15k Bone Stock! Mom's old friend is the 2nd owner, has been sitting on this car for 20yrs and decided it's time to liquidate his assets as he moves into his later years. Knowingly gave me a huge discount cause I've been bugging him about it forever. I consider myself very lucky...so far LOL. It's got some stuff going on but has been treated really well through it's 42yr life.

My eyes are bulging with the opportunity to make this baby beautiful again!! Paint is pretty good, prob just a cut and polish for now (driver). Needs interior refresh. Lived in a garage on a dusty ranch and definitely has some ranch love on it.

Tranny is solid but will need a synchro job on 1st and 2nd. Had to learn to drive it if you know what I mean. A little double clutch here and there but not too bad. The old tricks seem to work for now.

Suspension is acceptable but could use turbo tie rods and new bushings I'm sure. It's up to 115 degrees summertime at this ranch so all the rubber parts are seeming suspect to me right now. Strut bushings look pretty torn up.

The engine, while completely drivable and low milage needs some things.
Needs updated Carrera tensioners. Has some leakage from the oil return tubes and possibly some leaking from tensioner covers as well as triangle of death area but nothing severe....few drops overnight from each area.

So to my main question... It has 2 broken head studs but the seal is still strong with no leakage. Do you all think I can drive it (not crazy) while I wait to get these replaced or will I damage the engine???

Secondly...If I get the head studs replaced should I just ask my guy for a full top end rebuild? What kind of extra costs are incurred with the additional rebuild? My guess is there is significant teardown with a head stud replacement. I guess I just want to get as much done while I have the engine out. I want to go for it but I feel like I'm gonna end up deep in the hole. What do you think? Would really appreciate some advice.

Thanks,
Justin

[Flat6pac]

Do safety items first
You can’t fix everything at once
Synchros, try to adjust the clutch cable.
Make sure the clutch long arm can freely pivot on the vertical shaft
If you take the heads off, do a valve job and change all 12 bottom head studs.the cylinders have to come off to get threads cleaned and broken studs out
Don’t concern your self with Carrera tensioners, use tensioner guards with what you have and put the $1000 into the top end work
Turbo tie rod ends, that’s a concern when you have everything else done. Not a safety factor at 60 K miles
Just a couple thoughts
Bruce

[gssereik]

Some have said that you can drive it for a while with no issues but my advice is not to drive it with the broken head studs as it could lead to more damage. My 83 SC with 127k miles total was driven too many miles with broken head studs which resulted in seven broken studs and ultimately caused irreparable damage to the tops of four of the cylinders. The heads took an extra beating too. I was able to source a set of rebuilt heads rather than rebuild the old heads which will likely require a deeper fly cut to cylinder mating surface due to the damage caused by the heads beating against the cylinders. Best if luck. Looks like you have a great deal on what should ultimately be a great 911 for you. Based on mileage it sounds like full top end rebuild should not be necessary.

[Richey]

From my experience , your SC may not need a valve job at 50,000 miles , remains to be seen . I'm sure the rubber centered clutch disc has been replaced . The oil T-stat o-ring and the trans input shaft seal need replacing . And damage may occur if you drive the car with 2 broken studs , the cylinder and cylinder head may be damaged .

[Walt Fricke]

About everyone is apt to agree that fixing the stud issue is pretty important, and sooner rather than later. If there are reasons to put that off for a while, you are the one to balance the risk. But the engine and transmission are coming out at some point. Why not now?

Interesting that a low mileage transmission has 2d gear synchro issues. But you can't mistake those. 1st gear would be even less likely, but whoever takes the tranny apart can tell easily enough what needs replacement and where. 3d often is the most abused, as you hurry the upshift accelerating. That all will settle itself. Synchro replacement usually calls for replacement of the slider (which is moved into the synchro and engages the teeth).

If this really is low mileage, I'd be inclined to leave the bottom end alone., which seems to be your plan. For the top end, do (or have done) a leakdown test. You should have no leakage past the valves. And, at low mileage, basically none or very little past the rings. This would suggest leaving the heads alone. But a shop (or you, if you like this stuff) can check for valve guide wear. If basically none, something else to leave alone. But that is a wear area. Checking costs some money, but less than repairing something which doesn't need it.

I'd go with the tensioners unless this car has the updated idler arms and the "turbo" tensioners - there are those who think those fixes solved the tensioner failure issue, and the pressure feds were suspenders to what had become a just fine belt.

You can do the suspension stuff any time. If you plan on a shop doing it, and have the budget, it makes sense to have them do this stuff while they have the car there doing the engine work. If you are going to do it, you can wait. None of it is apt to be critical. I'm thinking wear rather than just age is the biggest factor here. These cars handle great right out of the box. As for the tie rods, you can inspect the joint at the inner attachment. It has rubber bushings, and they should have no slop to them. Stock is like a half a U joint, intended to allow up and down motion. Mine (on a 2.7) had somehow been installed upside down, so to speak, somewhere, so the obstruction to articulation this produced had about worn the rubber out and replacement was a no brainer. If they need replacement, no reason I can think of not to use the turbo setup. The turbo, after all, was designed and set up as a road car.

[ahh911]

Walt,
Been meaning to bring this up, but a leakdown tests may show false positives. I had most of the exhaust valves slightly warped, but the carbon buildup on the valve seats allowed no leakage. So basically an underdriven car would have passed. For me, compression is more important, it tells of massive issues, if the engine hasn't been rebuilt, it will need to anyhow (new valves, new valve stem seals at the least) and a leakdown seems like placebo. Am I wrong?
Phil

[Richey]

I believe you are wrong , a leak-down test is a good indication of engine condition . There is no way carbon buildup would stop leakage , something else was happening . The valves are always rotating , so carbon sealing a warped valve seems impossible .

[ahh911]

Possibly,
Every exhaust valve was slightly warped from heat and time I suppose. No strike marks. When I took the heads off, I put some degreaser fluid in the chambers, nothing leaked for three days. Then I pressurized the port using a pretty decent shop vac, no bubbles. I don't know, but it sure looked very well sealed up, but the carbon or hardened oil deposits would not leak. Now I remember, I rotated the valve a little from their initial seat position and cleaned off some carbon, then they leaked a little, but it wasn't much and the gunk just seemed to seal it up. Car drove fine, compression was good.

When the valves were replaced and the valve seats machined, there was less than 1/2 thou gap here and there, it still could pull 20inHG, but these things leaked like crazy with the same test as the original gunked up valves.

Maybe you're right, but this assumes that an old slightly warped valve in an oval valve guide bore still spins around (my guide wear was slightly oval on some exhausts, if I recall, I'd have to check my notes). Also, what if the seats are beaten in time and heat to the same angle as the valves. Do the valves still spin if all of this has occured? I can't say, but surely there are some who have done a leakdown and then pulled it apart and had slightly warped exhaust valves and gunked up seats/valve face.

Anyhow, more of just a thought process I'd had than anything else. A leakdown is obviously going to highlight certain elements. I'd run a leakdown on a rebuild before a 40 year old car, the 40 year old would get a compression and assume a top end rework down the road anyway, the compression would just highlight larger issues that would need immediate sorting, especially with head studs.

Checked my notes, some guides were about 2.5 thou oval, all the exhaust valves did not leak, just one intake slightly. Also, how warped were the valves? I checked them and they were 4 thous/inch gap between the valve face and the machined valve seat. It was just weird that nothing leaked much before the rebuild, i retried the original warped valves once the head came back, and boy did they let air through. I have no explanation.

Edited, read more of my notes, the original exhaust valves that sealed excellently before rework was done had 4 thous/inch gap between the valve face and the seat when tried on a the newly reworked heads, a leakdown would not have shown the warped valves for whatever reason So there I have it, a leakdown for this aspect would have given a false positive for my engine, mind you it ran okay.

Phil

[Jeff Alton]

You are getting some advice. Take all advice for what it is, advice. Including mine....

For sure, not addressing the Head Stud problem will lead to more damage to those cylinders and heads with affected by the broken studs.

A leakdown test will not reveal worn valve guides or seals. As long as the valve sits tight to its seat, leak down will not be affected. It will reveal other issues for sure. A leak down is done as a second test after a compression test that yields poor results. The leak down test will help pin point the cause of the less than optimal compression test results....

[breakerbar]

Just my experience with an 82 sc -

I drove it with a couple of broken head studs for 2 or 3 thousand miles. What finally forced my hand on a complete rebuild was a chain tensioner failure. It didn't seem catastrophic at the time. I actually shut the engine down. It was still running, just very poorly. That loose chain really made a mess in there, though. I went into the rebuild thinking I was just going to do the top end, but once I realized what had happened and began finding the results of it, there was no going half way. I don't really have a side on oil fed tensioner vs. lock debate, but will probably opt for the oil fed, just because of my experience. Of course the original part lasted 125k miles and 40 years. A $5 part to add some protection is an expense I really wish I'd made.

As for the head studs, it turned out 7 were now broken, all bottom of, course. I did not find any damage that I could attribute to this. The engine was really running pretty good up until the end, too. I find this kind of amazing.

[brighton911]

Congrats on the car Justin. Good advice on repairing the head studs. A local guy was not aware he had issues and kept driving his. Ruined heads and damaged crankcases + much more cost him plenty. As others have stated, compression then a leakdown will give you valuable information. Enjoy !

[Cairo94507]

You have heard it all above. That is a nice looking car and I hope you enjoy it and make it a beautiful car again. I had a brand new '79 SC coupe and it was a great car.