1979 911SC - Broken Head Stud - minimum scope?

[craig.wilson1]

I've owned a 1979 911SC targa since 2000, did some reliability upgrades in the early years and have enjoyed relatively trouble-free driving for years. This changed earlier this year when I discovered at least one broken head stud. This is a driver quality car and I'm hoping to be able to do the minimum amount of work to get it back on the road, but, if it makes sense to do some minor upgrades while the engine is out, I'm open to that. I believe that the fuel lines are original and wonder if I should replace them? I'm also planning to do the work myself so I'll need to buy a few tools (yoke/stand) and likely other specialty tools. Looking for advice from the "better-informed" folks out there...

[mepstein]

Do a leak down to help determine the state of the heads.
I personally don’t like doing just a top end. You’ve done 3/4 of the overhaul and then what happens when something goes wrong. I’d rather tear it all down and know everything is good and replace what’s not.

[mhjjvh]

If you have the engine out anyway, it would be wise to check all head studs. And I would personally take of all heads and cilinders and check & clean the valves and see if there are broken piston rings.

[sir911]

You can never be too cautious. I recommend you replace your engine bay lines (and tunnel lines to be safe). I thought my out lines looked good until I felt the new line and couldn't believe how much more flexible they are.

The fuel lines are certainly easier to replace with the engine out. I just did replaced the tunnel line and did it in under two hours.

I'm with Mepstein on starting with a leak down and on a full rebuild if you get to that point. I considered only doing a top end for my 2.7 but I'm glad I split the case because my crank was out of spec.

[yelcab1]

Well, you asked for a minimum work sheet and you were told to rebuild the engine.

I was in your shoes some years ago with a 1980SC. What I did was a valve job, and changing ALL dilavar studs to steel studs, leaving the bottom alone.

Cost was minimal and the labor was mine.

[930cabman]

$20.k

[Magyar Kiwi]

Hi
To give a work scope recommendation, we need more information:
How many miles has the engine done ?
How many of these miles have you done ?
Engine maintenance history for the last 25 years ?
Engine maintenance history before your ownership ?
Compression test results ?
Leak down test results ?
Hot oil pressure, at idle and different rpms ?
Oil consumption ?
Oil leaks ?
Oil analysis results ?
Hoping this helps.
Cheers

[craig.wilson1]

It looks like yelcab1 is the only one who understood the question. I'm not looking to end up with an engine that was good as the day it left the factory. The car was running fine, oil consumption was acceptable and then one day during a drive, a strange sound came up and got increasingly louder while power seemed to drop some. I limped the car home, removed the lower valve covers and discovered at least one broken head stud.

So unless I did some damage during that short period, head studs are the only must-do repair that I can tell. But with the engine out, if there are some other "must-do" items that make sense, I was hoping to find out what that list might be...

[$yncro]

Unfortunately broken head stud there might be more to come with original dilivar studs. I would replace them with steel and taking all the heads off to get to the case is a must do. Regardless how well your car was running before..no short cuts with broken head studs to do it right imo. I just saw another thread saying triple of death leak. I would address those too. While heads are out, inspect everything make sure it's within specs.
Good luck!

[Magyar Kiwi]

Hi
Minimum scope option:
Cheers
https://forums.pelicanparts.com/porsche-911-technical-forum/1160618-extracting-broken-head-studs-engine-still-car.html

[Ian Comerford]

There’s some suggestions here
https://forums.pelicanparts.com/porsche-911-technical-forum/440761-things-do-while-engine-out.html

[craig.wilson1]

The gent that removed the head studs with the custom tools has way more talent than I and his "garage" definitely has more tools! I haven't seen a lathe since Jr. High School... I will be removing heads and C&Ps to hopefully make the stud extraction easier and I will replace all exhaust studs with steel ones.

Also appreciate the list of "other fixes" so far...

[PeteKz]

I’m with yecalb. The aluminum SC cases and bottom end are much tougher than the magnesium ones. If you have no case oil leaks, and the miles on the engine are less than 200K, i advise you not split the case. DIYers are not rebuilding warranteed engines for customers. We can do as much or as little as we feel comfortable. I would probably get the heads reconditioned while they are off, if more than 100Kmi. Bit only by a shop that has lots of experience with Porsche heads.

Magyar Kiwi asked the right questions. How many miles on the engine, and what do you know of its history? Then we can provide better guidance.

[Ian Comerford]

I had my 3.0 SC engine rebuilt at 172k miles five years ago and I itally thought we would do a top end overhaul. I was advised that once the engine was out and all of the top end and ancillary items stripped it was only another ten hours work to do the bottom end. It wasn’t a huge extra cost driver in the total bill and felt opportunistic. It’s now at 204k miles and singing along very nicely. Of course we don’t know what mileage yours is at as Pete mentions above.

[theiceman]

Originally Posted by yelcab1

Well, you asked for a minimum work sheet and you were told to rebuild the engine.

I was in your shoes some years ago with a 1980SC. What I did was a valve job, and changing ALL dilavar studs to steel studs, leaving the bottom alone.

Cost was minimal and the labor was mine.

yup i did this exactly, the bottom ends on these cars are solid , i considered this a repair not a rebuild. left the bottom end alone. been running 6 years since with zero issues..

more detail :

ran with a tiny metal on metal noise for about 2 years zero performance issue .. thought it might have been an exhaust type ping ... decided to check valve clearances. went o so a valve adjustment and i found the broken piece .. a year later..lol.. decided to do top end, took engine out ,, turned it over on the engine stand and two more studs fell out..

ended up replacing the 12 lowers with steel, upgraded to later tensioner sprockets, replaced chain ramps and other wear items, new chains with links etc. Machine shop said heads were in perfect shape and were confused on why i took them there, ( 200k km ) .

Cost was about 3K CAD at the time. used Waynes book and this site with some really helpful people. About another 1K to do first and second gear in gearbox

[craig.wilson1]

I bought the car in 2000 with 114,500 miles. Minimal maintenance records. PPI included a compression test (135-145 psi across all cylinders) and recommended addressing major oil leaks and doing a major tune-up with valve clearance adjustment.

In my 1st year of ownership I installed a pop-off valve in the airbox and had the PPI shop do a Carrera style tensioners conversion.

25 years later the car has 126,900 miles on it (it's a special occasions car ). I've done annual oil changes and a few valve clearance adjustments. I haven't found any metal particles in the used oil but have never had an analysis done. There is occasionally a blue smoke event at cold start, but it goes away in a few seconds and hasn't gotten worse over the 25 years.

My goal is to have a reliable car to drive on better weather days for another 10+ years. I love the old-school mechanical feel driving experience of the SC and accept that it isn't a powerhouse.

Hoping to get some input on a couple of potential scope add-ons:

I had considered replacing the original 95mm P&Cs with Mahle 98 P&Cs, but it seems that in order to get any noticeable power increase one has to spend significant dollars on things like SSI exchangers, Carbs or EFI, Twin Plugging, Cams, etc., etc. But I do wonder if doing just the P&Cs might be worth it for the reliability of new P&Cs along with a modest power increase?

If I do go this route, what is the safe limit on compression ratio running 92 octane gas?

I think an overhaul of the heads makes sense. I notice that LN Engineering offers a head rebuilding service for $2K + parts. Does anyone have experience with their work?

Again, I really appreciate all the input from others!

[proporsche]

Craig in your case i would do all steel studs have LNE (one of the best in this biss)do the valve job-possibly worn out valve guides.
You can have the P and C measured for wear..Most likely ok.. i`d put new piston rings after you see condition of the old .Reseal the engine and you`ll be done for a long time.
I would not worry about the bottom of the engine .The 911Sc are work horse..
This way, less expensive - will for for your buggdet.
Ivan

[PeteKz]

Craig, given that you have only put 12,000 miles on it in 25 years, I don't think you should change anything unless it is worn out. You don't drive it enough to get your money's worth out of improvements.

I would not recommend changing pistons and cylinders. A set will cost around $4500 and will increase your torque only about 7%, unless you change the cam, exhaust, etc. Is that worth the money to you?

As Ivan recommends, replace all the lower Dilivar studs with stock steel Porsche ones. Others will break eventually.

CR: The general rule is that you should not go above 10:1 CR unless you install twin plugs. Note: Most P/C sets have higher advertised CR than actual. E.g., "10:1" pistons are usually less, sometimes a lot less.

Ivan also recommended you should get your pistons and cylinders measured. You should do that as long as you have it apart, but at 126Kmi, I would not expect them to show significant wear. Keep your rings and pistons clearly labeled and sorted. I would not even change the rings unless the end gaps are close to the wear limits. If they measure good, put them back on the same pistons in the same cylinders.

Heads: Ehh, I would measure the guide to valve wear, and if they are within spec, just lightly lap the valves/seats and put the valves back in and put the heads back on. If you can't do this measuring, any local auto machine shop can. Of course, if they need rebuilding, send them to LNE or another Porsche specialist machine shop.

Resealing the engine:. See the thread about recommended sealers to use.

Remember, you're at the edge of the "slippery slope." If you do more than you have to, it will not only cost you more money (potentially lots more), but also add weeks to months to the job. Sending your heads out will add at least a month, probably several, because the shops/people who know this stuff are very busy, and you have to get in line.

NOTE: You have two excellent Porsche specialists near you. Al Ikosmal at X-Faktory, and John Walker; both around Mt. Vernon.

[mike sampsel]

Originally Posted by craig.wilson1

Hoping to get some input on a couple of potential scope add-ons:

I had considered replacing the original 95mm P&Cs with Mahle 98 P&Cs, but it seems that in order to get any noticeable power increase one has to spend significant dollars on things like SSI exchangers, Carbs or EFI, Twin Plugging, Cams, etc., etc. But I do wonder if doing just the P&Cs might be worth it for the reliability of new P&Cs along with a modest power increase?

If I do go this route, what is the safe limit on compression ratio running 92 octane gas?

I went with 98 mm Cyl/Pistons (9.5 CR), 20/21 Web Cams (they claim these are the hottest you can do with CIS) and I have an active sport cat. "Crotchety guy" claims these provide same power as going to SSI exchangers (still have heat too).

The car is much more peppy than the stock SC was, I figure I'm close to 200 hp maybe a tad more. With our light cars this increase is not so modest.

At your milage I'd consider investing another $1000 (inflation might make this more) or so and I'd have the heads and valve guides done (you seem to be at the milage for this). Went with new valve springs too, do not want to float a valve.

Of course you will definitely want to change out all the lower head studs, might need to heat some for removal.

JE pistons were about $1800
Web cams about $1000
Head work about $1000 (shipped)
98 mm cyl I got a used set new (around $4000) can be pricy
Active sport cat $1000
Steal head studs (not sure how much)

You'll save a bunch doing it yourself. At 9.5 CR you need premium gas and cooler plugs than the stock SC. Tricky parts for me was sealing the engine (best to have a second set of hands for this) JW uses different sealant than the OEM style (OEM lock tight 574?) I used the OEM, and valve timing. The tool from Stomski racing really made making multiple checks of the cam timing a breeze for me. Check out the "Complete Engine Sealant" thread in the engine builders forum if you go this route. Henry has built many engines and this thread is great with much excellent advice from Henry Schmidt.

So in addition to the above costs there are tools you will need to obtain, for setting the ring gaps install of pistons etc. Also, if you get new pistons/cyl you will want to have someone install the wrist pins in you cylinders, and this step would suggest new rod bearings.

I had my crank polished and spaced, at 115K miles the crank was perfect almost (these cranks are impressive). Once I took the crank out I went with glycol mains, different make of rod bearings though (add another 500).

So you're looking at a neighbor hood of 10K (+- 20%) depending on what you pay for cylinders and tools to do your engine yourself, and other add ones (chains guides etc).

Oh and send your oil pump to Supertech (Henry Schmidt) I get great oil pressure now and Henry is great to deal with (about $350 is my guess).

It was a great project for me. My first and only rebuild was very satisfying but I knew there was some risk of having to spend more. I got lots of help here (most good advice some was a bit snarky, but oh well). And I had another helper too who has helped and provides some quality used parts too.

Cheers

[craig.wilson1]

I found a reference in Wayne Dempsey's Engine Rebuilding Book that suggests that if I happen to have an engine that used Alusil cylinders (vs. Nikasil) that they aren't re-usable? Not sure if this is still the conventional wisdom...?

If they do turn out to be Alusil, can I remove the cylinders with the pistons still in place (just lift the cylinder enough to expose and drive out the wrist pins) to avoid disturbing anything?