911SC Top End Engine Rebuild 1978 model

[richardstephens777]

After trying every trick in the book to cure the oil leaks on my 1978 Porsche 911SC I have finally come to the conclusion that I need to take the engine out and do a rebuild to cure this issue. I have owned my 1978 sport SC for 27 years. I purchased it with 100k miles on it and proceeded to add another 135K miles. For most of those miles it has run really well.

If anyone is thinking of taking their engine out then a hydraulic lifting table purchased from Machine Mart, as shown below, is a very handy device to have. Just undo the 4 main bolts on the engine & gearbox, disconnect the pipes and electrical connectors, oil pipes then drive shafts. Then a few handy pieces of wood to protect the engine and it can be lowered from its compartment.

I take the heat exchangers and rear exhaust box off before putting it on the lifting table. This means I do not have any vertical bolts to deal with. The engine still in the SC was looking very messy. The oil leaks seem to mainly be coming from cylinders 3 and 6. Let’s see if I was correct when the engine comes out.

Next part to follow shortly. Rich

 

[fxm911]

Nice work Richard.
Looking forward to following your rebuild and pick up a few tricks on the way.

 

[flat6buster]

Gosh I wish I had the skill to do this sort of thing myself. Watching this thread with interest.

 

[richardstephens777]

Part 2
Put a trolley jack under the gearbox to support it. Drop the engine onto the lifting table. You will need to remove the clutch leaver in order to slide the gearbox from the engine. The release fork is held on by a circlip.

Undo the four nuts holding the gearbox to the engine and slide it off. Then the lifting table can be lowered and the engine wheeled out into the open. On removing the clutch leaver arm I noticed where the cable attaches to it, in the hole at the top on the right fork below, the cable had worn a notch in it from over 40 years of use. The right one below is the old one and left is the new one.

I stripped down the engine taking the heads, bores, pistons and timing covers off. The biggest challenge is usually undoing the cam nut. Using the correct Porsche crows foot tools is very important. Clean the nut with brake cleaner to remove all the oil. Otherwise it will slip off. The camshaft securing bar is also a must tool to stop putting any excess force on the chains.

Removing everything is fairly straight forward. Remove the bores and pistons in the order stated in any good manual or web link. You will be left with a tripped top end with lots of dirty parts on the floor.

On the crank you can see the Clewett timing wheel for the OMEX fuel injection which runs on my SC. I still have the old CIS system if I want to go back to stock.
Part 3 to follow shortly.

 

[RoyS]

I cured a major oil leak on my 1978SC last year. It was the camshaft seals so oil was being pumped out under pressure. Local specialist wanted to do a top-end rebuild with estimated cost of £7K, so decided to do it myself as it can be done without removing the engine. Total cost in parts was about £60. However, I did buy the Stomski cam tool (cost £250 with postage!) but is rather better than the crow's foot. All in the job was just over £300, some saving on £7k but it's not a job for the faint hearted as the cam timing is critical. How did you compress the chain tensioner?

Roy

 

[RoyS]

Just looking again at the photos of your camshafts; the have different fixings. The one on the right has the cam nut as in my car but the one on the left has a bolt of the later type. Are you running different camshafts?

 

[richardstephens777]

Yes. A previous engine builder fitted a 964 cam by mistake. On the receipt was an SC camshaft number. I have put two new SC camshafts in now.
As for the chain tensioners. I removed the cam nuts/bolts and pulled off the timing cog. Removed the idle wheel. Put a piece of wood in the timing cover and levered a small crow bar against the top of the tensioner. Then slipped in a split pin the hold it in place.

 

[richardstephens777]

Part 3.
I took the engine to bits to see the reason why it was leaking so much oil. I inspected the heads to see that there was a groove in the head where it meets the top of the cylinder:

If you run your nail over the outer sealing area you can feel a step which will cause the heads not too seal properly. Some machining is required to flatten this so it will seal properly.

Both A and B need to be milled by 0.25 mm on all 3 or 6 heads. The standard cylinder gasket is 0.25 mm so you need to use the thicker one of 0.5 mm to keep the cam carrier lined up with the timing case. Otherwise you risk the camshaft snagging due to poor alignment.

Interestingly when I removed the starter ring from the clutch pressure plate I noticed a date code on it of June 1977. It’s nice to have the original and still ok to use but showing a bit of wear.

Part 4 to follow shortly.

 

[richardstephens777]

Now it’s time to fit some pistons. Which ones to go for? How about some Max Moritz 98mm pistons from Mahle:

Putting the piston rings on can be tricky. I use the tool shown below. Put the open end of the piston ring in the tool. Place the piston on a solid surface like a bench. Hold the adjacent end of the piston ring up against the piston. This means you will minimize the amount you open the piston ring when using the tool. Open the ring up with the tool and slide the ring down. There are some useful ‘youtube’ videos from Mahle on the subject of putting piston rings on.

Another real tricky job is getting the piston circlips in when putting the pistons on the con-rods. I use the Stomski circlip insert tool which is great. The SC uses 22 mm piston wrist pins so you need the 22 mm tool:

The pistons look great in the engine. It’s nice to takes the capacity of the engine from 3.0L using the old 95 mm pistons to 3.2L with these 98 mm pistons.

These pistons are good to use with single sparks plug engines since they follow the same design philosophy of the old swirl pot CIS pistons used as standard on the SC. You can see the wedge shape design in the picture.

Part 5 to follow shortly.

 

[richardstephens777]

If your engine sounds a bit clicky on idle it could be that the followers are worn. A common cause of followers wearing out quickly is a starvation of oil. This is caused by the sprays bars having some debris clogging the holes. This can easily happen to the followers on cylinders 3 and 6 due to the flow of oil in the engine and spray bar. So it’s very important to clean the spray bar. I removed the input connection and output bolt, which you can see at the top of the picture. I then sprayed brake cleaner into the spray bar and inspected the end of the bar for debris.

You can drill out the insert at the top of the big circle above and then clean the spray bar out. Then push a new insert into the hole. It depends how much crap is in the spray bar.

I took the opportunity to measure the exact TDC mark on the engine with the fan housing on. I used the gauge to see when the piston reached TDC and then took a picture of the mark on the fan housing for future reference. It’s very useful for the cam timing to the get this exact.

Jobs to do while the engine is out. Change the trailing arm bushes.

Then that really tricky brake pipe which goes from front to rear. Typically the end of the pipe rusts and it’s difficult to spot.

Part 6 to follow shortly.

 

[911hillclimber]

Nice idea to check tdc at that stage with the dti.
Were the marks on the pully/case exact? I've done 4 911 aircooled rebuilds, and have always assumed the marks are bang-on.

 

[richardstephens777]

I took a picture at TDC. The mark was slightly to the right hand side of the mark.
Porsche do state a bit of tolerance with the cam timing but its nice to get it spot on.

 

[911hillclimber]

I took a picture at TDC. The mark was slightly to the right hand side of the mark.
Porsche do state a bit of tolerance with the cam timing but its nice to get it spot on.

Thanks for the pic. I guess the Porsche steel pully may not be so accurately made as the Clewett?
I may have to fully re-build my 3.2 this year, so I learn something every day!
Graham.

 

[richardstephens777]

The flywheel was looking a bit worn. I decided to give it a Patrick Motorsport update using a lightweight steel flywheel saving 3.25 lbs.

I also found a lightweight aluminium 911 1972-86 915 Sachs Power Clutch Kit from Type 911 which saves 1.7 Kg.

Total saving of 3.2 Kg rotating mass which is nice to have and should make throttle response a bit sharper.

After assembling the engine the cam timing needs to be set. Make sure you set the follower gap correctly to 0.1 mm, keep the timing chain tight and only rotate the engine in the clockwise direction to achieve the final setting at TDC. Porsche fiddled about with the SC cam timing which was used in the Carrera 3.0, SC and 3.2 Carrera. The timing varied from 0.9 mm to 1.8 mm with 1.25 mm for the 3.2 which is what I set mine too. Out of interest I checked the valve clearance with this setting. Usually the closest valve-piston distance occurs at 10 degrees. My readings on the inlet were:
TDC – 4.5 mm
5° - 2.75 mm
10° - 2.85 mm
Porsche quote 1.5 mm min inlet and 2 mm min exhaust valve-piston gap.
Engine is now looking good:

Part 7 to follow shortly where we put the engine back in the car.

 

[RoyS]

How did you check valve-piston clearance?

 

[richardstephens777]

I used the follower screw method. Each complete turn of the follower screw moves the valve 1 mm. Set everything to where you want it and carefully turn the screw noting the number of turns until it touches the piston.

 

[richardstephens777]

Now it’s time to put the engine back in.

Use the jack to steady the gearbox and get the height to put it through the transmission hole in the chassis. The engine slots in nicely:

Make sure you cover the inlet ports. You do not want to drop anything in there.
Then it’s a question of assembling the fuel injection, connecting all the ancillaries, drive shafts, oil lines and exhaust.

As you can see I have a non-standard fuel injection system. I still have the original CIS system in working order.
I will be doing a separate post on adding electronic fuel injection (EFi) to your 911.
Watch this space.
Richard Stephens
911SC Technical Advisor