79sc Engine Out Story - backfiring at idle (Long)

[QuakerJacket]

I don't have any questions, but instead wanted the thank everyone that has helped answer all the questions posted on here (technical and engine rebuild forums) over the years - it was immeasurably valuable during my recent work. (Long - so stop reading here or skip to pictures if not interested! Mods, if this isn't appropriate for this forum - nuke it).

Backstory:
I've had my sad neglected '79 911sc for almost 20 years now, and two different house restorations over that time period have never given me to the time to properly take care of her issues.

It came to me with no heat, terrible seats, horrible shifting, and a significant oil leakage problem, along with an occasional backfire and even rarer no start during really hot weather. I sorted the seats and shifting right away, but hadn't done anything else (other than oil changes) till now.

I have a 993 c4 Cab and, as you can imagine it got driven way more than its unheated, leaky, backfiring, sometimes non-starting cousin. Neglect and lack of driving finally caught up last year when it started backfiring during idle through the intake and I put it away for good until it could all be sorted.

Enter COVID. Being able to work from home meant that I could trailer the car down to GA (from Chicago), stay with my parents and work on the car in my Dad's shop during the winter. Being there also meant I didn't have any option to work on my house instead of the car...

So the goal was to pull the engine, install oil fed chain tensioners (more on that later), examine and fix oil leaks, add heat with backdated system, check clutch, check valves, plus check and replace as necessary all the other normal things...

In addition, it's getting paint, new glass, new dashboard, new radio, new door panels... but that's not done yet and is for another post...

Off to Georgia... and end of first post

[walt]

Gold is a fantastic color hope you are not changing. Keep us up to date on your progress.

[QuakerJacket]

First up was getting the engine out. I'd never really worked on either of my Porsche's, so getting engine out successfully out was the first problem.

I probably spent as much time getting the car jacked up as I did on the rest of the engine removal... but with all the threads on here over the year's it came out with no problems. I was able to borrow an atv lift and a transmission jack and the combination worked really well getting it out and back in as I was able to raise the height of the engine and trans separately. Lots of pictures and labels at this point helped tremendously when putting it back in.





Next up - cleaning.
I put it on a cart my Dad had made and started cleaning everything I could get at while waiting for my engine stand adapter. I've dealt with some dirty engine before, but this was another level. Cleaning and more cleaning and then more cleaning. Ughh. The car will always be a driver, so I only wanted to get it clean enough to work on properly. On the negative side, it appeared that my engine was leaking from just about every possible spot - no area was spared and it felt like I would never get through all the gunk.





Next up - from cleaning to fixing and sealing

[QuakerJacket]

Once the engine was less dirty, I could finally get to work.

As I mentioned, the main problem was the backfiring/misfires at idle, so the first thing I wanted to do was check the valves. Checked and adjusted and nothing was too bad. Also held my breath while checking the engine studs for breakage. So far so good. Then did a leak down test... all was well until I got to 4 and I didn't get any pressure... A sticky valve was definitely one of the possible misfire reasons and would make sense with the lack of driving, but some gentle persuasion with a mallet and brass bar freed it up. I knew it could still be a problem, but it at least allowed me to breathe again.




I had been considering putting the RS rocker arm seals in, but that was the one part of the engine that looked good, so I just checked the torque on the bolts and moved on. I used sandpaper on a table saw top to flatten the upper valve covers, refinished with a little paint and put back on with new silicone gaskets (very impressed with these so far). Bottoms were upgraded to new turbo version.




With the really scary tests done and passed, valve tensioners were next. I had already planned on upgrading to the oil fed chain tensioners, but got quite the surprise when I found a set of solid chain tensioners. Replacement was easy, though I had to check twice to make sure I was using the spacer properly.






So much better...



With that done, it was on to the oil problems...

[QuakerJacket]

When I pulled the engine, it was apparent that the thing was leaking from just about every possible place. I'm not obsessed with having a completely dry engine, but figured I would try and fix what I could while I was in there. I'm not going to go over all the regular stuff that most do during this process in detail, but all new gaskets, any and all oil/temperature measuring devices and front and rear main seals were replaced. I also did the oil tubes (the hose clamp trick is brilliant).

What I will spend a minute on is the case seal outside the front crankshaft seal. Here's a pic of what I found when I removed the front pulley...



There's a kit to seal this with an aluminum ring, but I figured a custom one would be better. After removing all of the silicone from the previous owner, I had a friend that turned a piece of Aluminum just smaller than the diameter needed. I then used my Dad's lathe to open it up until it would almost slip on at room temp. I then drilled and tapped three holes on the side for set screws.

I'm not sure if I did the right thing in the next step, but I decided to use two different sealants when installing the ring. Based mostly on the love for it here. I decided to use Curil T on the inside of the ring where the fit would be tight. For the joint between the back of the ring and the case, I thought I would try Erling Dirko HT, a high temp silicone. The surface area of the case wasn't so great and there was no way the fit there would be as tight (It's working now, but we'll have to see long term)



I put my two sealants on the engine, used a heat gun to expand the ring and quickly put it on and set it with the set screws. One thing I did find during the test fitting process was that the main bearing that the ring sits on can move laterally a little bit (front to back engine wise) so it was important to pull out slightly on the bearing while installing the ring. Otherwise the bearing could move out a little bit and potentially ruin the seal between the block and the ring.




Still more to come...

[QuakerJacket]

I was trying to get the engine done as quickly as possible, so creating a work of art like some of you was out of the question, but I still wanted to do a few things to dress up the engine. Engine tins and various other parts were media blasted and painted with high temp spray paint.

I liked the look of the red fans I've seen here, so I cleaned that up and painted it as well.



Clutch was ok, so replaced rear main seal and put the trans back on. Also put on new starter to try and fix the occasional no start when hot. Replaced all hoses, including vacuum and put the CIS back on.


As part of the misfire diagnosis, I pulled all the injectors. They looked ok, but the sleeves were in terrible shape, so they were all replaced along with the o rings. (plan on pulling injectors and sending off later)




Almost ready...

Next up heat backdate...

[QuakerJacket]

Originally Posted by walt

Gold is a fantastic color hope you are not changing. Keep us up to date on your progress.

Definitely keeping the gold - though whether I am changing the color is always the first thing people ask!

[Flojo]

Originally Posted by QuakerJacket

As part of the misfire diagnosis, ...

… you didn't mention checking the ignition, did you?
what about the distributor and cap? what about the wires and plugs??

how did you check the injectors? did you set up a bench and check their flow volume according to spec (ml/sec)?

Then further I recommend you acquire knowledge about the K-jet system and doing a full step by step diagnosis instead of going further about cleaning and painting.

The K-jet is a homogene working unit of parts. if one goes off it coughs.
The components list may look scary long but is not that much.
Before a parts fail the more classic failure is an air leak at some point (cracked airbox, cracked injector O rings, all hoses…).
Then you start cheking things like the WUR, air regulator, cold start valve, etc..

[boyt911sc]

QuakerJacket,

You did a very nice job cleaning the engine and impressive engine dolly. One thing I noticed different is the cam bolts. The ‘79 SC engine should have the big 46-mm nut for the camshafts but yours has the later bolts instead. Someone had replaced the original camshafts to a later model camshafts. They might be even a 964 cam or other upgraded versions.

To fix your backfiring problem, start learning some basic CIS troubleshooting procedures. Using the CIS pressure gauge kit would be a good start to check your fuel pressures (control, residual, and system pressures). Then build a smoke tester to help you locate those hard to find air leaks.

The car looks great and enjoy driving the car.

Tony

[QuakerJacket]

Good questions - I think my post title is maybe a little off since the misfire issue was the trigger for all the work I did, but all the work I did was not to (just) solve the misfire issue.

Therefore, my order of operations was not at all what would be recommended under normal circumstances. I had kind of a one time opportunity with just enough time to get the engine out, try and fix as many of the oil leaks as possible, rule out major engine issues AND try and solve my misfire problem. So the engine was coming out anyway.

Back to the ignition - timing was off a bit during the initial check, but adjusting it, even to extremes, didn't get rid of the misfire. I knew the engine was coming out anyway, so I didn't want to start messing with the mixture or anything else until checking/replacing most of the other potential causes (vacuum, ignition, airbox, etc).

As far as the injectors go, I replaced the sleeves and all associated o rings as part of the potential vacuum leak correction strategy. The sleeves in particular were in terrible shape and needed to go. I didn't have time to go through the injectors so I cleaned the best I could and figured I would send them off when I could. I didn't have the time or the equipment for bench testing and also knew I could get them out pretty easy with the engine back in, especially with new seals and the heat backdate. New injectors as preventative were not in the budget.

Last thing for now is there was no major change that occurred with the start of the misfiring issue. The car was driven very little over the last few years, so in my mind at that time the most likely scenario was a sticking valve and/or old gas (and related issues like dirty injectors, which I realize makes my decision to not test them even more suspect!).

Wires, plugs, distributor, etc are also part of the story and I will get to that too.

BTW - I'm recounting what I already did and the engine is back in the car and running really well. The misfire correction part of the story is mostly at the end though, which I'll eventually get to.

-Joe

Originally Posted by Flojo

… you didn't mention checking the ignition, did you?
what about the distributor and cap? what about the wires and plugs??

how did you check the injectors? did you set up a bench and check their flow volume according to spec (ml/sec)?

Then further I recommend you acquire knowledge about the K-jet system and doing a full step by step diagnosis instead of going further about cleaning and painting.

The K-jet is a homogene working unit of parts. if one goes off it coughs.
The components list may look scary long but is not that much.
Before a parts fail the more classic failure is an air leak at some point (cracked airbox, cracked injector O rings, all hoses…).
Then you start cheking things like the WUR, air regulator, cold start valve, etc..

[QuakerJacket]

Thank you! I always thought the car had newer camshafts, but wasn't sure. At idle, it always sounded a little aggressive/lumpy. Someone added a second outlet to my muffler as well, which magnifies it since it's much louder than normal.

CIS issue is at least mostly solved - I will talk more about that in a later post, but thank you.

-Joe

Originally Posted by boyt911sc

QuakerJacket,

You did a very nice job cleaning the engine and impressive engine dolly. One thing I noticed different is the cam bolts. The ‘79 SC engine should have the big 46-mm nut for the camshafts but yours has the later bolts instead. Someone had replaced the original camshafts to a later model camshafts. They might be even a 964 cam or other upgraded versions.

To fix your backfiring problem, start learning some basic CIS troubleshooting procedures. Using the CIS pressure gauge kit would be a good start to check your fuel pressures (control, residual, and system pressures). Then build a smoke tester to help you locate those hard to find air leaks.

The car looks great and enjoy driving the car.

Tony