Scarred cylinder (bruised ego) - what to do?

[Glenfield]

A-team,

I have separate thread going on my experiences of 911SC ownership. To this point, it hasn’t quite been Pulitzer worthy as it’s been missing a plot twist. I may have just gotten it ...

I have scoring in my #5 cylinder. Confirmed by a bore scope and compression test results that I’ve quoted below. All were exceptional and then #5 leaks like a sieve. It’s happened early in my Porsche ownership, before I’ve had a chance to up-skill and get set up for a task like an engine rebuild. I will need to pay it forward a little here and rely on the skills of a quality mechanic.

The car is a 1980SC with 75k miles. I believe it to be a very good car with one major blemish. I have a quote from the mechanic for (a) a repair and replace (to the extent that’s possible or makes sense once its open); (b) a top end rebuild and (c) full rebuild. It’s a highly regarded independent here in Chicagoland. It does seem reasonable at <15k and 45 hours for a respected shop. He has a window in the shop and could do it in 2/3 weeks.

A lot of unknown unknowns here and some known unknowns that I’m scrambling to work out. Would greatly appreciate any insights or experiences you can relay on:
1. Continuing to drive the car with a scored cylinder - I’m loosely aware of the dangers of metal finding it’s way into oil and doing significant damage
2. Whether there is good sense in leveraging the sunk cost of a top-end disassembly to do some prophylactic pre-hab type work ... I know full well that the scope of these jobs increase “when you’re in there”
3. In a similar vein to 2, whether you go the whole shebang and do the bottom end too. as you’ll see from the quote, it adds 25%. Biggest expense is the upgraded pistons and cylinders in the top end rebuild
4. Anything I’ve missed or “traps for young players” when commissioning major mechanical works on the engine?

I’d be inclined to say no to a full rebuild. I am also doing my part to answer #4 through my own research but this is unfolding real-time.

I’m not dismayed. A lot of years and miles ahead with this car!

Cheers guys

Originally Posted by Glenfield

There's been a plot twist in this here journey. It's enough to make me want to run for the hills but I don't have my 911 because it's in the shop. Hence the plot twist, and the in-virtuous circle that I now find myself in.

In short, I have cylinder scoring in my #5 cylinder. Sadly, now confirmed by a bore scope and compression test. Results of the compression test were <5% for cylinders #1-4 and #6 and ~25% for #5. I don't know what's more scarred, my heart or the #5 cylinder? Won't know until top end gets broken down I guess ...

The mechanic is proposing a "snakes and ladders" type approach to the repair work. I appreciate the potential for more snakes than ladders once things open up and will address each appropriately:
1. Disassemble top end and replace only #5
2. Full top end rebuild - the expense here is the Mahle Nikasil P/C
3. Full engine rebuild

Car has 75k miles and is otherwise "an exceptionally clean and strong car" (mechanics words). The cost of a full engine rebuild is $$$. It breaks down as:
Step 1 above - 25% of total cost
Step 2 above - 50% of total cost
Step 3 above - 25% of total cost

I suspect that I'm at least looking at Steps 1 and 2 (i.e. top end), which would be 75% of the cost of a full rebuild. At this point, do you just do the full engine and then sleep easy for a few hundred K miles? I have read extensively on this question and I'd have been inclined not to, but at only +25% more, it may make sense to leverage the sunk cost now?

I realize that more details around cost breakdown and hours labor is needed but I don't know what the protocol around sharing costs of rebuilds etc is? I will of course not name mechanic publicly but will share additional details around quote if that's acceptable?

There's something fishy about this and also some important learnings that will advance the original intent of this thread, which I will detail in time. For the moment, I just need to borrow this forums collective intellect and experience to quickly plot of a course of action.

[yelcab1]

Decide how much money you have and stop just shy of that. If you are paying for someone to do the work, it would be wise not to pay it twice.

[Bill Douglas]

If you do the top end thing, or just the cylinder 5 thing, it may be timely to replace the dilvilar (spelling) studs. Good luck.

[Mike Andrew]

My thought is that if you are +25% for the whole show, do the full rebuild and be done with it and worry free for a very long time. As noted above, not paying twice is a big benefit of this approach. It will also address all of your oil leaks and give you a nice shiny engine when done. If you can afford to do a full, seems better than a piecemeal approach/band aids. And, with the open slot, you can enjoy most of our 6 month season here.
What shop have you selected?

[Glenfield]

Thanks all for the comments. Much appreciated.

Upon further reading, seems that outside of very advanced stages, compression tests often don’t indicate cylinder scoring. Expansion and oil can form a seal. I don’t have the smoking to suggest an advanced stage. It was however visually confirmed by a bore scope (which itself may only show advanced stages if scoring develops from bottom of cylinder). I haven’t been able to unpack that but it’s interesting.

Mike, I’ve visited a couple of the reputable shops. I’ve gotten a very good impression from Rick at Fischer. Pls PM me if you’ve had a different experience.

Regards,
Tom

[RDM]

I'd go with the advice you got on the other thread- drive it a while. If it runs strong, smokes only a little, then you can live with it a long, long time, even if the test is accurate.

And as time goes on you'll build your mechanical knowledge, confidence, tool selection, and network of local helpers to the point that you may be comfortable taking it on yourself.

[JSV798]

Back in 1978 my first 911 holed a piston on its first long journey. I could not afford to pay anyone to fix it so had to do it myself. I managed to strip the engine down as far as the blown cylinder and replaced just the cylinder and piston, put it all back together and it was going fine for the rest of my ownership. So my advice is just do the minimum: replace just the cylinder/ piston on #5 if the rest are good. And if you tackle it yourself get the Stomski cam tool. I bought it last year to do the camshaft seals; made it so much easier than the crow's foot tool.

[sugarwood]

Now that you got the valves adjusted, is the initial valve sound still present?

[walt]

Drive it a few days and repeat the leak down on #5, possible you had some carbon build-up on a valve seat. If you do a rebuild plan on replacing the Dilivar studs for certain and probably new valve guides as a minimum.

[sugarwood]

1987 Carrera Failed Compression Test

People here saying to see if driving it clears it up.

Just in case the shop is misleading you,why don't you add some Techron, if available,
and go for a longer drive with some pulls to 6k ?
Then go to a 2nd shop and ask for a compression test on just the #5 cyl ?


Purpose of leakdown vs. compression
leak down vs compression test?

Bad compression numbers, then do a leakdown to help pin point the problem before paying for a teardown and repair.


The ‘science’ behind an Italian tune up is to get the engine hot, put a lot of airflow/fuel through it. Any carbon pieces, sticky rings or others can get shaken loose.

BLUE SMOKE......panic ensues!!

I would put it back together and drive it for a day or so, then retest.
If number one continues to test low compared to the other cylinders, then do a leakdown to determine where the compressed air is leaking, (valves, rings, leaking head).
I wouldn't get too nervous over one test.
82SC Compression 5 in the 180s #1 @150


With the cylinder pressurized, the technician needs to listen to the exhaust pipe(s), intake system, and oil tank filler to determine where its coming from. This shows whether the exhaust valves are leaking, intake valves are leaking, or rings are leaking.

A high leak engine may simply need an "Italian Tune-up", a valve job, or new pistons & cylinders.
_____
Decipher these leak down numbers


https://forums.pelicanparts.com/porsche-911-technical-forum/930898-3-2-motor-issue.html

[sugarwood]

I know nothing about this topic, but am trying to help out however I can.

Is it odd that the shop did a compression test
and then did not do a leakdown,
but are talking to the owner about possible engine rebuilds ?

I wonder if the shop is trying to drum up business after seeing a drop in income.

Without a leakdown, they did not isolate intake valves or exhaust valves or rings or head stud.
If they isolated valves, at least they could have suggested an attempt at cleaning the valves first.
One thread talked about putting solvent to clean valves, or just running the car hard.

[911 SLANT]

I ran into the same dilemma. My #5 cylinder had high leak down numbers and zero compression. All other pistons at 1-2%. I did the same as the advise given and kept on driving it. After about 150 miles cylinder started make loud noise. I ended up pulling motor and notice I had broken rings. Motor was a 2.7. I decided to fork out a few more bucks and buy 92mm J&E pistons 9:5.1, hotter cams. I figured got it apart might as well beef it up to a 2.8. Good luck!

[sugarwood]

Also, did they do the compression test before or after adjusting the valves, or both?

Originally Posted by scarceller

In the 911 Engine a bad compression can also be valve lash to tight if done on a cold Engine. The valve lash grows wider by 3X when the motor is hot. A 0.1mm lash will grow to near 0.3mm fully warm motor. And the lash gets tighter as the Engine ages with milage, so it's possible to have a valve slightly hung open on a cold engine that has not had a proper valve adjustment.

[Glenfield]

Thanks guys. Sugarwood, those threads are interesting and I do appreciate you going digging for them. They make a strong case for the Italian tune up. I’d like to put the prospects of a different sort of “Italian job” (by mechanic on me) to the side for a moment. Very reputable shop and well deserving of the “innocent until guilty” treatment since named above. If I get the top end pulled apart, I will know the accuracy of their prognosis on #5 and would expect they’d stand by it (and button her up if it is just in need of some Italian loving).

If compression test reads bad, do people ascribe much value to follow up visual inspection via a bore scope? In the hands of the right technician. That visually revealed the scoring and cylinder damage. Perhaps a reason not to do compression and leak down.

[theiceman]

if its a reputable shop and he sees scoring its done he doesnt need to waste any more of his time and your money. no point in any further diagnosis. Porsche techs scope water cooled engines all the time when they see the flashing cell.... " engine is done" is what often comes back.. they just have so much experience they need no further tests. .


bottom ends on SCs and 3.2s are rock solid. i difd just a top end on my 250k km car 5 years ago and it has been fantastic

[ClickClickBoom]

First, does the engine run well?
Second, what caused the scoring, and when?
Third, if number 1 is yes drive until it doesn’t.
Fourth, if you can’t answer number 2, it doesn’t matter.
Fifth, if the compression test wasn’t done at engine operating temp it’s fairly useless.
Sixth, scoring won’t add metal to the sump in any quantity concernable.

[Glenfield]

I decided to have top end opened up. I trust the mechanic in question and will know shortly whether #5 conforms to the initial prognosis (and warranted the takedown). At that point, I will have options re: a course of action.

I wanted to put that out there to save folks in the “drive it” camp the key strokes. To be clear, I don’t mean that dismissively in the slightest. From what I’ve since read, it’s very likely a right course of action but I’d made the call. I’d seen and heard enough to form some confidence around a plan. If I was too hasty, I’ll know shortly and it will be a lesson for myself and a good guide for others.

@ticktickboom, I thought car ran well but I don’t have enough hours behind the car (or other 911s) to know how well. Mechanic thought it was underpowered. He thought significantly. His initial diagnosis was throttle plate bushings needed replacing and throttle needed checking, along with valves. The latter being corroborated by the abnormal tapping.

*edit: when valves were fine (a little tight on #2, 3 and 4 but ok on others), he wanted to do some more exploration. When compression test was bad he scopes the cylinder.

[pmax]

Originally Posted by Glenfield

The car is a 1980SC with 75k miles. I believe it to be a very good car with one major blemish. I have a quote from the mechanic for (a) a repair and replace (to the extent that’s possible or makes sense once its open); (b) a top end rebuild and (c) full rebuild. It’s a highly regarded independent here in Chicagoland. It does seem reasonable at <15k and 45 hours for a respected shop. He has a window in the shop and could do it in 2/3 weeks.

$15K's gonna buy a lot of tools !

If that's for the top end, seems high.

[Glenfield]

Sure would!

<15k would be for a full engine plus a couple of sundries though.

Originally Posted by pmax

$15K's gonna buy a lot of tools !

If that's for the top end, seems high.

[911 SLANT]

WoW! 15,000. I bought the parts myself for my topend rebuild. Paid 2,500.00 for new 6- new 92mm J&E pistons w/rings & pins, 6- Niksil coated cylinders, complete motor gasket kit, shipped. Got it from EBS Racing. 500.00 for reground MOD S cams. Mechanic charge to put together 2,500.00. For a total of 5,500.00. I would order your own parts and find a good price for labor. I dropped and will be putting motor back in myself. Try to do as much as you can yourself to save on labor.Good luck!