Friday, September 16, 2016

My Engine Went 'PFUT, Pfut, pfut' . . .

I'm Porscheless for the time being. The engine and transmission are now out of my car, because both are clearly ill.

Neither has been repaired, yet. The engine may need one new part: a crankcase. I'll explain why below. A good crankcase for a car that will soon enter its 44th year is not easy to locate, as my searching too clearly points out - if I need one.  

A leak-down test is about to be performed on my mostly naked engine.
The crankcases that I did find so far online are junk. They have the exact same issue as mine, and for these useless pieces big money is commonly asked. Locally there is a compatible rebuilt engine, but it hasn't been started and run, so I don't know what its new story might be. No to that, at this point. Also, there is a used engine in the region that is partially complete, but it looks as if it has been under water for years and it cannot be run as is. The would-be seller says that it will need a full rebuild. So far, zero success for me, but such parts are genuinely rare here.

My engine may need a crankcase, because it is made of light but weakish magnesium, and it appears to have suffered the fatal failure that cases of this type run into most of the time as they age. The magnesium engines of 2.7 litres, once they have lived this long, can pull their head studs out of the crankcase into which they are screwed, because there is an insufficient strength of metal to keep them in place. This didn't happen with earlier and smaller capacity engines using magnesium crankcases. I'm so lucky. Porsche failed to beef-up the magnesium cases as they increased the engine's displacement, and there's the flaw. A pulled stud makes the engine pop on acceleration, due to exhaust gasses leaking.

Several years after my engine was built, Porsche switched to stronger, but heavier, aluminum and this particular problem was eliminated. The reason for my woes, though, is bad engineering, probably at the behest of Porsche's bean-counters back in the day.

While more fully inspecting my engine before complete disassembly, a leak-down test was performed. This test assesses the condition of the pistons, rings, valves, valve guides, and cylinders. The leak-down numbers were excellent and comparable to a brand new engine (2% to 3+%), but there is still the stud issue. A worn out engine in need of rebuilding would typically have leak-down numbers of 30%, even more sometimes, so the top part of my engine is fine. My magnesium crankcase is likely bad, though, because while it has reinforcing 'Time-Serts' (I think they are that brand) already installed into the case for all of its 24 head studs, at least one of those inserts is pulling out of the case. This is damage that cannot easily be repaired (Some claim that this problem can actually be repaired by a proprietary means. It's unclear to me how this might be done, or if it is reasonable $$. This is not a special edition, numbers-matching engine. . .) Right now, I'm convinced that I own an ineffectively designed boat anchor, but I could be too pessimistic.

The obvious back-story for my engine is this - the engine wore out, and also pulled a stud, or more, from the case in the process. As well, cylinders were worn, etc. So, it was rebuilt, with reinforcing Time-Serts (?) installed for all of its studs, probably most of them prophylacticly. The job does not seem to have been done with absolute precision, but the main point is that the crankcase has to go, I think. There is an easy solution, but it involves cubic money: buy a complete engine (and transmission!) that has been re-manufactured by a well regarded, pro shop at the other end of the continent. Yikes.  

Hope. Sunlight from the window bounces up into the empty engine room.

A small update.

Naturally I've been looking everywhere.  Here is a partial quote from an email sent to me earlier, from a man who does restoration work:

". . . My idea with the engine I have [in my shop] is that we are right at the stage where the long block is finished; the cams are timed, valves adjusted, but no accessory has been installed: shroud, tins, alternator etc.. Which in your case is an ideal situation since you’ll want to keep all your ancillaries including fuel injection, exhaust etc.. In the coming weeks we will finish to fully reassemble ours and put it for sale as a complete unit . . . "

So, I sent him an email saying that I wanted to see the engine. I also wanted to ask some questions about building methods used, parts sources, and I wished to see some leak-down numbers, etc. 

A BIG update.

I went to look at that engine. If you can imagine an engine getting assembled using a meat cleaver and a very large hammer as the primary tools involved, then this was it. I was told that the studs, all 24 of them, were replaced with genuine Porsche 993TT 'Dilavar' studs, the latest version. New pistons, new cylinders, new valves, new heads, all of this was replaced (mainly used stuff, though). The reason for this was that the engine had been over-revved; the valves broke and went right through the heads, destroying everything. The crankcase appeared to be fine. And that crankcase was fitted with 24 Time-Serts.

I said above that my engine had Time-Serts, too. When mine was more fully disassembled, beyond what is seen above, it became obvious that this was not true. It had been machined for CaseSaver inserts. These are renowned to be stronger than Time-Serts and less likely to pull out. But at least one did, anyway.

Threaded stud holes machined for CaseSavers. ~1mm of material
 is left at the edges of the cylinder spigots. Not much room for error.
Web photo

Okay, CaseSavers are generally seen as a last resort, within $ reason. The thing is that when some of the machining for the inserts had been done on my engine it had not been done perfectly. That stud that is pulled may not have been installed well.

Here is where the above-mentioned rebuilt long block I looked at earlier becomes interesting. The first thing I noticed was that there were broken cooling fins at the base of at least one cylinder - I didn't need to examine more to be put off. I asked about this and was told that it was difficult to install the cylinders over the studs. That should not be the situation, but it happens when the studs aren't installed straight in the crankcase. So, the re-builder of this engine ground down the sides of those expensive 993 studs - in a very haphazard manner - in order to make them smaller so that the cylinders could be installed without breaking so many fins! I would like to know what that rough grinding did to the strength of those studs. I declined that engine.

Now, I still had my own engine to consider. 

Fortunately, my actual, chosen engine guy is very inquisitive and creative, and he has 40 years of experience working on air-cooled Porsches. He measured that my problem CaseSaver is around 20mm long, but the hole into which it is installed is about 30mm deep, and it is at the top of that hole. All that was needed was to screw it down to the bottom of the hole, and instantly it would gain back 50% of its original purchase on those newly available threads. He noticed that the damaged threads at the top were not fully destroyed, either. Therefore, he will use a high strength, industrial-grade aluminum-containing epoxy to coat the upper threads. This material can be cut to make new threads. The combination of the lower placement of the insert, along with the epoxy product, will recreate a substantial percentage of the insert's original strength. Plus, he will install a Dilavar stud into that insert (but I hope not ones from a 3.0 engine; they tend to break).

This is unconventional, to say the least. That's why I like it. Simple and not too expensive. The desirable thing is that the Dilavar material expands at roughly the same rate as aluminum, therefore, the stress placed on my  patched CaseSaver hole will be far less than before. With luck, I won't face this issue again."Don't go drag racing with a stone cold engine," my engine guy said. Good advice, but I have never done that, and won't. You have to warm these engines up. Also, he said, "I have every confidence that this repair will last well."

Unfortunately, there will be no report of the engine running in my car until next spring. It's fierce winter here now.

Oh, the transmission needs a new input shaft oil seal. 

For the continuation of this story, see The Return of the Reluctant Prodigal above.