worf928

Specifically?

VAGfan

The "bolts found in the oil pan" issue is about bolts loosening themselves, ie lack of locktite or a lockwasher.

The Timing Chain Cover issue is the above, PLUS some of the aluminum bolts have sheared, due to excessive stress versus their yield strength.

All the above are poor design choices by Porsche engineers.

worf928

@chassis I responded yesterday to your post, because your response can be construed to mean that you do not agree with my theory and that you know something I don't or believe that I'm an idiot. That's fine; I am genuinely interested in determining if I am indeed an idiot on this subject. Please post your thoughts.

Here are some written-by-my-hand(*) excerpts from "WM 153319 Removing and installing chain housing cover" for the 95B:

Fastening screw securing joint flange to chain housing cover, top
Replace aluminum screw
Initial tightening 4 Nm (3 ftlb.)
Final tightening +60°

Fastening screw securing joint flange to chain housing cover, bottom
Replace aluminum screw
Initial tightening 4 Nm (3 ftlb.)
Final tightening +60°

Fastening screw for chain housing cover
Replace aluminum screw
Initial tightening 4 Nm (3 ftlb.)
Final tightening +90°

Fastening screw for chain housing cover
Replace aluminum screw
Initial tightening 10 Nm (7.5 ftlb.)
Final tightening +90°

(*) I do not post a screen shot of these WSM pages because to do so violates the PAG TSI agreement while general descriptions of the content do not.

Note that bolt sizes are not specified. There are additional tables, pictures, and descriptions which theoretically allow an awake technician that prides themselves on their work to identify which bolts get which torque. In particular though, many of these bolts are M6 bolts from 30 to 55 mm in length and get the 4 Nm +90 spec.

First note that the WSM specifies replacement of the "aluminum screw." This supports my "theory" that the bolts are intended to be stretched to the limit of their elastic range i.e. stretched once and once only. Furthermore, we know that an aluminum bolt of the same dimensions as a steel bolt is weaker since aluminum is not stronger than steel on a by-volume basis.

Second - and this is something I have not experimentally determined (yet) - based upon 25+ years of turning M6 bolts into Porsche Aluminum engines this is something I believe to be true: the 4 Nm + 90 spec will result in a steel fastener "straight torque" in excess of 10 Nm which, based upon experience, may result in thread damage for the shorter bolts. Therefore I cannot believe that it doesn't significantly damage a short M6 aluminum fastener.

(If I get bored today I will see if I have some "scrap" threaded aluminum pieces and see if I can experimentally determine if my intuition is correct.)

In 25+ years I have never, not once, seen, *inside* a 928 engine, a factory-installed steel fastener "come loose" regardless of loctite, lock washer, etc. There are very few - if any, I can't recall any - engine fasteners where the factory used loctite or a lock washer. Properly spec'd and properly torqued steel bolts don't just, commonly, come loose.

In the case of the 95B timing chain cover, the "duty" of the fasteners is quite light; they don't have to 'worry' about anything other than sufficient clamping load to seal the gasket and to keep from vibrating loose. The plethora of M6 bolts on the chain covers would be more-than-sufficient for this duty if they were steel and torqued to 8 to 10 Nm without loctite and with just a simple flat washer. There is one exception: if the design of the interface is so poor, or the aluminum casting is so porous, that oil will seep into the threaded holes and "lubricate" the threads. The former is the issue with the 928's oil pan gasket: the design is poor and "oils' the M6 bolts such that they do get loose (easily solved with an appropriate gasket material and assembly procedure.)

I believe that this phenomenon on the 95B is exclusively due to either or both of 1) aluminum fasteners and 2) incorrect torque specs for assembly.

Having worked in, and managed technical organizations, if you define "Porsche engineers" as anyone exercising authority on choices then I agree. However, I define "Porsche engineers" not as widely. In this case, I would bet that

- the "Porsche drive train engineers" spec'd steel fasteners
- that some group of "Product Engineers" (i.e. bean-counters, weight-counters, etc.) switched to aluminum fasteners
- the "Porsche drive train engineers" spec'd a specific material and perhaps supplier for aluminum fasteners
- the "Product Engineers" then let the contract to the lowest bidder and QC was never done, or done poorly.

Also possible is that the drive train engineers where simply ignored or not consulted on the "production decision."

Bottom line though: yes, it appears to be a monumental screw-up at PAG and I'm just parsing out blame.

VAGfan

This very thread was started by someone who had 2 bolts loosen themselves in the engine, and eventually they backed-out so far as to hit the rotating balance shaft portion of the oil pump. There was a second incident with a Macan owner, same engine (Porsche V6), where the same thing happened to them. Read thru this post from the beginning.

And yes, any bolt where the Factory Workshop Manual specifies a tightening torque, plus some additional angular rotation, is a "Torque-to-yield" or a "stretch-bolt", which are all one-time use items.

worf928

I have. They were aluminum bolts weren’t they?

SpyderSenseOC

These broken bolts at the oil pump are not exclusive to the Macan. I have a 982 Spyder and there have been several catastrophic failures in the 4.0L engines that involve broken/sheared oil pump bolts that have been chronicled on the respective forum pages. Porsche knows something. But in the immortal words of Sgt. Schultz... "they know nothing!"

https://rennlist.com/forums/718-gts-...e-failure.html

romemmy

I think the backed out ones were steel. I originally assumed aluminum, and I replaced with steel, but I haven’t tested the removed bolts yet. I still have at least one of them - I’ll see if I can get something conclusive (by weight probably as stainless 300 series wouldn’t be magnetic either). They anecdotally do feel heavier than the AL bolts I removed from the timing cover (also all replaced with stainless, plus thread lock).

Thanks!

S.

worf928

Weight and volume displacement might provide sufficient data for material determination. If not pointing to one, then at least narrowing the field to a few choices.

Stainless is also a “mess” from the strength perspective. Many different grades. Some of them not as strong as 8.8 steel.

Unrelated…

@DHL is also correct that some combinations of aluminum and stainless are “no-gos” for galling or corrosion without a proper thread treatment.

I researched that topic 15 years ago. I have a bottle of Nickel-based anti-seize for stainless-into-aluminum-hole applications.

romemmy

Yeah, if you see one of my posts above I was a little concerned with galvanic corrosion. In practice it's probably not going to be an issue in an oil-filled area with minimal water though I think - especially with thread locker in there too acting as a barrier. As for the grade, I'm using no less than A2-70, which has a tensile strength of 700N/mm² vs 8.8 steel at 800N/mm². I purchase from a dedicated bolt vendor (BelMetric) so the quality should be high. Note that the next grade down on steel (5.8) drops tensile strength significantly (to 520N/mm²), so A2-70 is closer to 8.8 than to 5.8. As for aluminum we're probably looking at around 300-450N/mm² depending on grade, so significantly less than A2-70.

Thanks!

S.

romemmy

So, a few weeks on…

After driving a bit more (maybe 200 miles total), my observations were:

1) Lack of power. I hadn’t pushed it yet, but it definitely felt down. I assume that’s due to the boost deviation warning I got so the jury is out on that - probably a boost leak.

2) more worryingly, what almost sounds like rod knock, but only above 2000rpm. The sound is still there at 3500rpm, but I haven’t revved past that while I was shaking it down. There is a vibration felt too, but only at the 2000 mark - after that it’s just the noise. So I stopped driving the car for the past few weeks.

Normally I expect actual rod knock to be present at idle too, but in this case I don’t believe it is. I thought maybe the re-used tensioner is the issue (chain guide noise), so I got a new one that just arrived, but before I install it, I will do some more diagnostics.

I’ll take a recording of the sound and post it too. While it’s entirely plausible that the starvation has caused real rod knock, I don’t want to jump to conclusions - especially as the sound isn’t there at idle or below around 2000rpm.

If anyone has a video of a 3.6L Porsche Macan (or Cayenne I guess) engine really knocking for me to compare with, that might be helpful too.

I need to also check for bore scoring which is (*sigh*) another apparently “common” issue with these things, and can cause some noise.

If it turns out to be rod knock or bore scoring I’ll be furious at Porsche for causing this whole debacle, but I guess it will be rebuild time for more power..

Thanks!

S.

romemmy

A bit more info:

Idle - no abnormal noise
1800 - starts to vibrate a bit, low noise
2100 - noise/vibration subsides
2500 - noise starts again - less vibration, but sounds fairly low frequency, very pronounced, like knocking
3000 - getting louder
4000 - still there - gets faster with engine speed

I’m not revving past 4000.

I have a friend coming later today so I will be able to check the engine bay while he revs it - see if I can pinpoint it. I also have a new articulating borescope coming tomorrow so I can check the cylinders for scoring.

It doesn’t sound like (or behave like) rod knock. Oil pressure is good, rises like it should as it’s revved, seems to be perfectly in the right place.

I tried recording it and oddly it’s hard to capture - very audible to me, but not when I record it 🤦 Phone microphones suck.

Thanks!

S.

DHL

Man, I am sorry to see this saga continue. You have the patience of Jobe. At what point does it become diminishing returns?

romemmy

Have no choice really… We paid $120K for this Macan - it’s worthless without a fully functional engine. 🫤

DHL

Understood. What would a "crate" motor or factory rebuilt cost? I would be knocking on Porsche's door for this as you have documentation of a major failure that could have caused extensive damage that may not be repairable. Sure you have been down this line of thinking before, but even if you do finally repair the knocking will you really have confidence in the long term reliability? I can't recall if you bought this car new (probably did at $120k) but won't you have coverage under your State's lemon laws on this? Particularly since you have such good documentation of the failurers.

romemmy

I did think about the lemon law, but in California the car has to still be under “new car warranty”. So since this happened just over a year after the warranty expired, it’s not legally eligible.

My choices right now are:

1) replace with new motor - I believe those are $25K+
2) replace with used motor - those are between 5K and 15K, but have no real history with them, so are massive risks on their own.
3) Beg Porsche for a goodwill replacement. They’ll want to inspect it and if they say no, I’ll probably be left with the dealer inspection bill. If they say yes, I’d expect they’d want to only cover part of it - so I’ll probably still be left with a $10K+ bill. I did open a case with them so I might pursue it - I’m just not confident it will be worth it.
4) repair this motor myself.

The last one is the only way I can be as sure as possible that it’s done properly, with upgraded parts where possible to reduce the likelihood of failure, proper use of thread lock to ensure bolts don’t just fall out, etc.

Thanks!

S.