Dead Boxster S 986 - bent valves, not IMS

[mb230sl]

Hi all

I would really appreciate your thoughts on the issue I'm having with a 2003 facelift 986 S. I've been helping a friend register his S, having imported it to South Australia when he moved out from England. Yesterday was the big inspection day, and it passed with flying colours.

I'd previously driven the car several hundred km over the course of a few months - it felt very happy indeed, with no strange noises or any hint of issue. 

So, having completed the inspection, we were idling along in gear, exiting the car park, when a subtle bearing type noise was heard, followed by stalling. It sounded like an engine accessory bearing. We attempted to restart - turning over smoothly, but laboured, and unwilling to start. I removed the accessory belt and tried again. It started, noisily, and I switched it off straight away.

The car was towed back to my workshop and this morning I began investigations. Brought it up to TDC, and removed the exhaust cam plugs - bank one was out by I would guess a tooth. Plugs out - leakdown test fail.

The car has 120,000km, and has been sitting doing little for 18 - 24 months. It had been well serviced before then, and showed no signs of distress whatsoever.

We have removed the tiptronic trans to reveal the IMS bearing which we thought was the obvious culprit however this seems in good condition. Removing the rocker cover on the driver's bank revealed a small off yellow fragment of plastic lodged in one of the corners however I've no idea where this could have come from. It looks like a piece of chain guide. The chains appear healthy, the sprockets are all intact and the tensioners and guides are also in good condition. The oil filter did not reveal any shrapnel, but two slivers of metal were found upon removal of the sump cover. A leakdown test suggests the valves are bent on the driver's side head and tomorrow the head will come off so hopefully that will give some more information. 

I cannot fathom what caused the failure of the engine and the timing to be out. If you could share any thoughts/ideas I'd be really grateful. Many thanks in advance. 

 

 

[Peter M]

I have no idea but my guess:

Chain tensioner or a guide has failed allowing a chain to lose tension and skip a couple of teeth.

The aluminium fragments are part of the engine casing that chain has contacted when it became uncontrolled.

Did this model have the head mounted Variocam system that used a chain tensioner to vary the timing? 

 

I hope it's an easy repair and only requires some valves and chain tensioner parts.  Please post further photos as you go.

 

 

 

[mb230sl]

Hi Peter,

 

Thanks for your thoughts.

The metal is attracted to a magnet, so its not part of the casing. It looks to me like it was a machined part, rather than random debris.

I would love to identify the piece of plastic - it looks like part of a chain guide, but they seem intact on that side and I don't see how a piece of chain guide from the other bank could migrate over. It is possible, I suppose, that the plastic got caught between the chain and sprocket, causing the valves to collide. but, what is its origin?

It is a three chain engine, so VVT is on the sprocket.

A real and unpleasant mystery.

[CarreraG50]

MB, please keep this topic alive, and update us on your finding's. I have often toyed with the idea of a boxster

as a daily, they seem such a fine car for not many $$$$, and for the ratio $$$/Performance/Handling I think they would be hard to beat.

Thanks

[mb230sl]

This has been my first exposure to a Boxster. I'd had a little to do with a 924 and 928 previously, but only really dipping my toes. My workshop specialty is classic Mercedes and Rolls Royce, which is obviously a world away from a mid/flat engined sports car - much less something made in the 21st century.

A few observations - 

To drive, the Boxster is impressive. A great balance between fun and comfort. Compared to the tediously boring nature of other modern cars I'd experienced, the Boxster is a real joy. The worst bit is the silly steering wheel controls for the auto. It'd be much more useful with even just a gear lever controlled manual mode. I don't buy into the vs 911 snobbery - I don't want a difficult out and out sports car (and because of the curvature in my spine, I can't do a 911's offset pedals, anyway). 

I have, however, been left surprised and disappointed by the engine related tales of woe I've been reading about during my research for this project. It is a world away from what I'm used to - solidly reliable 500,000km+ cars that have never even had the head or sump off.

We'd hoped the IMS issue had reared its head here - at least it'd be a diagnosis. As it stands, with unidentified stray bits and no apparent cause, the engine can't be reassembled. 

 

 

[mb230sl]

Update, was hoping to augment the text with pics, but they wont upload.

Offered up the piece of plastic found days ago to the sprocket for an exact fit.

Head off, exhaust valves bent, pistons and bores ok.

The actual offending (larger) piece found, nicely minced up, just inside the block side of the timing case.

With the head off it can clearly be seen that the IMS rails are black plastic and therefore not the culprit.

I removed the other scavenge pump and rocker cover. The scavenge pump was not seized, and everything in there looks great.

That cover was sealed with clear silicone, whereas the bent side was sealed with black. Someone has been in there before - I wonder if the stray bits were from a past episode? Is there any other possible origin for the plastic?

What brand head gasket was used in 03/04? I presumed they'd use Elring. This one is marked, so far as I can make out, VD

If something has happened to this engine in a past life, it was at least 6 years and 40,000 miles ago.

[Peter M]

MB,

So do you think that getting that piece of plastic caught between the chain and sprocket was enough to cause the timing to skip a tooth and cause valve interference?  I wouldn't of thought only one tooth would be enough.  Is there any damage to that cam chain?

Is there any play in the crank to ims chain?

 

Thanks for posting BTW. 

[tazzieman]

What brand head gasket was used in 03/04? I presumed they'd use Elring. This one is marked, so far as I can make out, VD

Likely it is VR = Victor Reinz 

Jeepers , what is that plastic? Someone drop the lid off an oil container in?

[mb230sl]

Hi Peter and TM,

There was a much larger chunk, but it won't let me upload the pic. The pic of the sprocket is just to demonstrate there's been a plastic related incident.

The question now is where its from! My first thought and the general consensus is chain guide... but bank one (the offending bank) is perfect, and the other white one looks ok too. Based on parts supplier diagrams online, there are two white/yellow guides, and the rest are black, and that is in accordance with what I've observed. Does this type of plastic live anywhere else inside the engine??

VR, that makes sense.

Can't really gauge the IMS chain beyond to say the tensioner is clearly loaded when inserted.

Here is a pic of the bigger chunk of guide http://picpaste.com/guide2-Gs2tfVQI.jpg

 

[Airhead]

Plastic water pump impeller failure?

[Peter M]

Hi Peter and TM,

The question now is where its from! ........ Based on parts supplier diagrams online, there are two white/yellow guides, and the rest are black, and that is in accordance with what I've observed. Does this type of plastic live anywhere else inside the engine??

 

Hi MB,

I think you're doing the right thing to track down the source of all debris.  I'm sorry I'm of no help as I've never seen a complete M96 let alone a disassembled one so can't place where any of it has come from.  I'm keen to hear where that ferrous debris has come from too.   All I can do is wish you good luck! 

Plastic water pump impeller failure?

Found in the engine oil?  If that's the case there is no hope of resurrection I'd suggest!

[Airhead]

 

Found in the engine oil?  If that's the case there is no hope of resurrection I'd suggest!

A common issue I believe.

[Peter M]

A common issue I believe.

You're going to have to explain how that could happen.  I just can't even imagine it, let alone identify what would be salvageable!

[mb230sl]

Ok. We have an answer.

Today I pulled the engine and set about removing bank 2 cam cover, along with the water manifold, to enable removal of the guide. The guide was broken. How this was able to migrate to the opposite side of the engine and disable bank 1 is beyond me. 

http://picpaste.com/guide-0U8Ahbr8.jpg

Based on this, I'm going to replace the IMS bearing, reco bank 1, reassemble, and reinstall the engine. 

Will keep you all posted!

 

[qstoria]

As a 986 enthusiast I appreciate you taking the time to get this info on the forum and share with us all.  It sounds like you have done some solid detective work and found the answer so congrats and I hope that the fix goes well for you so you can be back on the road and enjoying the car asap.

[tazzieman]

Is there any way of finding out what previous work was done to that engine?

[990SD]

Great problem solving! Thank you for sharing your experiences and let us all know how it finishes.

Cheers

[mb230sl]

hi, the owner purchased it 6 years ago and hasn't had any internal engine work done. it came with receipts from a porsche dealer related to an engine light shortly before it changed hands. the engine was removed, and the inlet cam adjuster was replaced. two weeks later the engine came out again to have the other side done. 

isn't the specified sealant supposed to be black? on one bank it is clear.

anyway, my theory is that the guide broke when the work was being done and it found its way to a quiet spot. the owner winds it out, but had no awareness of the cornering potential until over the course of several weekends i gave him several demos - i think the g forces may have liberated the broken piece from its secret spot, and it found its way to the other bank. 

immediately before the breakdown it had a gentle 50km suburban drive, and the actual incident occurred at idle. 

 

 

[990SD]

How is this all going mb230sl? Has everything gone back together?

Cheers

Daniel

[Mike737]

Good work MB on find the cause. That's an amazingly long time for it to be floating around without causing damage. I'm slightly dubious on the timeline, but the theory is plausible.

[mb230sl]

18 months later and having been written off in a fire in the meanwhile, the car runs again. 

We ended up purchasing a parts engine, supposedly a 3.2, which actually turned out to be a 2.7. The plastic bits, all of which were melted, ended up on the 3.2. We replaced the IMS bearing with the pelican parts offering. Two 3.2 cams had a little corrosion, so after much deliberation, we elected to fit the 2.7 cam set, which on paper should give a bit more grunt down low. Memory can be a deceitful thing, but it certainly feels more muscular down low, and nothing seems lost higher up the rev range. 

Given the failure, it was imperative we replace the timing chains. Unable to locate split chains with a master link, and unwilling to split the casing, perusing the Iwis catalogue suggested the chain spec to be D67ZN-19 . This is the same specification as for a Mercedes M119 engine, which I know from past experience is available with a master link. We purchased two of these chains, wound one out of the parts engine to check the length, cut the Mercedes chain to length, and wound it through the 3.2. Sure beats splitting the casing, and I have never seen a master link come apart on a Mercedes V8, which has a longer and more highly stressed chain than the M96. These are my own observations, and I am not an engineer - consider this path at your own risk, etc. 

The car threw up a tiptronic warning and though it shifted, shifted poorly. Clearing the codes seems to have set it right.

An O2 sensor and the engine bay fan sensor remain to be replaced, along with the soft top and windscreen. We are awaiting the arrival of a new Porsche top from Holland. Evidently a specialist there has a few factory seconds (demister doesn't work) for a very competitive price. In winter, the hard top will be on it, so given the bargain price, it hardly seems worth worrying about a dead demister.

All told, very happy with the result. After everything, it hardly seems real its on the road once more.