24 bent valves
 

Hi all
I purchased a boxter 6 months ago. 2001 model 4 previous owners all women with 23,000 km on the clock and original tyres.
I replaced the IMS Bearing immediately and all was good having fun using as my daily drive and put 7000km on clock.
I went to start the car 3 weeks ago and the engine turned over, fired but didn't start. I tried again to start the engine and the engine turned over but sounded like all spark plugs were out.
I took it to a recommended Porsche mechanic, same guys that did the IMS Bearing.
After a few diagnosis and ensuing work path the engine sits on the floor and we have determined I have 24 bent valves.
They have only just touched the Pistons, you can see where they touched but no damage to the Pistons.
Non of the original diagnosis played out, and we can see damage but I still don't know why.
The thinking at this point is that the cause is to do with hydraulic cam system.
I am just learning about these engines, I am a boatbuilder and have a general knowledge of engines but I am reluctant be putting the engine back in the car without a smoking gun diagnosis.

Has anyone had this problem
Has anyone have a thought on what the failure might be.
I have seen that these engines do have some, should I be replacing anything else in the engine while it is on the floor

My first post on any forum so please excuse if I have made errors
Cheers Brett

24 bent valves? So something went wrong with the timing to both heads.

Did you only replace the IMS bearing or did you replace the IMS as well?

Have you checked the intermediate shaft? Sometimes the gear package at the ends of the shaft get loose / twists. Some put screws in to ensure the IMS sprocket does not twist on the shaft (i would recommed that). That would explain the complete bad timing.

Did you check chains, chain tensioners and chain ramps? I would replace chain tensioners and chain ramps. Chains have to be checked.

Regards from Germany
Markus

Hi Marcus
The mechanic checked the timing first up and all was in order.
I'm not sure about the IMS, I know that it was a retro fit kit that was installed. I will find out.

Hi Brett,

if a complete IMS kit including bearing was done, there is also a possibility that the timing was mooved, because chain tensioners have to be loosened to do that and there is a possibilty that the chains can skip one or more gear tooth.

Regards from germany
Markus

The original post says he drove 7000km after the IMS bearing was replaced. Then all peachy until one day it doesn't start.

That doesn't point to someone setting the timing incorrectly that far back.

IMS sprocket shifting on the shaft would still only affect the left cylinder head (the sprocket going to the right head is machined as a single piece with the primary IMS chain sprocket or at least it is with my "bicycle chain" type, so that failure wouldn't affect both heads.

What is more puzzling is that OP stated the mechanic checked the timing and it appears good now.

OP,
Did he test compression, or do you know about the valve contact because he bore scoped it?

The valve timing is perfect but you have bent all the valves ?
Can anyone explain that to me?
Like Flaps ,I rebuilt my M96 and am having difficulty understanding this unless....
The torque on the sprocket at start-up caused it to slip on the shaft. Mine is the Hi-vo chain system. That would explain the bent valves.
When you tried to start several more times, the sprocket continued to slip/rotate until it (magically) returned to the original, correct position.
Speculation pointless except for curiosity.
When you rebuild ,pin the shaft+sprocket.I posted a link to John Edwards Costa Mesa R&D doing this job some time ago.
https://www.youtube.com/watch?v=XP6GwqLvD7Q

Sorry but this post doesn't make sense.

If the only thing wrong with the engine is that all of the valves are bent, then the timing had to be off on both banks at some point in time. And if the timing was off, then you have a serious problem and you need to find the root cause before putting it all back together.

I'd completely tear down the engine. I am sure that you'll find your root cause...

Hi,

what engine are we talking about? 2.7 (220 HP) or 3.2 (252 HP) litre with Vario Cam heads - not Vario Cam Plus? Or am i wrong?

thstone:
You're right. If the tube to gear connection will fail, this would only affect one bank. See 8 and 9 on schematic.
I agree with the fact that the engine has to be completey inspected and the cause has to be found.

Possibilities:
When all 24 valves were damaged at the same time the only way could be that chain 7 sprung over - which i can't imagine. Maybe if chain tensioner 2 and 5 failed, or somebody did a fault when installing the new IMS bearing.
Both chain tensioners for chain 8 and 9 failed at the same time. Hm… i think no.

Regards
Markus

Yep, 24 bent valves is the definition of a cam timing problem. Perhaps your mechanic should check this again more carefully. :)

Even though the pistons still look useable, the impact force has been transferred to your rod bearings as well. How much damage has been done there? I suspect someone forgot to lock down the cams at TDC during the IMS retrofit and things moved. Perhaps a chain tensioner failed as well. This motor is not toast yet but someone needs to dig deeper to assess the problem and full extent of the damage.

Thanks everyone for your thoughts.
The engine is a 2.7 standard issue.
Our first thought was was something done wrong when the ISM was done, but 7000 km since should rule that out I think.
When we put the car on the hoist the timing was the first check.
As Gelbester said there has been some magic because for all valves to be bent the timing must have been incorrect.
A suspicious person might fairly say that the mechanic is not being totally honest with what they found. But the mechanics are a straight up team, I'm confident I'm getting the real storey.
It's Sunday in australia today and I will be visiting the mechanic tomorrow for further discussion.
We used a scope to look into the cyclinder first and there was a sludge type stain on all cyclinder walls.
The oil was only 5000km old and still golden.
What is being said is that they seem to have these problems with the low km cars.
Thanks for eve ones ideas
Cheers Brett

If it was timed correctly before, and is timed correctly now, and the valve marks are fresh then my theory is that you had a chunk of something take a ride around the primary chain that goes from the crank to the intermediate shaft.

It has happened before. In one case it was a rod bolt that came out. Could be a chunk of plastic chain guide too.

Either way, plan on that tear down

How much experience have your mechanics going inside and rebuilding M96 engines? How many Porsches are they working on right now? Are you better off buying a engine from a wreck? Or a rebuild from an expert?

I presume you know about Forums - PFA

Flaps - brilliant speculation !
The rod bolts are a well known weakness. I replaced all mine with ARP when I did the rebuild.
The need to pin the IMS sprocket is equally well known.
Looking forward to the"rouges gallery" tear down photos.

Hi all
Further update is
Once heads striped, not all valves bent
All exhaust valves bent and 2 inlet valves only.
No other visual clues.
Theory at this stage is the when starting the engine had a lean backfire and the engine rotated backwards .
The engine has VVT so I am thinking that this is possible.
Once the electronics don't know where the mechanical parts are we have problems.
I remember when I started the car I was in a hurry and when I heard it fire I let go of the ignition key, basically a tentative start.
This could have made the perfect conditions where almost start on a cold morning, just enough to kick back.
Is this a big stretch or plausible
Cheers Brett

I'm not a fan of that theory. The vario cam solenoid only varies timing of the intake can to the exhaust cam. They don't wander. They are commanded to rotate above a certain rpm.

The exhaust cam is a slave to the rest of the can chains. You say the exhaust valves are all bent. Keep digging.

Vario Cam is adjusted by chain lenght - so we don't talk about Vario Cam Plus, which works competely different.

Vario cam is not comparable to VVTi from Toyota or other cars. It's a Porsche specific design.

Vario Cam only adjusts cam timing on intake valves, not on exhaust valves. The solenoids that adjust chain lenght are electronically adjusted. The full adjustment only works at high rpms at approx. above 5.000 rpms.

So the Vario Cam theory doesn't work on that.

So what could cause that. For example if the plastic glider on the chain ramp is broken. So the timinig could be OK now, but when plastic parts came between chain and gear timing was wrong and caused the damage on the valves.

The only way is to tear down the engine and check everything.

Regards from Germany
Markus

I gotta go with Flaps and Marcus on this. VVT does not explain intake and exhaust valve damage. Now if you were on a spirited drive, spun the car clutch engaged, and allowed the motor to actually turn backwards, that would do the trick.

I like the ramp-material-chain-snag idea the best. Drop the pan and have a look around for big chunks of something.

In a spin, both feet in!

The chain length is not adjusted (actually not possible). The solenoid move the slack portion of the chain towards the cylinder and away form the cylinder which changes the relationship of the intake cam to the exhaust cam.

Worn chain carriers on the vario cam solenoid won't do this either. They would affect the intake valves but not the exhaust cams as others stated and only one side.

I can't imagine all 6 cylinder having loose connecting rod bolt at the same time so that isn't it either.

My bets go for the main chain tensioner failing, the sprocket is loose on the IMS shaft as other noted, the scavenge pump on the side with the bent intake valve ate something, or the motor spun backwards.

Hi jsceash,

yes, you're right. :D What i've meant is not the chain length, i've meant the ratio.

I didn't mean the chain tensioners / gliders of the camshafts. I've meant the chain ramps / gliders of chain 7 (scheme above) or the chain tensioners of chain 7.

Sorry, somtimes i struggle explaining things because i'll have to translate everything. ;)

Regards from Germany
Markus

Hi all
Motor back together and running well, we dropped the sump and all was clear.
When I laid all the parts on the bench what we had was 12 exhaust and 2 intake bent valves. Only very slightly bent just enough to not to seat correctly.
There is evidence that the engine was running lean.
I laid out all the information I had and the mechanic had also done his own investigation with his Porsche peers. With the lack of distinct evidence of a failure we have put this damage down to a lean backfire the engine suffering a reverse rotation. The rotation was only slight just enough for the valves to kiss the Pistons.
One of the Chain guide tensioners was weak but still working so both were replaced. The tensioner could have some ownership in this affair but it is not conclusive.
I feel strange having pulled an engine to pieces and really fixed nothing, it certainly appeared to be an one off event.
Anyway if someone else has a similar problem I hope this string of comments can offer some help.
Thanks for everyone's thoughts
Cheers Brett

You'll find the cause the second time around. At least I did with my engine. :)

That's a comforting thought :ah:

Quick summary;

Engine failed at 136,000 miles due to a single lifter failure.

Full professional rebuild of engine including replacement of all 24 lifters with brand new lifters (and replaced all of the collateral damage).

Engine failed again within 500 miles of highway driving due to ... wait for it.... lifter failure.

Why? Lifter carrier was worn and excess tolerance was allowing the lifter to wobble ever so slightly. Slight wobble resulted in uneven stress causing failure.

Another full professional rebuild along with more collateral damaged parts replaced including another set of 24 brand new lifters but this time included two new lifter carriers.

Second time is the charm if you don't find the root cause of the failure on the first go around. Lesson learned. :)

Hi thstone,

i think lifter means hydraulic lifter, right?

If the lifter carrier was worn, how was that repaired? As far as i know the lifter carriers are an integral part of the cylinder head. So did you overbore and use a kind of sleeve?

Or did you replace the complete cylinder head?

Thanks & regards
Markus

Hello Markus,
I believe that the lifter carriers are bolted into the heads (between the heads and the cams), they look like cast aluminum egg crates :p
.

What year? The IMS sprocket on older cars is known to rotate. It is press fit.

Problem is -- you can't tell. I did one complete rebuild and ran and idled great.
Took it for a test drive and the first time I jumped on it, it christmas treed on me.
Bent valves -- all on one side.

Sure enough -- the IMS sprocket had rotated. That was an expensive lesson.

Mike

Maybe the backfire was caused by a failing fuel pump. Check fuel pressure!

This. Lifter carrier bolts to the head.

Markus, your English is much better than my german.

If a backfire trashed engines I would think that would be a very common failure.

Thanks flaps10 and Gilles,

found the carrier in the parts catalogue (number 15). So there is bolt on a hydraulic lifter carrier for each cylinder head. Now i understand how this works and can be repaired.

http://986forum.com/forums/uploads01...1439065334.jpg

Thanks & regards
Markus

Flaps,

Thanks for the correction (honestly..), sometimes my spanglish surfaces and goes undetected, and I noticed that after a couple of beers with tequila it just gets worse… LOL

I had the same problem with my 2001 2.7, bent valves everything still in time. Happened while trying to start the motor.

Sold the motor to Jake with a request to tell me what happened. Never got a answer that made sense (stretched timing chain) Page 7 of the short lived engine thread.