S3 8L 1 bent exhaust valve

P

pyle

Registered User
Joined
Jan 30, 2019
Messages
101
Reaction score
5
Points
18
Location
Sofia
Hello there,

As the title states my S3 8L bent 1 exhaust valve . I cannot specify the exact moment that happened. I did a random pull joining the highway 2-3-4th to around 6300rpm and then backed of the gas and changed to 5>6th on the overrun waiting for my speed to lower enough so I can join the rest of the traffic. @ 2000rpm doing 50mph I just put my foot on the gas to maintain the speed and the engine starter to sputter and I pulled on the hard shoulder... Voila 1 bent exhaust valve. The car is completely standard apart from a "Bosch Motorsport" 110 DV and an extra extension spring on the waste gate - 0.9bar. 1 week earlier on a 3 day cold start I heard upper clatter which went away in 2-3sec (I run a 10w50 grade oil) and I though it could be the oil too thick.
Can anyone help me figure out as to why that happened. No overrev ever happened, the car misfired every now and then when left to idle for a while and was fully warmed up since I've had it. No oil consumption (400ml per 4k miles).

Thanks in advance,

Ross.
 
A Banging Donk said:
So... you stiffened the wastegate actuator on the stock map?
Click to expand...

It wasn't reaching the requested boost, the spring is not stiff at all, I loosened the gate as much as possible. This it just a helping spring.
<tuffty/> said:
Pictures?

<tuffty/>
Click to expand...
The head is still on the engine, it's visible with the cam followers removed. I'll take a few pictures when we take it of. Anything specific?
 
I bought the car with 3k miles after a supposed 3k engine rebuild and I've done 6k since then with quite a lot of thrashing especially on highways doing continuous 120mph with no issues... The only sign sth was not right was a bit of top end rattle on very cold start and not every time as well.. I had a few issues I've asked and since fixing them the car pulled perfectly. It has however always had a rough cold start.
 
Its plausible the follower was faulty and jacked out... is there any contact damage on the piston?

<tuffty/>
 
I too suspect the follower and it feels quite solid but no marks on it. We will be removing the head in the next few days. My last car had an ABF 2.0 engine and it hit valves @ idle and the damage was quite severe with oil making it's way in the cylinder and blue smoke coming out of the exhaust, but this time it happened at max revs, I feel a valve contact this time would have been spectacular .. but no smoke what so ever, only unburnt fuel smell of the back. Coils are working, they are the old Hitach with the yellow ballast which are presumably better than the facelift one.
 
Head came of yesterday. 1 bent valve, this is the piston damage. I'm waiting for a call back from the shop after they've taken it apart to check what's the condition. This is the piston damage, is it safe to drive like that, there's no damage else where.
 

Attachments

  • received_639570846618074.jpeg
    received_639570846618074.jpeg
    41 KB · Views: 207
I personally wouldn’t risk it.... put it all back together for it to get worse and end up replacing more stuff. I’d look at getting what needs replacing now and if funds can stretch uprate parts.


Sent from my iPhone using Tapatalk
 
  • Like
Reactions: pyle
Er not a good idea,

Everything flexes under load, metal will crystallize , denature stress cracks will migrate from the damage
'corners , / deep scratches , ...and at some point , sooner than expected
The piston crown will probably detach from the skirt , or across the little end = game over

I'd make the most, of the fact , the bore is not scored and the side of the block is not missing .

Had someone tune a Aermacchi ex works vintage race bike ,a while ago, did a good job , even to scratching 'F' on the front of the
con rod , with a scriber, so he wouldn't get it in , the wrong way round .. very thoughtful -(
strangely, that was the last time the engine was re-built
 
Thanks for the input guys, any idea on what could've cause my valve problem, we still haven't found what cause it.. and it's only one. How can I tell if for example the cam follower is bad, there's not excessive wear marks or scratches on it.. Could it be the oil I use 10w50 Total Racing, the car was fully warmed up with 10+ miles of stop/start traffic and 10min idle before give it the beans when it happened.. I'm still waiting on the machine shop though..
 
6-7k miles roughly. Always topped up, she uses barely any oil..
 
racing oils , may not have the life of road going variants
no additives etc , early shell Q , had a short working life ,
probably better now , you would of seen extensive aging ,
if the oil had failed , metal picking up etc

The only sign sth was not right was a bit of top end rattle

without seeing the bits , hard to say, could of broken a spring
tappet broken , at a guess , something was missed during the re-build
 
Have to check the one associated with the damaged valve , was it a single valve that stuck down ?
the guide might be scored , the face of the tappet cracked/broken , may be the oil feed was blocked
resulting in a large gap , so the cam impacted the face ,causing a hammer rather than a sliding action,
did the tappet jam in the guide, did the valve stem , bind in the guide , these look to be very small
items, so don't have the luxury of large tolerances to play with , in bygone day's bent valves used to
unbend themselves ..
 
We have 2 bent valves one quite a bit one slightly and seats need doing and .. the bigger problem.. piston 1 and 4 have 1mm difference in height .........
 
Just curious.... but is your car mapped at all?


Sent from my iPhone using Tapatalk
 
Something had to of let go, for two valves to hit the crown ?

From what I can see the cam follower are floating , with the cam , direct acting on the top, with the tappet in a guide , directly acting on the top of the valve stem ? unlikely there the problem , no side loading ? guess something jumped ship , pivoting rocker unseated ? over speeding the engine ?

Honda used to sell you a race kit for the 900 cc dohc bike engine, with shimmed tappets , if you took it over 10.500/11,000 the shims used to
jump out of the retaining recess , and knock the side of the inlet cam box out , due to the high lift cam , what they did'ent sell you where the under tappet shimmed version that the works engines used , safe to n thou rpm ..oh chain, rather than shaft drive to the cam's as well , something else to fly apart ... are these engines in the same boat , there not very new now either ?

- I doubt re map , other than increasing the max rpm limit could cause this , more likely a mech duff build ?

if the piston is 1 mm down, rod must be bent as well , what ever was rattling , was perhaps , not installed correctly at the re-build ?
 
The car is not mapped, it's 100% stock, only has Bosch 110 DV, I never rev it pas 6500rpm... The weird part is it had equal compression across all 4 cylinders.. Probablt someone didn't do a good job when rebuilding the engine..
 
Yeah that was mainly my query regarding a re-map. Raising the Rev limit.

Do you have knowledge that the engine has been rebuilt and when?

Like AGB-S3 says, that 1mm will be a bent rod.

This is what I would do.....

Upgrade the rods and exhaust valves. Then you’ve got a base for safely adding more power when funds allow it. I.e. bigger turbo, etc.


Sent from my iPhone using Tapatalk
 
The engine is supposedly @ 10k after a rebuild with updated rods, not where or by whom it was done..
 
Hmmmm, fingers point to a not very good rebuild potentially then.

If your not planning on going more than a “stage 2” remap. Then rebuild with standard parts.

Anymore than that then general consensus would be to do rods and exhaust valves.

I would weigh up your costs.

I know what I would do in your position :)


Sent from my iPhone using Tapatalk
 
  • Like
Reactions: danny_dj3
GOOD NEWS! Careful measurements with the dial gauge revealed there is sub .1mm difference in deck height, the head is also ready.
 
Still haven't found the reason why it bent the valve in the first place.. Machine shop said nothing in the head points to anything specific except the regular wear. My only unknown are the cam followers.
 
Still not seeing the cause ? whats the valve gear like round the valves that hit the pistons ?
cam/ rockers / tappets all in good order ?

Don't forget, if the big end nuts back off then the piston can lift at the top of the stroke and
bash something , valves don't have to stick and if two are damaged its something common
so have to have identical issue's in two sets of gear

the followers would be damaged , if they had jumped out .pretty obvious to spot , be a lot of mangled ally .. looking to be something below the piston crown
 
I haven't heard any bearing tap, I unfortunately know what it sounds. All the valve gear looks perfect, cam lobes, followers cam caps everything looks spot on. A few of em are a bit on the firm side, I'll break em open and soak em in petrol for a day or two to wash the build up and see if they will soften a bit.
 
to bend things , there had to be significant load transfer , if the valve gear has survived , then the loading must of been axial , if nothing is sticking, something was in the wrong place at the time , is the cam retained by one of those bolt-up timing wheels , did it decide to slip ?

next has to be sump off and the piston/rod out for inspection
 
Is there any wear in the exhaust valve guides ? . They tend to wear quite a bit compared to the inlets. Were the washers refitted under the exhaust valve springs. On the 225 engines to get more pressure on the exhaust valve spring they fitted a washer/ spacer under the spring to effectively increase the spring rating. If the wastegate is not opening correctly or sticking this will cause a lot more back pressure in the exhaust manifold and can cause the exhaust valves to open at high rpm. Check the springs thoroughly as a weak or faulty spring will also cause you issues.
 
All the valves guides are fine, the shims where there and were fitted after the rebuilt. I asked the machine shop to check all the springs, they said have normal rate or at least equal. I can't say anything about the wastegate. Could be, it isn't making excess pressure and as far as VAG-COM is concerned the turbo pressure is released immediately. I have loosened the wastegate as far as it could and fitted an external spring to "help" the current gate as it's the original one.
 
Have you looked at the piston's / rods /' crank ? anything there to explain the height difference and damage ?
shut off on over run, should be no pressure involved , only vacuum . negative loading on the bottom end ?

Did the engine run on after the ''event'' or stop / lock up ?

If it had lost timing and run on , it would of proceeded to bend all the valves on that side ....
 
The height difference is nonexistent, all is well after more detailed measurements. The engine ran almost fine after the "event". Timing was spot on. The was actually a cracked valve on another cylinder.. Not sure what causes those.
 
cracked valve,, at least that's explains it ?

could be anything from fault at manufacture , something out of alignment,
metal fatigue , someone used a cheap set of pattern valves , where is the
crack , in the valve head or the stem ?
 
It's on the radial rim of the valve. They couldn't tell me why it happened though.. What does the cracked valve explain, it's on another cylinder. What are the usual symptoms of cracked valves?
 
classic place to fail, That could be due to over heating , or mechanical misalignment , had the seats been re-cut , new guides fitted ? valve seats recessed ? mixture too lean , wrong parts , [ just google 'cracked valve head' ]

If there are other valves in poor shape, that probably explains , what happened , valve failure ,
which explains , why everything else looks normal , the point of failure was the ''valves'' themselves
at this point , may be another complete recycled ''un touched'' head might be a option?
 
Seats have been re-cut, guides were okay, mixture didn't look lean the spark plugs were orange. It was the only valve cracked. He said the seats were higher on one side of the valve maybe that explains the crack.
 
Don't know , what anybody else thinks , but , looks to me , who ever built the engine , trashed it .

if the seats were higher the seat was not 100% aligned with the valve head, then it would stress the valved head, ie flex it which in turn
develops stress fractures and the valve fails

I would abandon the head and get a 'good' standard second hand , complete head,
 
The head is done and is perfect now, I think I might have overkilled it with the extra spring on the gate and had excess EGTs, sorry ..
 
You must log in or register to reply here.

Similar threads

Mr Fixit
S3 8L exhaust
Replies
3
Views
965
ayfreetee
ayfreetee
scotty_24
S3 8L exhaust
Replies
2
Views
1K
scotty_24
scotty_24
D
S3 8L Exhaust
Replies
22
Views
11K
Roadtrain
Roadtrain
malaz44
S3 8L exhaust
Replies
4
Views
961
malaz44
malaz44
E
Audi S3 8L Exhaust
Replies
6
Views
981
JamieOS
JamieOS
Top
Back