Bent valves...
Thread Starter
Racer
Joined: Jun 2009
Posts: 470
Likes: 0
From: Aurora, Co
Bent valves...
Ok...
car is an 80 U.S. 4.5 automatic
When I purchased.. it was not running... I ended up draining the fuel out of the tank and replacing the fuel. Once I replaced the fuel with fresh and replaced the fuel pump. Motor started and idled well...
I took it around the block for the first time, at 2500 rpm it seemed to not be able to rev any higher. I attributed to possibly a vac problem...
So I pulled the motor, because I noticed coolant weeping on the outside of the motor between cylinders 2/3, 5/6 on both sides... Bought a seal kit, and while the heads were off, decided to get it a valve job.
The machine shop is telling me that there are 6 bent exhaust valves, and 1 bent intake valve.... Not sure which cylinders the valves are bent on.
Anyway. The 4.5 16v is a non-interference motor... and I asked what could possibly cause it to have bent valves?? Because it was running when I tore it apart, and did not attempt to pull valves myself. He suggested either it was over-revved or that the bad fuel caused the valves to get stuck...
Any suggestions??
Oh and by the way I need valves like yesterday!!!
I'm gonna get it running, I'm not giving up... but DAMN...
Thanks
car is an 80 U.S. 4.5 automatic
When I purchased.. it was not running... I ended up draining the fuel out of the tank and replacing the fuel. Once I replaced the fuel with fresh and replaced the fuel pump. Motor started and idled well...
I took it around the block for the first time, at 2500 rpm it seemed to not be able to rev any higher. I attributed to possibly a vac problem...
So I pulled the motor, because I noticed coolant weeping on the outside of the motor between cylinders 2/3, 5/6 on both sides... Bought a seal kit, and while the heads were off, decided to get it a valve job.
The machine shop is telling me that there are 6 bent exhaust valves, and 1 bent intake valve.... Not sure which cylinders the valves are bent on.
Anyway. The 4.5 16v is a non-interference motor... and I asked what could possibly cause it to have bent valves?? Because it was running when I tore it apart, and did not attempt to pull valves myself. He suggested either it was over-revved or that the bad fuel caused the valves to get stuck...
Any suggestions??
Oh and by the way I need valves like yesterday!!!
I'm gonna get it running, I'm not giving up... but DAMN...
Thanks
Administrator
Joined: Aug 2001
Posts: 27,634
Likes: 3,127
From: Up Nort
Compression test was perfect compared to other cars with the same motor, leakdown told a different story. He pulled the head, most of the valves were bent.
In his 30+ years of fixing foreign cars this was a first.
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Joined: Jun 2001
Posts: 6,469
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From: Ball Ground, GA
A bent valve leaks at a certain rate. At cranking and idle speeds, the time available for leakage is three or four times that available at higher speeds, so there is much more leakage. The loss of compression is a much bigger portion of the usable mixture at cranking/idle than it is at high speed.
The combination of these factors should make the negative effect of bent valves much more noticeable at cranking/idle than at high speed.
Odd.
The combination of these factors should make the negative effect of bent valves much more noticeable at cranking/idle than at high speed.
Odd.
Thread Starter
Racer
Joined: Jun 2009
Posts: 470
Likes: 0
From: Aurora, Co
The local havana machine shop is pretty good, I've had work done there before, and they've dealt with lots of 944 heads... so I know they're not jerking my chain...
I will get the bent valves from them for my "How not to buy a 928" memories in the future...
As Hacker said it, I've heard of this problem too with some other vw's, but just shocked.... that it was my heads!! DAMNIT... Anything that can go wrong does go wrong!!
I will get the bent valves from them for my "How not to buy a 928" memories in the future...
As Hacker said it, I've heard of this problem too with some other vw's, but just shocked.... that it was my heads!! DAMNIT... Anything that can go wrong does go wrong!!
Administrator
Joined: Aug 2001
Posts: 27,634
Likes: 3,127
From: Up Nort
A bent valve leaks at a certain rate. At cranking and idle speeds, the time available for leakage is three or four times that available at higher speeds, so there is much more leakage. The loss of compression is a much bigger portion of the usable mixture at cranking/idle than it is at high speed.
The combination of these factors should make the negative effect of bent valves much more noticeable at cranking/idle than at high speed.
Odd.
The combination of these factors should make the negative effect of bent valves much more noticeable at cranking/idle than at high speed.
Odd.
He was using my car to swap parts since the good compression numbers pointed away from bent valves (didn't do the leakdown right away). After we swapped everything within reason (MAF, computers, sensors etc...) he did a leakdown. We were both a bit surprised by the results.
Nordschleife Master
Joined: Jan 2009
Posts: 5,609
Likes: 84
From: MA
Bent valves and high rpm problems? How about the possibility that high-rpm problems and bent valves are both symptoms of some other problem. For example, say valve springs are f'd up. Fouled valve springs might cause valve float which takes out the high-rpm power and this might also man-handle the valves to the point that they get bent. If the valves are bent slightly enough, they are not causing obvious problems on their own and the car runs at low rpm.
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Three Wheelin'
Joined: Feb 2009
Posts: 1,808
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From: Washington "Dc"
Maybe it overheated. Bent valves usually wont 'leak coolant'. A severe overheat could weaken the valvesprings, causing a float that would bend valves.
Check your valvespring pressure also I would wager a cold one that they are weaker than spec..
Check your valvespring pressure also I would wager a cold one that they are weaker than spec..
Thread Starter
Racer
Joined: Jun 2009
Posts: 470
Likes: 0
From: Aurora, Co
Bent valves and high rpm problems? How about the possibility that high-rpm problems and bent valves are both symptoms of some other problem. For example, say valve springs are f'd up. Fouled valve springs might cause valve float which takes out the high-rpm power and this might also man-handle the valves to the point that they get bent. If the valves are bent slightly enough, they are not causing obvious problems on their own and the car runs at low rpm.
I just talked to the shop, and he checked the height on the springs/compression and they were all very close... He didn't have the spec sheet handy so I couldn't get the #'s from him
Anybody know what the specs should be?? I don't have the manual handy it's at home!
Thread Starter
Racer
Joined: Jun 2009
Posts: 470
Likes: 0
From: Aurora, Co
A severe overheat would have also warped the heads... and most likely ruined the headgaskets... allowing coolant into the chambers there was only a weep causing crusty things on the side of the block, no drips, and no coolant in the exhaust..
I also asked about the heads, and they are in excellent shape, they were square and flat. They replaced all 16 guides, and are now awaiting new valves... WEIRD...
What's the compression on the spring supposed to be?
I also asked about the heads, and they are in excellent shape, they were square and flat. They replaced all 16 guides, and are now awaiting new valves... WEIRD...
What's the compression on the spring supposed to be?
Three Wheelin'
Joined: Feb 2009
Posts: 1,808
Likes: 0
From: Washington "Dc"
Hey 4drgl,
Check this out - http://www.ehow.com/how_5143166_check-valve-spring.html
Your machine shop should be able to confirm if the springs are within spec. I would contact Roger or Mark for specs on spring seat pressure.
Check this out - http://www.ehow.com/how_5143166_check-valve-spring.html
Your machine shop should be able to confirm if the springs are within spec. I would contact Roger or Mark for specs on spring seat pressure.
Three Wheelin'
Joined: Feb 2009
Posts: 1,808
Likes: 0
From: Washington "Dc"
From 10-1 of the WSM
Valve guide/valve stem
lntake
Exhaust
Compression
Clearance
When lnstalled new Wear Limit l
Intake 0.80
Exhaust 0.80
Compression 8 bar and more 6. 5 bar
(8 bars = 116.03019)PSI (6 bars = 87.0226426)PSI
Valve guide/valve stem
lntake
Exhaust
Compression
Clearance
When lnstalled new Wear Limit l
Intake 0.80
Exhaust 0.80
Compression 8 bar and more 6. 5 bar
(8 bars = 116.03019)PSI (6 bars = 87.0226426)PSI