My Porsche 928

[ANF]

Thanks Gavin, I am a little perturbed as to why the Valve has broken (just below the retainer) as well as why the spring broke..... inner spring is fine though.....

I will also add that these are a bloody big and heavy engine, quite a bit of "fun" to get out..... 

[Gavn]

Yes, thats interesting.  I know far too little about why that might happen but would love to hear from others with more knowledge.  yep, big heavy engines....and read your comments about exhaust studs/bolts with interest.  I swapped out the exhaust system on our 55 beetle (they're simple cars right.....right) and could not believe how bloody hard some of the bolts were.  Heat , pressure, banging etc...lots of swearing and the inevitable bleeding afterwards.  No fun at taking out old bolts...

[P-Kay]

Feel your pain Adam,

On a positive note, you can get in the engine bay and get into all the crevices to make it sparkle again (appreciate this is the least of your concerns)

[ANF]

16 minutes ago, Gavin (CliffToCoast) said:

Yes, thats interesting.  I know far too little about why that might happen but would love to hear from others with more knowledge.  yep, big heavy engines....and read your comments about exhaust studs/bolts with interest.  I swapped out the exhaust system on our 55 beetle (they're simple cars right.....right) and could not believe how bloody hard some of the bolts were.  Heat , pressure, banging etc...lots of swearing and the inevitable bleeding afterwards.  No fun at taking out old bolts...

I would think that one would cause the other.... broken spring caused valve to hit piston, breaking it? But then why did spring break??

Yes, old cars can be very cantankerous!! It seems on the 928 they tried very hard to eliminate waste - any excess air or space around something would seem to be wasteful 

12 minutes ago, P-Kay said:

Feel your pain Adam,

On a positive note, you can get in the engine bay and get into all the crevices to make it sparkle again (appreciate this is the least of your concerns)

Thanks for thinking of the small things 

I have actually already thought about that, and how I will tow the car out of the garage to clean it...... 

[StevepGT3]

56 minutes ago, ANF said:

I would think that one would cause the other.... broken spring caused valve to hit piston, breaking it? But then why did spring break??

Yes, old cars can be very cantankerous!! It seems on the 928 they tried very hard to eliminate waste - any excess air or space around something would seem to be wasteful 

Thanks for thinking of the small things 

I have actually already thought about that, and how I will tow the car out of the garage to clean it...... 

Old sodium filled valves (they are from the era that it was common, so would assume that they were) can inexplicably do that, which is why most replacements will not be sodium filled.

[ANF]

17 minutes ago, StevepGT3 said:

Old sodium filled valves (they are from the era that it was common, so would assume that they were) can inexplicably do that, which is why most replacements will not be sodium filled.

Interesting, I have heard of sodium filled valves and thought they were only used on exhaust valves? This is an inlet valve that has broken. Either way I cannot trust any of the remaining valves or springs and all must be replaced.....

The part of valve that I do have (from the retainer up) is solid, will find out soon what the other end is.....

[StevepGT3]

17 minutes ago, ANF said:

Interesting, I have heard of sodium filled valves and thought they were only used on exhaust valves? This is an inlet valve that has broken. Either way I cannot trust any of the remaining valves or springs and all must be replaced.....

The part of valve that I do have (from the retainer up) is solid, will find out soon what the other end is.....

could be right, was just guessing, has it broken at the retainer groove? as millions of cycles can just do that at the weakest point unfortunately.

[Coastr]

Hurts to see.

broken valve - most commonly timing - did belt skip a tooth?  Or maybe engine was leaning out and burning too hot and the valve weakened?  I think you'd have to check carefully to determine what broke first, the valve or the spring.  I know that 911 engines break the valve train after the valve touches the cylinder...you'd have to guess the valve hit the cylinder, then broke the spring and the shaft.  But I'm no expert.

it must have sounded awful - a noise that sends fear into every old car owner.

[ANF]

49 minutes ago, Coastr said:

Hurts to see.

broken valve - most commonly timing - did belt skip a tooth?  Or maybe engine was leaning out and burning too hot and the valve weakened?  I think you'd have to check carefully to determine what broke first, the valve or the spring.  I know that 911 engines break the valve train after the valve touches the cylinder...you'd have to guess the valve hit the cylinder, then broke the spring and the shaft.  But I'm no expert.

it must have sounded awful - a noise that sends fear into every old car owner.

It was a horrible noise! Belt not slipped, non-interference engine. The broken valve/ spring is the cause not the result I would say. Just hoping the bore is not too scored, need to find an hour or so and get the head off next.

Cheers

The car was running lean when I got it, not sure for how long and ultimately how lean... 

4 hours ago, StevepGT3 said:

could be right, was just guessing, has it broken at the retainer groove? as millions of cycles can just do that at the weakest point unfortunately.

From the little I have read sodium filled valves are to remove excess heat from the exhaust valve and have been used in all sorts of cars and not that long ago too.

Broken just below the retainer, not at a groove, you can just make it out in a pic, retainer is in tact due to slight deformation where valve stem broke

[Buchanan Automotive]

With twin valve springs per valve ( most Porsche engine's have twin  )  & if you have a broken spring ( one of the two through metal fatigue or just a minute fault that's been there for decades ) then the engine will still run but with a strange subtle off beat firing impulse on one cylinder ( out of 8 cylinders )  , in this case an inlet valve( bigger and heavier than the Ex valve ) will valve bounce very badly even a mid RPM range , this in turn will fatigue the valve stem until it just lets go ( breaks ) & they mostly break up high ( this is where the max shock is )

If an engine runs too lean & at high RPM the valve head will just burn ( looks like some one has cut a V in the valve head) & this is instant loss of compression but no engine damage , meaning the piston etc is not effected at all

If an engine has very badly worn valve guides ( this mostly applies to exhaust valves & mostly in air cooled 911 )& the engine RPM is high & sustained , the worn valve guide will not alloy the heat from the valve head to dissipate into the air cooled ( 911cylinder head ) & the valve head gets so hot it drops off the stem close to the valve head ( down low ) and naturally this causes massive damage to the piston & cylinder

Note } Valves , be it inlet or exhaust will never hit the cylinder ( unless they fall off ) , they just contact the top of the piston , but if the valve drops into the cylinder , well this will damage piston & cylinder

Note 2 )  with rockers ( air cooled 911 engines have rockers ) at engine over rev the over rev can & will cause a rocker to fail , that's the problem with rockers

Note 3 )  Over Rev , meaning you are racing the engine ( may be on a track or street ) and you are ( say ) in 4th gear and you are going deep into a corner & you quickly change down to 3rd , but you miss 3rd and get 1st gear , as you bring the clutch up the engine will be forced to over rev ( mechanical over rev ) , on the 911 up to & including the 964 they will also stretch their con rod bolts along with breaking a rocker or two

Note 4 )  With last century 2 valve per cylinder Porsche engines as opposed to 4 valve per cylinder last century Porsche engines , be it the 2 valve 911 air cooled engines or the 2 valve  944 ( single cam engine ) or the 2 valve  928 4.5 or 4.7L single cam per bank engines , the individual valves are quite large & very heavy as compared to the 4 valve per cylinder twin cam engines , be it the 32V 5.0L 928S/S4/GT / 5.4L 32V GTS or the 2.5L 16V 944S or 3.0L 944S2 or 968 engines which the valves are much smaller & a lot lighter , meaning the twin valve springs per valve only need to a fraction of the tension & size to control a( heavier 2 valve per cyl )  valve at high RPM ,which( being smaller and lighter) in turn is a bit more reliable ( IF ) the engine has to be spun up to very high RPM a lot , however if a 2 valve per cylinder , be it 944 / 928/911 does not have to be driven at high RPM all the time , then its quite adequate 

So , to recap , this engine needs all new valves and valve springs if the heads are to be reused  , be very careful on quality , there has been some issues with some aftermarket stuff over the last 10 years

Nearly forgot to mention , Sodium ( Porsche used to use the older terminology of Natrium) filled valves , mainly exhaust valves , Porsche only used this with their road cars sold to the public ( mainly ) with their Turbo charged engines , like the 944 Turbo , but not the 928 ( no need )

Regards
Bruce B

[Ozvino]

Adam - great to see the progress. Pulling your 928 engine elevates you to a new status mate - them balls you have are made of steel. Most people shit themselves just looking at the engine bay of a 928, let alone ripping it out. 

This will be worth the effort !

Dave

[ANF]

3 hours ago, Buchanan Automotive said:

With twin valve springs per valve ( most Porsche engine's have twin  )  & if you have a broken spring ( one of the two through metal fatigue or just a minute fault that's been there for decades ) then the engine will still run but with a strange subtle off beat firing impulse on one cylinder ( out of 8 cylinders )  , in this case an inlet valve( bigger and heavier than the Ex valve ) will valve bounce very badly even a mid RPM range , this in turn will fatigue the valve stem until it just lets go ( breaks ) & they mostly break up high ( this is where the max shock is )

If an engine runs too lean & at high RPM the valve head will just burn ( looks like some one has cut a V in the valve head) & this is instant loss of compression but no engine damage , meaning the piston etc is not effected at all

If an engine has very badly worn valve guides ( this mostly applies to exhaust valves & mostly in air cooled 911 )& the engine RPM is high & sustained , the worn valve guide will not alloy the heat from the valve head to dissipate into the air cooled ( 911cylinder head ) & the valve head gets so hot it drops off the stem close to the valve head ( down low ) and naturally this causes massive damage to the piston & cylinder

Note } Valves , be it inlet or exhaust will never hit the cylinder ( unless they fall off ) , they just contact the top of the piston , but if the valve drops into the cylinder , well this will damage piston & cylinder

Note 2 )  with rockers ( air cooled 911 engines have rockers ) at engine over rev the over rev can & will cause a rocker to fail , that's the problem with rockers

Note 3 )  Over Rev , meaning you are racing the engine ( may be on a track or street ) and you are ( say ) in 4th gear and you are going deep into a corner & you quickly change down to 3rd , but you miss 3rd and get 1st gear , as you bring the clutch up the engine will be forced to over rev ( mechanical over rev ) , on the 911 up to & including the 964 they will also stretch their con rod bolts along with breaking a rocker or two

Note 4 )  With last century 2 valve per cylinder Porsche engines as opposed to 4 valve per cylinder last century Porsche engines , be it the 2 valve 911 air cooled engines or the 2 valve  944 ( single cam engine ) or the 2 valve  928 4.5 or 4.7L single cam per bank engines , the individual valves are quite large & very heavy as compared to the 4 valve per cylinder twin cam engines , be it the 32V 5.0L 928S/S4/GT / 5.4L 32V GTS or the 2.5L 16V 944S or 3.0L 944S2 or 968 engines which the valves are much smaller & a lot lighter , meaning the twin valve springs per valve only need to a fraction of the tension & size to control a( heavier 2 valve per cyl )  valve at high RPM ,which( being smaller and lighter) in turn is a bit more reliable ( IF ) the engine has to be spun up to very high RPM a lot , however if a 2 valve per cylinder , be it 944 / 928/911 does not have to be driven at high RPM all the time , then its quite adequate 

So , to recap , this engine needs all new valves and valve springs if the heads are to be reused  , be very careful on quality , there has been some issues with some aftermarket stuff over the last 10 years

Nearly forgot to mention , Sodium ( Porsche used to use the older terminology of Natrium) filled valves , mainly exhaust valves , Porsche only used this with their road cars sold to the public ( mainly ) with their Turbo charged engines , like the 944 Turbo , but not the 928 ( no need )

Regards
Bruce B

Thanks Bruce, yes all new valves, springs, retainers, seals, guides will be going in.

Cheers

39 minutes ago, Ozvino said:

Adam - great to see the progress. Pulling your 928 engine elevates you to a new status mate - them balls you have are made of steel. Most people shit themselves just looking at the engine bay of a 928, let alone ripping it out. 

This will be worth the effort !

Dave

Thanks Dave!

It will rise again, much better than before

[KGB]

14 hours ago, Ozvino said:

 Most people shit themselves just looking at the engine bay of a 928, let alone ripping it out.

Was it that obvious?  I still got the job done though, even having to grunt whilst pushing the plastic cap's neck into the rubber tube.

 

Good job Adam! 

[ANF]

48 minutes ago, KGB said:

Was it that obvious?  I still got the job done though, even having to grunt whilst pushing the plastic cap's neck into the rubber tube.

 

Good job Adam! 

Thanks Mark!

Those plastic caps can be a bit tricky at times....... 

[ANF]

WARNING!!

Some viewers may find the following images distressing (I did.... )

Saturday - intake removal..... not a lot of words needed.... from this damage I was shattered as to what may lay beneath....

Sunday - head removal..... while fragments of head had been distributed to all cylinders the marks were extremely light, not even deep enough to catch a finger nail!! I was somewhat surprised. Whether head can be saved is dubious.....

I need to measure the gouges to no. 7 cylinder but they are looking deeper than 1st oversize piston (97.5mm the only oversize you can still buy....) 

 

 

 

 

 

 

 

[WOKA]

I had to look away.  I took a swig of my beer and had another swig.  I'm still swigging. 

 

[Coastr]

Um do you have a boat?  Cause it looks like you have a new anchor there.  Head is toast, bore is toast, valve is a desk ornament to scare the kiddies with.

[ANF]

21 minutes ago, Coastr said:

Um do you have a boat?  Cause it looks like you have a new anchor there.  Head is toast, bore is toast, valve is a desk ornament to scare the kiddies with.

Block is fixable by boring it and using custom made pistons, which may be my best choice. Hoping that the gouge is manageable with 1st oversize, head.... ??

Yes valve is now a desk ornament 

38 minutes ago, WOKA said:

I had to look away.  I took a swig of my beer and had another swig.  I'm still swigging. 

 

Keep going, it can't hurt you... maybe it will look better after 

[Troubleshooter]

46 minutes ago, Coastr said:

Um do you have a boat?  Cause it looks like you have a new anchor there.  Head is toast, bore is toast, valve is a desk ornament to scare the kiddies with.

I'm triggered

[tazzieman]

Being a professional optimist , I will say it could be worse

[ANF]

Yes, yes it could 

[Stew F]

@ANF Adam, you might be able to find pistons from something else that will do the job. I'll sms you a JP Pistons catalogue.

[ANF]

Does anyone know the min wall thickness of the 4.7 bore, Bruce at @Buchanan Automotive ?

[Buchanan Automotive]

Porsche originally ( back in the mid 1980's ) list two oversize piston sizes for the 4.7L 928S  , first over size & 2nd oversize 

Standard bore size =    97.00mm  for the 4.7L

1st oversize             =   97.50mm  ( .25mm per material machined off the inside of cylinder in any one spot measured in relation to wall thickness )

2nd oversize            =  98.00 mm  ( .50mm per material machined off inside of cylinder in any one spot measured in relation to wall thickness )

However the Porsche PET ( parts )   only lists the 1st oversize because almost no one ever purchased that size , 2nd oversize was the one that was needed for most bore wear over the decades & they are long been sold out

So officially the answer to you're question  =  you're Cylinder Wall thickness  ,then  subtract .5mm = 1mm increase in the total bore size if bored to the 2nd oversize

Bruce B

[ANF]

Thanks Bruce, do you know what the limit actually may be (min actual wall thickness)? There are stories of being able to take the 4.7s out to 5.0 litre, any truth in this?

Cheers