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Bang after 102 days

scarletboarder said:
The dealer had the rebuild done.

I would think this puts you in a strong position as almost certainly the dealer should get compensation from the rebuilder, and thus has less to lose by compensating you.
 
infrasilver said:
I think the reason for the catastrophe is clear regarding the clip but why it took so long for it to fail is a mystery, I could understand 50-200 miles before it went walkabout but not sure why it would last a few thousand miles unless the clip simply failed or was misaligned but still held in somewhat, there isn't really that much sideways pressure on the clip.

Two reasons. 1) It had been "run in" for several thousand miles with a low rev limit which would limit load on the wrist pin and 2) This bank had cast iron liners fitted which when faced with a hardened steel wrist pin will last way longer than a coated ally bore especially when you consider the pin is below the oil scraper ring so this area has good lubrication. It can take a surprisingly long time for a pin in an iron bore to wear it to the point that it picks up.

infrasilver said:
I have fitted new clips and also re-used clips as there is no strain on them at all when installing and could be fitted a ton of times before any fatigue would occur. I just think the clip was misaligned on install and has took this long to shift.

It's more likely whoever removed them the first time over compressed them in doing so which slightly reduced their overall diameter. This diameter is critical in their ability to lock the wrist pin in place. For such a cheap component that has such a catastrophic failure mode it's best practice to consider them single use.
 
I was struggleing to see how it could be a clip as i was always told its 50 miles or so till it lets go .. cheers to Pop and infrasilver and from the pictures as i can see it now especially the score marks .

Also i still hate engine rebuilds !

Never too old to learn something no matter what you do for a living ..

OP .. im still so sorry this has happened . .. but i know that an engineers report is very valuable if it goes legal .
 
poppopbangbang said:
infrasilver said:
I think the reason for the catastrophe is clear regarding the clip but why it took so long for it to fail is a mystery, I could understand 50-200 miles before it went walkabout but not sure why it would last a few thousand miles unless the clip simply failed or was misaligned but still held in somewhat, there isn't really that much sideways pressure on the clip.

Two reasons. 1) It had been "run in" for several thousand miles with a low rev limit which would limit load on the wrist pin and 2) This bank had cast iron liners fitted which when faced with a hardened steel wrist pin will last way longer than a coated ally bore especially when you consider the pin is below the oil scraper ring so this area has good lubrication. It can take a surprisingly long time for a pin in an iron bore to wear it to the point that it picks up.

I'm not disagreeing with you as I can see this has happened, the gudgeon pin (I'm in the UK) has sat there going up and down with the bore holding it in place, I get. I'm not sure if you know the whole gudgeon pin actually fully clears and goes about 2-3mm lower than the skirt of the bore at its lowest point, it hasn't picked up on the bore but gone below it and this is why I'm confused it lasted so long and had not caught the bottom of the bore earlier especially after all of those miles.
The only thing I think it could be that the speed at the bottom of it's stroke is so fast it doesn't allow the gudgeon to shift over any before once again sitting against the bore wall, maybe it had chipped away at the bottom of the bore, bit by bit until one day it just caught and that was the end.

poppopbangbang said:
infrasilver said:
I have fitted new clips and also re-used clips as there is no strain on them at all when installing and could be fitted a ton of times before any fatigue would occur. I just think the clip was misaligned on install and has took this long to shift.

It's more likely whoever removed them the first time over compressed them in doing so which slightly reduced their overall diameter. This diameter is critical in their ability to lock the wrist pin in place. For such a cheap component that has such a catastrophic failure mode it's best practice to consider them single use.

I do slightly disagree here though :lol: there is very little stress on the clip when removing or inserting (it is possible to insert with your fingers and a plastic tool) and these would last many times of removing and refitting no problem, this is where I draw my own conclusion that it wasn't the clip that failed but the clip not being fitted correctly and has made a break for freedom at some point after the engine rebuild, then it has ran for a while waiting for the inevitable.
 
Wow, that is a seriously terrible circlip design :sad:

Having not rebuilt one of these engines, is it not possible to fit the wrist pins and circlips to the pistons/conrods before fitting to the engine, or does the design/configuration not make this possible :?:

That is what I always do with my V8`s :grin:
 
Bank 1 you can fit them first then drop the conrod/piston unit into the bore but bank 2 it's not even possible to see the clip when fitting it so you have to do it blind through a 1 inch hole on the outside of the crankcase then you have a look afterwards with a tiny inspection mirror to see if you got it in.
 
infrasilver said:
I'm not disagreeing with you as I can see this has happened, the gudgeon pin (I'm in the UK) has sat there going up and down with the bore holding it in place, I get. I'm not sure if you know the whole gudgeon pin actually fully clears and goes about 2-3mm lower than the skirt of the bore at its lowest point, it hasn't picked up on the bore but gone below it and this is why I'm confused it lasted so long and had not caught the bottom of the bore earlier especially after all of those miles.
The only thing I think it could be that the speed at the bottom of it's stroke is so fast it doesn't allow the gudgeon to shift over any before once again sitting against the bore wall, maybe it had chipped away at the bottom of the bore, bit by bit until one day it just caught and that was the end.

Okay think about the angle of the rod relative to the piston little end bosses at BDC and the force this will impart on the pin. Then what it's like at the other end and where in the cycle the wrist pin load will degrade to all most zero. Then all will become clear with regards what walks where and why it doesn't pick up on the bottom of the bore.


poppopbangbang said:
infrasilver said:
I have fitted new clips and also re-used clips as there is no strain on them at all when installing and could be fitted a ton of times before any fatigue would occur. I just think the clip was misaligned on install and has took this long to shift.

It's more likely whoever removed them the first time over compressed them in doing so which slightly reduced their overall diameter. This diameter is critical in their ability to lock the wrist pin in place. For such a cheap component that has such a catastrophic failure mode it's best practice to consider them single use.

I do slightly disagree here though :lol: there is very little stress on the clip when removing or inserting (it is possible to insert with your fingers and a plastic tool) and these would last many times of removing and refitting no problem, this is where I draw my own conclusion that it wasn't the clip that failed but the clip not being fitted correctly and has made a break for freedom at some point after the engine rebuild, then it has ran for a while waiting for the inevitable.[/quote]

That's all fine until some clog handed ogre digs the clip out with a pick and bends it past the point where it is elastic. Then matey boy who is next up probably does everything just right but clip still gets out a little while later. If you can spot if it's two tenths of a mm off round by eye you're better than me :D or if it's deformed from one edge being pried out and fails to clip into place as it should then you won't know until the above happens. With proper inspection of course you can use them again if you have knowledge of how they were removed but why bother when they're so cheap, it's less than £25 for a full engine set. We'll agree to disagree on this I guess but I'd always spend the 25 quid, I'd be beside myself if I didn't and one got out!
 
I going from how I would uninstall/install as I think all engine builders would, care and precision but then I found these that both show you how not to do this job and the theory of a ham-fisted ogre makes more sense.

Hammer the clip into the insertion tool with a screwdriver



How the hell does he know if the clip tab lined up?

 
Just a thought the two scores down the bores show the pin moving out and cutting the bores, would there not be scores between these lines as the clip would touch the bore first.
Or could the clip not have been fitted at all.
Just thinking :?:
 
I too wondered if the clip was never there while this engine ran.

Possible that the clip was either left out when piston 5 was built up or dislodged by the process of fitting the other circlip in some ham fisted way.

This is the only part of my upcoming engine build that I'm not looking forward to, though I have aftermarket Pistons which use flat circlips without the hook.

Good YouTube posts for how it should be done.
 
Griffter said:
As an aside, the 6 months thing has always puzzled me. What's the point of a 3 month warranty (which more often than not is more exclusions than cover)?
I once asked a dealer this as he proudly explained the terms of the complimentary warranty and invited me to upgrade to 6 months. He just looked at me blankly!

It's a con. The warranty is for the seller's benefit! He's liable for 6 months , no matter what. The warranty is his Insurance, not ours.
 
This is definitely the seller's responsibility, so do not offer to pay for anything, Phil.

For our own protection, can you find out who did the rebuild (so we can all avoid!!!)?
 
EGTE said:
This is definitely the seller's responsibility, so do not offer to pay for anything, Phil.

For our own protection, can you find out who did the rebuild (so we can all avoid!!!)?

scarletboarder said:
The dealer who sold it to me on 05/08/16 was the one who had the rebuild done. The son then used the car for the time in between. The car is back with the garage that did the rebuild and I await their report. I haven't contacted the dealer yet. Phil.

http://www.d9autotech.co.uk/default.asp
 
EGTE said:
This is definitely the seller's responsibility, so do not offer to pay for anything, Phil.

For our own protection, can you find out who did the rebuild (so we can all avoid!!!)?

I've used this company for years for other non 911 Porsches and they've always been excellent. They seem to do a lot of 996 work and people on this forum use them without issue. I wouldn't want this thread to suggest that they are no good and should be avoided. This seems to be an isolated incident and subject to further discussion.
 
I would think even the best company can make mistakes* the test is how they put things right for customers if a mistake is made.

*Porsche come to mind :)
 

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