Dave, just a loud "pop",then the smokescreen and loss of power.

 

I'll be interested to see the forensic pics when you get it apart Paul. Good that the oil dump didn't cause you or someone else to lose it at high speed. Good luck with the engine transplant ... hope you're back out again soon.

 

I removed the heads and sump today. Broken bit was a conrod. It had snapped up near the piston. After then it had flicked around and punched the hole in the bottom of the V, then bent and tucked in beside the adjacent conrod. Damaged was very localised: broken conrod, hole in base of cylinder, hole in the V, one bent valve. Lots of metal bits in the sump. I will post some pics later.

 

Some pics of the damage. One of the engine on the stand. A couple of the conrod, snug up against the one beside it and one of the snapped conrod at the piston end.

 

Now that the piston and conrod are out, I have to ID them. The pistons are 100mm and there are numbers and marks inside inside. is this a standard 928 piston? The conrod has GKN marked on it. Is it a standard 928 conrod?

 

Looks like the rod for 3 or 7. Usually 2 or 6 so a bit different failure than typical. (I got full marks with snapping 2 and 6 at one time.)

Best of luck with the new engine!

 

Very odd.........a clean snap of the rod...........how to the rod bearings look? Can't really tell in the photo?

 

GKN sounds like Guest-Keen-Nettlefold maker, but thats just a WAG The multiple valve reliefs look like S4 pistons fly cut for 16V heads....
jp 83 Euro S AT 53k

 

Paul,

Photographs look interesting especially the top of the piston crown, which looks like valve indents walking around the crown in a cloclwise direction. This poses the question, did the piston rotate in an anti clockwise direction during the failure process?

Have you given though to having the broken rod inspected metallurgically to try and determine the cause of the failure, the failure process, as the connecting is mainly under compress stress with its greatest compressive load during the firing stroke and basically it is only under a tension load when on the inlet down stroke.

Hope you have luck in aquiring a block or spares to get it back on the track.

Regards,
Tails 1990 928S4 Auto

 

THose pistons are from the early US 32 valved engine , so it has been apart , did you know that ?

I cannot recognise the rods as I limited experience with the early engine , so it would appear that someone has bored this to use the larger pistons .
This type of piston is designed to orient in a certain way in the later engines , which way are they nounted here ?

can you identify the mark on the pistons to help with this ?

ALso how thin were the bore walls ?

as if this was an early engine , I know here in Australia there is not a lot of support for this type of engine rebuild .

 

IIRC this engine was rebuilt at very large expense prior to Paul's ownership, by a crowd who do engines for the V8 Supercars series?

It will be interesting to see what other modifications they made - certainly a 5.0L "hybrid" makes sense. What heads, valves and cams did they use? I wouldn't be surprised if they're 4.5 heads that have had porting, and possible 928S cams?

Paul - I know you've been running the car at the track pretty heavily for at least the last 4 years - any idea what the log book time tally is since the engine build?

 

SO it is a 5.0L euro......that explains the 100mm pistons with extra cuts...

Still the rod failure is interesting.....its hard to tell from the piston, but aren't most rod failures from detonation? Maybe a failure in the fuel system led to the lean condition?

 

Googling 'gkn conrod porsche' gives:- "KN wins 'best in class'in PF con rod race - Elsevier
You +1'd this publicly. Undo
linkinghub.elsevier.com/retrieve/pii/S0026065704001274Similar
Bernard Williams reports on his visit to GKN Sinter Metals' powder forging ... at GKN in the UK of the first volume production con rod for the Porsche 928 ..."
but fiollowing the link, I cant find the 928 mention, but it looks like it might be a stock rod. Inside the link gives "Bernard Williams reports on his visit to GKN Sinter Metals' powder forging plant in Hückeswagen.."
No sign of a 928 number on it ?
jp 83 Euro S AT 53k

 

Thanks for all the information. It looks like it has 928 conrods and pistons which will help with the rebuild. As Hilton said the engine was extensivley re-worked but I do not have paperwork and this is the first time I have opened it up. Don't know the cause, but suspect possible small water leak into the cylinder. It was a 3/7 rod failure, I cant remebmer which one. The one rod bearing is damaged but nothing visible on the crank. The piston was just lose in the bore, the rod broke and left the piston up the top, one valve got hit and jammed just slightly open, the piston tapped the valve lightly a few times and piston settled out of range. I have not identified the heads yet. They are beautifully ported. Cams are hight lift anf valves are unknown. Once we settle on a block then the rest of the options will fall into place.

 

Have you got some pics of the heads Paul? ... I'd be interested to see the porting and the chambers.