GTS liners cracked, not pretty
11-16-2012, 04:17 PM
#16
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There are no "liners".
The 928 block is made of Reynolds 490 high silicon (not silicone) aluminum
alloy. It is precision cast, with controlled cooling for the bores, so as
to bring the silicon to the surface. After boring and honing, the block is
chemically honed to remove a very thin layer of aluminum from the surface
of the bores, leaving a very hard, slightly porous layer of silicon for the
pistons and rings to rub on. Since aluminum does not function well rubbing
against this silicon surface, the aluminum pistons receive a very thin
coating of iron as a wear layer.
Interesting that the bores are cracked, but the pistons look undamaged.
The 928 block is made of Reynolds 490 high silicon (not silicone) aluminum
alloy. It is precision cast, with controlled cooling for the bores, so as
to bring the silicon to the surface. After boring and honing, the block is
chemically honed to remove a very thin layer of aluminum from the surface
of the bores, leaving a very hard, slightly porous layer of silicon for the
pistons and rings to rub on. Since aluminum does not function well rubbing
against this silicon surface, the aluminum pistons receive a very thin
coating of iron as a wear layer.
Interesting that the bores are cracked, but the pistons look undamaged.
11-16-2012, 05:04 PM
#17
Former Sponsor
Hi Hilton,
motor is slowly being dismantled, Don is looking at the liner option as he would like to keep the engine number.
He thinks it was just never given a good hard drive to blow out the carbon now and then, the owner has several cars. There was a bit of oil in the intake runners.
It certainly has not sat for years as suggested. There was no water in the bores, or oil in water etc. A boroscope was used but no damage was seen!
motor is slowly being dismantled, Don is looking at the liner option as he would like to keep the engine number.
He thinks it was just never given a good hard drive to blow out the carbon now and then, the owner has several cars. There was a bit of oil in the intake runners.
It certainly has not sat for years as suggested. There was no water in the bores, or oil in water etc. A boroscope was used but no damage was seen!
You might be able to machine out the entire cylinder and insert a "stand" alone liner, much like Mike Simard did, with his race engine.
Pretty typical carbon build-up for a high mileage GTS. All that oil, in the intake system and from the pressure in the crankcase, has to go somewhere.
The sitting allowed some of that carbon to come loose and fall down to the bottom of the cylinder. When the piston stopped moving, before it got to TDC, somethings had to give. You can clearly see the head, where the carbon impacted the combustion chamber.
Most likely those two rods that got stopped will be bent, too.
BTW....pretty damn frightening that a professional "mechanic" wouldn't turn an engine over, by hand, that had been sitting for a long period of time, before sticking in a fresh battery and cranking it over. For Christ's sake! A professional "mechanic" is supposed to have enough knowledge to know not to make a rookie mistake, like this.....that's supposed to be what makes him a professional! If I owned that car, I'd be really pissed. That mechanic turned a viable engine into scrap metal.
Last edited by GregBBRD; 11-16-2012 at 05:35 PM.
11-16-2012, 05:43 PM
#18
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11-16-2012, 05:50 PM
#20
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Pull it apart.
If the pistons/crank/rods are ok, they can track down an S4/GT block which had the same piston tolerance group in it, and use that.
Or they can try to fit a replacement liner (IIRC the liners can still be had from Porsche) for that cylinder. The factory liners used in some GTS engines are alusil.
Looks like massive carbon buildup - this is probably a GTS engine which drank oil?
If the pistons/crank/rods are ok, they can track down an S4/GT block which had the same piston tolerance group in it, and use that.
Or they can try to fit a replacement liner (IIRC the liners can still be had from Porsche) for that cylinder. The factory liners used in some GTS engines are alusil.
Looks like massive carbon buildup - this is probably a GTS engine which drank oil?
update: oh, i guess that seam that we can see at the top of the cylinder is a "liner" but as greg said, it cant be replaced.
yep, best just to find a 5 liter block and put it back together again! or replace all the rods and bearings too, just incase a rod was damaged in that start up. sounds simple, im sure its more complicated than that, but the valuable part here is the crank and pistons.
time to go 6.5 liter!!
11-16-2012, 06:03 PM
#21
Rennlist Member
The lined blocks from the factory were the fix they arrived at, re the issues with the late gts s , it has been docummented many times here . on the list. The block cannot be repaired , anyone who thinks it can be done within a reasonable budget of the value of the car and still be reliable is delusional .
Get an s4 block check all the components and transfer contents as GB has stated , simpler and much cheaper , reliable. You can even restamp the engine code if you needed to , if the original is scrapped .
I am sure GB would be able to do a deal an any components that may be needed or do so .
Get an s4 block check all the components and transfer contents as GB has stated , simpler and much cheaper , reliable. You can even restamp the engine code if you needed to , if the original is scrapped .
I am sure GB would be able to do a deal an any components that may be needed or do so .
11-16-2012, 07:09 PM
#22
Rennlist Member
Thread Starter
BTW....pretty damn frightening that a professional "mechanic" wouldn't turn an engine over, by hand, that had been sitting for a long period of time, before sticking in a fresh battery and cranking it over. For Christ's sake! A professional "mechanic" is supposed to have enough knowledge to know not to make a rookie mistake, like this.....that's supposed to be what makes him a professional! If I owned that car, I'd be really pissed. That mechanic turned a viable engine into scrap metal.
regards Nigel
11-16-2012, 07:26 PM
#23
Former Sponsor
Greg, you musyt have missed the second line of my original post, I have now highlighted this, it is a well used car, its never sat for long periods, it has a full service history, the type any buyer would love to see in a book. It was driving fine before.
regards Nigel
regards Nigel
Really strange that all that carbon fell off, at the same time, to suddenly restrict that piston from reaching the top...especially in two separate cylinders.
Hopefully, there's more to be more to the story than just this...otherwise no on who owns a stock GTS should be running it!
Like I said, this is pretty "normal" carbon build-up for one of these engines.....tough to figure out why they "ping".
11-16-2012, 07:43 PM
#25
Rennlist Member
Considering the state of the gasket I think hydrolock is still a possibility ... it wouldn't take much. The lack of coolant in the bore after the 'event' and after stripdown could be explained by seepage past the rings or out the cracks.
11-16-2012, 08:02 PM
#26
Rennlist Member
Thread Starter
Dave, car was started when cold, no water or oil mixed, and yes I think the other ccarbon bits have fallen off when the head was removed. I agree that the rust colour on the top of pistons looks like that.
Don is pretty adamant that the cracks came about when it went clang, as there is no carbon in them, theylook clean & fresh, I ma not sure if I agree with that. It will be interesting to see what it looks like when the sump is removed....
Don is pretty adamant that the cracks came about when it went clang, as there is no carbon in them, theylook clean & fresh, I ma not sure if I agree with that. It will be interesting to see what it looks like when the sump is removed....
11-16-2012, 09:13 PM
#28
Rennlist Member
I have great sympathy for the owner ... that'd be enough to make me cry.
11-16-2012, 09:27 PM
#30
Rennlist Member
I have seen similar damage on other motors when foreign objects had entered the combustion chamber. It appears to me that the only explanation here is that the piston wasn't able to compress all of that build up in this event. Something had to give. I would follow GB's suggestion to closely look at the rods if you plan on keeping the rotating assembly for use in a different block.