1991 Porsche 928 GT- M2847 engine- PISTON Question
10-04-2013, 08:26 PM
#16
I just don't get it when people can't just take a few minutes and do some research. LFA if they honed a cylinder - what was the plan after that?
10-04-2013, 08:37 PM
#17
Drifting
Yip he just Fcked your block
These engines are cast with a unique process, developed by Porsche (I Believe)
where aprox 83% aluminum and 17% silicon are blended to pore the casting.
After the bores have been done they are not honed but a acid rub process (Dont know the details) removes the aluminum leaving a super hard silicon lining that should be good for around 500,000 if you look after your engine.
Now my details may be off and if they are others will correct me but the bad news is you need to take a bat and after you beat the mechanic you need to smack yourself for letting him touch it.
Sorry for the bad news
These engines are cast with a unique process, developed by Porsche (I Believe)
where aprox 83% aluminum and 17% silicon are blended to pore the casting.
After the bores have been done they are not honed but a acid rub process (Dont know the details) removes the aluminum leaving a super hard silicon lining that should be good for around 500,000 if you look after your engine.
Now my details may be off and if they are others will correct me but the bad news is you need to take a bat and after you beat the mechanic you need to smack yourself for letting him touch it.
Sorry for the bad news
10-04-2013, 08:42 PM
#18
Nordschleife Master
I have checked and unfortunately they have honed one of the cylinders. Is this a disaster or is there a solution?
Can you please give some information on the ''special process to hone Alusil bores''
( If the Alusil bores look good with no wear step on the top and bottom of the bore and the pistons special coating is intact and the tolerance numbers for the piston and bore match (its either going to be 0,1, or 2; 1 being the most common) I would reassemble with new rings and be done with it. And by the way make sure your mechanic doesn't hone the bore like they do with steel bores. Alusil bores requires a special process. If he doesn't have access to this process its best to just clean the bore with a soft plastic brush to clean off the carbon deposits and oil stain. )
Can you please give some information on the ''special process to hone Alusil bores''
( If the Alusil bores look good with no wear step on the top and bottom of the bore and the pistons special coating is intact and the tolerance numbers for the piston and bore match (its either going to be 0,1, or 2; 1 being the most common) I would reassemble with new rings and be done with it. And by the way make sure your mechanic doesn't hone the bore like they do with steel bores. Alusil bores requires a special process. If he doesn't have access to this process its best to just clean the bore with a soft plastic brush to clean off the carbon deposits and oil stain. )
https://rennlist.com/forums/928-foru...il-blocks.html
If there are visible scratch marks in the bore from the honing they've ruined the bore - Alusil must not have the cross-hatch style of honing. The bores should appear and feel smooth. The only way out of the mess at this stage is to do one of these options:
1. overbore to a Porsche standard size, following the correct Alusil process and pay porsche for the correct oversize pistons/rings
2. Bore all the blocks out to a special size, nikasil plate the block, and have custom pistons made
3. Buy a used engine with good bores/pistons/rods/crank.
4. Buy a used block with the exact same tolerance group as your pistons.
The cheapest option is likely 3 - but you'll be rolling the dice on the condition o the head gasket etc., and as your car is a 91 GT, you need to be looking at 89-91 used engines only (87/88 had lower compression pistons). The most expensive is option 2 - and its a process that very very few shops could be trusted with to get right (1, maybe 2, in the USA)
Seriously - it sounds like the shop you're using doesn't have the requisite Porsche experience to deal with these cars, as they aren't familiar with Alusil blocks. You need to find a local Porsche shop, or if you're in whoop whoop, failing that, a good BMW or Mercedes shop (they also used ALusil).
Your best bet is to add your location to your profile, and ask for recommendations from locals on this board.
10-04-2013, 08:48 PM
#19
Nordschleife Master
I think you should collect your parts from whomever is doing the work, and get that engine to someone who knows what they are doing with the engine!
10-04-2013, 08:50 PM
#20
Nordschleife Master
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Regular honing turned the existing bore into absolute junk.
You now have no choice but to have the block over bored and correctly honed, by someone who knows this process.
The only pistons that will work need to come from Porsche.
And seriously, if your mechanic doesn't know enough to not run a hone through one of these cylinders, you are in a "world of hurt".
You now have no choice but to have the block over bored and correctly honed, by someone who knows this process.
The only pistons that will work need to come from Porsche.
And seriously, if your mechanic doesn't know enough to not run a hone through one of these cylinders, you are in a "world of hurt".
Why post these questions AFTER the **** is done escapes me.
Yip he just Fcked your block
These engines are cast with a unique process, developed by Porsche (I Believe)
where aprox 83% aluminum and 17% silicon are blended to pore the casting.
After the bores have been done they are not honed but a acid rub process (Dont know the details) removes the aluminum leaving a super hard silicon lining that should be good for around 500,000 if you look after your engine.
Now my details may be off and if they are others will correct me but the bad news is you need to take a bat and after you beat the mechanic you need to smack yourself for letting him touch it.
Sorry for the bad news
These engines are cast with a unique process, developed by Porsche (I Believe)
where aprox 83% aluminum and 17% silicon are blended to pore the casting.
After the bores have been done they are not honed but a acid rub process (Dont know the details) removes the aluminum leaving a super hard silicon lining that should be good for around 500,000 if you look after your engine.
Now my details may be off and if they are others will correct me but the bad news is you need to take a bat and after you beat the mechanic you need to smack yourself for letting him touch it.
Sorry for the bad news
Where are you located?
10-04-2013, 09:02 PM
#21
Three Wheelin'
Yes, please give your location.
What about Nikasil coating the bores and reusing the original pistons? I'm assuming special piston rings are supposed to be used with Nikasil bores?
I would send the engine pieces to Greg Brown and have him built it, since he has been building them for years.
Why did the engine come apart in the first place? ~90,000 miles is pretty low for these engine if proper oil (20W50 weight) was used.
Oh well I was trying to jump ahead before any damage was done, but I guess I was too late.
Your GT is a valuable car with number matching engine, I believe something like 500 were brought to USA. A nice clean sorted similar mileage car can sell from mid low 20s to high 20s, or maybe more.
What about Nikasil coating the bores and reusing the original pistons? I'm assuming special piston rings are supposed to be used with Nikasil bores?
I would send the engine pieces to Greg Brown and have him built it, since he has been building them for years.
Why did the engine come apart in the first place? ~90,000 miles is pretty low for these engine if proper oil (20W50 weight) was used.
Oh well I was trying to jump ahead before any damage was done, but I guess I was too late.
Your GT is a valuable car with number matching engine, I believe something like 500 were brought to USA. A nice clean sorted similar mileage car can sell from mid low 20s to high 20s, or maybe more.
10-04-2013, 09:20 PM
#22
Instructor
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I will change my mechanic today.
Do you think the following might work?; Only one cylinder is honed and 7 are untouched. Can I just have this honed cylinder processed properly for Alusil and have a new Porsche oversize piston ( 100.50) installed only to this cylinder. The rest will be the same.
Do you think the following might work?; Only one cylinder is honed and 7 are untouched. Can I just have this honed cylinder processed properly for Alusil and have a new Porsche oversize piston ( 100.50) installed only to this cylinder. The rest will be the same.
10-04-2013, 09:27 PM
#23
Team Owner
LFA where are you typing these posts from?
What city does the mechanic that honed you a fine hone job work in?
What city does the mechanic that honed you a fine hone job work in?
10-04-2013, 09:33 PM
#24
Are there even oversize pistons for these? I'm wondering if the engine is by chance tolerance 0, if the honed cylinder maybe could still be final honed to tolerance 2.
10-04-2013, 09:34 PM
#25
Officially suspicious now- tell us in general where you are.
10-04-2013, 09:37 PM
#26
Three Wheelin'
People here are just trying to help, we all love 928s. You have a very special car there.
Someone here may know a 928 mechanic local to you that can get the job done properly, specially if your in the US.
Someone here may know a 928 mechanic local to you that can get the job done properly, specially if your in the US.
10-04-2013, 09:53 PM
#28
Nordschleife Master
I will change my mechanic today.
Do you think the following might work?; Only one cylinder is honed and 7 are untouched. Can I just have this honed cylinder processed properly for Alusil and have a new Porsche oversize piston ( 100.50) installed only to this cylinder. The rest will be the same.
Do you think the following might work?; Only one cylinder is honed and 7 are untouched. Can I just have this honed cylinder processed properly for Alusil and have a new Porsche oversize piston ( 100.50) installed only to this cylinder. The rest will be the same.
10-04-2013, 10:16 PM
#30
Nordschleife Master
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I will change my mechanic today.
Do you think the following might work?; Only one cylinder is honed and 7 are untouched. Can I just have this honed cylinder processed properly for Alusil and have a new Porsche oversize piston ( 100.50) installed only to this cylinder. The rest will be the same.
Do you think the following might work?; Only one cylinder is honed and 7 are untouched. Can I just have this honed cylinder processed properly for Alusil and have a new Porsche oversize piston ( 100.50) installed only to this cylinder. The rest will be the same.