piston swap?
#1
Burning Brakes
Thread Starter
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
curious if anyone has preemptivly swapped pistons on a 996 to head off scoring? seems cheaper than waiting for scoring which requires sleeving?
could also pin IMS, add oil pump new hex etc also at the same time.
thoughts?
could also pin IMS, add oil pump new hex etc also at the same time.
thoughts?
#3
Pro
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
I don't believe the issue lies with the pistons, my car is in the midst of having an engine rebuild which includes liners, as part of the process my engine builder measured all the bores and they were all out of shape, I believe this causes the piston skirt to contact the wall of the cylinder, as it rotates past TDC and gives rise to the scoring.
Poor block design is the issue here.
Poor block design is the issue here.
#4
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
I have thought about this and the best idea is probably put the money away for rebuild when it actually happens.
When scoring happens, my understanding is they mill it off and sleeves it, so it doesnt matter. Just don't wait too long that it destroy other parts in the block. So drive it until it happens.
Or you can do a preventative rebuilt. Send the car to Jake and do a rebuild into 3.8/4.0 and have all the goodies installed that'd take cares 2 birds in one stone.
I plan to enjoy it as it is until I want more HP or until something is wrong before I spend the money.
When scoring happens, my understanding is they mill it off and sleeves it, so it doesnt matter. Just don't wait too long that it destroy other parts in the block. So drive it until it happens.
Or you can do a preventative rebuilt. Send the car to Jake and do a rebuild into 3.8/4.0 and have all the goodies installed that'd take cares 2 birds in one stone.
I plan to enjoy it as it is until I want more HP or until something is wrong before I spend the money.
#5
Rennlist Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
I mean, if 100%, or even 20% of these engines positively absolutely ended up having this issue, maybe, but...
#6
Intermediate
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
I have nothing overly meaningful to add other than this is complete lunacy.
Years from now prospective buyers (or writers like Jack B) will read this thread and believe that all 996 pistons are bad and require replacement as a PM.
This is what perpetuates the ill feelings towards our engines!
Years from now prospective buyers (or writers like Jack B) will read this thread and believe that all 996 pistons are bad and require replacement as a PM.
This is what perpetuates the ill feelings towards our engines!
#7
Burning Brakes
Thread Starter
Trending Topics
#8
Rennlist Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
Cylinders wear oval
#9
Rennlist Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
The cylinders don't wear into the oval shape, they distort at the top of the cylinder where as in one dimension it gets smaller and in the other it gets bigger, in the middle it is still round. I have asked my tool and die maker to make me a tool ( a jackbolt inside of a fitted inner cylinder) to jack the cylinders back round. Then a cutter to true the outer top of the cylinder so that a support ring can be installed to keep the cylinders round. With the right tooling this could be done by hand similar to machining the ring ridge out of the top of the cylinder we had to do on the old school engines that would wear the cylinders so bad that the groove left at the top would damage the pistons on removal, and if not trued and new rings installed it would destroy them in short order. Most all m96 engines above 50k have significant ovaling, some as much as .006-.008 ,
#10
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
The cylinders don't wear into the oval shape, they distort at the top of the cylinder where as in one dimension it gets smaller and in the other it gets bigger, in the middle it is still round. I have asked my tool and die maker to make me a tool ( a jackbolt inside of a fitted inner cylinder) to jack the cylinders back round. Then a cutter to true the outer top of the cylinder so that a support ring can be installed to keep the cylinders round. With the right tooling this could be done by hand similar to machining the ring ridge out of the top of the cylinder we had to do on the old school engines that would wear the cylinders so bad that the groove left at the top would damage the pistons on removal, and if not trued and new rings installed it would destroy them in short order. Most all m96 engines above 50k have significant ovaling, some as much as .006-.008 ,
#11
Burning Brakes
Thread Starter
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
still seems a strange that piston scoring happens on the skirt rather than the ring land, if the cylinders are most oval at the top you would assume scuffing would start there?
do the early 2.5 boxster m96 motors suffer less? as far as i know they have the thickest walls
do folks feel it is the piston thrust load against the wall that deforms them?
do the early 2.5 boxster m96 motors suffer less? as far as i know they have the thickest walls
do folks feel it is the piston thrust load against the wall that deforms them?
#12
Rennlist Member
![Default](https://rennlist.com/forums/images/icons/icon1.gif)
still seems a strange that piston scoring happens on the skirt rather than the ring land, if the cylinders are most oval at the top you would assume scuffing would start there?
do the early 2.5 boxster m96 motors suffer less? as far as i know they have the thickest walls
do folks feel it is the piston thrust load against the wall that deforms them?
do the early 2.5 boxster m96 motors suffer less? as far as i know they have the thickest walls
do folks feel it is the piston thrust load against the wall that deforms them?
Last edited by Porschetech3; 07-02-2017 at 05:15 PM.