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If anyone is working on a budget forced-induction project, these components might be of interest. We are building two '87 engines for high rpms and the otherwise excellent stock '87 rotating assembly can't take high rpms due to its weight.
Set 1:
+8 low compression '87 piston assemblies with a machined dish. By my understanding, tolerance group 2, but this would need to be confirmed with measurements. The piston dishes were machined by REBCO into the thick-top '87 pistons. The pistons come with 951 top rings and Total Seal second rings, same as in jorj7's engine. The dish is 28 cc, which amounts to lowering the compression by approximately 0.4 points relative to early '87 pistons (about 23.6 cc dish) and 0.8 points relative to later model pistons (about 20cc dish). Stock pins.
+8 recently rebuilt '87 PPF rods with coated Glyco bearings with coatings still intact. These are matching set to the above piston wrist pins.
I would be comfortable running all these components "as is" in a budget boosted project.
Set 2:
+8 entirely stock low miles (under 80k miles) '87 pistons with stock rings and pins.
+8 entirely stock low miles '87 PPF rods. The bearings are somewhere, but should be replaced because the currently sold Glycos seem to give good clearances.
Set 1 pistons $300, set 1 rods $300, or both set 1 pistons and rods $500.
Set 2 pistons $200, set 2 rods $200, or both set 2 rods and pistons $300.
The whole shebang (set 1 and 2 pistons and rods) $700.
+ shipping
John Kuhn's commentary on the parts:
"...the machined pistons [set 1] were out of a tolerance group 2 engine (assuming those were the ones with that block). The scuffing on the machined ones is indicative of all of them in that set. If someone has a tolerance group 0 or 1 block, these would be perfect because the bores can be light honed and re-paste/etched and then you have a great setup for not a lot of money. In other words, these are the largest piston in the 100mm size group, the actual piston measures 100mm. I believe your other set (the stock ones [set 2]) was a group 1, but not sure. I'm not unpacking the block now to inspect that but they are not the group 2 like the machined ones are. All the parts are in workable order, and remember the other rods [set 1] have the longer studs with the taller nuts. I never realized it, but I had a set of those in the store room as well that we removed from a Callaway engine a long time ago...they also had the same upgraded studs and nuts. The stock piston set [set 2] has the rings on the pistons, the machined set [set 1] has the total seal rings in a box. The rods from the blue engine [set 1] have the bearings with coating in tact. The other rod bearings [set 2] are somewhere around here but not of any value...should be replaced.
Assuming no damage, these are an absolute bargain for a future boost build. It can be a kompressor rather than turbo(s) where the reduced compression will help a lot with possible detonation. Except for bench-bragging rights, street-driven boosted 928's don't need or really want >7000 RPM capability.
Assuming no damage, these are an absolute bargain for a future boost build. It can be a kompressor rather than turbo(s) where the reduced compression will help a lot with possible detonation. Except for bench-bragging rights, street-driven boosted 928's don't need or really want >7000 RPM capability. Somebody help this poor man out and buy the bits.
These are all used parts, but they are in condition shown in the photos which I consider decent.
If I were working on a budget boosted project, I'd buy the whole shebang and find the best matching pistons in best condition for each bore from the 16 and, if necessary, have the identical dishes machined to some of the pistons. The dish design is in my opinion a great compromise between piston crown strength, tumble generation, and compactness of the combustion chamber. This dish however should only be machined in an '87 thick top piston, and the other set is / consists of those so they could work as cores. The "blue engine" rods and bearings I would use as is, as they have only about 15 (admittedly _hard_) hours on them.
To be brutally honest, whether I receive $700 for these parts or not will not make a large difference for me in terms of my projects or overall quality of life. I just want to help out someone who wants to build a low-compression boosted 5.0 engine with stock redline on a budget.
I’ll keep bumping up this thread periodically in case someone starts a budget build for a boosted engine or wants to replace the later cast rods with the better PPF rods.
If anyone is working on a budget forced-induction project, these components might be of interest. We are building two '87 engines for high rpms and the otherwise excellent stock '87 rotating assembly can't take high rpms due to its weight.
Set 1:
+8 low compression '87 piston assemblies with a machined dish. By my understanding, tolerance group 2, but this would need to be confirmed with measurements. The piston dishes were machined by REBCO into the thick-top '87 pistons. The pistons come with 951 top rings and Total Seal second rings, same as in jorj7's engine. The dish is 28 cc, which amounts to lowering the compression by approximately 0.4 points relative to early '87 pistons (about 23.6 cc dish) and 0.8 points relative to later model pistons (about 20cc dish). Stock pins.
+8 recently rebuilt '87 PPF rods with coated Glyco bearings with coatings still intact. These are matching set to the above piston wrist pins.
I would be comfortable running all these components "as is" in a budget boosted project.
Set 2:
+8 entirely stock low miles (under 80k miles) '87 pistons with stock rings and pins.
+8 entirely stock low miles '87 PPF rods. The bearings are somewhere, but should be replaced because the currently sold Glycos seem to give good clearances.
Set 1 pistons $300, set 1 rods $300, or both set 1 pistons and rods $500.
Set 2 pistons $200, set 2 rods $200, or both set 2 rods and pistons $300.
The whole shebang (set 1 and 2 pistons and rods) $700.
+ shipping
John Kuhn's commentary on the parts:
"...the machined pistons [set 1] were out of a tolerance group 2 engine (assuming those were the ones with that block). The scuffing on the machined ones is indicative of all of them in that set. If someone has a tolerance group 0 or 1 block, these would be perfect because the bores can be light honed and re-paste/etched and then you have a great setup for not a lot of money. In other words, these are the largest piston in the 100mm size group, the actual piston measures 100mm. I believe your other set (the stock ones [set 2]) was a group 1, but not sure. I'm not unpacking the block now to inspect that but they are not the group 2 like the machined ones are. All the parts are in workable order, and remember the other rods [set 1] have the longer studs with the taller nuts. I never realized it, but I had a set of those in the store room as well that we removed from a Callaway engine a long time ago...they also had the same upgraded studs and nuts. The stock piston set [set 2] has the rings on the pistons, the machined set [set 1] has the total seal rings in a box. The rods from the blue engine [set 1] have the bearings with coating in tact. The other rod bearings [set 2] are somewhere around here but not of any value...should be replaced.
Photos:
I'd sure like to be able to talk to this piston....it certainly went through some sort of severe hell....and it would be great to have it tell its' story.
Those scratches on the sides look exactly like the pistons I've been seeing that are damaged from silicon beads.
And the scratches above the rings certainly indicate that whatever damaged the skirt came from the intake side.
Here's a piston that I took out of a 951 engine, a few weeks ago. Someone "cleaned" the outside of the intake for the client with silicon beads (bead blasted) and failed to clean the inside of the intake. (And a 951 engine has vacuum runners built into the "webs" between the runners, which are very difficult to clean.)
The wear in one of the cylinders was so severe that the only oversize piston offered by Porsche (100.5mm) would not clean up the bore and I had to install an Alusil sleeve in that one cylinder.
And I don't believe this piston is nearly as badly damaged as yours...
No, this piston was not run with glass beads. You’d see the marks of that in the bore and the rings. The engine block from where these pistons came had normal high mile block bore wear and is back in service anyway.
The wear in one of the cylinders was so severe that the only oversize piston offered by Porsche (100.5mm) would not clean up the bore and I had to install an Alusil sleeve in that one cylinder.
As a purely technical matter and leaving the business considerations aside, it’s incredible to me that some glass beads alone could take out 0.25mm off the exposed silicon aluminum bore of your engine, especially given the corresponding photos of your pistons you posted. How would that even physically work out? If that were possible I’m sure Sunnen or someone else would be boring these cylinders with cheap glass beads instead of all those expensive cutting tools.
As a purely technical matter and leaving the business considerations aside, it’s incredible to me that some glass beads alone could take out 0.25mm off the exposed silicon aluminum bore of your engine, especially given the corresponding photos of your pistons you posted. How would that even physically work out? If that were possible I’m sure Sunnen or someone else would be boring these cylinders with cheap glass beads instead of all those expensive cutting tools.
Yeah, it's amazing stuff. Tiny amounts of it do insane amounts of damage. It will "sand" down the top two compression rings until they have no wall tension left....even with the steel compression rings of a 951. On the 928's with cast rings, the silicon will "sand" on the rings until they are paper thin bands of iron.
The one piece oil control rings will "loose" the two integral oil wipers and eventually become completely flat.
On your one piston, what do you suppose caused all those linear scratches....many of which continue up past the rings? Perhaps the two pictures are at the perfect angle to empathize the scratches, but it appears like someone ran a belt sander on the sides of that one piston.
I just don’t believe that either of these piston photos that you posted, Greg, is a photo of a piston that took out 0.25mm of the bore because of foreign object contamination (blasting beads):
If those pistons in your photos mike the correct diameter and if there is no material transfer from the piston ring grooves to the piston rings, I’d run those pistons in a heartbeat with out any concerns. If they don’t mike within spec or if I see material transfer from the piston to the piston ring, then I wouldn’t.
Yeah, it's amazing stuff. Tiny amounts of it do insane amounts of damage. It will "sand" down the top two compression rings until they have no wall tension left....even with the steel compression rings of a 951. On the 928's with cast rings, the silicon will "sand" on the rings until they are paper thin bands of iron.
The one piece oil control rings will "loose" the two integral oil wipers and eventually become completely flat.
Yes, that is what happened to me.
I was amazed at how far the rings were ground/polished down, also, lots of wear on the skirts too.
I just don’t believe that either of these piston photos that you posted, Greg, is a photo of a piston that took out 0.25mm of the bore because of foreign object contamination (blasting beads):
If those pistons in your photos mike the correct diameter and if there is no material transfer from the piston ring grooves to the piston rings, I’d run those pistons in a heartbeat with out any concerns. If they don’t mike within spec or if I see material transfer from the piston to the piston ring, then I wouldn’t.
Those are pictures of the same piston, from #1 cylinder of a 951 engine.
I respect what you think, but that's the reality of this one example....and reality is always the Ace of Trumps.
Another obvious thing to ponder....what agenda could there possibly be for me to make this stuff up?
Having seen way over 20 engines with failure from silicon beads, I've been able to learn a bunch about how different amounts/different sizes of the silicon beads affects different engines.
In simpler terms, think of silicon beads exactly like it is sandpaper (which it actually is, right?) If the size of the grit is "60", the damage is completely different looking than if the grit is "400".
This particular failure was the result of very fine "dust", which got down into the triangle "vacuum" areas of the 951 intake manifold. Probably "400" or even as small as "1200" size grit. This very fine grit gets sucked into the cylinders, gets stuck in the oil on the cylinder walls, and just stays there. (There's no mechanism to remove this grit off of the cylinder walls...there's not enough "oil flow" to rinse it away.) The rings ran through it and gently "lapped" the cylinder walls....away. The scratches in the piston, since the grit was very small, are very minimal. And yes, one could automatically assume that these pistons could be re-used....until the ring land clearance is measured (tremendous wear, here, because of the grit wearing the rings and lands.)
That one particular picture of your piston looks more like other pistons I've seen in 928 engines....where the "grit" is very course and scratches the sides of the piston. (That looks more like "60" grit damage.)
Here's a picture of the #1 cylinder bore of this 951 engine, part way through the re-boring process.
This picture is when the bore is .050mm from being finished. That rectangular wear area would require another .15mm of boring, just to clean the damage....and then it would need to be final honed and lapped. The piston to wall clearance would have ended up being way too big.
Alternative solution required.
Porsche does not make 101.0mm oversize pistons. (They should, for both 944 engines and 928 engines, but that is a different topic.) The only viable solution is to install an Alusil sleeve.
Please understand that I'm not trying to say that your piston that I'm referencing is not usable....that would be stupid.
I just find scratches on pistons (especially above the rings) interesting and wondered if anyone knew the "back story."
07-02-2020, 02:20 PM
FS: '87 S4 pistons and rods
