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Verstehen SIE das Argument. Die Flüssigkeit Moly LM 48 löst sich jedoch vollständig im Öl auf. Es sollte nicht an den Zylinderwänden bleiben. Trotzdem werde ich den Rat von Greg annehmen und etwas anderes nehmen.
Heutzutage verwende ich nicht viel konzentriertes Moly.
Im Laufe der Jahre habe ich mehrere Motoren (nicht meine) gesehen, die ausgefallen sind, weil das konzentrierte Moly den Ölfilter verstopft.
Da Sie für die Montage etwas Moly verwenden, würde ich vorschlagen, dass Sie den Ölfilter nach den ersten 20 Minuten des Betriebs wechseln.
Stellen Sie außerdem sicher, dass Sie einen Ölfilter mit internem Bypass verwenden, falls der Filter verstopft.
Unfortunately, there were some problems with the piston rings. The company where I bought the rings should also adjust the butt play.
This was necessary because I had my block honed to 100.11mm, and of course there are no piston rings for that. The next oversize is 100.5mm, but then you have to grind in the joint play accordingly to approx. 0.3mm.
Theoretically, one could have taken a set of piston rings for the original dimension of 100mm, but then there would have been a gap of about 0.6 to 0.7mm and that was too much for me. Porsche specification is 0.2 to 0.4mm for the first and second ring.
The clearance always changes by the factor PI x difference because U=D x PI (circumference)
So with a change in the diameter of 0.1mm (like me) to the original dimension 100, the joint play is about 0.3mm larger (PI x 0.1).
I had to send the piston rings back twice because they were each too tight with a gap of 0.1mm in some cases. Too little play will inevitably lead to engine damage, since the rings can no longer expand when they get warm, you can imagine the rest....
Excessive shock play does not destroy the engine, but leads to more blow-by gases, depending on the extent to a slight loss of power/compression.
But now it finally fit and I installed the rings today.
The ring in the first groove is the compression ring. It mainly dissipates the heat and has to seal the combustion chamber.
The basic principle of the 3 piston rings comes out quite well here:
Here you can clearly see why more blow-by gases occur when there is a lot of idling. Since the combustion pressure is low at very low speeds, the sealing to the cylinder wall is also not optimal.
This could result in increased oil consumption via the crankcase ventilation.
My new rings now have an angle on the inside, a small step. This optimizes the contact pressure on the cylinder wall, because that is what is desired.
Here is the comparison to my old piston rings, which only had a bevel on the inside.
The new ones are only available with a diameter of 100.5 and a height of 1.75 mm. Since my first ring groove was 1.5mm in the piston, I had it pierced so that the 1.75mm rings would fit.
The oil scraper ring is now a two-piece instead of the original three-piece. Somehow it looks way better.
Here is a comparison of the old three-part oil wiper and the new two-part ones.
The new ones with hose springs should guarantee an even better oil supply.
With a little practice and the right tools, the rings can be fitted without them, e.g. to destroy by overstretching, not difficult.
And now the pistons are equipped with new piston rings.
When installed in the block, the joints are twisted by approx. 120 degrees. This is only necessary for the first engine start.
In the course of operation, they always stand on top of each other anyway, since they rotate in the groove.
It seems somewhat "strange" to me to read of a bore being honed to fit a specific oddball piston ring size- was there a reason for this?
Presumably given the bore size increase you would have to etch the bores once more to expose the silicon crystals of the alusil material.?
Whatever the case I hope it works out well for you.
Hi.
The bores showed only slight wear, something had fallen into the cylinder.
The bores were only honed until they were clean and round.
That was at 100.11mm.
They were then of course treated with etching paste and lapped, the silicon crystals were exposed again.
if original piston rings had been used, the joint play would have become too large.
So I took piston rings for a 100.5mm bore and had them adjusted
Hi.
The bores showed only slight wear, something had fallen into the cylinder.
The bores were only honed until they were clean and round.
That was at 100.11mm.
They were then of course treated with etching paste and lapped, the silicon crystals were exposed again.
if original piston rings had been used, the joint play would have become too large.
So I took piston rings for a 100.5mm bore and had them adjusted
Interesting- never read of anyone doing that before so it will be interesting to see how it pans out. I presumed you might have some custom piston/ring sets that you were trying to mate. Given the lengths Porsche go to with tolerance groups etc it seems a little surprising that the stock piston can be used with an over bored dimension but then I do not have the specific knowledge to know what the sensitivity limits are.
Interesting- never read of anyone doing that before so it will be interesting to see how it pans out. I presumed you might have some custom piston/ring sets that you were trying to mate. Given the lengths Porsche go to with tolerance groups etc it seems a little surprising that the stock piston can be used with an over bored dimension but then I do not have the specific knowledge to know what the sensitivity limits are.
Porsche stipulates a piston clearance of 0.025mm to 0.04mm for new pistons.
Wear limit is 0.08mm.
My original pistons were 99.9mm.
my cylinder bore is now 100.11mm.
That's why my pistons are coated to a size of 100.07mm with a MoS2-based bonded coating.
so i have a piston clearance of 0.04mm.
The coating of pistons has been done here in Germany for a long time and works very well.
maximum layer thickness is 0.1mm, so that a maximum diameter of 0.2mm can be applied.
Then you don't need to buy new oversize pistons. Of course, the cylinder must also be in order with only 0.2mm larger.
Otherwise you cannot use this technique.
That you can get the pistons coated in Germany is not a surprise but the fact that you can get them coated to "high build spec" to compensate for a small increase in bore size as you have done is for very interesting and a good piece of info. Instinctively I would have thought that such was just not possible but that is precisely why we have this forum- to improve and expand our knowledge base- well done indeed!
That you can get the pistons coated in Germany is not a surprise but the fact that you can get them coated to "high build spec" to compensate for a small increase in bore size as you have done is for very interesting and a good piece of info. Instinctively I would have thought that such was just not possible but that is precisely why we have this forum- to improve and expand our knowledge base- well done indeed!
Fred, if you google you can find a lot of information about coatings, far too much to post here.
Åke
Fred, if you google you can find a lot of information about coatings, far too much to post here.
Åke
Ake,
i have quite a fair bit of professional experience on coatings for static kit - just not on pistons. I would never have thought to consider such a possibility thus why i am intrigued. I figured that the stock iron coating on the pistons is what it is and other possibilities would not be on the table as it were.
ich habe ziemlich viel Berufserfahrung mit Beschichtungen für statische Kits - nur nicht mit Kolben. Ich hätte nie gedacht, eine solche Möglichkeit in Betracht zu ziehen, weshalb ich fasziniert bin. Ich dachte, dass die serienmäßige Eisenbeschichtung auf den Kolben so ist, wie sie ist, und andere Möglichkeiten würden sozusagen nicht auf dem Tisch liegen.
Audi eg. also coats its pistons with MoS2 ex works in their alusil engines.
As I said, you can determine the diameter of the piston with an accuracy of 0.01 mm.
This is also done here in many old 911 engines, all alusil. And is significantly cheaper than buying 8 new pistons. there are no oversized pistons for the 928 anymore. you would have to have some made, but then you no longer have the original pistons. So I paid 450€ for coating the 8 pistons and can continue to drive the original ones.
Making 8 new pistons costs about 3000€
From what I read online, this type of coating should be wear resistant but the question is how long it will last. Guess it wears faster than the original ferro-coating. To have new pistons manufactured, who can do the correct ferro-coating? This has always been a problem, Mahle seems to be the only one who can do ferro-coating.
Åke
Nach dem, was ich online gelesen habe, sollte diese Art von Beschichtung verschleißfest sein, aber die Frage ist, wie lange sie hält. Schätze, es nutzt sich schneller ab als die ursprüngliche Ferro-Beschichtung. Um neue Kolben herstellen zu lassen, wer kann die richtige Ferrobeschichtung durchführen? Das war schon immer ein Problem, Mahle scheint der einzige zu sein, der Ferro-Coating machen kann.
Ake
The factory Ferrostan coating is more robust, that's true.But 100.000 km are no problem with the Mos2 coating. I don't think I'll drive another 100.000km in my life with the 928.
The factory Ferrostan coating is more robust, that's true.But 100.000 km are no problem with the Mos2 coating. I don't think I'll drive another 100.000km in my life with the 928.
Warum denkst du, dass du mit dem 928 keine 100.000 km im Leben fahren wirst?
Hast du Pläne für zuküftlige E-Mobilität?
Why do you think that you won't drive 100,000 km with the 928 in your lifetime?
Do you have plans for future e-mobility?
Åke
01-02-2022, 06:47 PM
