Hello from Germany.
Some pictures how to rebuild my engine of my S4.Honed to 100.1mm
Piston coated with lubricating varnish based on Mos2 with a diameter of 100.07mm
Outlet Valve guides renewed, valve seats milled, valve stem seals, valves ground in, heads plannedCylinder head gaskets with 1.4mm are installed
Piston rings new
main bearings new
Connecting rod bearings new

I use Mos2 assembly LM 48 Liqui Moly paste for the cylinders, is that ok?








Piston before coated

 

Assembly piston with connecting rod






Thats my 89er S4

 

Looks great - nice work, thanks for sharing. Can't comment on the LM 48 Liqui Moly on the cylinders, where did you get the piston coating done?

 

Thank you.Here in Germany, 3 companies that I know do that.

 

Hello and happy new year.
I have a question about the cylinder head bolts in the photo.
Some are like new and yellow galvanized, some are black.
Have the black ones been yellow and have become black due to embrittlement or corrosion?
I read here that you can no longer use them, is that correct? Besides the color, the screws still look very good.

Many thanks for the help.

 

Your photos suggest that prior to the rebuild your cylinder heads experienced the corrosion attack mechanism that I outlined some three years ago. This problem is caused by a major design flaw that over time allows coolant to seep into the unsupported gap beween the gasket and the heads and this in turn seemingly induces a phenomena called crevice corrosion to take place over the longer term.

A consequence of this problem is that as and when the corrosion takes place free hydrogen is formed. Unfortunately many metals experience hydrogen emibrittlement when exposed to hydrogen and stress. I suspect that the hydrogen diffuses through the head casting with little resistance and then hits the annulus that the head bolts sit in. I suspect but do not know for a fact that the black discolouration of the bolts is a visual indicator that hydrogen embrittlement has taken place. The hydrogen embrittlement is reversible with heat applied to degass it but unfortunately the torque applied whilst removing the bolts in the embrittled state probably does for them.

As the corrosion progresses the acids formed not only attack the alloy they also cause the binder [that holds the aramid fibres together in the head gasket] to break down. In some cases it seems this can lead to the acids penetrating the head bolt annulus causing the alloy to be attacked [probably a galvanic corrosion attack] and this seemingly forms a cement like compound that can lock the heads to the bolting - more a problem for earlier engines with studs. That however does not explain the blackening of the bolts as that is almost certainly the hydrogen embrittlement phenomena.

Bottom line: if the bolts come out nice and bright they can be reused- if they are blackened then they are most likely garden ornaments.

 

Very nice looking! What color is that?

 

I’m not an expert, but LM should be fine. I think just about every machine shop/service station in Germany uses it. 🙂

I’m in Kaiserslautern these days, would be great to link up sometime!

 

Thank you.

Thats color is " samtrot metallic " (german name)
In english velvet red

 

Thanks for the pictures!

 

Beautiful car!

I'd be wary of using a Moly lubricant on the cylinders/pistons/rings.
The moly will "delay" the needed friction for the rings to break-in.
It is generally accepted that rings need to "seat" very quickly...or they may never seat.
Even a bit too much fuel and rings will have difficulty breaking in.

For what it is worth, I use a non detergent "dyno" oil, for this function.

 

https://www.dynolite.com/de/product/...nlaufoel/maybe something?

But that is intended to be filled for retraction. I mean a lubricant that is used during installation for the cylinder and piston to lubricate, maybe some time passes from installation to the first start of the engine, then normal oil has already expired and the cylinder is dry?

Maybe red line assembly lube?

 

just build a aircooled motor, was not sure about the 928, the consensus on my build was just old school 40 or 50 weight type motor oil in the cylinders for the same reason Greg outlined above, it will stay in place months if not years, you want some fiction to seat the rings, also to not to drive too easy in first miles, torque pulls but not high revs help seat the rings

 

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.

 

I'm not qualified to discuss alternative piston/cylinder lubricants.
I can only offer up what I do, when I build these engines.
I'm guessing that there are plenty of other lubricants that work quite well.

Over the 50 years of building Porsche engines, I've had to modify my assembly techniques several times.
In the 1970's, my main focus was on 356 engines, 911 engines, and 914 engines.
The 356/912 engines were incredibly difficult to get the rings to seat because they all ran fairly rich and the horizontal engine design tossed tons of oil out onto the cylinders (as the 911 and 914 engines did.)
If the rings did not seat in the first 30 minutes, they were likely to never seat.
I actually assembled those engines using WD-40 as the piston/cylinder lubricant.

928 engines, with Porsche or OE rings, are very easy to get the rings to do their initial sealing fairly quickly.
If there is any significant "oil smoke" after the first 30 minutes or so, there is probably something wrong and ring sealing may never occur.
In terms of complete ring sealing on a 928 engine, it can take up to 5,000 miles before oil stops washing the carbon off of the edges of the pistons and the carbon starts "sticking" in these areas. (the best indication of complete ring sealing is an even layer of carbon on the pistons.

Hope some of that information helps you!