megagtiguy

megagtiguy

Hi everyone im new here, this is also my first audi. its a 2012 audi A4.

Im rebuilding the engine. it has 180k miles on it. Cyl3 piston broke.

i measure all the bores and they seem to be within spec but on the low end on all cylinders 82.43mm

My question is, there are some lines on the cylinder walls. not sure how bad it is to have those lines. See attached video and images.

So my plan is to use the (83mm) Flex-Hone Cylinder Hone Tool 240 Grit. then use stock size rings and new stock size pistons. will be replacing all pistons with new aftermarket DNJ.

Should i be good to hone and use stock rings and pistons?

Airbag

impossible to tell visually .. does a fingernail catch on any of them ?

many will tell you not to hone as the bores have a coating.... I honed anyways and slapped in some OE Audi pistons and good to go .. ( I have the larger wrist pins )

megagtiguy

Thanks for the reply. There's 1 or 2 that catch my nail but its very minimal

142 guy

Since there are oversize piston kits for the B8, I think that no-hone advice does not apply. That is something that applies to liner-less cast aluminum blocks that use a nickasil, or hard chrome coating or FRM cylinder lining.

If you can catch a finger nail on the marks that is death to a piston ring. As an observation, other than a few bucks you have nothing to lose by trying the hone to see if it removes the marks. Because honing will generate debris I assume you will be removing the engine to do this so that everything can be cleaned. Honing with the engine in situ and the crankshaft with exposed big end journals just seems like a bad idea. This is something that I might want to take the block to a machine shop and ask them whether they can hone out the marks. If they say no then you might want to re think the pistons and do an over bore for over sized pistons.

If you are getting OEM equivalent pistons make sure you are getting pistons with the later style ring design. DNJ lists pistons with 21 mm wristpins and if that means an exact OEM replacement with the 2012 style oil burner rings that would be a poor choice. There are upgrade kits to the later piston ring design which uses a 23 mm wrist pin. If the DNJ pistons with the 21 mm wrist pins have an improved ring design then maybe they are OK. You really need ot do your homework on piston and ring selection with a 2012 engine. You don't want to replace with exactly the same thing that came out.

silver_tt

Nikasil needs to be honed also but requires a special hone.

142 guy

I think that might be the preparation for new rings to make sure they seal if there was any glaze on the cylinder. I don't think honing to remove marks in the cylinder wall is acceptable. My Nickasil experience is limited to 40 years ago when it was in use on some motorcycles. Is Nickasil still being used on current production (non race) engines? I remember Honda had the FRM lining in the '90s; but, I don't know whether any of their current engines use it. Some Porches used Nickasil; but, I don't know whether it is still used.

silver_tt

Nikasil has been discontinued due to environmental concerns (it is dirty). Porsche last used it in the Mezger platform so it has been gone for 10-15 years (last 997TT was 2009 and the GT3 RS ~ 2012 I believe). But there are aftermarket Nikasil solutions for example if you are rebuilding an Alusil engine (Millenium).

The newest engines come instead with plasma spray technology like SUMEbore. This is the best technology you can get for cylinders as it is effectively impervious to bore scoring but it is expensive even in mass production so you will only see it on the newest high end racing type engines (like a 911).

Porsche made changes "in between" the switch from Nikasil to SUMEbore with the 9A1 engine (997.s and 991.1) that is far less prone to scoring but it can still happen and for slightly different reasons which I won't dive into.

You are right Nikasil has been used back a long time even before the 90s and was very popular in the 90s in high end engines (Jaguar, etc)....

Airbag

im pretty sure Nikasil is still used in engines today. Maybe not as prevalent as it used to be due to its breakdown with modern fuels, But it is certainly still out there being used.

Its been around a long time .. very early engines used it and even my 78 has it. probably now used more on sleeves.

silver_tt

The sulfur thing with Nikasil would be a non-issue in USA or Canada where we have access to "good quality" fuel (at least as far as sulfur goes). I do not know of any new engines that are using Nikasil, especially now that SUMEbore is being used and it is better, but you are right they are plating and sleeving blocks with it for sure. Mahle developed it back in like the 60s......

I asked ChatGPT and it gave a pretty accurate answer:Yes, some modern engines still use Nikasil (nickel silicon carbide) coatings, although its usage has become less common in recent years due to advancements in materials and coatings technology. Nikasil was first introduced by the German company Mahle in the 1960s and became popular for its hardness, low friction, and ability to withstand high temperatures.

Some manufacturers, particularly in the motorcycle industry, have continued to use Nikasil coatings in their engines for its benefits in reducing friction, improving durability, and allowing for tighter tolerances. However, other technologies like plasma-sprayed or diamond-like carbon coatings have become more prevalent in modern engine design due to their improved characteristics.

Nikasil-coated cylinders are still found in some high-performance motorcycles, such as certain models from BMW, Ducati, and KTM. However, the specific use of Nikasil can vary among manufacturers and models, and some have transitioned to other coatings for their engines.