Nikasil ring ridge question

[Forrestkhaag]

Hello Fellas:
Has anyone encountered a diagnosis of “Piston Ring Ridge” on your Nikasil cylinders?

This apparently is a condition where, over time, the Nikasil coating migrates to the top of the top ring’s travel up the piston wall and is detectable by feeling the inside of the bore at the top of the cylinder.

My machinist did the bore gauge and they all were within spec as to tolerance for std rings etc. Then my sage engine builder with three decades of high level 356. 904, 911, 912, 9-everything experience did the feel test and noted a miniscule “ridge” on the inside top edge of one or two of my six perfect looking cylinders.

He said it would be best to find a used set within spec and to buy all six if possible…… and he doesn't sell parts.... Yikes!

Thoughts?

Cheers

[prschmn]

The problem with ridges is that They are great at breaking top rings. Then again if your ring lands have worn as well it may not be an issue-though not perfect you might be able to get away with it.
I don't think Nickasil has the ability to "migrate"

[Forrestkhaag]

I am replacing the rings in the rebuild but I was hoping to reuse my cylinders. This barely perceptible "ridge" occurs on two or more cylinders at the very top of the cylinder and I am wondering if the rings actually get to that point in their travels up the cylinder...... I say this because the cylinder walls are smooth and seem uniform until that little brownish stain at the point in the cylinder where the "ridge" is / if it is a ridge......

This engine is going to Webers or PMO's not CIS or MFI of any sort..

See picture / I am also thinking that the risk of reusing the cylinders is limited to one set of rings (that didnt seat) and one more tear down and reassembly after finding a better set used or new JE's... What do you think based on the wide breadth of engine experience out there? Thanks again for the sage advice.

[Mark Henry]

My nikasil cylinders didn't have a traditional ridge like an iron cylinder, more of a wave. I can see a hint of this happening in the top 1/2" (below the "ridge") of the cylinder pictured. It was also bell mouthed, the bore was bigger at the top than the bottom.
It didn't matter to me because my NIB Mahle pistons were a hair undersized and I had no choice but to get them replated and resized.

Check your JE's top ring location, it may be lower than the original pistons.

[Forrestkhaag]

Hey Mark: thanks for the data. I am reusing my pistons as they are in great shape with all of the little horizontal "lines" are intact and the ring gaps are all good as Std. measurements. what was the ticket for a replating job / as i heard or read (maybe in one of Wayne's books) that they could not be honed, replated, or anything done to alter their orignal finish??? Maybe I am dreaming dragons.

Cheers

[Tippy]

What kind of mileage did those have? Mine didn't even have the faintest sign of a ridge.

[Mark Henry]

Originally Posted by Forrestkhaag

Hey Mark: thanks for the data. I am reusing my pistons as they are in great shape with all of the little horizontal "lines" are intact and the ring gaps are all good as Std. measurements. what was the ticket for a replating job / as i heard or read (maybe in one of Wayne's books) that they could not be honed, replated, or anything done to alter their orignal finish??? Maybe I am dreaming dragons.

Cheers

First are you sure they are nikasil? The dull grey colour makes me think alusil but it's impossible to tell from a pic.
A magnet should have a slight pull, SC have the only cylinders where you can count the fins to tell.

Do a search as some who say they have successfully honed them, but you will not find a single pro shop that will hone their cylinders.
Deglazing Nikasils - my method
My cylinders were done by LN/Millennium, but EBS or US chrome is cheaper.
Cylinder Plating Prices | Cylinder Modifications | Piston Coatings | Diamond Honing | U.S. Chrome Corporation of Wisconsin Cylinder Repair Company

[Tippy]

Ditto

[Mark Henry]

BTW if you do have alusil cylinders they can be plated with nikasil.

A few guys have honed alusil, special process on a sunnen hone machine, but again no pro shop would chance a build on this. Alusil needs special rings and pistons.
You can't run JE's in alusil cylinders unless plated with nikasil.

[Trackrash]

Agreed, they don't look like Nikasils.
Here are what mine looked like.

[Mark Henry]

My jugs and slugs, nikasil is shiny like brushed stainless steel, alusil is a dull grey.

[Mark Henry]

Originally Posted by Mark Henry

A magnet should have a slight pull, SC have the only cylinders where you can count the fins to tell.

Looking at Trackrash and my pic's IIRC SC Mahle cylinders with 11 fins are nikasil.
Alusil are 10 fin, all KS and I believe Mahle made some as well.
Pretty sure SC cylinders are the only cylinders you can count the fins.

[911pcars]

No mention of measured piston-to-cylinder clearance. If still within spec, the "ridge" can be removed with conventional tooling or precision grinding. However, perceptible ridge (unworn cylinder) indicates the oil clearance may be out of spec. Confirm, then proceed.

Sherwood