Deglazing Cylinders

[earossi]

As you may know, I am in the process of having one of my Nikasil cylinders reworked to repair a scored area found during a recent teardown of the motor for an upper end "refresh". Since all but one of the cylinders appear to be reusable I had done some research on what to do to prep the walls of the cylinders for new rings.

The common wisdom on this board, when working with Nikasil cylinders, is to merely remove the glaze from the cylinder walls since the original hone marks are clearly evident. The suggested technique seems to be using hot water and Dawn dishwashing soap as a lubricant and degreaser along with Scotchbrite pads to remove the glaze. That appears to work well in the opinion of most on this board. However, in discussing the deglazing with the firm that will be reworking the damaged cylinder, they are of the opinion that the Scotchbrite does not remove all of the hydrocarbon varnish that has accummulated in the etched areas produced by honing. They believe that the Scotchbrite simply takes off the "high spots" leaving glazing material in the bottom of the honed etch marks.

Instead, they recommend the use of Muriatic acid as an acid wash to dissolve all of the hydrocarbon that fills the honed areas. So, I thought that I would recant their instructions with the hope of getting some comments back from those of you who have done deglazing a few times.

The instructions were to purchase hydrochloric acid at the hardware store and dilute it with water going 3 parts water to 1 part acid. This weak "Muriatic Acid" is then to be wiped over the glazed walls of each cylinder using just a shop rag (and protective equipment to protect yourself from the acid). Once the acid has been applied, you are to allow it to remain on the walls for 5 to 10 minutes which should be sufficient time to dissolve all of the hydrocarbon glaze that resides on the walls and in the trenches of the honed areas. At that point, simply wipe the remaining acid and dissolved hydrocarbon off the cylinder walls using another shop rag.

Finally, throughly wash the cylinders using hot water and the Dawn dishwashing soap so that 100% of the acid wash is removed.

I was told that I could use the Scotchbrite to apply the acid wash, but that they did not consider it necessary.

Comments on this process?

[DaveA]

Please see information from Henry Schmidt at Supertec. He has discussed this topic a number of times, what he talks about works. No theories, just practical experience. He uses red Scotch Brite, do a search on the topic. See below. R/Dave

"It has been our experience that if you hone Nicasil cylinders the hone cuts into the Nicasil and because it is so hard that the new ridges are too abrasive on the rings. The rings will seat but they will not last as long as they would if the cylinders are prepped properly. We have had great results from Scotch Brite with soap and water. This breaks the glaze but doesn't cut the Nicasil. Don't forget to check for roundness. I've seen Porsche cylinders .004 out of round.
P.S. use only Goetze rings. Hastings in a pinch".
__________________
Henry Schmidt
SUPERTEC PERFORMANCE
Ph: 760-728-3062

[AlfonsoR]

Just writing out loud here...I believe the main purpose of honing is to provide small grooves where oil can reside so that it lubricates the piston rings as they travel up and down the cylinder. Another purpose is to provide suitable quality surface for the rings to provide a "long" life, given that good operating parameters are maintained.

I could see how you could argue that scotchbrite will only take off the highs. Perhaps this would be good for a quick job, or perhaps it would be good for longer. I don't think there's any good reliable information/ data that tells us at what point piston ring life is severely affected. If the surface finish spec is 4-6 Ra, does piston life go to hell when you reach 9 Ra? How long will you stay in spec (4-6Ra) if you only use scotchbrite brite, effectively only removing the highs? I don't think you are going to get solid answers on those. It's a judgement call.

However, if you are reworking one cylinder to as new condition, then I would probably get the others re-honed instead of just scotchbrite. I would want as symmetrical/similar conditions from cylinder to cylinder.

[jcge]

Nikasil is SiC embedded in a nickel matrix.

I would suggest that acid will not dissolve the hydrocarbon/varnish....it will etch (dissolve) the nickel (and any exposed aluminium) thereby lifting the glaze, further exposing the SiC thereby increasing surface roughness.

I am not an expert...