RonnyÅ

Is it possible to lightly hone the cylinders in the 928? Or do this always need some special treatment because of the silicone layer?

BC

Google Alusil.

It is a material type, it is not a coating.

You can lap the bores with felt pads and AN-30, a paste made by sunnen. It will prepare the bores for new rings. It will not remove gouges or scratches - this is only for good bores that need to be touched up for new rings.

It is not a coating. ALUSIL is an alloy of elements Al and Si

GlenL

The correct answer is to not do _any_ metal removal to the bores. Check ring gaps and put the pistons in. It might not feel like the right thing if you've done iron blocks but it is the right thing for these engines.

People will chime in with what they did and there's no end to human creativity. The workshop manual and the block manufacturer both say to not machine, hone or lap the bores. Clean, oil and go.

I'll tell you this: I use a Scotchbrite pad and lacquer thinner to remove the discolored band at the top so there's no carbon flakes scraped off on installation. Otherwise I wipe the bores clean and lightly oil them.

The break-in period for new rings is 500 to 1000 miles using organic oil. Don't use synthetic until the rings are seated. 1000 miles for best results.

I've done fewer when I need to track the engine and just didn't have time to do a good break-in. Still run it at the track with VR-1 50W regular oil for a day before switching. Gotta balance ring break-in against rod bearing life.

RonnyÅ

Thanks. And this would probably also be fine if I supercharge?
How does the oil lubricate if the cross pattern is "missing" in the cylinders?

FredR

It would be good to know what the consensus of opinion is on this one from a "practical experience" point of view.

I am aware of the mineral oil run in bit but then I currently run mineral oil on a daily basis as I was struggling to find anything 20w50 in synthetics over here- I just change it every 5k km or so.

I presume the mechanical logic would be that if the alusil has bedded in as it should be with the silicon bits exposed on the running surface they will be hard enough/rough enough to bed in the face of the new rings that will lap preferentially on the harder surface of the cylinder wall- correct?

Regards

Fred

Mark Anderson

There never was a cross hatch pattern so it's not missing

Strosek Ultra

Everything about machining of Alusil block by Kolbenschmidt/Pierburg.

http://issuu.com/dr.culata/docs/alusil

Ake

jeff spahn

^ that was fascinating.

RonnyÅ

Perfect!

BC

The Paste is a chemical process, not a mechanical one. I learned this just recently even though I have known for a while to prepare the bores for new rings with the lapping. The material change in the bore is not even really a change in dimension as much as it is a change in the prepared surface that the rings see. As the document below shows, this is suggested as best practice for new rings.

GlenL

I'm not finding that. Where is it in the doc?

The purpose of the paste is to etch the metal, the aluminum, and make the silicon be the primary surface that the rings ride on. Picture bumps of silicon sticking out from a surface of aluminum. As a used engine has had this done there is no purpose to doing it again.

BC

The title, for one - "RE conditioning" - meaning the block is taken apart after use and this is what you do when you wish to RE condition it.

Everything wears. The crystal structure IS affected over 100s of thousands of miles. You can measure bores of blocks and see that they are changing over time. This process RE prepares the bores for new rings (so they seat).

I am sure with this material that people can re ring and be done with it - but the lapping stage is best practice for as-good-as-new rebuilds.

GlenL

Right. It's not in there. The doc describes boring a block and putting in sleeves. IIt doesn't mention what to do in other cases like re-ringing pistons. In that case it's already conditioned.

Do what you want. I think you're just wasting time and money.

BC

It does describe the lapping process, and in my interpretation of the wording infers you will get many "more" miles from doing so, during the reconditioning.

I'll put a thread together about the lapping process you can do in your own garage. There is also a thread by someone with even less interest in buying the right tools on the 924S forum somewhere.

Felt pads - 80 bucks
AN-50 - 50 bucks I think (or visa versa)
An old sunnen hone to hold them (I got ripped off - 75 dollars)

Have at it. It removes no real material - just prepares the bores through an etching procedure for new rings (or old rings in my case- taking a chance they will seat - on my "used parts" rat motor) (or "ratty motor").

Hilton

Thanks Ake - I've grabbed a pdf copy of that one.

I had this other doc on hand too: