Steve,
The recommendations for the alusil from Sunnin and the manufacturers was to use the stiff felt pads with the AD-30 silica paste to get the finish you desire on the bores. I had a shop do this for me and would immagine that the nikasil would react the same way. Not 100%, though.

One hundred and fifty miles is not enough to seat in rings.
When considering that you put new rings (round) in a used (possibly out of round cylinder) I would guess that it would take 500-1000 miles for complete seating.

As the engine builder it is always your call but in this case I believe that your test model is lacking in sufficient longevity for any accurate conclusion.

I would use oil consumption measurements and visible smoke
to determine how well the rings are seating.

Remember that most honing processes will not make out of round cylinders round again.

Interesting read.......
 

Henry and others,

I read this whole thread and found it quite interesting. I'm getting ready to re-build a 3.0L using the factory Mahle 9:3.1 pistons Nikasil cylinders.

BRM makes Flex-Hones in 600 and 800 grit and according to their information a 800 grit hone will achieve a Ra finish range between 3-10 and the 600 the Ra is 8-12. Henry found that the 320 Grit hone ends up at a 10.5 finish because the Nikasil is so hard but still way too rough compared to the new finish of Ra 4.9. BRM lists the Ra finish for a 320 grit hone to be 18-30.

Here is my logic because the Nikasil is so hard I'm thinking a light hone with a 600 grit should get everything clean/deglazed and ready to accept the new Goetz rings.

If the 320 grit Ra was 10.5 and BRM lists the Ra of the 600 grit to be 8-12 cutting each in half due to Nikasil being so hard it should be right in the ballpark.

Here is a link to BRM's specs:

Flexhone for Cylinders - Instantly improve Ra and surface finish!

Thoughts?

Henry,

After reading all your post it seems like using scotch brite pads is the safe way to go. I dropped of my case parts to a reputable Porsche mechanic but my feeling is he is the great trouble shooter and repair mechanic but doesn't have the experience on rebuilds. I asked him about honing the cylinders and he was quick to make the fix. But when I asked him about replacing the piston squirter's he had no idea. I'm nervous to allow him to deglaze the cylinders due to lack of knowledge. I feel that I should just let him perform a bore gage readings and I should go ahead and use scotch bright till there is a dull look. I also asked him to rebuild my case and he straight out told me he wasn't to comfortable doing it. Would that be your course of action scotch bright and be done with it?

Andy

The Key to success (ring seating) and longevity is RA factor. Too smooth and the rings won't seat too rough and the rings wear out prematurely.
If a company offers a product that will produce the correct RA factor it seems reasonable to try it.
If SccotBrite will produce the correct RA factor then use that.
It really is a judgement call as to the condition of your cylinders.
Cheers

clearing the waters with grape hones with non-nikasil liners

I can speak with direct experience with grape hones and ring wear on iron liners. I just pulled apart a Ferrari engine which I rebuilt last spring with high compression pistons and Ferrari's older racing spec camshaft (P6 grind). This engine had over 3000 very hard miles as the engine was used for a good amount of rallye work. The engine is being pulled apart at the owners request for a stroker crankshaft to be installed.

Regarding the rings I used last spring: I used what came with the Wiseco pistons which were a 1.5mm coated steel top ring made by NPR which is the OEM supplier for many Asian brands followed by a tradional ductile iron second ring. I honed the liners with a torque plate (must be done with these engines) with a grape hone of the finest grit available which I believe was 320 grit and using 30 weight non-detergent oil as the cutting lubricant. I made 5 passes in a clockwise direction of rotation and two anti-clockwise. The rings were gapped to .014 for this 3.12 bore and the rings seated quickly. I used a grape hone for the simple reason that they remove less material than a Sunnen type hone and the owner already had a set of standard size pistons he requested I use. To make matters worse the piston to wall clearance prior to honing was already .003 meaning I didn't have maybe .0005 to work with in getting it right regardless as aything over .0035 clearance is just not ok in these engines. In all, the grape hone removed less than .0005 as opposed to a traditional hone which usually removes between .0005-.001 but does indeed do a better job.

Upon dismantling the motor I measured the rings for wear in the bore, and in short there was little to none. The gap in all of the rings was no more than .015 and the bottom end of the engine sealed well.


In a pinch, they work ok and I experienced zero out of the ordinary wear issues with these particular non-nikasil iron liner cylinders I work with. In a perfect world, use a traditional hone like a C10 and then follow up with a plateau finish for a moly top ring.


Another thought process on Ra levels has to do with ring tension. Lately with good brands top, second, and oil rings have very little tension which makes them somewhat more of a challenge to seat at times but also have less dependency on Ra levels. Total Seal came out with their 'Quick Seat' product for this specific reason.

Henry, I'm confused as to how you get rings to seat with an Ra below 10? With chrome top rings, it is just not possible or at least very difficult. With moly rings it's probably possible but I would be concerned with the liners abilities to hold oil with it being that smooth. Apparently it's not an issue with Porsche engines but with Cup motors and Ferrari engines the Ra absolutely must be above 10 for the rings to seat. The grape hone did not bring it up to its advertised amount which they listed to be 18, but IIRC it was less than 12.

A cast iron bore will plateau very quickly while a Nikasil will plateau very little or not at all. The Finish has to be close to opperating finish or ring and skirt damage will occur.

As a result, Chrome rings are not compatable with Nikasil cylinders. You can use ductile iron and special moly rings.

This thread changed the shape of my head.

"The mind, once expanded to the dimensions of larger ideas, never returns to its original size."
Oliver Wendell Holmes

Yes, given the variables mentioned, it's a miracle any combination of piston, ring set and cylinder will work for long - then there is the break in method and oil used.

Sounds like it's safe to say that Nikasil Ra should be close to a 'run-in' Ra as once Nikasil is honed it retains the hone pattern for a substantially longer period than iron. Where with iron a slightly higher Ra can be used to begin with as the material inherently 'breaks in' and smooths out for the simple reason that iron is softer than Nikasil.

You still need a little bite. If you do not prep a used nikasil cylinder you will most likely have ring seat issues.


We have pulled 100,000 + mile Nikasil cylinders and can see the hone pattern quite nicely.

I don't do too many 308 QV, 328, or TR engines so I can't really comment much on Nikasil wear patterns, but the top end work I have done always shows a very robust cylinder liner with almost no wear when checking leak. The bottom ends very rarely need to come apart. The earlier 308s and V12s with iron liners all have to be bored and all have leakage now and need to come apart. Thankfully with modern light tension rings and modern materials iron liners last substantially longer than ever before but are still nothing compared to Nikasil.

I definitely hand it to Porsche for their crank and bottom end engineering as they are remarkably robust. Those head studs that make me crazy though

Correctamundo :)

Good stuff Henry.

Probably not the best pic in the world, but the hone angles can be seen. Also, finish is just the brand of 'dull' I prefer with vanilla iron liners. These are from a recent project where liners were honed with a flexhone (Ra of 11-12ish).

http://forums.pelicanparts.com/uploa...1327067092.jpg

By prepping a used nikasil cylinder, are you referring to the previoiusly discussed scotchbrite + soapy water method, or something further?

here's how I did mine. homegrown but rings seated well and no issues 3 years and a lot of miles later.

http://forums.pelicanparts.com/911-engine-rebuilding-forum/448165-de-glazing-nicasil-cylinders-new-approach.html

The issue is not so much "ring seating" but ring seating vs ring wear.

As long as the RA factor and groove plateau is consistent with the surface being honed, all should be good.

Desired cross hatch or 30-40 degrees can be achieved by a hone speed of 500-800 rpm and a feed rate of about 120-180 inches per min. 45 seconds per/ cylinder seems to be about right.
http://forums.pelicanparts.com/uploa...1327259414.jpg


To reach this roughness, I recommend honing Nikasil cylinders.
• Conventional stones #280 -#320 grit or
• Diamond stones #550 grit

After honing with either the conventional or diamond stone, finish your honing by smoothing the surface with a fine grit conventional abrasive (#400 - #600 grit) or to sweep the bores with a flexible brush or a nylon bristle plateau honing tool. This is necessary to get rid of jagged peaks and folded or torn material.

http://forums.pelicanparts.com/uploa...1327259604.jpg

Important Note:
Be sure to confirm with your honing equipment manufacturer that the recommended stone grit will produce the following Rz and Ra roughness recommendations.

Seriously amazing wealth of information. Thank you.

Threads like these are what makes pp such a great place to be.

Henry,

back in 2004 you were against the use of flex hones and recommended the use of red scotch brite to remove cylinder glaze. Now, fast forward 8 years and in your last post, it seems you recommend the use of flexhones. I guess you have you experienced something new in these last 8 years to make you change your mind?

I have come across this post a couple of times before and only today have I had the chance to read the whole thread.

At the outset of this thread, I was really bought into the scotch brite camp. I was relaying this to my limited experience in reciprocating compressors. In Recips, you have similar concerns on cylinder wall finish.

In recips, at least the ones I work on, the cylinders are non-lubed and use a ring and rider (similar to a ring) made of a type of teflon. The API specification for non-lubed 25" diameter iron cylinders is 16-24 microinches Ra.

So what lubricates the rings/ riders is the teflon material that wears (slightly) into the honed cross hatched surface. Once the machine runs a few hours, then the surface of the cylinder can come in at approximately 3 microinches Ra, as an example.

So how does this relate to Porsche cylinders? Just conjecture here, and maybe more of a question for anyone that knows better...

I believe that a similar process happens in the engines too.
1. you have a specified cylinder finish, 4.9 - 6.0 Ra
2. the lubricant is oil instead of being built into the ring material, but the oil goes into the cross hatching to lubricate
3. some small amount of ring material wears and gets deposited into the cross hatched surface along with hydrocarbons from fuel (spent & unspent) and oil


So #3 is what we call cylinder glaze, right?? And this is what we want to remove. A good solvent and scotch brite should be sufficient, I would think.

PS: If you are in the Houston area and would like to get your cylinder surface measured, I have access to a Mahr PS1 profilometer. I will offer to measure your cylinders.

PPS:
I found this interesting article on "enginebuildermag.com"

Cylinder Bore Surface Finishes: Engine Builder




Cylinder Bore Surface Finishes

By Larry Carley


What’s the best type of cylinder bore finish for today’s engines? Most would say it’s a finish that allows the rings to seat quickly and completely so the engine doesn’t use oil. For many applications, that may mean a plateau finish. The surface finish must also meet the piston ring manufacturer’s specifications and have the proper crosshatch so the cylinder walls will retain oil and provide adequate lubrication for the rings. The finish must also be relatively free of torn and folded metal (swarf) as well as abrasive residue.

Also important is bore geometry. The hole should be as round as possible with little or no taper or variation vertically. Bore distortion caused by deflections in the casting or improper boring or honing techniques will have an adverse effect on ring sealing and blow-by.

The OEMs and ring manufacturers have developed very specific surface finish and bore geometry specifications for their engines and rings. The recommendations vary somewhat depending on the engine application, type of rings, and honing procedure used. But, generally, engine rebuilders should strive to achieve a finish that meets all of the criteria we’ve just described.

To better understand what these requirements are, let’s take a close look at the surface of the cylinder bore itself.

Close up
To the naked eye, a freshly honed cylinder bore looks pretty rough in comparison to a used cylinder bore. Honing leaves a scratched surface that should show a strong crosshatch pattern. A used cylinder, on the other hand, will have a smooth polished appearance with much less crosshatch visible depending on how much the cylinder is worn.

At a microscopic level, the profile of a freshly honed cylinder wall reveals many little peaks and valleys. The valleys are cut out of the metal by the abrasives during the honing process, and the peaks represent the highest point on the surface that will make contact with the rings.

Large, sharp peaks won’t last long once the engine is started because the tops of the peaks will be gradually sheared off by the rings as the rings break in. As the tallest peaks are knocked off, the "mountains" become flattened creating a "plateau" effect. This increases the bearing area for the rings and makes it easier for the rings to glide over the surface on a film of oil that is retained in the valleys.

According to one ring manufacturer we interviewed, once the rings have seated, wear virtually ceases because the rings are now supported by a thin film of oil and do not make physical contact with the cylinder wall. The ideal cylinder bore surface, therefore, should essentially duplicate this condition. By using the right honing procedure, you can create a surface finish that allows the rings to seat quickly with minimal wear and which will retain the proper amount of oil so the rings receive proper lubrication.

By the numbers
To minimize the formation of sharp peaks on the surface, the cylinders must be finish honed with stones that have a relatively fine grit size. The finer the grit size, the smoother the finish.

The average roughness of the surface is called "RA" and is typically specified in microinches (one microinch is one millionth of an inch, or 0.000001"). To measure RA exactly, you need an electronic instrument called a profilometer. A profilometer drags a diamond-tipped stylus across the surface to measure the size and distribution of peaks and valleys.

Most OEMs and ring manufacturers specify a surface finish of 15 to 25 RA for moly faced rings, which can be achieved by finish honing with #280 grit stones. Cast iron and chrome rings can tolerate a somewhat rougher surface finish (20 to 35 RA), so coarser #220 grit stones can be used to produce this type of finish.

Unfortunately, RA alone doesn’t reveal much about the actual profile of the cylinder bore surface. A bore finish with tall peaks and deep valleys can have the same average roughness number as one with short peaks and shallow valleys. More measurements are needed to accurately analyze the surface. These include:

•RPK – the peak height;

•RVK – the depth of the valleys; and

•RK – the average core roughness depth based on the RPK and RVK measurements. A surface with a low RK value will have long life characteristics.

•RMAX is the highest peak-to-valley measurement taken from five samples.

•RZ is the mean highest peak-to-valley measurement taken from five samples.

When all these numbers are taken together, it creates a more complete picture of what the surface finish actually looks like. Some profilometers can take this information and plot a graph that shows how much bearing area is on the surface. This is called the "Abbott-Firestone Curve." The curve plots profile height on the vertical axis and percent of surface contact on the horizontal scale. The flatter the curve and the greater the area enclosed by the curve, the better the surface finish.

An easier way to tell whether or not the surface finish has all the "right" numbers is to compare the various "R" numbers to the OEM and ring manufacturers’ specifications. The numbers will tell you if the surface has the proper depth of crosshatch, enough bearing area to properly support the rings, and is smooth enough to minimize ring wear during the seating process.

According to one honing equipment manufacturer’s guidelines, the RMAX and RZ numbers should be about 10 times the RA number for a properly honed finish. If the RMAX or RZ numbers are less than one seventh the RA number, the surface is "glazed" and won’t retain oil properly. If RMAX or RZ is more than 12 times the RA number, the surface has too many deep scratches.

What are "good" numbers for a properly honed cylinder bore? Sunnen offers the following guidelines:

•RA should be 12 to 24;

•RPK 6 to 24;

•RVK 20 to 80; and

•RK 28 to 48

John Scott of Perfect Circle Piston Rings says the numbers will vary depending on the honing procedure used. Perfect Circle’s finish specifications for automotive engines honed with a single stage process are:

•RA 10 to 20;

•RPK 10 to 20;

•RVK 30 to 60; and

•RK 25 to 50.

continued....

Fax film
Another useful tool for evaluating surface finish is "fax film." Though few rebuilders use this technique, most OEMs, as well as some PERs, find it is extremely helpful for identifying certain types of surface finish problems.

After the cylinders have been honed and washed, a small piece of thin plastic film is placed on a bore surface with a solvent that softens the film. This allows the film to take an impression of the bore surface.

The film is then removed and examined under a microscope at 100X magnification to check for excessive torn or folded metal, burnishing or glazing, embedded particles and debris. It also makes it easy to accurately measure the exact angle of the crosshatch.

Crosshatch
Most OEMs and ring manufacturers say the angle of the scratches in the crosshatch pattern should be about 45° to each other, or about 22° to 32° to the horizontal deck surface. The crosshatch angle should be the same throughout the length of the cylinder and not flatten out at either end.

If the crosshatch angle is too steep, the rings can pump oil or experience excessive rotation which will accelerate wear in the rings and piston lands. If the crosshatch angle is too shallow, it can have a ratcheting effect as the rings pass over the valleys, preventing the rings from receiving proper lubrication.

A proper crosshatch will also have enough valleys to retain oil, but not too much oil. The secret here is getting the right amount of retained oil volume (Vo). If the crosshatch scratches are too deep or there are too many valleys (not enough peaks and bearing area), the engine will use excessive oil.

The greater the retained oil volume, the higher the oil consumption. This can be caused by finish honing with stones that are too coarse (#150 or less). On the other hand, if the crosshatch scratches are too shallow or there is too much plateau on the bore surface, the volume of retained oil may not be enough to keep the rings lubricated; this will cause accelerated ring and cylinder wear. This can be caused by finish honing with stones that are too fine (#400 or greater).

Plateau pitfalls
A plateau cylinder bore finish is a popular one because it combines all the "good" numbers: low peak height (RPK); plenty of bearing area (Abbott-Firestone curve); and adequate valley crosshatch (RVK) for good oil retention and proper ring lubrication.

To achieve a plateau finish, one of two methods can be used: a two-step honing procedure or a one-step honing procedure, followed by a brief brushing process.

With the two-step plateau honing procedure, the cylinder is honed with coarse to medium stones followed by a very fine abrasive for a few strokes to remove only the tops of the peaks. For example, the cylinder would first be honed with #150, #220 or #280 grit stones followed by a few strokes with #400 grit stones.

The trick here is to shave only the peaks off the cylinder walls. You don’t want to remove too much metal with the finer stones or you will be down to the base metal and lose all or much of the required valley depth in the crosshatch.

The second way to produce a plateau finish is to hone the cylinders with #220 or #280 grit abrasive (or #400 or #500 grit diamond abrasive), followed by a few strokes with a "Plateau Honing Tool" or "Flex-Hone" tool. There are both engine rebuilders and diamond hone head suppliers, however, who say that a proper surface finish can be achieved through just the use of diamond honing without a separate step utilizing a plateau honing tool.

The Plateau Honing Tool or Osborn brush has silicon carbide abrasive embedded in nylon bristles. The brushes are designed for mounting in a hone head so pressure and feed rate can be controlled.

A plateau effect is created as the brush sweeps across the surface to remove sharp peaks and other debris. The amount of metal removed is minimal because the tool is only applied for a few strokes in each cylinder.

The Flex-Hone tool (manufactured by Brush Research Mfg. Co., Inc.) has numerous round abrasive balls mounted on wire bristles. The tool is typically mounted in a hand drill and manually stroked up and down in each cylinder bore a few times to plateau the surface. This style of brush has a more aggressive cutting action than the nylon bristle tool, but is only used to remove just a small amount of material to plateau the surface.

Opinions differ as to which type of brush gives the best plateau effect and why, but both types are used successfully by a wide variety of engine rebuilders to "precondition" cylinders and improve the overall bore finish.

The advantages of a plateau finish, regardless of how it’s achieved are:

•Significantly shorter break-in time;

•Reduced blow-by for cleaner emissions;

•Reduced oil consumption in a new engine; and

•Less ring and bore wear for improved engine longevity.

According to research by Perfect Circle, a plateaued bore surface will stabilize after about two hours of running. In other words, the rings will seat very quickly and experience almost no further wear. A more conventional surface finish, by comparison, may take anywhere from three to 12 hours to seat in depending on the grade of stones used. A bore finish honed with #280 grit stones will seat faster than one finished with #220 stones.

Honing procedures
When cylinders are bored to oversize, they are generally bored or rough honed to within about .0025" to .003" of final size to allow for finish honing. The finish honing step removes the fractured and torn metal created by the boring process, and produces the kind of surface finish and crosshatch we’ve been talking about.

Whether vitrified abrasives or metal bond diamond or CBN (cubic boron nitride) stones are used to finish hone the cylinders makes no difference as long as the final surface geometry conforms to the desired numbers.

Most OEMs and production engine rebuilders use diamond to hone cylinders because it improves consistency and reduces honing costs.

A set of diamond stones will typically do 20,000 to 100,000 cylinder bores compared to maybe 50 to 80 cylinders for a set of vitrified stones. Diamond stones are much more expensive than vitrified abrasives, but over the long run actually cost less, especially when labor savings are factored in (provided you don’t damage or break a stone!). Because diamond wears very little, the honing process takes less babysitting and yields more consistent results, according to those we interviewed.

The honing characteristics of diamond honing stones have also improved in recent years due to changes made to the matrix that supports the diamond. Some stones now use a titanium surface treatment that slows the erosion of the supporting matrix. This improves the cutting action of the stone, which in turn reduces the tendency of diamond to "plow" through the metal. The result is less torn and folded debris on the surface and a better overall surface finish.

Many small shops are making the transition to diamond honing too because of the advantages it offers. But for some, diamond honing may not be the best way to go. Because diamond stones wear so slowly, the stones do not conform very quickly to changes in bore diameters. So if a shop is honing a variety of different bore sizes with the same hone head, they may not get as good a finish as they’d get honing the same sized bores over and over again.

Also, some diamond hone heads can only handle a limited range in bore sizes so you may have to shop for a hone head with a wider range in bore sizes, or buy a second hone head.

Andy Rottler of Rottler Manufacturing says 90% of his honing machines and honing heads are now being sold with diamond stones. He estimates that probably 75% of all the engines that are being rebuilt today are being diamond honed.

"The most common procedures are to use #400 or #500 grit diamond stones, which may be followed by a nylon abrasive brush to plateau the finish," explained Rottler. "The #500 stones typically leave a finish in the 18 to 22 RA range, while the #400 stones leave a 24 to 30 RA finish which requires brushing to bring the RA down to about 20."

Ray Fink of AER in Carrollton, TX, a large production remanufacturer that is a contract engine remanufacturer for Ford, General Motors and Nissan, says AER uses a two-step diamond honing process on almost all of its engines. AER rebuilds more than 400 engines per day at three different plant locations.

"After the cylinders have been bored with a CNC boring bar, they are diamond honed on machines to remove the fractured metal and crosshatch the bores. The bores are then plateau finished using vitrified stones in our honing machines," said Fink. "We currently do not use a brush or plateau honing tool to finish the cylinders."

Bob Jones of Jones Automotive Engines, Inc. in Spokane, WA, says his company rebuilds 25 to 30 engines a day. "We’ve been using a two-step diamond honing procedure for about five years," said Jones. "After the cylinders have been bored to within .0025" to .003" of final size, we use a #270 to #325 diamond to rough hone the cylinders to within .001" of final size. We then finish with a #500 grit diamond. This procedure gives us a consistent surface finish in the 17 to 22 RA range."

Jones said he is considering changing to a one-step diamond honing process and using a brush to plateau the cylinders, but he has not yet fully evaluated the process.

"One thing we’ve found with diamond honing is that harder blocks like Chrysler 383 and 440 engines are too hard for rough honing with #325 diamond, so we use #270 diamond to get a better finish," said Jones.

continued....

Aluminum honing
Though we’re not yet seeing many all-aluminum engines in the aftermarket, a growing number of engines with all-aluminum blocks (no liners) are being built by the OEMs. Tim Meara of Sunnen says both Mercedes and Porsche have aluminum blocks that use an alloy similar to that used by Chevrolet in the Vega engine years ago. The 390 alloy has a high silicone content that provides wear resistance.

Honing this type of alloy requires a four-step process. First the bores are honed with a #220 vitrified abrasive, followed by #400 stones and finally #600 stones. The cylinders are then finished by lapping with cork and a special lapping compound that removes just enough aluminum to expose the harder silicone particles.

Meara says a different procedure must be used on Honda Prelude aluminum blocks because the cylinders are fiber reinforced. On these engines, a two-step procedure is used. The cylinders are first honed with #280 grit stones, followed by #400 stones. No lapping is required.

Bore distortion
As important as surface finish is for proper ring seating and lubrication, bore geometry is probably even more important on today’s engines. Bore distortion is common in the upper cylinder area because of the forces created by the head bolts when they are tightened down. Changes in coolant temperature and circulation within the block can also cause bore distortion as can normal and abnormal combustion pressures. To get as round a hole as possible, many engines with thinwall castings should be honed with a torque plate and head gasket bolted to the block. The torque plate simulates the loads placed on the block when the head is installed, allowing the bore to be honed to truer dimensions.

Bore distortion can be described by levels of "order." A first order bore is one that is perfectly round with no distortion in any direction. A second order bore is one with an oval distortion, typically caused by machining errors or heat transfer. Rings can usually tolerate some second order distortion by conforming to the bore. But the lower the ring tension, the less able the rings are to conform to bore distortion. A third order distortion results in a triangular shaped hole, and is usually caused by a combination of second and fourth order distortions. A fourth order distortion is a bore with a cloverleaf or squared shape. This type of distortion is caused by the location of the head bolts.The amount of distortion can vary from almost nothing up to a couple thousandths of an inch! With today’s tight piston-to-wall clearances, even .0005" of bore distortion may be too much on some applications. So the rounder the bore the better.

Some performance engine builders don’t want to see less than plus or minus 8 microns (0.000003") of bore distortion! Perfect Circle says a plateau finish should only be used if bore distortion is less than 0.01 mm (.0004").
Click here for a chart on Common Deviatins From a Good Bore Finish.

Cleanliness
To wrap up our article on bore finish, we need to say a few words about cleanliness. All your efforts to produce an ideal bore finish, crosshatch and near perfect geometry can be undone if the cylinders are not thoroughly cleaned after they’ve been honed.

Scrubbing with hot, soapy water is still one of the best ways to remove honing debris that can cause ring problems if it remains in the cylinders. Some rebuilders tell us they even do a second cleaning step that involves wiping out each cylinder with ATF or WD-40 oil to remove anything that might have been missed by the soapy water.

And finally, for optimum assurance of proper surface finish and bore geometry, many rebuilders also vacuum test the cylinders to make sure the rings are giving the proper seal after the engine has been assembled.

Found the missing info...

Rz = 59 - 138 µ in [=1.5 – 3.5 µm]; or
Ra = 15 - 35 µ in [=0.4 – 0.9 µm]

I'm not sure how I found this , but I think it's worthy of a bump

Being originally posted 15 years ago the answer is NO.

Dear Henry,

It may be too old a thread to revive, but I think there's an important subject that hasn't been addressed at all.

When any "grape hones" were mentioned here, it was always about silicon carbide hones.

BRM offer a Flex-Hone (grape-type) plated with aluminum oxide instead of silicon carbide. AO is a much softer material and whill definitely not roughen the surface as much as SC.

BRM claim its specifically designed to deglaze nikasil cylinders.

Can an AO grape hone be spot on between Scotchbrite (maybe not rough enough and potentially inconsistent) and SC hone (too rough)?

Would you recommend aluminum oxide grape hone to deglaze a nikasil cylinder?

Thank you for ykur invaluable input!

Sent from my ONEPLUS A3003 using Tapatalk

Yes re aluminum oxide Flex-hone on good nikasil cylinders. 3 or so passes one rotation, 3 in the opposite direction using standard 30w oil as lube. This is Audi's official honing method for the 2.0T engines that were all recalled a few years back due to oil burning issues. Audi replaced the pistons with those with larger oil rings to fix the issue, but the honing method was specifically to use an aluminum oxide Flex-hone.

"in opposite direction" - of a drill? Sorry for the dumb question, but I've never done it before. Trying to revive a 166,000 mile oil munching r1150gs engine...

Sent from my ONEPLUS A3003 using Tapatalk

Aluminum oxide sounds like a really bad idea to be honing a Nikasil cylinder with.

Not because it can even phase Nikasil, but if it leaves behind aluminum particulates in the crosshatch?

Correct. A few passes in one direction of rotation, a few in the opposite direction. Try and use even quick (but not too quick) strokes back and forth so the walls have about a 45 degree cross facing. Audi actually sent a guy out from Germany to demonstrate and that's just how it was done.

So Audi uses Nikasil coatings on their cylinders?

Yeah it's their version of Nikasil which has some sort of graphite in the mix as well. Audi uses a laser honing technique at the factory.

Whats the best way to use scotch brite on the cylinders. you guys say use scotch brite but how do you use it. do you just cut out scotch brite and put it the pads under the stones"? i find this interesting.

You can do it by hand or if you want put it over stones, but make sure you dry and oil your hone or it will rust. You want to do it in soapy water. I just picked up an 800 grit aluminum oxide brush does what red scratch Britt does just faster

I wrapped green scotch brite pads over my spring hone and used soap as a lubricant. It worked very well to clean but not alter the surface finish.

I’ve been using the AO BRM hone with good success. Like someone said above 3 strokes one way the 3 strokes the other and your done…minus a lot of cleaning

I’ve been using a brush research 800 grit aluminum oxide brush does a great job. Also getting ready to fire up my home nikasil plating soon, just for the hell of it, fun for the whole family!!

Thanks Guys on the scotch brite. I like Henry's idea as its not harsh on the cylinders.
I'll also bore scope the cylinders and hope they are all round.:)

DP, the hone you are using is the same one I use and recommend to others .
It is designed for the nikasil cylinders that we have . I have been told by Brush Research to use , Mobil 1, 0-20 full synth oil for the honing process.
Allowing for six strokes for each cyl, my goal is an RA of 7-10. I have my own Profileometer .

I agree that the Brush Research 800 grit aluminum oxide is the best to revive our cylinders . PS, one hone will do aprox 200 cylinders at a cost of $250 per
Ian