Nikasil & NSC Cylinder Platings
Frequently Asked Questions about Nikasil and NSC Cylinder Platings
LN Engineering has been in the business of manufacturing billet aluminum cylinders and reconditioning of aluminum engine blocks for aircooled and watercooled Porsche vehicles since 2002. The Porsche cylinders sleeves sold by LN Engineering feature Nikasil and NSC cylinder platings. This includes Mahle Motorsport and LN Engineering aircooled Nickies cylinders and watercooled Nickies sleeves.
In those years, we've been asked many
questions about Nikasil and NSC cylinder platings and we have put together what
we feel is the definitive guide to everything Nikasil with a treasure trove of
information available nowhere else on the internet in one single place. We hope
you find this information both interesting and useful as it's applicable to more
than just our Porsche clientele but also to anyone with an engine that has
Nikasil plated cylinder bores. Whether you need a new set of pistons and
cylinders for your Porsche engine or need to have your used cylinders or an
Alusil or Lokasil engine
block repaired and reconditioned, please give the Nikasil and NSC cylinder
plating experts at LN Engineering a
call!
What is Nikasil?
Nikasil was developed by Mahle in 1967 in conjunction with NSU (later acquired by Volkswagen in 1969), Citroen, and Mercedes to provide a wear resistant, oleophillic coating for Wankel aluminum rotary engine casings to allow the apex seals to run directly against the aluminum housings. As aluminum is very soft, it would wear out almost instantly without a hard surface for the apex seals (or piston rings) to run on. Nikasil plating was applied to the aluminum alloy casings using an electrolytic deposition (electroplating) process in which silicon carbide (SiC) particles dispersed in a nickel (Ni) matrix were applied, providing the wear surface.
The first Porsche engine to use Nikasil was the Porsche 917 starting in 1969 then all future race engines starting from the 1973 Carrera RS.
Kolbenschmidt later developed their Galnical plating, which is similar in appearance and function to Mahle's Nikasil.
If hard chrome plating is still used for cylinders in certified aircraft
engines, why is Nikasil better?
Prior to the availability of cylinder platings, aluminum blocks or cylinders
would have to be fitted with iron liners or a cast iron block or cylinders would
have to be used. The ability to run aluminum cylinders without iron liners
provided improved thermal conductivity and allowed for running tighter
tolerances, both important considerations for high performance engines. The
answer was hard chrome plated cylinder bores. In addition to being much harder
(69-72 Rc) than cast iron, chrome plated cylinder bores allowed for reduced
friction and weight reduction, however chrome plated bores suffered from poor
oil retention. In fact, Mahle Chromal cylinder bores for aircooled Porsche
applications predating Nikasil were dimpled to improve oiling.
However with the development of Nikasil by Mahle in the 1960s, oiling issues
were overcome, providing superior wear resistance, and compared to chrome,
Nikasil has the ability to retain its hardness at much higher temperatures.
Lastly, Nikasil provided improved ring compatibility over chrome plated
cylinders that could only be run with cast iron piston rings.
Porsche was the one of the first to use Nikasil in a piston engine both in race
and production engines. This superseded Porsche’s use of chrome-plated “Chromal”
aluminum alloy cylinders with improvements in ring seal, resulting in a
reduction in oil consumption, less blowby, and an increase in power output.
What is the difference between Nikasil, Alusil, or Lokasil?
Where Nikasil is a plating composed of nickel, silicon, and carbide that is
electroplated onto the cylinder bore, Alusil is a hypereutectic aluminum alloy
characterized by high silicon content exceeding 12% dissolved silicon crystals
by weight. As part of the manufacturing process, both Nikasil and Alusil bores
have to be honed, but for different reasons. Specific to Alusil, Lokasil, and
other high silica substrates, the finishing process for these bores exposes the
silicon particles. Coupled with the tribofilm that forms on the cylinder bore,
it is these silicon particles that support the piston/ring/cylinder system.
Engines with hypereutectic bores also require special piston coatings to prevent
the aluminum pistons from wearing against the uncoated aluminum bores where
pistons fitted to a Nikasil bore do not require any specific piston coating.
Lokasil is similar to Alusil, however the entire block is not cast out of a
hypereutectic alloy but rather a freeze cast sleeve holding silicon particles in
a resin binder is inserted into the mold for the casting. Molten aluminum is
injected into the mold and the resin binder is replaced by aluminum, resulting
in localized high silicon content only in the area of the cylinder bores.
Is Nikasil magnetic?
Yes, Nikasil is slightly magnetic meaning a magnet will indeed stick to the cylinder bore unlike Alusil and Lokasil which are not magnetic.
What is the difference between Nikasil and SUMEbore?
Like Nikasil, SUMEbore can be applied to an aluminum engine block or cylinder
to provide the required wear surface for the pistons and rings. Where Nikasil is
applied by electroplating, SUMEbore is an APS (atmospheric plasma spraying)
coating. Oerlikon offers several different powders that are superheated to a
plasma and sprayed onto the bore. The superheated coating fuses with the
cylinder substrate. After cooling, it has to be honed. However, unlike Nikasil,
a finish honed SUMEbore coated cylinder has no visible cross-hatch as there are
microscopic pores in the coating that hold oil to provide the required tribofilm
to support the piston/ring/cylinder system. Oerlikon offers several different
powders with varying compositions to provide specific benefits like reduced
friction or improved corrosion resistance.
Aside from Oerlikon’s SUMEbore APS process, there are also several other
competing technologies being utilized by OEMs including Plasma Transfer Wire Arc
(PTWA), High Velocity Oxygen Fuel (HVOF), Laser Alloying, or Twin Arc Spraying,
just to name a few.
What is the difference between Nikasil and NSC cylinder bore platings?
Just like factory Porsche Nikasil plated Mahle cylinders, LN Engineering’s
Nickies aircooled cylinders and watercooled sleeves feature a Nickel Silicon
Carbide (NSC) cylinder plating made up of very small (1-3 μm) silicon carbide
particles (~7-14% by volume) in nickel matrix, forming an extremely hard and
durable surface. Equally important to the even dispersion of silicon carbide particles
is the hardness of the nickel to ensure proper adhesion and prevent abnormal
wear. The way Millennium Technology explains it, their NSC plating is like
cement - the silicon carbide is the rock and the nickel is the mortar that
holds everything together. Silicon carbide is used because of its uniform
particle size and being second only in hardness to diamonds, it provides
excellent wear characteristics. In fact, the resulting wear surface for the
pistons and rings to ride on is about ten times harder than cast iron with a
surface hardness of about 90 HRC (typical Nikasil plating hardness is 500 +/-
100 Vickers).
The NSC plating is electroplated onto the cylinder bore and then the bores are
diamond honed with a plateau finish. After honing, the plating ends up being
.004-.005" thick (per side) and unlike a steel, ductile, or cast iron sleeve,
the NSC plating does not hinder cooling and allows for excellent heat transfer
into the aluminum, up to five times that of cast iron. A cooler running engine
results in a higher volumetric efficiency, resulting in more power.
There are other Ni-SiC composite cylinder bores platings similar in composition and performance to Nikasil or NSC that go under the trade names of NiCom, Electrosil, Electrofusion, Revasil, SCEM, Apticoat, NikaSeal, ElNiSil, and Galnikal.
What type of cylinder plating does LN Engineering use for its Nickies cylinders?
Nickies cylinders feature Millennium Technology's NSC plating and are
finished to our specifications. For those who don’t know who Millennium is, they
are one of the largest platers of cylinders, sleeves, and engine blocks in the
USA, servicing both OEMs and the aftermarket. With over twenty years of
experience, LN Engineering has relied on Millennium Technology’s NSC plating
ever since we produced our first set of Nickies cylinders.
After our cylinders are plated and honed by Millennium Technologies, LN
Engineering carries out several additional quality control checks for cylinder
geometry including precision measurements of the cylinder bores for ovality and
taper using a Sunnen GA-2125 dial bore gauge. Surface finish parameters are also
verified using a Mitutoyo Surftest SJ-210 to ensure proper RvK, RpK, Rk, and Ra.
LN Engineering’s extensive quality control inspection process prior to shipping
ensures optimal performance from your cylinders on your engine rebuild.
Can you reuse Nikasil plated cylinders by simply re-ringing the pistons?
The only real disadvantage to Nikasil is rapid wear and degradation of the
plating due to ingestion of dirt, however this can be mitigated using proper air
filtration. In most cases, if there is no visible damage or measurable wear, the
cylinders and pistons can be re-ringed after the cylinders are thoroughly
deglazed and cleaned. Equally important when reusing components is that they are
all measured to make sure they are within wear limits- that also extends to the
pistons.
There are several techniques that can be used to prep cylinders for re-ringing:
Typically the most common way to prep a used Nikasil cylinder is to deglaze the
bore using hot soapy water and a red general automotive grade 3m scotch-brite
pad. The final cleaning step involves using denatured alcohol and lint-free
Kimwipes. This is the process LN Engineering recommends for cleaning cylinders.
Brush Research Manufacturing offers glaze breaking flex-hones with a 240
grit aluminum oxide abrasive that can be used as well to deglaze your cylinders
but should also be cleaned thoroughly after using a flex-hone. As the aluminum
oxide abrasive is softer than the Nikasil plating, it will not embed into the
plating and can be easily washed away after use.
An ultrasonic parts washer run at 130-180 deg F is very effective at cleaning
engine components and will not harm the Nikasil plating. Be sure to rinse the
part after it has been run in the ultrasonic with hot water to prevent spotting
or staining of the aluminum. If the cylinder bores become stained or spotted,
you can use graffiti remover to clean the bores of any discoloration.
A 20% solution of muriatic acid can be used to deglaze the cylinder bore. Apply
to a cloth and then wipe it onto the bores. Allow 3-4 minutes contact time,
scrub, then wash clean with soap and water.
Regardless of what method is used, a final cleaning with denatured alcohol and
Kimwipes is highly recommended. With all these processes there is no need to oil
the bores after cleaning or use a corrosion inhibitor as Nikasil does not rust.
Applying oil to a cleaned bore prior to engine assembly will just attract
airborne contaminant particles that can cause wear to engine components.
Can Nikasil cylinders be re-honed?
Since the Nikasil plating can be anywhere from .002-.006” thick, re-honing a cylinder bore can be tricky. Although it is possible to restore cylindricity to any wear areas with light honing, generally the rule of thumb is that if the wear is greater than .001”, the cylinder should be stripped and re-plated. Another consideration before choosing to re-hone a Nikasil cylinder is the piston to cylinder clearance. Some engines have as little as .0007” total clearance, so honing the bores may result in piston slap due to excess piston to cylinder clearance.
Can Nikasil cylinders be re-plated?
Although it’s very common for Porsche Nikasil plated cylinders to last
hundreds of thousands of miles with regular maintenance including proper air and
oil filtration, when it comes time to rebuild your Porsche engine, there are
instances where the cylinder plating may need to be redone. Beyond the
traditional fingernail test to see if you can catch your nail on any scratches
in the plating, use of a dial bore gauge to measure ovality and taper is
required.
Upon inspection of your cylinders, if scratches, chips, nicks, cut-through, or
worn spots in the plating are discovered, the cylinders should be re-plated.
Silicon (dirt) ingested by the engine due to poor air filtration or from foreign
object debris is a likely culprit for wear in Nikasil cylinders. Debris caught
between the pistons and rings can impart damage to the cylinder bores, rings,
and pistons, so it’s important to inspect all components during teardown.
One final consideration when deciding whether to repair or replace your Nikasil-plated
cylinders on an aircooled engine is whether or not the engine has been
overheated. Sustained EGTs over 1450F or cylinder head temperatures over 400F
can result in softening of the aluminum alloys and loss of strength.
The Nikasil plating can be removed either by honing through the plating down to
the bare aluminum or stripping the existing plating using acids. The cylinder
then goes through several pre-treat baths to prep the cylinder or block before
the Nikasil plating and honing process, allowing the cylinder or engine block to
be reused an almost infinite number of times.
What is porosity and will it affect my cylinders?
Porosity is gas trapped in the base metal aluminum during the casting process for cylinders or engine blocks. These holes are exposed when the cylinder is machined or subjected to various chemicals in the plating process. The pits are usually small in size and will not adversely affect the performance or longevity of the cylinders or engine. These pits will not cause the coating to peel nor will a ring hook on them and is considered a cosmetic problem only. We typically only see porosity in original cylinders when they come in for reconditioning. In most cases, porosity in the bores does not pose any problem, but occasionally if there is porosity at the sealing surfaces or in ring travel, especially close to the combustion chamber where the cylinder will see higher pressures and temperatures, we may recommend the cylinder be replaced.
Can you resurface the deck on a cylinder or engine block with Nikasil cylinder
bores?
Care must be taken if you have a cylinder that needs the cylinder head sealing surface (deck) resurfaced to prevent chipping or separation of the Nikasil plating. Millennium Technologies offers a service where the deck can be surface ground to safely renew this surface after the cylinder has been reconditioned, avoiding possible flaking or separation, however if the cylinder has an existing cylinder head gasket groove, the depth of the groove will need to be re-machined to provide the correct depth for the head gasket.
Likewise, if resurfacing an engine block, it is important to verify that
thicker MLS head gaskets are available to make up for any material removed from
the deck during the reconditioning process. Furthermore, if the bores size was
enlarged during the reconditioning process, custom head gaskets will also be
necessary to accommodate the larger bores size. Cometic Gasket offers thicker
head gaskets for many applications to accommodate stock diameter or oversized
bores. It is critical to verify head gasket availability before doing any work
to the engine block.
What is the best way to repair hypereutectic aluminum Alusil or Lokasil engine blocks?
Cast iron, ductile, or steel sleeves can and have been previously fitted to aluminum engine blocks to repair Alusil or Lokasil engine blocks with damaged bores with mixed success. This requires dry or wet sleeves to be installed with an interference fit varying from as little as .002” to as much as .005”. An interference fit is required as dissimilar expansion rates between the sleeve and block would otherwise allow the repair sleeves to move during engine operation if there is insufficient interference. Typically the engine block is heated up and the sleeves are chilled using dry ice or liquid nitrogen to have a difference in temperature of about 392F (200C).
Some engine castings are more robust than others and fitting sleeves in this manner can cause these blocks to crack, which is the case with many cast hypereutectic aluminum crankcases used by most European automobile manufacturers as they were never designed to be sleeved.
There are also performance downsides including poor thermal conductivity and lower horsepower and torque due to increased friction as well as reduced thermal and volumetric efficiency. Kolbenschmidt also recommends that piston to cylinder clearances need to be opened up .0004-.0008” over factory specifications if iron or steel sleeves are fitted to an aluminum engine block which can cause piston slap until the engine has reached full operating temperature.
That said, the best way to repair a linerless all-aluminum engine block is to use a NSC
plating to restore the surface finish. This includes damaged cylinder bores in
Alusil engines that have suffered bore scoring or piston seizure. Assuming the
engine was not overheated and is still otherwise serviceable, the cylinder bores
must be bored out roughly .0085” to allow them to be coated using Nikasil or an
equivalent NSC plating which is then honed to final size. This has the added
benefit of reducing friction and wear while not negatively affecting performance
or cooling, unlike iron or steel liners.
Some engines like the Lokasil M96/M97 engine block used in Porsche Boxster,
Cayman, and 911 models from 1997 through 2008 can suffer from scoring as well as
other cylinder issues like slipped sleeve failures or cracking that requires
these blocks to be wet sleeved to prevent future failures. Rather than fitting
iron or steel sleeves or direct plating the bores, LN Engineering specializes in
the repair of Lokasil engine blocks using billet aluminum NSC-plated cylinder
mid-stop sleeve or liner and has successfully fitted their Nickies both dry and
wet sleeves to many other hypereutectic engine blocks since 2002.
What is the best way to repair an aluminum engine block with PTWA, APS, or similar thin-wall coatings?
We would treat any PTWA or APS coated block like we would an Alusil engine
block. This requires us to remove the existing coating and then direct Nikasil
plate and hone the cylinder bores to size. If there is deep scoring, we will
typically bore the block out 1mm and do the same process. If the customer wants
to keep the stock bore size, we can fit a dry aluminum sleeve to the block which
can then be direct Nikasil plated, but this adds significant cost.
Can you re-use your original pistons when repairing or reconditioning an aluminum engine block?
In most cases, if you have an aluminum engine block that requires reconditioning, the original pistons are likely worn or damaged, requiring replacement.
Another consideration when it comes to reusing pistons is whether they are compatible with Nikasil bores. For example, the pistons used in Alusil and Lokasil engine blocks feature an iron-clad plating or coating which prevents galling that would otherwise occur with an aluminum piston running on an uncoated aluminum cylinder bore. These piston coatings are not compatible with Nikasil cylinder bores or any other cylinder bore finish other than the original Alusil or Lokasil.
Lastly, the original pistons may be set up for piston rings that are not compatible with Nikasil, however it may be possible to source custom piston rings from Total Seal to fit the original pistons that are compatible with Nikasil. Alternatively, it might be possible to re-cut the piston ring grooves to fit compatible rings, but this can be costly.
The best solution is to fit new pistons to any reconditioned aluminum engine
block with Nikasil-plated cylinder bores. LN Engineering stocks popular
replacement pistons for Porsche engines, however we can supply
custom forged pistons to suit any application as long as we are supplied
a sample piston from which to base the new replacement. In some cases, engines
were originally fitted from the factory with bank specific pistons, so in that
case we'll need a sample piston from both banks. Piston to cylinder clearance
may also need to be adjusted when switching from a cast to a forged piston,
especially if using a 2618 forged alloy piston.
How does the Nikasil plating process work?
Depending on if you are starting with a new cylinder or reconditioning a used cylinder, the first step is to remove or mask off all steel components, otherwise they will dissolve later on during the plating process. The cylinder is then cleaned before the existing plating (if any) is chemically removed. If reconditioning a used cylinder, once it is down to bare aluminum the bore can be inspected for damage. With light damage, the cylinder can be slightly over-bored to remove the damage and then plated back to the original size with slightly thicker plating than is normally used on a new cylinder. If the damage is severe, in some cases the cylinder can be welded then bored to restore a usable surface for the plating to adhere to. Prior to plating, the cylinder will go through an etching process to ensure it’s clean and oxide free to ensure proper adhesion of the plating. Although some refer to Nikasil as a coating, it’s actually an electroplating process where a negative charge is placed on the cylinder and a positive charge on the anode. The potential difference causes the nickel to plate out onto the cylinder bore, entrapping the silicon carbide in the process as the mixture of nickel salt and silicon carbide is pumped up through the cylinder. When properly applied, the bond strength of the NSC plating is about 25,000 psi. After plating, the cylinders are then honed using diamond stones.
How thick can the NSC plating be applied to a cylinder?
Although typical thickness is .004”-.005” (0.1-0.13 mm), the plating can be applied up to .040” or 1mm thick, however the plating can become brittle if applied too thick. In most cases where there is damage to the cylinder bore such as scoring, the bore can be bored out to provide an undamaged surface for the plating. When repairing Porsche Alusil engine blocks, if there is damage and keeping the stock bore size is desired, an aluminum dry sleeve can be fitted to one or multiple cylinders prior to plating.
Which manufacturers have used Nikasil or equivalent nickel silicon carbide
plating?
Nikasil cylinders are used in great quantities in aircooled two- and four-stroke engines as well as in watercooled four-stroke and racing engines with great success. Although Porsche is probably the best known consumer of Nikasil cylinder platings used in its aircooled engines, Nikasil is still very popular in motorsports and powersports and has been used by Audi, BMW, Chevrolet, Citroen, Ducati, Ferrari, Ford, Honda, Jaguar, KTM, Lotus, Maserati, Mercedes, Polaris, Renault, Suzuki, Yamaha and many other manufacturers of high performance engines.
Is there a problem with Nikasil and high sulfur fuels?
There are few disadvantages to Nikasil when it’s done right. Done
incorrectly, peeling and bubbling as well as excessive buildup of the plating
can occur, but BMW’s M52 and M60 engines and Jaguar’s V8 used in the XK8/XKR
experienced issues with Nikasil and high sulfur fuels in the 1980s and 1990s.
Before 2000, fuels in the United States and some other markets had much higher
sulfur content than typically found in unleaded fuels sold in the UK and Europe.
This increased sulfur concentration in low quality fuels led to the formation of
sulphuric acid in the crankcase during normal operation that would damage the
Nikasil linings, resulting in scored bores and worn piston rings that could no
longer seal leading to low compression and high oil consumption. Short distance
driving where engines cannot reach their intended operating temperatures for an
extended period leads to condensates forming producing sulphurous acids together
with sulphur contents from the combustion of sulphurous acids. Operation in
colder climates further contributed to the formation of these acids and engine
damage.
Sulfur occurs naturally in crude oil and these oils with high sulfur content are
referred to as “sour.” Sour crude oils are cheaper but require additional
refining. The oil is run through a hydrofiner to remove sulfur during refining
but this process also reduces the octane level of the gasoline produced,
requiring additional processing and increased additive levels to restore the
octane level of these fuels. The United States Environmental Protection Agency’s
(EPA) Tier 2 Gasoline Sulfur program reduced sulfur content by up to 90% in 2000
and Tier 3 later imposed a 10ppm limit in gasoline beginning in 2017, so it is
unlikely to experience these issues in engines with Nikasil plated bores with
modern fuels.
However it is worth noting that Porsche never experienced any of these issues
with their Nikasil cylinders in the decades before sulfur limits were placed on
fuels sold in the United States. In the 20+ years LN Engineering has been using
Millennium’s NSC plating, we’ve never seen or heard of any failures due to
sulfur content in unleaded fuels.
What is the correct surface finish for Nikasil?
An important part of honing the NSC plating is to provide a proper surface finish. If too rough, ring wear will be harsh, and if too smooth, the rings will not seat properly. Oil retention in the bore can also be negatively affected if the crosshatch is not the proper depth. A surface profilometer is used to check the roughness average (Ra) and the RpK (reduced peak height), RvK (reduced valley depth), and Rk (core roughness) of honing patterns to ensure proper engine performance. With this equipment, it is possible to calculate the actual volume of the oil held on the surface, or bearing area curve (also referred to as the bearing ratio curve or Abbott-Firestone curve). Examples of typical Nikasil surface finishes can be found a bit further down on this page.
What is the correct crosshatch angle for a Nikasil cylinder?
Crosshatch angle is important to ensure proper ring rotation. The big difference between Nikasil and cast iron cylinders is the honing crosshatch angle - Nikasil cylinders usually have a 10-15 degree crosshatch angle compared to 45 degrees used for honing cast iron cylinders.
What is Rk, RpK, and RvK and why are these surface texture parameters important?
The core roughness or Rk is a measure of the core roughness with the major
peaks and valleys removed.
The reduced peak height or RpK is a measure of the peak heights above the core
roughness. The RpK is also a measure of the material that may be removed during
break-in. However in the case of Nikasil, it’s very important that the bores are
plateau honed which removes these peaks as the engine will not be able to wear
away the higher peak material. Plateau honing simulates mating of cylinder bore
surfaces and piston rings during break-in in engines with iron bores by
eliminating these peaks, reducing break-in and improving sealing, while leaving
crosshatch to retain lubrication. As Nikasil is many times harder than iron
bores, if the RpK is too high, the piston rings will wear out prematurely well
before the peaks can be removed.
The reduced valley (scoring) depth or RvK is a measure of the depth of the
valley below the core roughness. Rvk is also a measure of the lubrication
retention ability of the cylinder walls.
How do you check the surface finish on Nikasil cylinders?
The only way to properly inspect the surface finish on any cylinder is with a profilometer. We utilize a Mitutoyo SJ-210 Portable Roughness Tester to verify that cylinders are honed properly. The SJ-210 utilizes a stylus that resembles the needle on a record player that when dragged across the cylinder bore surface, a trace showing the surface texture is generated. You can use the following steps and settings to properly configure your SJ-210:
1.0 Mitutoyo SJ-210 Profilometer Settings
1.1.0 Power up Profilometer
1.2.0 Slide Open Cover to Expose Options Pad
1.3.0 Press Enter/Menu
1.4.0 Select Set Environment
1.4.1 Select Switch Unit
1.4.2 Select Inch
1.4.3 Press Esc/Guide
1.5.0 Select Measurement Condition
1.4.1 Select Setting
1.4.2 Standard: Select ISO1997 for Roughness Standard
1.4.3 Profile: Select R for
1.4.4 Filter: Select Gauss
1.4.5 Ác: Select 0.03
1.4.6 Ás: Select 100
1.4.7 N: Select 5
1.4.8 Pre/Post: ON
1.4.9 M-Speed: Select 0.02 in/s
1.4.10 Range: Select Auto
2.0 Setting Parameters
2.1.0 Press Enter/Menu
2.2.0 Select Parameters
2.2.1 Select Ra
3.0 Stylus Location and Positioning (Correlation)
3.1.0 Ensure Stylus is Parallel with Surface
3.2.0 Approximate Depth of Sample 2.25” From Deck Surface
It is imperative that the stylus tip is inspected daily using a microscope to
ensure it’s not damaged and that the SJ-210 is calibrated before use using the
calibration square provided by Mitutoyo.
We also recommend using QMP
Racing Engines Stylus Holder which allows you to place and secure the
SJ-210’s stylus anywhere in the bore.
What are typical surface finishes for Nikasil?
According to Mahle, a typical Nikasil cylinder has a 0.4 μm (15.7 μin)
roughness average with 96% bearing surface and an average valley depth of 1.2 μm
(47.24 μin).
Over the years, we’ve had the opportunity to measure surface finishes on
numerous new OEM cylinders with Nikasil plating. Shown below are results from
profilometer traces from our Mitutoyo SJ-210 using the ISO1997 standard.
Capricorn Sleeve
Ra | Rk | Rpk | Rvk |
14.63 | 39.55 | 17.10 | 33.53 |
Mahle Cylinder (aircooled Porsche)
Ra | Rk | Rpk | Rvk |
3.85 | 11.64 | 4.55 | 9.54 |
Mahle Sleeve (watercooled Porsche)
Ra | Rk | Rpk | Rvk |
7.98 | 24.28 | 9.68 | 15.11 |
Polaris
Ra | Rk | Rpk | Rvk |
7.39 | 20.07 | 7.29 | 19.13 |
What piston rings can you run with Nikasil plated cylinder bores?
Historically, phosphate coated cast iron piston rings have been primarily
used with cylinders with Nikasil plated cylinder bores. Hard chrome plated
piston rings should never be used with Nikasil bores, but CrN (Chrome Nitride)
coatings typically found on carbon steel piston rings are compatible with
Nikasil or equivalent nickel silicon carbide plated cylinders. Likewise ductile
iron or “plasma-moly” rings can also be used with Nikasil cylinders. Titanium
Nitride (TiN) coatings provide improved ring performance for engines with
Nikasil plated cylinders as this coating is a relatively soft
material that beds well against cylinder walls and helps the piston rings seal
up better and faster than uncoated rings.
Once you choose the right ring material and coating, selecting the correct
second and oil control ring is probably the most important thing to consider.
Aside from the oil control ring whose function is self-explanatory, the second
piston ring’s primary function is actually oil control. Although a napier style
second ring’s hook acts like an oil scraper, a taper face ring will actually
wear better over time and is a much better choice for Nikasil bores. It is
equally important that the second ring is light checked to ensure the ring is
“light tight,” which refers to how round the ring is. Unlike the top piston ring
that is OD ground to ensure proper sealing, the 2nd piston ring is not ground or
lapped, so if it’s not light tight it will not seal properly and lead to
increased oil consumption.
And when it comes to the oil control, most of the factory ring sets for Nikasil
bores, like those used by Porsche, have a 2pc cast oil control. However, a
modern 3 pc oil control will provide excellent results as long as the correct
rails and expanders are used. Besides the ring material or coating type used for
the oil control rails, having the correct oil control ring tension is critical
to low oil consumption. Unlike cast iron bores where standard or high tension
3/16 ring with 20-24 lbs of tension can be used to provide low oil consumption,
Nikasil bores require the use of low tension rings. As a result, oil consumption
is typically higher than an engine with iron bores, but lower tension rings do
have their benefit: reducing friction, freeing up lost horsepower, and lowering
oil temperatures. When selecting your oil control rings, ideally the tension
should be around 10 lbs but no less than 7 lbs. Remember, after break-in, ring
tension will typically drop about 1 lb, so in a perfect world choosing an oil
control with closer to 11 lbs of tension will provide optimal oil control. For
reference, a 2mm oil control typically has 7-8 lbs of tension where a 3mm is
9-11 lbs.
Lastly, the top piston ring serves as the compression seal and is often gas
nitrided. The gas nitriding process hardens the piston ring, providing extended
life and protection under extreme conditions, which is especially important when
running Nikasil plated cylinder bores. PVD (physical vapor deposition) coatings
can be applied to the top ring to further improve performance to effect reduced
wear, faster break-in, or some other benefit imparted by the coating’s
properties.
Even if you use the correct piston rings, if the surface finish is not correct
for the cylinder bores or the cylinders are not properly cleaned before
assembly, the piston ring faces will be damaged due to the hardness of the
cylinder bore plating.
What is the best way to break in an engine with Nikasil cylinder bores?
It's critical after the initial 20-30 minutes to break in the camshaft and lifters (or rockers) and get the engine up to temperature that the engine sees a load to ensure the rings can seat properly. You need cylinder pressure to seal the rings against the cylinder walls. Without access to a dyno to break in your rebuilt engine, driving the car while varying the speed and load as well as applying full throttle (without going to redline) and engine braking to seat the rings is required to break in the engine correctly. Remember, without a load, parts can't wear in.
Remember excess idling of a fresh engine without any load will result in the bores glazing over, requiring tear down to deglaze the cylinder bores and re-ring the pistons. It is equally important that the engine is not running rich during break-in as over-fueling will result in the cylinder bores being washed down with fuel. Remember fuel is not a lubricant and excess fuel will break down lubrication and cause damage to the rings and possibly even to the cylinder bores.
Is a break-in oil needed to properly break in a new set of Nikasil cylinders and
piston rings?
If you have fitted a new camshaft, lifters, rockers, or any other new valvetrain related components as part of your rebuild, a break-in oil should be used. We use and recommend Driven break-in oils for the first 20-30 minutes or however long is recommended for breaking in the camshaft and followers, followed by the appropriate conventional non-friction modified engine oil. Beware running a break-in oil too long - doing so can actually hinder seating the rings on engines with Nikasil cylinder bores. However if you are simply replacing your pistons and cylinders or re-ringing an engine, the aforementioned intermediate oil can be used instead. It is critical that you do not use any oil containing Moly or equivalent friction modifiers nor semi- or full-synthetic oils until the piston rings are fully seated.
How long does it take for pistons rings to break in on an engine with Nikasil
bores?
Depending on how the engine is broken in, the time and mileage for rings to be fully seated can vary greatly. Ideally an engine should be broken in on an engine or chassis dyno where air fuel mixture, temperature, and loads can be closely monitored. However, an engine broken in on the street can take anywhere up to 5,000 miles to have the rings to be fully seated. It is common for engines with Nikasil bores to consume more oil during this period and depending on what oil and rings are used and also how specifically the engine is tuned and run-in will greatly affect the length of time required for break-in and success of the engine rebuild. A friction modified, semi-synthetic, or full-synthetic engine oil should not be used in any rebuilt engine with Nikasil cylinder bores unless the rings have fully seated and the engine is completely broken in.
Why are my Nikasil cylinders streaked after break-in?
When bore scoping a fresh engine, what you are seeing can be commonly
misdiagnosed as cylinder bore scoring, when it is in fact
cylinder bore streaking. Millennium Technologies
states that "a certain amount of streaking is normal during break in as the
rings and the coating wear into each other. The marks are lot like tire marks on
pavement and need some time to wear off. More time on the engine in most cases
will help ring seal. The extra time will not damage the coating further."
It is completely normal to experience streaking caused by transfer during break
in of piston and ring coatings. During the break in process, streaking is
analogous to a "footprint" left behind from the rings, piston coatings, and
Nikasil while they all mesh together and is cosmetic, not affecting ring seal or
engine performance. Given time, streaking will dissipate with continued normal
usage.
Aside from streaking, scuffing of Nikasil cylinders can commonly be attributed
to improper ring tension, incorrect ring end gaps, lack of attention to detail
when gapping rings, or insufficient cleaning of the cylinder bores.
It has also been reported the streaking is common in Ford Coyote engines with
PTWA cylinder bore coatings, so this is not isolated to just engines with
Nikasil cylinders.
Do Nikasil cylinders suffer from scoring?
It is uncommon for Nikasil cylinders to suffer from bore scoring as seen in hypereutectic Alusil or Lokasil engine blocks. However, there are instances where the Nikasil can be damaged. This is typically due to poor preparation and cleaning during assembly, over-fuelling and loss of proper lubrication, or ingestion of dirt or other contaminants due to poor air filtration.
What is the typical oil consumption for an engine with Nikasil cylinder bores?
On average, an engine with Nikasil cylinder bores will consume about 1 quart
per 1,000 miles, however there are many variables including surface finish of
the cylinders, what rings are used, selection of oil, how the engine is broken
in, and tune of the engine that can affect oil consumption.
Where can I learn more about reconditioning ?
Introduction to Reconditioning Engine Blocks discusses various aspects of engine blocks, including the differences between closed deck and open deck designs, their advantages and disadvantages, and suitable applications. It also covers engine block reconditioning and repair processes, the characteristics of Alusil and Lokasil hypereutectic aluminum engine blocks, and cylinder platings and coatings like Nikasil, PTWA, and APS. The article further explores techniques for reconditioning cast iron and aluminum blocks, the importance of cylinder bore surface finish, and an overview of engine block sleeving, including wet and dry sleeving. Lastly, it emphasizes the significance of proper honing for engine efficiency and longevity.