Cylinders (iron, Nikasil, Galnikal); boring, honing, cylinder shims, sealants
© Copyright, 2012, R. Fleischer

cylinders.htm,
article 60, sub-section 3

For information on the cylinder studs, and Helicoils, see:  BREAK-IN

BMW has used both Galnikal and Nikasil in describing their late cylinders, and never explained the difference.   BMW used at least two companies in producing these cylinders for them.  It may have varied by year, and model, maybe not.   Nikasil is a registered trademark of Mahle Gesellshaft (yes, the piston makers).  Coated cylinders are done via a plasma process, in Stuttgart, and is a blend of nickel and silicon carbide.    Galnikal is a trademarked name for the process used by Kolben Schmidt, which is a major German foundry and castings maker.  They also make pistons.   If you have Kolben Schmidt cylinders, or whatever, they use a symbol which is a letter "S"  on top of a letter "K"...looks something like a U.S. Dollar ($) symbol.

***As far as this article is concerned.....and, for most purposes anyplace, cylinders are referred to as iron, or, Nikasil....even if Galnikal.

So...just what is/are Nikasil or Galnikal?    
Instead of an iron sleeve, cast or pressed into the aluminum finned cylinder barrel,  the barrel is one piece of an aluminum alloy, VERY precisely manufactured as to roundness, etc.  Then, a very uniform and very hard coating of silicon carbide is put on the inside surface, and that substance is part of an electro-deposited nickel coating.  That 'plating' is NOT very thick, about 0.003" and the silicon carbide particles are about 4 microns in size.  The result is a light-weight cylinder with extremely long wearing surface that the piston and rings work against.  Baring a mechanical problem that injures the coating, the cylinders will last nearly forever, and only rings, and sometimes pistons, which both wear FAR faster than the cylinder coating, are replaced at fairly high mileages.  The cross-hatch pattern of the cylinder is precisely controlled, and may well look almost original after many tens of thousands of miles, and a precisely done cross-hatch is one key to good ring break-in (controls rotation too!) and good oil control.  The cross hatch valleys are what retains the necessary microscopic amounts of oil for lubrication.  The Nikasil process was originally developed for race cars, and now is quite standard on many cars and bikes.    The Nikasil cylinders are VERY dimensionally stable on the bore and have very low distortion.   The microscopic pores retain the oil in the crosshatch valleys, so the bores can be finished to quite smooth tolerances.  Nickel silicone carbide coatings are VERY hard, VERY wear resistant, have LOW friction, and the surface hardness is about 90 HRc.  It is generally...and wrongly... accepted that one can not successfully bore a Nikasil or Galnikal cylinder...which is why BMW does not offer oversize pistons.  IT CAN be successfully done and one of the aftermarket sources for cylinder repair, listed in the references section on this website (under C for cylinders), can do it.    For the Nikasil or Galnikal cylinders, these might then be reclaimed if damaged, but they generally do not wear in normal use enough to talk about, and should not generally be honed in the classical honing sense, with a new rings job.     The early iron cylinders CAN be 'plated' with a Nikasil-like coating.    That does NOT preclude, IF YOU WANT TO, to using what is called a Ball Hone.

Re-boring the older iron cylinders:   Possible (and very difficult to do REALLY correctly on the R100 cylinders).  Best method is to use an inside diameter type of grinder, and then a final honing.  That is tricky work indeed.    Re-boring on conventional equipment often fails.   Re-boring using pressure plates can be done successfully on the smaller bore, and not likely with the R100 bore.  I recommend HONING of the R100 cylinders to size; or, replacing them.     The Airheads smaller than the R100 can be bored, honed, etc.   This is a bit complicated to explain this early in this article about which sizes, pistons, etc.   Some, in not most, early cylinders can be reclaimed by plating them with a coating that is similar to Nikasil or Galnikal. 

Many places rebore cylinders.  For our Airheads, it can tricky, to maintain concentricity and avoid taper.   I highly recommend against BORING R100 cylinders...they should be HONED to size; IF that can be done.   Honing and boring, in any case, should be done using pressure plates.

What happens when boring is improperly done is that after awhile, you find your engine is using a fair amount of oil, and an inspection of the inside of the cylinders will show areas where the rings are not contacting properly, and those are always at the places opposite where the cylinder studs go by!

The boring of the iron cylinders (non-Galnikal, non-Nikasil, ~pre-1981) is tricky, and if not done with proper equipment including a thick plate, will not work.  Altogether too many re-bore jobs end up being junk.  Might be best to just get new cylinders.  IF you are going to re-bore them, my first choice would not be conventional boring, but what is called center-less grinding, done with great care to grind on center and grind straight, they can then be finished with honing in the normal manner.   

HONING, in general: 
Honing is always done on the old iron cylinders, but NOT necessarily, nor actual true honing, on the Nikasil/Galnikal cylinders.  

There is some controversy about the type of cross-hatching that is best.  In the past I mentioned an ideal 28°.  Generally, the common 45° angle, using 220-280 grit stones is likely going to be OK. 

NOTE!!!....Finish honing is best done with the SofTool brush hone made by Osborn International.  Ball honing is adequate but not as good, as the ball tips wear after awhile and the hone does a poorer and poorer job.  The SofTool does not exhibit such characteristics.

The crosshatch pattern is very important for ring wear, ring rotation, and even piston groove wear.   The accepted proper angle is about 28° which is why I have mentioned it in the past.   If the angle is too shallow, the rings will rotate too slowly, the engine will use oil, the rings might skate.   If the angle is too steep, then starts can be rather dry, with fast ring wear and piston wear.  As I noted, the common 45° usually is OK....but I DO think that 28° is better.

If you must, or want to, hone a Nikasil/Galnikal cylinder, I suggest you use ONLY the "Brush Flex-Hone" which is also called a Ball Hone.   WWW.brushresearch.com
Use ONLY the aluminum oxide 240 hone.  Do NOT use the silicon carbide hone 320, as there can be a potential problem with that fast cutting hone.  The purpose of the honing, IF you want to do it, on Nikasil/Galnikal, is simply to deglaze and clean up.
I do NOT hone Nikasil except in heavily glazed situations...  I simply use 3M green industrial pads, soap and water; and these particular pads do not leave particles of silicon carbide in the walls.

For recommendations, and some information on repairing and boring and plating cylinders, see the REFERENCES page!!!...under C......I suggest you do look at that references page.
 

The original 'squish' pistons are no longer available.  One can modify the head and cylinder (deck height change, about 0.050")  and thereby get your own squish pistons in practical use.
The 900 cc model's pistons are pricey.  Reclaiming the cylinders to allow use of those pistons is something to be considered.

Cylinder Base Shims:
There seems to be a lot of confusion over metal and paper shims or gaskets.  I will try to straighten this out for you HERE:
Firstly, NO paper gaskets have been used BY BMW themselves.

I will use the term gasket and shim interchangeably, below!

The stock cylinder base SHIM, during 1970-1975, was 11-11-1-255-001, it was aluminum, and 1/2 mm (about .020).  This was used for all the /5 models, and was used on the /6 models up to 08/1975.  To reduce the compression ratio one point (1.0 in compression ratio), a thicker gasket is used, 11-11-1-257-092, which is 1.2 mm thick (0.047"), has a 97 mm hole, and is used IN PLACE OF the -001 metal gasket.  See more in the next two paragraphs.  NOTE THE DATES in these three paragraphs!  There is some confusion if you look at the parts books, etc.   Long ago there was a 1.0 thick gasket, and there were literature mentions that were sloppy about the thickness, being only approximations.    Note that early engines do not have O-ring grooves, although machining for use of them is certainly possible.

For 1976 to May 1979, TWO SHIMS were available,....the so-called Step 1 compression lowering gasket was .7 mm (.028"); and the very low compression gasket was 1.2 mm (.047").    BMW HAS used the word GASKET for these SHIMS.    These were STEEL, had 99 mm central holes, and are thus easily distinguishable from the earlier aluminum ones.  Not only was the hole enlarged from 97 to 99 mm, but the cylinder top studs area now uses O-rings, the cases being machined for them.  NO standard cylinder base gasket was used!
NOTE that the compression lowering gaskets WERE AVAILABLE.....it was 11-11-1-335-650.   Aluminum, 0.7 mm (0.028"), reduces compression from 9.2 to 8.6.  NO large O-ring groove was used on the cylinder spigot...so you do NOT add an O-ring!
BMW changed the sizes of pushrod seals and tubes.

Again you COULD machine a cylinder for a base large O-ring (see how such a case opening for them looks).  No big need.

For 05/1979 to 1980 models, BMW added the O-ring groove at the spigots, so an O-ring could be used.   The original O-ring was 11-11-1-335-866, which was WHITE, 93 x 2.0 mm.  It is no longer available.  The replacement is 11-11-1-337-567, and is 93 x 2.2 mm.  I suggest OILING IT JUST BEFORE (certainly within ONE hour) you snug the cylinder up to the engine....because it can swell, and the oiling makes it fit much better, and you want to oil it just before assembly.   Keep in mind that BMW makes calendar year bikes at the end of the prior year, just after the Annual Vacation, thus NOT ALL 1978 manufactured as 1979 models were so-machined for the large O-rings.  There have been reports of some 1978 models having the machining.
 

The R100 engine from 1977-1980 used steel lined cylinders, NOT the Galnikal or Nikasil of later cylinders.  These early liners are very thin, and usually can not be successfully bored to the 0.5 mm oversize....they would be too thin.  Pistons and rings were offered at 0.25 mm oversize.  If these cylinders show a lot of wear, one can probably just use 0.25 mm oversize rings.....be sure the end gaps are proper, if not, grind them so they are within specifications.   The smaller engines have enough material to be bored 0.5 mm over, so 0.25 oversize rings are not offered, only 0.5 and 1.0 over.  These do not work well in worn cylinders...tend to twist and cause problems...even piston or ring breakage.   Some will get away with doing it.   Usually, this type of usage will cause rapid wear of the cylinder.    NOTE that boring is rarely successful unless the proper equipment....including alignment/holding plates... are used.
NOTE:  I have had rather good results using new or oversize rings (grinding for proper end gap) even on cylinders with a considerable amount of taper, etc.
NOTE:  plating the old cylinders often works, but it is iffy on the R100 cylinders, only a specialist with much experience is to be trusted here.

For the 1981 bikes (and later), the ALUMINUM alloy cylinders were fitted.  These had a special coating inside, called early-on as Galnikal (all were called Nikasil by most of us).   The difference in name had to do with the manufacturer's name. ...so I will use Nikasil from now on in describing them.  Nikasil cylinders maintain roundness and oil control much better than the old steel cylinders.  They can last almost forever.   They use two each 11-11-1-262-141 O-rings at the top studs, 11 x 2 mm.  They use the large O-ring, mentioned above, at the cylinder spigot base.

You can tell that the -141 O-rings are needed, as the case is countersunk at the top two studs fitting area.    I actually wet all the O-rings with engine oil JUST prior to assembly. 

It is potentially possible that the 2.2 mm large O-ring might not fit a few very early cylinders, but the 2.0 mm O-ring is supposedly no longer available.   This has not been clarified, I have received conflicting information on what BMW has shipped at times.   The cylinder O-ring area appears to be:  OD 3.8899"  98.78 mm; groove depth is .024" or .61 mm; groove width .104" or 2.64 mm

NOTE:  the /5 model used a 11-12-1-255-167  15 x 2.5 mm O-ring under the rocker blocks at the head on some bikes.   Please see my break-in article for photos to identify YOUR bike regarding these.

One last bit of information about the cylinders needs to be made here.  In the later 1980's, BMW added a sort of "step" machined into the cylinder spigots, and a similar matching step was in the crankcase opening.   If you try to fit late cylinders to an early bike, you MUST machine-off the step.

 

SEALING:

Because of the annoying amount of labor to fix a tiny leak, in the past I ALWAYS used Hylomar SQ-32L, even on the late cylinders with the big O-ring at the base, all years.  I have never had leaks, and I oiled the O-rings within minutes prior to reassembly.
BUT:  I no longer recommend you use Hylomar.
Hylomar can fail if not done perfectly, and use of later types of sealants is fully approved by me.  Please see my CHEMICALS article for sealant recommendations!  link:  CHEMICALS.
You can use Yamabond 4 from Yamaha or the gray ThreeBond liquid gasket 1194....which is the same, and sold by many under different names and numbers.  Suzuki supposedly sells the same thing, black, as sealant 1207B.  Remember that only the thinnest coating is used on the CYLINDER BASE, and the case surface must be dead-clean.  It is very important to have the sealant around the outside of the studs, but be very careful about using too much at the top studs where the oil delivery holes are.

rev:
01/26/2008:  new
06/22/2009:  clarifications, minor only.
03/06/2011:  updates, clarifications, move some cylinder recommended places to where it should be, in the REFERENCES article.
01/07/2012:  Clarify the shims information

© Copyright, 2012, R. Fleischer

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