Replacing Pushrod Tubes & Seals. Collars.
Pushrods. Valve cover studs. Sealing Cylinders.
BMW Airhead Boxer Motorcycles
© Copyright 2018, R. Fleischer
Article 60, sub-section 8
This article contains some multiple redundancies about use of sealants, etc. They were incorporated on purpose!
Pushrod tube rubbers and tube diameters, etc:
The pushrod tube rubbers are NOT the same for all models. They have been made in THREE types.
1970-1975 have 16 mm pushrod tubes, and the seal is 11-32-1-250-267.
Anton Largiader has measured brand-new tubes, and he says that the 16 mm ones are 15.88 mm.
After 1975 they are 18 mm tubes, and the seal is 11-32-1-262-995.
Anton Largiader has measured brand-new tubes, and he says that the 18 mm ones are 17.98 mm
Don't forget that you need a new head gasket ...and depending on model you may need the very large rubber O-ring that fits on the cylinder stub. OIL that large O-ring JUST BEFORE you mate the cylinder (with piston back inside it, and connected to the con-rod), to the engine case. You will need two new top stud rubber O-rings, except for the earliest models (like the /5 series), which have no recess at the top studs for an O-ring. There is more to know, so see http://bmwmotorcycletech.info/cylinders.htm and, especially, http://bmwmotorcycletech.info/break-in.htm and note the photos in that article.
Push rod tubes are available, aftermarket, in stainless steel.
Taking things apart and putting them back together:
DO NOT remove the pistons outwards, unless the bores are brand-new, fresh, or there is absolutely no ridge at the top in the cylinders; or, you could break the rings. It is safe, if careful, to remove the cylinders off the pistons; the pistons being still attached to the rods. You do NOT have to remove piston pin circlips; you do NOT have to remove the piston from the rod. You do NOT have to remove the piston rings from the piston.
Pull the spark plug caps off the spark plugs. Remove the valve covers. It is best to unfasten the head from the cylinder, so unfasten the head to the cylinder and unfasten the valve gear to the head, and now you can pull off the the valve assembly, then the pushrods, then the head, and last the cylinder. That means you must remove 4 each rocker nuts (and 2 each head nuts at 12:00/6:00). You must pull the cylinder off slowly, a bit at a time, until the piston is exposed some ...only. At that point, you have enough room to stuff a rag in the bottom of the cylinder hole in the engine case, so that as you pull off the cylinder all the way, you Do Not drop the piston/rod onto the crankcase opening. Doing so will NICK the crankcase, and if you do, the nick must be 100.00% dressed-out, or you will never stop the oil weeping from the cylinder base that will haunt you forever. Using a good size soft rag will also protect the piston and its rings.
When removing the valve gear, remove one rocker with its end blocks, as an assembly ...don't let it fall apart. Do ONE cylinder at a time ....and don't mix up the valve gear.
It is possible to remove and replace a cylinder with the head still attached via just the 12:00 and 6:00 nuts (not loosened). If you want to do this, it saves having to install a head gasket; but I do not approve if you leave the cylinder/head off the engine, not tightened by the rocker nuts (4), for more than a short while.
Some folks remove the cylinders with the piston still inside it. If you do this, here are some suggestions. Start at TDC (OT mark) and slide the cylinder off just enough to enable removing a piston pin clip; but without the rings exposed. Don't bugger the clip area! If the pin does not slide out easily, either you have a trace of fouled ('proud metal') metal at the clip area....or, you need to heat the piston/cylinder to expand the aluminum piston so the steel pin comes out. If, after heating the piston, the pin is still too tight to be moved with your fingers, you can use a home-made drawbar for doing that job, with assorted large washers and sockets and a piece of All-Thread from the hardware store. In just about every instance, heating the piston will enable the pin to be withdrawn easily, with fingers (and leather or cotton gloves).
When you are ready to reinstall the cylinder, and assuming the piston was not left inside it, it is best to do it using the proper ring compressor; or, being careful, using your fingers. You can use your fingers if strong and careful ...or make up a thin metal compressor from a tin can or shim stock ....or, get the correct type of ring compressor. There are many types of ring compressors, be sure to get the type that allows usage at the area between engine casing and cylinder base ...these are types that work when the piston rod is still attached.
The cylinder base and the engine case must be very clean, and not at all oily either, before you apply sealant. You want to avoid getting any sealant into the oil passageways at the two top studs. You want the sealant to be applied very thinly ¬ leaving even a single brush bristle. I usually do it with my fingertip and not a brush. Less sealant and careful is better than too much sealant wrongly placed. I want to emphasize, again, that the amount of sealant used is as thin as you can apply (but evenly). For the cylinder studs areas, apply the sealant around the outer case portion at the top two stud areas, keeping sealant thinly applied (and out of the stud oil passageway at those top two studs). If you have compression lowering gaskets, those need sealant on both sides.
Sometime during the 1978 production year BMW did some minor machining changes to the cylinders; they added a GROOVE. The groove was for a large O-ring, at the base of the cylinder. Always use a new one. Have the pushrod seals in place, and everything ready to assemble, before oiling that O-ring. Just before re-installing the cylinder to the engine, smear the O-ring with engine oil. That O-ring may swell, and you have only maybe 15 minutes or somewhat longer, to assemble the cylinder, or it may well not seal correctly from swelling ...and can actually cause problems if swollen too much. The original O-ring was 2.0 mm in thickness. Oak once told me that the 1978 models that use the O-ring (some 1978 do not), up until 1980...all without the Nikasil cylinders ...can use the optional 2.2 mm O-ring for better sealing. There is some controversy over the color and size of these O-rings. AFAIK, the early 2.0 mm were white, the later 2.2 were black, and if a 2.0 is ordered, you may get the 2.2. It may be that sometime in the early 1990's that BMW changed the engine casting opening, again, for the O-ring, and thus started up the controversy? I've never had a problem with any large O-ring, they all have fit OK, and not leaked; because I use sealant properly at the engine case. I am fairly sure that only the larger 2.2 size is now offered. See my cylinders article: http://bmwmotorcycletech.info/cylinders.htm
Last versions of the cylinders had a step machined into them, which must be machined off, or the engine case machined for the cylinder, if you are swapping very late cylinders into an early engine. See prior paragraph link to the cylinders article.
Sealants discussion: http://bmwmotorcycletech.info/chemicalsetc.htm
I prefer to use engine oil on the outside of pushrod tube seals, where they slide into the engine block, so they slide in smoothly. I have preferred a faint fingertip smear of silicone grease (common dielectric grease from auto parts stores) on the inside bore of these seals ...so the pushrod metal tubes can move faintly and smoothly during engine heat-cool cycling. I believe that some pushrod tube rubber wear comes from metal heat expansion, not just repeated heating cycles, with dry tubes; ...silicone grease may help keep the seal from grabbing on the pushrod tube, especially in the critical new stage of operation. I have not seen incompatibility with pushrod seals, so far. Install pushrod tube seals with the mold line directly downward.
In some instances of small oil leaks, and you have dressed the pushrod seal hole, etc., a small amount of RTV will effect an oil seal; this is for use with new pushrod seals. Never reuse pushrod seals. The pushrod tube seals are one of the few places I may add a faint amount of sealant, where BMW never mentioned doing this.While RTV is OK, Permatex #2 (non-permanent) Form-A-Gasket works nicely and does not tend to ever leak, over time. It does not peel or disconnect, like some RTV can. Use the Form-A-Gasket in a quite thin amount ...use your fingertip. Use on well-prepared block and pushrod tube surfaces. Nicks, brush bristles, old sealant and such are absolutely not allowed. I'm pretty careful about making sure the surfaces are good ...I never wanted to have a customer come back and say my pushrod seal job was leaking.
With the new pushrod tube seals in place; the rod re-attached to the piston, and your sealant applied at the cylinder base (do this exactly as required, in the right place, no brush hairs, etc.), you are ready to reassemble the cylinder and then the head to the engine. If you have the large O-ring model, now oil it sparingly, just before you are ready to draw up the cylinder to the engine. Install the cylinder onto the piston. Install the head gasket (be sure the gasket is put on correctly, if wrongly, a small amount of the pushrod hole in the head will be covered by the gasket). Reassemble the rocker gear onto the cylinder head, and the 6 nuts, and you are ready to begin tightening.
I suggest giving a tad of bias (slightly higher torque during initial tightening ...you are not likely even using a torque wrench yet for this) on the two lower rocker nuts ...to avoid any slight canting of the cylinder due to the pushrod seals acting like springs. Be sure to 'stage' the torqueing of the 6 nuts, in a criss-cross-pattern. The exact value of the staging is probably not critical, some use 11 ftlbs and then 18, and topping out at 25 or a maximum of 26 ftlbs, all with a known good torque wrench. Just use several stages ...I use four. I use 25 ftlbs as the final value on all Airheads. Use of beam wrenches of the type without round dials on them is dangerous to your engine block threads. Round dial beam wrenches are extremely costly, and used industrially. I suggest you use a known good tubular torque wrench ...unless you have a really good torque wrench of some other style. Although the non-Nikasil cylinders were originally specified to be torqued higher, don't do it. Torqueing above 26 ftlbs is a VERY BAD idea.Do not try to adjust the collars on the 1981 (?) and later pushrod tubes ...they are brazed in place. It is unclear to me exactly when the brazing first began; I believe it was phased-in during the 1981 production year. I have seen earlier brazed ones. Some literature will state that it was from the 1981 change to Nikasil cylinders. Some have said that it started with the R65. I do not know. If you have earlier adjustable ones, you could back them off a bit before assembling the cylinders to the block, and adjust them after you are all done. I think these should not be touched at all unless grossly wrong; and setting them too tight to the seals is hard on the seals, particularly the /5 types. A bad thing would be to bang on them and damage them or the tubes ...or, worse, move the tubes. Get this all settled befor you bring the cylinder home to the case. If you insist, there is a BMW tool to adjust the old style un-brazed pushrod tube collars. However, a very simple tool from a piece of old electrical conduit can be used to work on the collars. See any Clymer's or Haynes for the sketch ...but, again, I feel you should leave the movable version of the collars alone, unless grossly at the wrong distance. The collar ring is located about 5 mm below the cylinder base seating plane surface at the highest point.
One thing you sure want to do is to avoid ever having to replace a pushrod tube, as the process is not pleasant, and a special mandrel tool needed or you can substitute the front axle sometimes, and you may ruin at least one new tube in the learning process. Aftermarket stainless steel ones are the way to go if you do replace them. You need a well-fitting mandrel. Seibenrock makes one. More information later in this article, because some of you will someday replace tubes. Perhaps yours are rusting or leaking. Further down this article are details on how to replace the pushrod tubes.
Except for the earliest models, the top two cylinder studs have O-rings located at the engine case. Always replace them if the cylinders are pulled even slightly off the engine base. If you do not, you will likely have oil leaks. Be very careful about using sealant. See my article, http://bmwmotorcycletech.info/chemicalsetc.htm. Be especially careful with sealant around the upper two studs ...that is where the oil, under pressure, comes out for the rocker's oiling. The engine oil, under pressure, is applied to tiny holes located IN the engine case area where the TWO TOP studs screw into the engine casting. All except earliest models use small O-rings at that point, and the design is such that oil under pressure follows the outside of the studs up to the cylinder head. Any sealant around the studs must NOT be squeezed into the oil channel when the nuts are all torqued down, and that sealant is specified to be used on the OUTSIDE flat surface surrounding the studs. Use sealant very sparingly! Do not let brush bristles get into the coating ...if they do, remove them. I do this job with a fingertip! Since the oil passageway is, essentially, the long cylinder cavity surrounding the 4 cylinder studs, it is a good idea to clean the studs before re-assembly! ...you do not need crud/dirt in the rocker bearings! I clean the cylinder passageways too; something hardly ever mentioned anyplace.
I always use a sealant on all cylinder bases, no matter model/version. Use sealants very smoothly, very little, using your fingertip to be sure it is relatively very thinly applied and relatively smoothly. Mostly avoid the area towards the case cylinder (97 or 99 mm) hole (from the studs), but do coat on the outer area of the studs FLAT area. That is, seal the outer portion of the cylinder base and case. If you have an Airhead with compression-lowering plates, you must coat all surfaces. If you use a brush, leave NO bristles!
It is critical that the base surfaces be nick free (absolutely no metal proud of a FLAT surface), flat, and exceptionally clean. Surfaces MUST be well cleaned with an evaporating solvent, before applying the minimal, THIN, coating of sealant at the cylinder base area. Do NOT get sealant near/into the oil passageways at the top studs! THIN layer only! When I used Hylomar exclusively years ago, I diluted the Hylomar with a few drops of acetone and applied it with my finger ...especially carefully around the top studs. Hylomar is not necessarily the best sealant these days, although it is a safe sealant. I have seen Hylomar failures, but not often. Some sealants require setting-up time. See my chemicals article for discussion of sealants: http://bmwmotorcycletech.info/chemicalsetc.htm.
The way most engine cases get oil weeps, besides improper sealant installation, is from the piston rod falling when you are removing the cylinder with the piston intact in it, creating nicks on the edge of the engine case cylinder opening. Use a rag under the rod to prevent nicks. If you have nicks, you MUST dress them out. The faintest nick, that has proud metal on the case, will allow leaks.
Keep in mind that the pressure exerted at the cylinder base (when you torque the 4 rocker mount nuts) will squeeze out the vast majority of sealant if you apply too much ...and it can squeeze that sealant into the oil passageways ...and thus, the engine innards. DO NOT over-apply the sealant! I sometimes even thin the sealant as noted. Use your fingertip to apply the sealant. Do NOT lay a bead of sealant down! DO NOT leave brush bristles on the cylinder base area ....they WILL cause leaks.
HINT: If you have a cylinder off, you can use a magnet to remove the valve lifters (cam followers) and inspect them for scoring, pitting marks, cracks, pushrod contact areas, etc. You can also look at the cam faces. Reinstall oiled all over, using engine oil; if things have not been run in a very long time, assemble with Royal Purple or other high pressure assembly lube. DO NOT mix them up! Remove ONE at a time, and replace it before removing another, to prevent mixing them up. Don't mix up pushrods either, although that is hardly as critical. Rolling a pushrod on a flat piece of glass will show up any bent pushrods, usually caused from exceeding redline rpm.
Retorque the heads & check rocker arm end play after a day of sitting. Then set valves, checking the full rotation of the rockers first (the valve clearance must be enough, that is, adjusters very well-loosened, in order to check full rotation of the rockers). Check rockers end play too. Follow the procedures elsewhere's on this site. The earlier the valve gear version, the more care in aligning the rockers (such as the very movable /5 types). 1985 and later models, or any earlier models having some or all of the 1985 parts, may have no rocker blocks alignment adjustment possible (not applicable to 1985+ shimmed models).
Since you have installed a new head gasket, check the torque and valve clearances at 500 or 600 miles, and again at 5000 miles at valve adjustment time. If you have a fresh valve job, then I'd check them more often after the first adjustment ...noting when they become quite stable (less than .001" change per 5000 miles is considered totally stable). I like keeping records for years ...of the valve clearances, as found, before any retorquing & resetting. Instructions on how to set the valves are elsewhere's in this website; primarily here: http://bmwmotorcycletech.info/setvalves.htm
I seldom check head torque after 5K or so. To do so you must back off the 6 nuts (ONE at a time) a small fraction of a turn, then re-torque each one separately to 25 footpounds. If a nut squeaks, back it off, OIL the threads, then re-torque. (Do not specifically oil the two HEAD nuts, although a faint oily film is OK).
If you have reasons to remove and install a new pushrod tube, you must clean the head thoroughly in detergent and hot water, then heat the head to about 250°F to dry it thoroughly, and purchase or make an installation tool on a lathe ...but you can use a front axle. I suggest you do NOT remove pushrod tubes unless you have a STRONG reason. They are a PIA. When installing the tubes, preparation is critical. The actual installation will take seconds, if you've got everything ready. If you're not ready, destroying the tubes, and possibly the cylinders, takes only slightly longer! Check Siebenrock for mandrels if you don't want to have one made, or can not borrow one, or don't want to use an axle ....YES ...Luckily for you, BMW included a stepped mandrel with some bikes: It's the front wheel axle. There are two sizes of axles used on the old airheads, the early one, from the /5 and early /6 is 14 mm, the later one is 17 mm. You need the one to fit your size of pushrod tube. Make a mandrel or get the proper axle. Siebenrock has pushrod installation tools:
Another source for a tool: http://www.cycleworks.net/
BE SURE that whatever tool you make, obtain, or use, it FITS THE PUSHROD TUBES PROPERLY!
Check carefully how the old tubes were installed, depth-wise. Then, measure the amount that the new tubes will project from the cylinder flange to the stop ring for the rubbers. This is a critical distance, and there is no 'stop' to assure you of proper installation depth. Make a mark inside the cylinder hole where the tube ends. Refer to Scot's article. You may want to make a sketch of the collar distance.
Chamfer the edges of the tubes where they enter the cylinder using a little stone or sandpaper. Further prepare the new tubes by cleaning them thoroughly and stuffing all but one tube with strips of rags soaked in water. Put the Tool or axle in the last one. Set all the tubes, including the one containing the axle, into the freezer overnight. Don't remove any from the freezer until you're totally ready to install them. If you have dry ice (frozen CO2) you can try that, as it works even better.
Remove the old tubes from the cylinder. Grip them right above the seal stop ring with a pair of vise-grips, HEAT the cylinder around the tube, and hammer smartly (never hammer dumbly) on the vise-grips to knock the tubes out. Try to go nice and straight, and don't crush the tube. They ought to come out pretty easily.
Now chamfer the lower edges of the tube bores in the cylinder so that the new tubes with their slightly 'stoned' end edge will start in easily when you are ready to do so. Clean the inside of the bores with a brass brush. Wash the cylinders completely with solvent; rinse with hot soapy water, followed by hot clear water. Heat the cylinders to 250 degrees F or even a bit more, in your oven, to dry and to expand them. Remove from the oven WHEN YOU ARE READY TO DO THE JOB, as you do NOT want them to cool off.
Remove JUST the axle/tube from the freezer, line it up in the bore, and push it in, assisted with a hammer (I use a brass hammer or dead blow hammer) on the axle, until it is seated just to the correct depth. You HAVE planned ahead for the depth, ...right? This has to happen very fast, or the tube will stick, and you'll be tempted to hit it again, which will crush the tube and gouge out the bore. (If you've planned ahead and gotten an few extra tubes, you can knock out the tube and try again with a new one).
When the tube is installed, reheat the cylinder, or maybe you have a hot plate, which is what I do, or some such method, keep that cylinder HOT! Return the axle to the freezer for a while, and then go on to the next one. Use the axle to push the frozen bits of rag out of the tube as you're ready to install.When everything is cooled off (but still slightly warmish is best), drip a couple drops of Green "Wicking" Loctite around the tubes where they entered the cylinder, to prevent oil seepage and air leaks. No matter what you are told or read, allow a full day or even more if possible, for the Loctite to set-up.
Valve cover gaskets can be reused almost forever, depending on the type and situation. BMW coated valve cover gaskets need to be installed in one direction, as the black side goes to the head. If aftermarket, or BMW changed the design, they MAY NOT be sided. Only ones I remember like that were, more or less, a common brownish gasket color, and I think they were a bit thicker too. I use dino oil on the head side of only those, which eventually carbonizes and acts like a high temperature glue. Do NOT oil the outer surface of the gasket nor the surface of the metal valve cover surface. The reason you want the head side of the valve cover gasket to stick to the head is so when removing the cover (always slowly and carefully), you do not tear the gasket.
HINT for the /5 models:...There may be O-rings, probably red ones, at the rocker blocks (wait until you price those O-rings!). On the /5, using those pricey red O-rings at the rocker blocks, I oil them JUST BEFORE assembly ...in fact, it is the final thing I do before putting the rocker assemblies onto the head. NOTE that to identify the /5 (two versions of the heads!), you can look at the photos here, in my head assembly article:
Valve cover center stud:
Inspect the valve cover center stud ...and if it has moved outward, or is not engaging ALL threads of the HEAD (visible at the spark plug area), reinstall it to proper depth using Loctite RED. The two-nut method of removing the stud works well. If very tight, heat the head, you will need upwards of 300°F. Before installing with Loctite Red you should test for possible depth of assembly INCLUDING fitment of gasket and valve cover ...does it leave enough threads for the acorn nut? After all, if that is not correct, you may need the longer stud that BMW offers. The proper depth is for the stud is to JUST barely be proud (barely sticking inwards towards the engine block, matchbook thickness or tad more perhaps) of the inner surface ...the backside, engine side that is, of the threaded hole. Early studs may be too short, a longer one is available: early ones were 65 mm length, the longer one, 07-12-9-908-142 is 70 mm long. The threads are standard 8 mm.
It was around 1977 that BMW changed the pushrods to a multi-part design, incorporating some sort of aluminum alloy center section that expanded closer to the rate the cylinders expanded. Their lowered weight also helped offset the mass of the larger intake valves for the 77 US R100S and R100RS models, and the reduced diameter reduced any likelihood of the pushrod hitting the inside of the head. The pushrods were not, however, redesigned again for the Nikasil cylinders, probably the factory found out that the 77 redesign was adequate. The tappets and rockers got changed too. One could now use a bit closer valve clearances.
One can quiet a /5 or /6 by fitting these later multi-part pushrods. They're smaller in diameter, and don't hit inside the smaller early pushrod tubes, and they expand closer to the rate needed to keep the valves quieter.
All Boxer pushrods are the same length and end button diameter, except the R65/R45, which are NOT interchangeable with any other.
01/17/2008: Combine all previous changes and move to Article 60, sub-section 8, and edit for clarity.
01/26/2008: Update with additional information from old engineinternals.htm article.
02/03/2008: Remove hyperlinks engineinternals.htm and OTsetvalves.htm.
03/15/2010: Some emphasis here and there.
01/29/2012: Minor clarification about top stud O-rings and Siebenrock mandrels.
10/02/2012: Clarify some details; add R65 seals number; add QR code; add Language button; update Google Ad-Sense code.
09/01/2014: Add link at beginning of article to gunsmoke.com.
09/28/2014: Finally got around to re-arranging the entire article, for better flow.
03/15/2016: Update meta-codes, layout changes, fonts, justification to left, clarify details and do more 'how-to'.
04/25/2017: Clarify use of RTV and Form-a-Gasket.
04/01/2018: Greatly reduce excessive HTML, colors, fonts. Cleaner layout. Minor advice improvements.
© Copyright 2018, R. Fleischer
Return to Technical Articles LIST Page
Return to HomePage
Sunday, April 01, 2018
Last check/edit: Sunday, April 01, 2018