Disassembly and Assembly of heads, pistons & rings to cylinders & break-in procedures; cylinder studs; Helicoils; Timeserts, etc.

© Copyright, 2012, R. Fleischer

break-in.htm
Article 60, section 1

I am well aware that you may think that pulling off a jug is major surgery and frightening to contemplate. Once you do it, say at a TechDay, you will no longer have apprehension about doing it yourself.  

It is possible to remove a head, perhaps for a simple de-coking (and NOT pushrod tube seals), and NOT have to do any work at the cylinder bottom (no O-rings, no sealants).  In order to do this, you must very securely wrap bungees...or via some other means, around the cylinder fins, across the motor, and all-around the motor.   Or some such.  This keeps the cylinders from moving off the base area in the slightest. This little secret method has been done many times by myself, when I only needed to work on the heads.   In order to do this, the bungees must be super-tight, and evenly surround the cylinder, for and aft.  Generally speaking, I REALLY recommend against YOU trying this.

Never reuse a head gasket.  Whilst it is possible to leave the two head-to-barrel nuts in place, and try to reuse the gasket by never separating the head from the barrel, this is a poor idea.  It MIGHT result in distortion of the assembly. I have NOT seen that distortion, if the assembly is done fairly quickly, within minutes.   These 2 head nuts (located at 12:00 and 6:00) are supposed to be the first to be loosened, the last to be tightened (in the usual cross-staging). 

Information on the cylinder base shims is found, in depth, in the CYLINDERS article, #60-3

It is NOT necessary to remove the piston from the cylinder when just replacing push rod tube seals. It might be a good idea, for such as to remove the rings to check end gaps, etc.You do NOT absolutely have to have a ring compressor! There is an inside taper at the bottom of BMW cylinders, thus you have a built-in ring compressor, in case you do decide to remove the piston from the cylinder...for such as measuring ring wear, cylinder taper, whatever!!  You need to be careful, of course.  Ifyou are intending to do a thorough de-carbonizing of the piston and rings area, or, otherwise want to...then it is fine to use a ring compressor during reassembly.   Although de-carbonizing the top of the piston can be done without removing the piston/rings assembly, this is NOT a good idea, and it is VASTLY BETTER to do de-carbonizing with the piston out.  A thorough job may involve soaking and brushing, over days, of the combustion chamber, piston, and the piston, possibly with the rings removed (I do not always, but I rotate them over the time period). It can involve an overnight job with 50-50 mixture of such as Simple Green and water.   If you remove the rings, pay attention to the top/bottom orientation of the rings, a chamfer usually is towards the engine, and DO make note of from which groove the rings came, and don't break them, they are VERY brittle. If you do remove the pistons from the cylinders, remove them from the cylinder bottom.   When doing a de-carbonizing job, you MUST clean and clean, and clean, again, and again, to be sure there is ZERO carbon particles when you are done, in such as ring grooves.

AVOID allowing the piston rod to fall against the engine cylinder opening....this will create nicks....and the nicks WILL prevent the cylinder from properly sealing.  If you nick the case, dress that nick out!

Head gaskets fit PROPERLY only one way...be sure the pushrod holes are not the slightest bit partially blocked.   This should occur with the writing side of the gasket outward.   Do NOT use sealants at the head gasket, nor, usually, at the valve cover gasket, unless that gasket is brand-new (see below). For the valve cover gasket, use of a NON-permanent NON-hardening sealant to get you by,,,before fixing the warping...is OK.   There are aftermarket thick soft silicon cover gaskets available....you cannot take up much pressure on the cover nuts.....be sure that the nuts do not loosen...if worried...use a SMALL droplet of blue Loctite. I don't use those gaskets.

Valve cover gaskets can be reused over and over.   Suggestion:   install the stock original type valve cover gasket slightly oily (common dino motor oil) on ONLY the surface facing the head.  Over a long time, it will carbonize somewhat and bond pretty good.  Bonding makes for less gasket tearing upon gently removing the cover.  The valve cover gaskets CAN last for MANY years...unless you tear one; oiling as mentioned, will help against potential tearing.   Leave the OUTER surface of the valve cover gasket (and facing inside part of valve cover) clean and dry.  Clean the cover inside with a rag, so no oil gets on the gasket during assembly of cover to head.   When doing valve adjustments, WIPE any oil off the cover and that OUTER gasket surface....there will then be far less tendency to have the gasket peel and break as the cover is removed.  NOTE!....BRAND NEW valve cover gaskets SHOULD have a heat-activated 'glue' on the HEAD side of that gasket.  Thus, if installing a BRAND NEW gasket, the surface between gasket and head must be clean and dry, not oily.  

A longer, and NOW STANDARD 70 mm length of central stud for the valve cover is available, and always install these with Loctite RED at the head end.  This longer stud is 07-12-9-908-142; the original was -145 (8 mm x 65 mm).    I recommend the longer one be installed if:  you cannot get the stud to engage ALL of the HEAD threads and still have 4+ threads on the acorn nut engaged, AFTER the flat washer.

Once in awhile a question comes up about such as the R90/6 and R90S, about a roll-pin, and that they used different head gaskets.   That is true, but the old gaskets are not available, and you can just remove the roll pin and use the later gasket.  For the nerdy (??), the R90/6 changed to the other style (no roll pin) at serial 4961244; and the R90S at serial 4980480.   The cylinder head was modified to eliminate that roll-pin sleeve, and the associated gasket hole was made smaller.   You CAN use the later gasket with the earlier head AND keep the roll pin, if you really want to.  
Regarding the larger hole:  The later gasket can be modified to 14-1/2 mm hole, original was 10-1/2 to 11 mm.
 

The long studs that are screwed into the cases, 4 per side, that are used to hold the cylinders and heads to the engine are these:
11-11-1-257-397   275 mm cylinder stud, 10 x 1.5 mm
11-11-1-265-195   297 mm cylinder stud; used at right side, rear, both, 10 x 1.5 mm
The above longer cylinder studs are used on the RIGHT side cylinder, top and bottom rear

The /5 models had valve gear that was movable by quite an extent.  Adjusting them is elsewhere's on this site.   However, a question comes up now and then, whether or not an O-ring is used under the rocker block area.   The O-ring was  11-12-1-255-167  which became the later number 11-11-1-460-470, 15 x 2.5 mm.   Here are two photos that will identify which head is which:


                                           
The above head does not need the O-rings                            The above head needs the O-rings
 as the casting surrounds the tube.                                            as the tube appears with no surrounding
                                                                                                 casting.

Disasssembly:

Information on the cylinder base shims is found, in depth, in the CYLINDERS article, #60-3

First set the pistons at the OT mark on the flywheel/clutch carrier; that means pistons are fully outwards. Then remove the valve covers and spark plugs.   Loosen the rocker arms valve clearance adjusters almost entirely, so the rocker is very free to move over a wide arc.  Check the rocker bearings, whether the old /5 pressed sleeve type, or the later needle bearing type, by twisting the rocker sideways.  Inspect the ends of the rocker arms, particularly the lower side, where the needle bearings are pressed-in...if bad, replace the bearings.    Then, undo the 6 head nuts, in stages, evenly, and remove the valve gear. Do NOT disassemble the valve gear (keep the shafts, rockers, blocks, all together as units), nor mix the parts from one cylinder to the other, nor mix up exhaust/intake.  Do NOT pull the rocker assemblies apart.  Needles may fall out.    If you do, and you have the needle roller type, the correct number of needles is one less than what will JUST fit, and they can be a hassle for some folks to install.  Again, leave things together, remove the rocker assembly as just that, an assembly.  It is not a bad idea at all to inspect the needle bearing rockers for any problems with the needle cages; and I DO recommend that.  Look particularly at the rolled-over ends of the needle bearing holders.  Don't pull the shafts unnecessarily out of the rockers.  There are tiny needles in the later models, and some can move into the center area.  Those can be a minor PIA to put back in place as noted.   

NOTE:  The punch-prick OFFSET marked shafts CAN be rotated 180° for additional life, with the mark now facing inwards.  But, check the drilling in the shaft first...be sure yours are such that oiling is maintained. NOTE that the rocker shaft will likely have a round darkened area on TOP, or you will seen a punch prick mark. You have probably been told before that the darkened area MUST be on top, the punch mark MUST BE OUTwards, when reassembled. Actually, having the punch mark outward is not absolutely necessary, due to how the internal part is drilled from the factory.  Best for you to just do as I mentioned:  top, outwards, to AVOID me having to make a very lengthy technical explanation and have graphics here, and have you check your particular shafts for proper drilling.   The #60 article on this website has information on just how to switch the original type of /5 shafts (bushings in the rockers, no needle bearings) to extend life of them.

Remove the cylinder head and remove the pushrods.  Pull the cylinder outward JUST enough so that the rear piston pin clip is JUST fully showing. By NOT pulling the cylinder off more, which means not removing the piston farther, you keep the piston rings inside the cylinder. ...BUT... IF you are doing a thorough de-coking, or measuring taper or ring gaps...then remove the cylinder off the piston, but in any case...don't let the piston and rod fall.  If you decide to remove a piston clip and remove the piston pin (you MAY have to heat the piston to remove the piston pin), be careful with the pin clip groove, and note the VORN and arrow on the top of the piston, it means that the arrow points forward on re-assembly!!!  THAT is IMPORTANT!!

If you are leaving the piston and rings inside the cylinder, you are removing that piston pin clip, so do NOT bugger-up the piston doing that, and now you can push the pin to rear (heat piston if needed), and carefully place the rod downward, and pull the cylinder off, piston and rings still in the cylinder.   NO NICKS are allowed from the rod onto the cylinder base area!   Do not mess up the piston circlip if you intend to reuse it.   I most often replace them, which is the best policy. When removing or installing circlips, do not do more than just the amount of pressure and movement needed.   BTW....the wrist pin circlips have a sharp side, and a rounded side; the rounded side goes INWARDS, and the gap towards the engine case.  Be SURE the piston pin clip is 100% properly seated, try rotating it.

Keep in mind that any nicks on the cylinder base and engine pad base will cause oil leaks.

If the piston pin seems too tight to push rearward, push the pin forward a teensy...if it will...it likely won't move hardly. Look for metal fouling at the clip area (the tiniest amount is too much), and also (especially) try using a hair dryer or? to heat the piston.  Heating the piston expands the aluminum far faster than the steel pin.  The teeniest metal fouling will keep the tight fitting pin from smoothly being pushable.

Only in a rare case with a heated piston have I had to use a simple home-made device to remove the pin, the so-called 'draw-bar' method.  A draw bar (DO get rid of proud metal at the clip place, and DO try heating the piston pin area quite hot first) CAN be simple! Try a piece of all-thread from the hardware store (get 2 nuts), not too fat, or it won't fit through the pin, and use some sockets from your socket set, or a big selection of washers, and nuts, and draw the piston pin out. An example of how you might do this is the following:

NOTE...NOTE!....you must NOT put pressure on a piston clip!  Huge amounts of pressure are NOT NEEDED, and are NOT TO BE DONE, in this pin removal procedure!
I assume that you have removed the REAR piston pin clip.  That clip is usually called a KEEPER.  This procedure works well for piston pins that have the center hole totally available to put a piece of all-thread through it.  There ARE types of piston pin keepers that don't allow this unless BOTH are removed.
1.  If your all-thread is not cut to reasonable size with the nut ALREADY on the end to be cut, do that first, have the nut on first, and clean up the end with a file, wire wheel, whatever, and use the nut to finish chasing the threads .  The all-thread needs to be long enough to enable nuts, washers, sockets, whatever, as spacers on it.  Read this procedure THROUGH, before doing any cutting.  THEN....put the appropriate length piece of all-thread through the hollow piston pin. At the forward end, put a washer or socket, sized such that it fits the piston pin end, but does NOT pull into the insides of the pin, NOR put pressure on the piston, nor clip, if it is there.  In other words, it is sized just a bit less than the pin diameter.   Add a nut. Check and recheck the size of your items being used as a spacer/mandrel.    UNDER NO CIRCUMSTANCES do you want to damage a piston pin bore or clip, or pin.  
2. At the rearward part of the pin, where you removed the clip, put a large socket that is fairly sturdy and is much larger on its INside than the piston pin, and add a washer if needed for the nut to bear on.  Put on a nut. Tighten this rear nut. The tool will draw the pin to the rear, until the pin contacts the washer. HAVE THE PISTON HOT.   WATCH what you are doing...you DO NOT want to injure the piston pin bore area.   You may have to put a large socket or piece of pipe, etc., that fits and clears, over the pin, and repeat the pulling, over and over.. Note that you can improvise, a lot, on this technique.  Done properly, you will NOT scratch the piston bore.  The pin is a much easier fit in the rod, and you need only remove the pin enough to free it from the rod (don't let the rod fall).    Some pins fit tightly, and heat and more rarely heat and the drawbar method are needed.  Do NOT go to the effort of the drawbar method if a simple heating of the piston with such as a hair drier (to quite hot) works to allow you to push the pin out with your thumb.  Pins and piston bores are a VERY carefully machined fit.    Be really careful not to damage the piston pin keeper area....if you put the slightest nick in the area, you will have to remove it with a sharp knife or some other method, or the pin will not go back in place later.

OK....NOW the pin is out of the piston and rod; and the rod is gently placed on a rag on the engine casting hole;.....and you can pull off the cylinder, with the piston and its rings still in the cylinder.....you need to remove the piston, of course, if doing a ring job, honing, ...etc.

Assembly and break-in:

Information on the cylinder base shims is found, in depth, in the CYLINDERS article, #60-3

Preliminary information to know:

I suggest that you do not use the BMW owner's booklet method of break-in; it is for an engine already run at the factory. 

Most of you will be 'breaking in' a ring job or pistons, rings, cylinders, or bore job, or some combination.   BMW, way back when, used a special 20W20 oil delivered with the new bikes.  There is NO need for that if you are breaking-in new rings, ETC.  I suggest a SG type oil, non-synthetic, and maybe even a 10W40 for break-in.  

I suggest that you do NOT! flood the rings with oil.   I don't flood anything in the cylinder/pistons/etc., with oil.  Use a few drops of the engine oil ON YOUR HANDS, and then wipe your hands onto the piston skirts and rings.  I do it to the cylinder walls too, but some feel that is not necessary, and inhibits break-in somewhat.   I like the faintest oil film...REALLY THIN on things.

I recommend that the engine NOT be babied. This is especially important at high altitudes, like where I live...where cylinder pressures, even with full throttle, are much lower.   Lower cylinder pressures mean that the rings MAY not be forced against the cylinder walls with adequate pressure.   Before ever starting the engine, I install a NON-synthetic motor oil.   I use grade SAE 10W40 or 15W40 or some-such, and often I simply purchase a couple of quarts of a diesel type of oil, because it contains a goodly amount of ZDDP, which is protective.  You can use a name brand.   You do NOT have to do this, and most folks WILL successfully break-in new rings or cylinders, with almost any non-synthetic motorcycle oil.  The break-in oil should be one with a goodly quantity of ZDDP additive already in the oil....to protect the camshaft and followers primarily, although it helps some with piston rings too.

****Install a new oil filter, using the starter (no fuel in carbs so engine will not start) to fill the oil canister area (OIL light goes OUT).   Start the engine, using a minimal amount of 'choke', and within seconds move the rpm to about 3000 and hold it there for maybe 15 seconds, then move it upwards to maybe 3500 or even 4000... for perhaps a minute,  I shut it off after that minute, check for oil leaks, then I restart and IMMEDIATELY, no waiting, go for a ride.  I DO NOT baby the engine...I use a fair amount of throttle. DO NOT, however, use over about 4500 rpm for the first dozen or so miles.  Keep the engine around 3000-4500, as best you can, backing off the throttle fully every few blocks, then increasing throttle so the rpm is back in that range. As you get a couple of miles on the engine, you can use longer stretches without backing fully off the throttle (backing fully off 'sucks' oil into the top end, a good thing).   The idea is for oil to be sucked into the rings and valve guide areas when the throttle is snapped OFF.   It is OK to use a fair amount of throttle, but not wide-open throttle, and do not use extremely high rpm.  After a few miles, you can move slightly higher in rpm.   Don't idle the engine for long periods of time.  After a fair amount of miles, stop, turn off the engine, and again check for oil leaks.  If no leaks, continue your ride.  I suggest finishing the initial break-in in the usual fashion as in such as the Rider's Manual...modest rpm, vary the rpm, vary the throttle, etc., and avoid very high rpm.   After 50 miles or so, return home and change the oil to a quality 20W50 (or proper grade, depending on weather conditions for riding)...but do NOT use a FULL synthetic until the engine is FULLY broken-in, which can take a few thousand miles sometimes.   You probably will want to change the filter, and to inspect the pleating (disassemble the filter by prying the metal ends off the filter, then slit the outer wrap, then unroll and inspect all pleats. both sides). It's a good time to check the valve clearances after that 50 miles.   I'm ready for Golden Spectro 4 in 20W50 about this time.

Assembly and break-in;....In more depth:

This so-called dry cylinder method information was posted more than once to the Airheads LIST by Tom Cutter.  My own methods were and are somewhat similar, and I am using his posting as a basis for what follows.  I have edited it slightly for syntax and clarity.  In those areas where I have made particularly personal comments or changes other than minor, they are in blue.  I have NOT changed Tom's meanings nor intent in his own text, although I have changed first person grammar.

PISTON  RING SEATING - THE "DRY CYLINDER" METHOD

 The "Dry cylinder " method  does not mean 'don't oil anything'.   RATHER, it ESSENTIALLY means don't flood everything with copious amounts of oil on  assembly.

 Hone (be very careful you understand what honing means here, as it means different things to different folks, and is not the same thing for honing a fresh bore job on an older iron cylinder, as what it means for a Nikasil or Galnikal cylinder) and then thoroughly  wash the cylinders and pistons, rings, etc. with a solvent.   (Tom uses Safety-Kleen solvent), then  finish with hot soapy water, then a hot water rinse.  Snowbum uses any convenient VOLATILE solvent and does NOT hone Nikasil or Galnikal cylinders....although he feels a simple ball-hone could be briefly used.....Snowbum uses 3M type plastic scouring pads with soap and water to clean those particular bores. 

Blow dry  with compressed air and leave in the sun to dry. If you don't have compressed air, use very clean and soft and absorbent cotton to dry the cylinder bores.

Use an oily (clean motor oil) rag to lightly wipe the cylinder walls. This prevents surface rust, and makes everything slide together well. You want the surface just barely oily.   The Nikasil and Galnikal cylinders do not really rust.  Snowbum uses the faintest amount of oil on both the iron and Nikasil/Galnikal cylinders...a very faint amount.  On the iron cylinders, Snowbum generally lets the cylinders, after the soap, water & drying, to sit in his garage to get a very very faint patina of rust, which may or may not be noticeable.  The VERY SLIGHTLY oily rag...or hands...is then done, the next day or two or three.   I have nothing against NOT oiling (using a drop or three of oil on the hands) the cylinder walls themselves. I do, but VERY faintly.

Assemble the rings onto the pistons (need I caution that you MUST install them correctly and not upside down, and at 120°, and the gaps at the O'clock I specify elsewhere's??), then install the pistons into the bottom of the cylinders until just  the skirts and wristpin hole is showing.   I surely hope there is no need to mention that VORN and the arrow on the top of the piston faces FORWARD!!   Then slide the cylinder onto the studs, and  line up the conrod wristpin holes. Put a few drops of oil on your fingers and oil  the wristpin and bores, then install the pin and clip. If the pin is tight heat the piston a bit with a heat gun. If the pin is still tight, pull the cylinder back off and clean the burrs in the pin bore. Once the piston pin is installed and the clip is secure (put a rag in the crankcase hole to keep the  pin from flying in there) you are ready to finish installing the cylinder.

Apply a thin coating of your sealant of choice (snowbum no longer recommends Hylomar) onto the cylinder base sealing surface and both sides of the gasket (if  the bike uses gaskets or compression plates) as well as onto the crankcase surface. I warm the Hylomar on the radiator in the winter, or leave in the sun in the summer, so it's brushable. The film must be very thin, and even, and there can't be any brush bristles left on the surface.  There have been problems using Hylomar, the sealing fails.   Most of us are now using a more modern sealant.
Please refer to my CHEMICALS article for recommendations on cylinder base sealants and applying them!  Hyperlink:  Chemicals

Apply two or three DROPS of oil to each side of the piston skirt, top and bottom, smearing it on evenly. Don't let any drip on the Hylomar (or? sealant).

 Lightly oil the pushrod  tube rubbers on the outside so they can slide into position. Snowbum uses a faint smear of silicone grease on the INside of the pushrod tube rubbers, where the pushrod tube goes, and uses engine oil on the OUTside of the rubbers.

Push the cylinder fully home, install the head gasket so the writing faces you, (double check that there is NO gasket covering ANY portion of the pushrod tube holes...if there is, the gasket is reversed), and install the  heads and rocker arms without delay.

Torque the heads in a progressive 3-step sequence, and adjust the valves.

Start the motor,  rev it to 2500-3000 RPM and  hold it there for about 30-45 seconds.
Shut it OFF.

The rest is edited slightly and a bit paraphrased by snowbum.  It should be noted that there is very little difference between what Snowbum does, and Tom Cutter does, in all the above, and below:

Put on your helmet; take a brisk 5-10 mile ride. 
Shut off the motor, prepare the carburetor adjusting tools, start the motor, adjust the carbs and shut it off.

Let it cool overnight, recheck the valve clearances and in 600-800 miles do another valve clearance check. Snowbum rechecks the head torque at this time.

Snowbum recommends the dry method, but also recommends that as soon as you ride off, you follow his break-in method, found at ****, several paragraphs above.

Information on the cylinder base shims is found, in depth, in the CYLINDERS article, #60-3

The "other" details, in depth:

NOTE:  BMW has never specified, in any detail, if the 4 rocker nuts and associated studs are to have oiled threads, or not, when assembling and torquing them.  It is MY OPINION that you SHOULD lightly oil the threads before screwing on the nut.

Tighten the 6 nuts holding the head and cylinder EVENLY.   It is not necessary to have oiled threads on the two head bolts, located at 12:00 and 6:00, although a trace of oil film is fine on them and is what I DO. IF you are reinstalling the cylinder, it is BEST to start with slight tightening first at the two rocker nuts which are opposite the pushrod tube seal rubbers. The reason for that is that your new (of course) push rod seals, installed oily to the case, and slightly silicon greased..or oiled.. on the inside (or on the tubes), create a slight cocking pressure on the cylinder...and tightening a tad first with some slight bias will make sure the cylinder comes up to the engine block more squarely. As the cylinder comes home to the engine, BE SURE to do actual tightening EVENLY;...even before your torque wrench would register at its lowest setting.... and use the typical cross-tightening routine. Once the cylinder is pretty well up to the engine, then be sure to 'stage' the torque settings, perhaps first at 11 ftlbs and then 18 ftlbs.  I may use a stop at 23 or 24, wait, and then I go to 25.   Do NOT go directly to the final 25 ftlbs value!!! The final torque setting varies officially by year and cylinder type, but if you use 26.0 ftlbs as an absolute MAXIMUM for ALL BMW airheads, and try for 25, that IS my recommendation.  I set my known-good wrench to 25 ftlbs.   I suggest you disregard any advice in literature that, especially on the old iron sleeve cylinders, says to use 29-31 ftlbs.

 ***BEWARE!!....many torque wrenches have an extremely soft 'feel' or 'click' at lower settings. I have seen folks set a wrench to maybe 11 or 12 or so and put a LOT of torque on those bolts...beyond the 26ftlb max...simply because they did not know what to feel for. If you do not know how this torque wrench feels, test it on something other than your top end nuts!   I absolutely will NOT use a beam type torque wrench for this job, unless it is the industrial type, that has a GAUGE on it.

Rockers:

A good reference for the rockers, which has some photos and discussion, is:  http://largiader.com/tech/rockers

Repairing pulled cylinder stud threads:

 

I like Helicoils FAR better than TimeSerts or similar;...for this application.   Properly done, the Helicoil has no oil flow problems from those oil passageways.  If you are repairing a botched-jog, you may well require special advice, perhaps on the Airheads LIST.

NOTE:  BE SURE you FULLY understand that ALL the oiling for the valve guides and the rockers and pushrod tips, ETC., all comes from the OIL GALLEY, which is supplied to the top end via two holes located at the engine cases at the TWO TOP CYLINDER STUDS.   If you are going to repair pulled threads, where a stud has pulled out of the engine case, it MUST be done properly, as there is a lot of torque on those studs when tightening the 4 head nuts, and you MUST ensure that the oil passages continue to be functional.  Note that the path of the oil is along the two upper studs themselves!

Helicoils work fine if properly installed...I recommend AGAINST Timeserts!

The standard fix for pulled threads is to use the Helicoil drill and Helicoil tap and tool that comes in the Helicoil kit.   The thread that you are going to make in the case is 12 x 1.5.  The Helicoil is then inserted in that 12 x 1.5 thread, and the Helicoil has the same pitch (1.5), but is now 10 mm where the stud screws-in. 

There is no need to get the entire BMW kit.  You can order the special long Helicoils from BMW, and use regular Helicoil tap tool, etc.
     Rags should be stuffed into the engine, and grease on the TAP, to grab chips, during the repair process.  A GUIDE is absolutely necessary to ensure a dead straight and square repair.  You can obtain longer Helicoils from Helicoil dealers.   Use of the longer Helicoil, or long BMW Helicoil, ensures a very strong repair.    My information on some of this is in the 12/92 microfiche, page 3, area I23 and J23.  The SI was 11-047-91 (2461), and covers ALL R models.   The SI calls out installing the Helicoil to a depth such that it is 2 mm below the surface.  NOTE, that BMW had a note on this SI....stating, my words here, that the correct specification for torque, using a known calibrated torque wrench, was 25 +-  2 foot pounds, and that "this did not mean torque to 27".    In the top oil galley holes, they are at 12:00, be exceptionally careful about those oil functions....do not block the galley hole, and ensure that the Helicoil does not interfere, ETC. Remember, there is a Rubber O-ring used on most models there too.

BMW apparently wants Loctite on its inserts, and supplies the 12 coil insert with such a coating, per their books.  HOWEVER, I have literature from the Helicoil company that says NOT to use such on their inserts, as it can cause them to slip (rotate).   I think BMW is correct in this instance.

The threads in the crankcase are particularly vulnerable to overtorquing at the left cylinder, front (left) front stud!  The BMW factory issued a bulletin quite some time ago, that said that THEY were installing, as standard, a Helicoil [they NAMED the brand Helicoil], at that front stud. The Bulletin was not overly clear.  Factory installed Helicoils are special, 12 turns, and a sort of bottoming internal-facing bump down partway, and these were usually installed only at the upper front left stud threads.  We don't know the official reason, could be some weakness in the casting there, or?? 
Those of you that have these should know that it is quite possibly a FACTORY installation....rather than a previous owner boo boo. 
***Some of BMW's literature is vague on this point, but it is the LEFT SIDE front, that typically has the factory Helicoil (although can be other top stud holes).

BMW does not use the standard 9 coil (typically) that one finds in stock at the local Helicoil dealer.  BMW uses one that is LONGER, with 12 coils. The BMW part is...or is supposed to be...coated already with Loctite. The BMW supplied Helicoil is a bit different, and not just that they are longer than the typical Helicoil.  They are INexpensive, and I definitely recommend the BMW Helicoils, which are 11-11-1-338-630.  About $3.    You need the appropriate Helicoil drill size and tap, of course.  BMW makes an entire Kit, but it is pricey.   INTERESTINGLY, Helicoil themselves do not recommend use of  Loctite, feeling it detracts from the holding force the Helicoil exerts on the stud (spring effect)....but, my GUESS is that since the Helicoiled thread is so vastly stronger than the non-Helicoiled, that this is moot!   In any event, when I install regular Helicoils, I use Loctite BLUE.  NOTE!!!....when I install with Loctite, I let it cure a couple of days, then I clean out the excess Loctite VERY thoroughly, with acetone, long before I install the stud.   The entire kit is BMW part number 88-88-6-112-730, included a Helicoil tap, a tool, and a drift tool.  Expensive!   Perhaps worth it though!    BMW rightly said that if the threads were totally pulled out, one need not drill (guide needed!!!), and one could proceed directly to the tapping for the Helicoil.   NOTE that tapping MUST be done with the special Helicoil made tap.   I suggest, MOST emphatically!... that this job never be done, drilling or tapping, without a truly proper GUIDE!!!  Drilling & tapping is critical!!

  Drilling and tapping has to be done VERY squarely to the case area.  Any decent machinist will know that, and comply with a specially made up tool; but that tool is likely to be so-so, although MAYBE OK.  I used, years ago, a modified cylinder base, with the holes bored and long hardened inserts in those holes.    Few in the USA have the really proper fixture to do this job squarely and properly in every respect. 
Those that do are:
Oak, in Chicago area.
Tom Cutter in Pennsylvania.
Anton Largiader in Virginia.
Ted Porter in California.
The above have fancy versions of these tools, that do an excellent job.
Want to do it yourself?...see my tools.htm article, item #20.

 

Note:  Once in awhile we see a badly repaired thread.  It might have had a Timesert installed, or a Helicoil improperly installed, ETC.
Keep in mind what I said about the longer Helicoils that BMW uses and sells.   But, for a pulled Helicoil, there is a good fix, if you are careful.   Helicoil makes a TWINSERT....it is a Helicoil inside a Helicoil, and is available extra long...which is a MUST.
Try www.olander.com for the proper parts, including the 12.5 mm drill, the Twinsert tap, and the long Twinsert inserts....or just rent most or all of the stuff you need (see that tools article, item 20, as noted above).

MORE on cylinders, O-rings, etc.

NOTE!....Excellent head work (valve jobs, dual plugging, all that sort of thing) that I know of, is done by OAK.     Contact him at:    AskOak@aol.com

You folks on the WEST coast can use Ted Porter, whom I can recommend for ANY type of Airhead work.

rev:
01/26/2008:  All prior revisions incorporated, and information added from obsolete engineinternals.htm article, etc.
01/29/2008:  Correct the Helicoil part number (-1- was missing in the number)
05/28/2009:  Add head photos and description
01/27/2010:  Update information on tools.
01/31/2010:  Re-arrange the sections on Helicoils, make clarifications, clean it up some too.
03/xx/2010:  Final version of the update information in the cylinder stud thread repair tools area.
10/29/2010:  Clarify the thread oiling and some minor details on the Helicoiling, etc.
05/21/2011:  Clean up article here and there.
02/04/2012:  Edit description below head photos to make it exceptionally clear which heads do and do not need the rocker block O-rings.
03/24/2012:  more information on the studs

© Copyright, 2012, R. Fleischer

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