Cylinder Head Nuts Torque Setting

Discussion in 'Airheads' started by akabeton, Apr 16, 2014.

  1. akabeton

    akabeton Adventurer

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    I just wanted to double check this before I screw up.

    Haynes - 18 - 23 Nm. ( 13.5 - 17 ft.lb )

    Clymers - 35 - 39 Nm. ( 26 - 29 ft.lb )

    Snowbum - 33.9 Nm max. ( 25 ft.lb max )


    Bike is a 95 r100 GSPD with 35,000 miles.


    Thanks
    #1
  2. Big Bamboo

    Big Bamboo Aircooled & Sunbaked

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    I use 25 ft.lb which is less than recommended, but my fasteners are oily. Factory specs are for dry fasteners.
    #2
  3. Solo Lobo

    Solo Lobo airhead or nothing

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    I'd say not to re-torque unless you have had the heads off and need to double check
    #3
  4. chollo9

    chollo9 Screwed the Pooch

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    I agree with both statements above. Studs pull out of the cases way too easily.
    #4
  5. disston

    disston ShadeTreeExpert

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    I use 25 ft/lbs. Three stages.

    I do retorque my heads sometimes. 1975 R90/6. I think the early bikes are less prone to pull the threads tho.
    #5
  6. supershaft

    supershaft because I can

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    I have torqued literally 100's of heads to 26ftlb and have never had any troubles for it. I have torqued a lot to 28ftlbs and never had any trouble for it. The studs do not pull out of these cases way too easily unless they are over torqued. It's the same story with oil sump bolts and many others. Pay attention and do the job right with the right tool and there should be no problems. Threads that ARE easy to strip? Drive shaft fill and drain bolts, late model final drive oil height inspection bolts, and fork drain bolts. All for very little thread purchase but go figure.

    Now I have read a couple of times that the early cases don't pull their cylinder stud threads as much as the later ones. I have been around these bikes a lot for a lot of years and I have never noticed that. But then again I hear all kinds of nonsensical stories about how the later engines are not as good as the earlier ones. My experience is just the opposite. The later cases are much better in many ways starting with much stronger main bearing carriers and it gets better from there. The real bad years IMO as far as trouble with the cases are /5 and early /6.

    I don't re-torque heads as often as BMW recommends but they do need re-torquing. I would guess about half again of what BMW recommends is about right.
    #6
  7. chollo9

    chollo9 Screwed the Pooch

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    Right. You're exactly right.
    #7
  8. Stan_R80/7

    Stan_R80/7 Beastly Gnarly

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    Both my Haynes manuals for BMW twins, 1970-1988 (published 1989) and 1970-1995 (published 1999) have a three stage torque specification for the cylinder head retaining nuts:

    Up to 1980:
    1st: 11 ft-lb
    2nd: 26 ft-lb
    3rd: 29.5 ft-lb
    Final: 28-31 ft-lb

    1981 on:
    1st: 11 ft-lb
    2nd: 18.5 ft-lb
    3rd: 26 ft-lb
    Final: 26-29 ft-lb

    Personally, I use a maximum torque value of 25 ft-lb with a second stage torque value of 18 ft-lb which seems to work fine on my 1978 R80/7. I also check the calibration on my torque wrench before tightening the cylinder head nuts.
    #8
  9. jackd

    jackd Long timer

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    Are you doing some head work or just checking the torque prior to setting your rocker arm gaps? I just bring it up to around 20 ft/lbs if I'm doing the annual rocker arm check - no need to go the full torque.

    On another note - I've been exchanging e-mails with our mutual friend. It would seem that we have many common acquaintences in our line of work - aviation is a small world. I'm sending him pics from my collection to remind him of his youth. He wants us all to get together for a ride over here on the Island - I'm hoping you can join us...
    #9
  10. GrahamM

    GrahamM Been here awhile

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    I use 25ft-lbs on the r80 and r100. Three stage approach as well. All good, no leaks or troubles.
    #10
  11. Boxer Metal

    Boxer Metal Mad Scientist

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    +1:d
    #11
  12. Stagehand

    Stagehand Imperfectionist

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    torque specs here are there so they are not exceeded, rather than run up to. I should think all about equally snug anywhere between 20 and 25 will keep them from pulling anything. whats the cross section on 4 10mm bolts? Its a chunk of metal that would hold twenty bikes in shear, lol its not like the nut torque is gonna be what holds the cylinder on, even with the potato masher inside.


    I haven't had any problems since that one time, and of course good judgment comes from experience which comes from bad judgement. Aint saying I haven't pooched it, but thats how I learn :D
    #12
  13. ysrebob

    ysrebob Adventurer

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    On a closely related note, is this kind of oily/sooty stain along the left cylinder base a sure sign of pulled cylinder studs?
    [​IMG]
    Photo is from an '85 R80RT I bought last Tgiving and spent a lot of time restoring over the winter. Previous owner had botched all kinds of things to the point I'm amazed the bike was even driveable... loose suspension bolts, messed up wiring, butterfly plates backwards in the carbs and mismatched needles, etc etc etc... basically an unbelievable amount of ham-handed work had been done. Last thing he told me after I bought the bike was that he had just retorqued the cylinder studs. So it was with a vague feeling of dread that I noticed a fresh sooty leak along the top of the left cylinder base after I finally got it running again the other day and took it out for a test ride. Haven't had the heart to redo the stud torques yet... afraid of what I will find.
    #13
  14. disston

    disston ShadeTreeExpert

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    That is a small amount of seepage at the base of the cylinder. It is not a sign of anything except poor application of sealant or poor choice of sealant that was used. I get a bunch more seepage than that on my bike. Easy to clean. Will stay clean for awhile.

    A retorque of the cylinder stud nuts would be advisable.
    #14
  15. 100RT

    100RT Long timer

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    I agree with Disston. In the past I used Hylomar and got seepage. Now use Yamabond and stays dry.
    #15
  16. infinityedge

    infinityedge Been here awhile

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    What version of Yamabond (4, 4 marine, 5, 6b, 7) works best?
    #16
  17. 100RT

    100RT Long timer

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    I have only used the #4.
    #17
  18. garthg

    garthg Been here awhile

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    No, you don't use sealer goop on these cylinders.

    If the O-rings on the cylinders are original, they may need replacing. (There's three--one big one around the barrel, and two little ones around the top studs).

    If your pushrod seals are also leaking, that is a good time to re-seal the entire cylinder.

    I re-sealed my R80RT cylinders of the same vintage, including O-rings, and there is no leakage whatsoever.

    I agree with Supershaft 100% on the torquing recommendations. I use 11, 18 and 25 ft-lb sequence, just because it's easy to remember. (7 ft-lb increments).
    #18
  19. Stagehand

    Stagehand Imperfectionist

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    something about just a film of goop, not an actual seal.

    Dont go and crimp the top stud o rings like I did, either.
    #19
  20. supershaft

    supershaft because I can

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    I have had the best luck with Durko sealant spread real thin with a #18 Exacto blade. A sealant virtually no one recommends but I think it is the best.

    I always use new pushrod tube seals installed clean and dry with the release agent scrubbed off the inside and outside of the seals.

    A very important tip IMO that pretty much no one else mentions is putting just a very small dab of sealant on the stud O-rings in order to keep them in place while installing and tightening down the cylinders. I always have a mirror handy and double check when there is just enough room to see and make sure that those O-rings have not fallen down on the studs during installation. If they have they will deform the cylinder/case where the cylinder pinches them and cause leaking issues that are very expensive to fix with certainty since it F's up the parts! I have seen many a late model airhead that has had this F up done to them. Part of my n00b, charlatan experience. :lol3
    #20