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Thread: cylinder gasket

  1. #1
    1978r100s
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    cylinder gasket

    I am putting new pushrod boots and cylinder gaskets on my 78 r100s.
    The old cylinder base gaskets were flat metal, The new ones are a rubber O ring. I looked on the partes fiche and that's what it shows. The cylinders "seem" to have a very slight groove and the crankcase has a recessed shoulder which looks as if it would accomodate the ring.

    Aftr putting on the cylinder with new O ring base gasket, I noticed that there was some rubber kind of showing as if it was squeezing out. Is this normal?

    Does any one know what model bike the old metal gasket could have come off of. Thanks for any and all help
    EJ

  2. #2
    Liaison 20774's Avatar
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    The metal gasket was not stock for the '78 bikes AFAIK...they may have been used on the /5 or possibly /6 bikes. To use one would have been a desire to reduce compression...maybe something the PO did. I would think that you would use either the gasket or the o-ring...the o-ring probably being standard. But if you go without the gasket, you'll need to pay attention to the upper range of the cylinder where a ridge may have formed because the gasket pushed the cylinder out a little bit. If you eliminate the gasket and don't remove the ridge, you may damage the upper ring when it hits the ridge.
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    '78 R100/7 & '69 R69S & '52 R25/2
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  3. #3

    cylinder base gasket

    If the base of your cylinder has the groove machined in it BMW calls for the O-ring seal. The ring should be seated in the groove as the cylinder is slid home to the engine block. It should not be seen squeezing out once the head bolts are torqued down, and may leak oil if it is. The flat metal gaskets from BMW were designed to slightly lower the compression ratio to allow use of lower octane fuels after unleaded became more prevelent. You should be able to use both the flat metal and O-ring together (metal gasket to the crankcase side, O-ring to the cylinder side), or just the O-ring, but not the metal gasket alone.

  4. #4
    Stage Crew beemerPhil's Avatar
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    The metal base gasket was used on your model.

    Originally, the base gasket was very thin steel- like a paper gasket. Thicker aluminum gaskets were introduced as available fuel octane dropped; they were used to reduce the compression ratio to alleviate engine knock.

    These gaskets don't wear, and can be re-used- unless you break one!

    No base o-ring was used (except the two little ones around the upper cylinder stud bases) until the first nikasil cylinders appeared in the early '80s bikes. DON'T try to put one there on your bike, it'll get crushed, and leak, and possibly distort the sealing face of the block and/or cylinder base!

    Sounds to me like you're looking at the wrong parts fische!
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  5. #5
    Liaison 20774's Avatar
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    Quote Originally Posted by beemerPhil View Post
    Sounds to me like you're looking at the wrong parts fische!
    So what's wrong with this picture? Here's the RealOEM fiche for a '78 R100S:

    http://www.realoem.com/bmw/partgrp.d...90&hg=11&fg=15

    Shows the o-ring but no gasket...
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
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  6. #6
    Stage Crew beemerPhil's Avatar
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    This fische is wrong- and they show the same fische for a 1984, which used the o-ring in question and NOT the base gasket.

    Your bike used the flat metal gasket and the o-rings marked #6 on the fische, but not the larger #5 o-ring.

    Oddly, the fische shows the base sealant that was used with the gasket, but never with the o-ring! I wonder where they got this illustration?
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  7. #7
    Liaison 20774's Avatar
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    Quote Originally Posted by beemerPhil View Post
    This fische is wrong- and they show the same fische for a 1984, which used the o-ring in question and NOT the base gasket.

    Your bike used the flat metal gasket and the o-rings marked #6 on the fische, but not the larger #5 o-ring.

    Oddly, the fische shows the base sealant that was used with the gasket, but never with the o-ring! I wonder where they got this illustration?
    Interesting...then every available fiche has it wrong. I've checked my own ETK as well as Max BMW, RealOEM, A&S Cycles, Bob's BMW, Hucky's. They all show the o-ring and not the gasket. The o-ring is 11 1 337 567. Hucky's says from '76-on. Bob's says from '79-on. Bob's PDF catalog has an interesting comment for 11 11 1 335 650, cylinder base gasket, '76-'78 (low compression):

    "Note: 76-78 models normally don't use a base gasket at all, except in the unusual cases where lower compression is desired!"
    Last edited by 20774; 05-19-2008 at 03:07 PM.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  8. #8
    Registered User AntonLargiader's Avatar
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    Quote Originally Posted by 20774 View Post
    "Note: 76-78 models normally don't use a base gasket all, except in the unusual cases where lower compression is desired!"
    That is exactly right. I know this has been covered here before, so a search might be in order for some people.
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  9. #9
    1978r100s
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    Quote Originally Posted by AntonLargiader View Post
    That is exactly right. I know this has been covered here before, so a search might be in order for some people.
    I want to make I understand what you have written. It is "exactly right" that there was no gasket for 76-78 models? On my bike there is not a groove on the cylinder that would hold the O ring. I am the second owner and bought it back in
    1984.

    Also, I see you live in C'ville Va. I'm up the road from you.. 30 miles in Madison County.

    thanks for your help and all who responed. It has been interesting.
    EJ

  10. #10
    Grammarian no, Rider yes ISAMEMON's Avatar
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    my 78 had/has no gasket
    like many others....orderd parts before tear down
    when I did tear down I found nothing...not even a trace of goo
    so with input here and Oaks manual, I just used a thin coat of goo
    just sealent
    very thin sealent
    no leaks
    and I'll agree the micrfiche at the dealer is wrong
    so now I have two expensive rubber bands.....used them to replace the ones that hold my side covers on

  11. #11
    Stage Crew beemerPhil's Avatar
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    OK, I had to look this up to make sure. It's been a while; I should know by now not to stick my 2 bits in before I've had my coffee!

    There were indeed some early /6-7 bikes that came through with no gasket at all, just the small o-rings at the upper studs(to contain oil on its way to the rocker shafts), and a skinny o-ring around the cylinder base spigot (this didn't fit in a groove like the later nikasil models- 2 different o-rings).

    But as available fuel deteriorated, most had some kind of gasket; IIRC, there were three different thicknesses, from the hard steel 'stock' gasket which was not much thicker than a paper gasket, to one that must have been about 1.5mm or so, made of aluminum.

    Note that the page in question lists only nikasil cylinders, with a starting serial number for each model; there's no mention of the iron sleeved cylinders used on the earlier bikes.

    Out of curiosity, I looked around a bit- realoem.com doesn't list any older stuff, but they do have a parts page for one model that was never available with nikasil barrels- the R75/7.
    (http://www.realoem.com/bmw/showparts...28&hg=11&fg=15)

    This page shows the base gasket and the o-ring, but gives no part numbers or further information about either.

    Looking a bit further, I found that Capital Cycle still lists all three base gaskets- a .5mm, a 1.25mm and a 1.5mm, described as 'normal', 'low-test /5-6', and 'low-test 76 on'.
    (http://www.capitalcycle.com/body_html/catalog.html)

    This is the way I remember it.

    They also, however, list a 93mm base o-ring that they say is used from '76 on- but this isn't the same o-ring used on the '81 and later nikasil bikes; different thickness and different part number.

    IIRC, base gaskets were only used on the iron-liner bikes, and the skinny base o-ring was used with some of the base gaskets but not with others...

    We always tried to stay away from the thicker shims, since the loss of compression was accompanied by a proportionate loss of performance.

    The o-ring used on the nikasil bikes was thicker, fit into a groove in the spigot and actually slipped inside the bore on the block. The o-ring on the sleeved bikes was trapped under the cylinder base in the taper of the block, but didn't go into the bore.

    My best advice would be to consult an old BMW parts BOOK for specific applications- BMW's fische has always been full of errors, and you can't make notes or corrections on microfilm!

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  12. #12
    Registered User AntonLargiader's Avatar
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    Quote Originally Posted by 1978r100s View Post
    I want to make I understand what you have written. It is "exactly right" that there was no gasket for 76-78 models?
    Here's one thread.

    http://forums.bmwmoa.org/showthread.php?t=23702

    Lostboy seems to know his stuff.

    There are no base gaskets for '76-on, but there are optional compression-reducing plates (which I have yet to encounter on any bike). These cylinders are normally sealed directly to the case.

    For pre-76 there is a normal base gasket/shim, and an alternative thicker one for compression reduction.
    Anton Largiader 72724
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  13. #13
    1978r100s
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    I received an email from Oak. This is in part what he had say:

    "The 78 models were a mixed bag in production. Some had the large O ring around the cylinder base, others did not. If you do not have the groove for it in the cylinder base, do NOT use the large O ring. There is no room for it.

    There is NO base shim or gasket on ANY of the engines produced beginning 1976 unless someone added them. Some did, to reduce compression ratio as a means of dealing with lower octane fuels. The best fix of course for that is retaining the stock compression ratio of 9.5 to 1 and going dual plugging."

    So to keep everything as was when taken off, I got the same gaskets from Bench Mark Works. I found that most dealers are more in tune with the newer models.

    Thanks for everyone's help.
    ej

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