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  1. #1

    /7 pushrod tube replacement

    I know this has probably been covered here many times but I am new here so Please bear with me.
    I have a 1978 R100/7 that I am in the process of resealing the cylinders and replacing the pushrod tubes.
    I am replacing the pushrod tubes because they leak badly from both the seals and the joint where they join the cylinder, The sealing flanges on at least two tubes are loose to the point where I can move them with my fingers.
    My motor has NO groove on the cylinder for the big O ring and when I took it apart I noticed NO base gasket. Is this normal or am I missing something?
    I have been trying to research just how far to install the new pushrod tubes into the cylinder but I am finding differing opinions. The answers I am finding range from flush with the base of the cylinder to 5mm from the base of the cylinder?
    Also Do I need a base gasket or just some good cement/sealer at the cylinder base.
    Permatex has a product called Right stuff that I have used before to seal aluminium transmission cases and it works great. Has anyone tried this at the cylinder base?
    I understand that bmw airheads are prone to leak oil at the pushrod tubes and cylinder bases so this fix has been done a lot. I am hoping to tap into the wealth of knowledge that exists on this forum.
    Thank you one and all for any replies I might receive.
    David Legg

  2. #2
    Liaison 20774's Avatar
    Join Date
    Sep 2005
    San Antonio, TX
    I did a top end on my '78 R100/7 3-4 years ago. I'm on my phone now and can't find it. Will add more later.'s my thread on the top end for my bike...I did more than just the pushrod tube seals:

    My bike is a Sept 1977 build. No base o-ring, no groove, no base gasket. There are of course the small o-rings on the upper studs.

    I used Permatex Ultra Grey as a thin layer for the base of the cylinder...I believe I applied it on the engine side, avoid an excess of sealant around the upper studs.

    Here's a post which shows where the collars need to be on installation:

    Note that you will need to refix the collars onto the tube...they must not move around otherwise you'll not get the right pressure on the seals. If they're loose, maybe you can find a shop that can braze them into place.

    Snowbum is a great resource...I've also run across this website for pushrod tube seal replacements...some differences to your bike:
    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!

  3. #3
    The base gasket was not really a base gasket, but rather a shim to reduce compression on some earlier models to use them with lower octane gas. They came only with a slight smear of sealant from the factory regardless of whether the cylinder used a large o-ring. Oak's top end manual is the premier reference, but it may be hard to find one now. Here is a voluminous reference from Snowbum, which you may have likely seen. It can take some effort to digest, but the right warnings are there and some specific information on tube replacement (which I have not personally done).
    Lee A. Dickinson - Danielsville, GA USA
    Airheads #3480 | Iron Butt Assn. #8914
    1976 R75/6 - 1992 R100RS - 1993 K1100RS - 2013 R1200GS

  4. #4
    I have oaks manual and have emailed him questions but gotten no reply. I hope he is still with us.
    Thanks for the info, Parts are on their way from California.

  5. #5
    Fortis Fortuna Adiuvat Omega Man's Avatar
    Join Date
    Jan 2010
    Quote Originally Posted by View Post
    I have oaks manual and have emailed him questions but gotten no reply. I hope he is still with us.
    Thanks for the info, Parts are on their way from California.
    Unfortunately not-

    "You can do good or you can do well. Sooner or later they make you choose." MI5
    Mod Squad
    2009 F800GS 1994 TW200

  6. #6
    So sorry to hear of his passing, I talked to him briefly on the phone a couple of years ago and was greatly impressed with his kindness and patience for people of limited knowledge. He will be missed by us all.

  7. #7
    I made a drift today on the lathe for the removal of the pushrod tubed and they came out surprisingly easy. I used no heat and they came right out with a couple of taps from a small hammer. I will heat the cylinders for installation.

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