Replacing Pushrod Tubes

Discussion in 'Airheads' started by R100RT Mark, Apr 15, 2012.

  1. R100RT Mark

    R100RT Mark Been here awhile

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    The pushrod tube seals on my 1993 R100R have started to weep. If the problem gets to be a real concern, I will do a “simple” replacement. If it does not get worse, I will put off doing anything about this until the end of the year (when I tend to ride my R100RT more than this bike) to do a comprehensive top end clean/overhaul. My plan for the latter is to also to replace the stock pushrod tube with stainless steel aftermarket versions. I have read all the stories about how difficult this is, and may well hand over this aspect to one of the airhead “gurus”. However, I have not read any accounts from a “regular” wrench yielding airhead owner who has actually completed the task. Anyone out there with real world experience to share? Thanks
    #1
  2. bereahorn

    bereahorn Long timer

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    :lurk
    #2
  3. mark1305

    mark1305 Old Enough To Know Better

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    After reading Snowbum's articles on replacing the tubes; and after having replaced valve guides in other motors, which are much more robust for driving into place with a mandrel, ain't no way I'm disturbing mine until they rust through. Just clean them up with some emery cloth tape and paint with your chosen engine enamel (along with the cylinder barrels to keep it simple and easy)

    I have had to reseal the tubes on the left cylinder. The right side awaits the opportunity/reason to put the new seals on it - and it isn't even weeping yet like the left side was.
    #3
  4. Padmei

    Padmei enamoured

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    Don't get too caught up with Snowbums stuff. Yeah he is a guru however many ordinary people have done it.
    I've ordered & received half the parts needed before I did deeper research into what I'd need(Doh) & am ordering the rest from motobins tonite.
    I was going to just keep the heads on & replace them however curiousity has got the better of me after reading the de-coking thread & I want to see what insides are like & check the valve condition.

    Here's some threads that I have bookmarked

    http://www.pbase.com/dqmohan/prtseals

    Joergs

    http://jhau.maliwi.de/mot/r80gs.html#pushrod


    If anyone from the Antipodes could spread some lite on what silicon grease is called over here it would be appreciated? (And don't say silicon grease:lol3)

    Hope this helps.
    I will be doing mine in a few weeks when the weather starts getting too nippy for riding.
    #4
  5. disston

    disston ShadeTreeExpert

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    Talking about valve push rod tubes, not guides.

    I've never done it. Did you see the big thread last year where somebody built a jig to do this on a press? That actually scares me because it makes me think I have to build a jig and the expertise needed in that article was beyond me. Well there is a tool made for doing these by hand. I think it probably involves heating the head, doesn't everything involve heat with aluminum? And I would at least read the Snowbum article. I don't alweays do things exactly like he says, in fact I don't always do things exactly like I say, but I find it helpful to read a lot when doing anything the first time. I would also read both those articles you have and then I'd give it a shot.

    Didn't read any of that stuff yet because I'm not there yet but I have one thought. It's actually key to know which hammer to use in these operations. I say this is a two (2) lb drilling hammer operation. Not a little or even medium size ball pean hammer.
    #5
  6. rambozo

    rambozo Been here awhile

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    i replaced mine recently, my engine was in pieces though so it wasn't a hard decision to replace them with stainless ones

    as diston has said snobums site is worth the read about this

    i left the tubes in the freezer over night and heated the barrel, a hot air gun done the job for that, snobum recommends using the front axle as a mandrel to fit the tubes and for me it worked well for removal and refitting, heat the barrel for removal as well of course

    the old tubes should of left a mark and i just tapped the new ones in to that level

    i didn't find it a hard job and everything went together pretty easily, only thing is it'll be the weekend until i get to start the bike for the first time so i have to cross my fingers it's done right:pope

    if you're confident enough to take the heads off yourself you should be fine changing the tubes, just make sure the barrels hot and the tubes are cold

    stainless ones do look good as well
    #6
  7. pkboxer

    pkboxer Been here awhile

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    Not really as hard as snowbum makes it out to me.

    The proper mandrel makes the job much nicer and easier.

    I cut a small plastic dowel "spacer" to the length between the cylinder and the seal compressing ring on the tube.

    Then I just held the "spacer" on the outside of the new tube and tapped until the spacer hit the cylinder.

    The new tubes had a slightly champfered leading edge and they pretty much self aligned and went in no problem.

    I froze them over night and had some frozen wet paper towel stuffed inside also.

    heat the cylinder and tap them in.
    #7
  8. Airhead Wrangler

    Airhead Wrangler Long timer

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    My only addition to the above is that you might not get them set at the correct level. Better to go too far in. Then if it weeps a bit when running, with a hot engine, tap on the flange of the pushrod tube pushing it into the seal to load the seal a bit more and that should fix your weep.
    #8
  9. R100RT Mark

    R100RT Mark Been here awhile

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    Useful thoughts and links. Thanks.

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line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} </style> <![endif]--> This is not an antipodean answer in either the common use of the word (which would be UK vs. New Zealand/Australia) or the scientific use, i.e. the true opposite side of the world (which for New Zealand is somewhere in Spain, and in the middle of the Atlantic for Australia), but I hope it helps.

    Dow Corning &#8220;Molykote&#8221; products are often quoted when talking about industrial silicone greases. I use #4 as a dielectric grease applied to the outside of electrical connections to improve their resistance to weather exposure (note that dielectric greases do NOT conduct electricity) and #111 as an assembly lubricant for o-rings and the like if I have any to hand, otherwise #4 gets used. Images are Dow&#8217;s spec sheets.

    [​IMG]

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    Commercially silicone grease is sold in hardware stores as a plumbing supply for use as a lubricant on faucet/tap o-rings.
    #9
  10. supershaft

    supershaft because I can

    Joined:
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    That tradition started with the earlier two piece push rods and doing that didn't move the entire push rod. I see push rods leaking at the cylinder all the time so I am a little concerned with what goes on up there too. I put green loctite on them there in the hopes that is keeps them from weeping there. I think it does. At least for a good long while. That's what concerns me about the stainless push rods. The ones I have installed are damn tight there. I hope not too tight but only time will tell. It's like I always warn people about putting in valve seats: An interference fit that is too tight and moves material isn't an interference fit at all.
    #10
  11. Ben Carufel

    Ben Carufel Boxer Addict

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    Dec 2, 2010
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    Wish I could help, but I don't speak much Kiwi.

    I've got a friend in Nelson whom I need to get back down and visit. He's got a bunch of credit at Sprig & Fern that he's suggested I come help him use up. Sounds like a plan to me!
    #11
  12. Padmei

    Padmei enamoured

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    Cheers for that. I'll see if they're sold locally.

    :roflMate you gotta get sum fush & chups & go to the Freehouse instead - they've got a Yurt there!!
    #12
  13. Dirtyboydeadly

    Dirtyboydeadly AKA. Shineyboydudley

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    I pulled mine out with pliers and measured them. Made new ones on the lathe at work and tapped them in with a hide or rubber mallet.

    I didnt heat the barrel or cool the tubes.

    I have been leak free for 2 years now

    [​IMG]
    #13
  14. Ben Carufel

    Ben Carufel Boxer Addict

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    899
    Location:
    San Diego
    Freehouse, huh? I'll check it out. Had some great fish and chips a few times at Guyton's...
    #14
  15. lphil

    lphil lpihl

    Joined:
    Apr 16, 2012
    Oddometer:
    6
    Location:
    Shaky Christchurch,New Zealand
    Originally Posted by Padmei
    ....If anyone from the Antipodes could spread some lite on what silicon grease is called over here it would be appreciated? (And don't say silicon grease)....

    You can try a dive shop and get silicone grease as its used for the o-rings on the tanks, and I have seen it in Repco in small sachets by the counter marked as dielectric grease sold along with light bulbs
    Phil
    #15
  16. mark1305

    mark1305 Old Enough To Know Better

    Joined:
    Feb 7, 2005
    Oddometer:
    6,318
    Location:
    Merritt Island, FL
    Sorry I wasn't more clear on the analogy, but valve guides are way more robust than the tubes and even with a proper mandrel, it can be easy to ding or bend them up while driving them into position. Even with heated heads and frozen guides. DAMHIK.

    P/R tubes, being more fragile, present an even greater opportunity to screw up.

    However, given the success stories posted so far, I feel better should I have to do any of mine one day.
    #16
  17. Velocipede

    Velocipede Been here awhile

    Joined:
    Mar 9, 2006
    Oddometer:
    490
    Location:
    Kingston Ontario Canada
    I've given this problem a lot of thought over the years that I've owned and wrenched on Airhead Beemers.I am far from being a BMW Guru as some of the inmates undoubtably are but it occurs to me,where were the heads of the BMW engineers when they redesigned the motor and moved the pushrod tubes from over to under the cylinders.Why didn't they forget the tubes altogether and just cast the pushrod tubes into the cylinders.

    I've owned Triumphs and BSA twins over the years and I've always found that it was easier to build an oil tight motor on a BSA with cast in pushrod tubes than a Triumph with external tubes.

    John
    #17
  18. disston

    disston ShadeTreeExpert

    Joined:
    Mar 22, 2011
    Oddometer:
    12,366
    Location:
    Silver Spring, Md
    I'll bet the reason is weight reduction. I don't know this for fact but think cast in passages would mean more weight.

    The reason for moving the cam shaft from above the crank to below I don't know. I think I might have heard why that was but I forgot.

    Crank on bottom was a selling point I think. My friends who rode /2s would tell me the center of gravity was lower.
    #18