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Thread: /7 pushrod tube replacement

  1. #16
    If you look up the page you can see the drift I made to install the new tubes. I think the information I received here on how deep to seat the tubes is wrong. At least in my case the tubes are too far in towards the block and have distorted the seals. Also I can see oil at the cylinder base where there shouldn't be any. I am thinking of machining a groove in the cylinder to accept a o-ring. I would like to hear from some moa members who have replaced their tubes as to how far they seated the tubes and how it worked out for them.

  2. #17
    Liaison 20774's Avatar
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    The information I provided for depthing the pushrod tubes is correct. Oak was the one who gave us that information. I would be looking elsewhere for the problem.

    I'm not sure I understand, though. You say the leak is around the cylinder base but you're concerned that the pushrod tubes are not seated tight enough. Sounds like something is holding the cylinder out from seating. And since the pushrod tubes aren't seated, it doesn't seem like that's the problem.

    You first mentioned that you were doing this job because the pushrod tube seals leaked badly and where they join the cylinder at the head. Does that mean that you didn't have an initial leak where the cylinder meets the engine case? If that's the case, then I don't see the need to pursue an o-ring for the cylinder base...if it wasn't there when you removed the cylinder and it wasn't leaking then, you don't need one now.
    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. #18
    Before my last repair you could actually see the oil oozing out from the area of the top studs when the engine was running. Now that area seems to be ok but I can see oil coming from the bottom of the area where the cylinder meets the block. Not a whole lot of oil but enough to cause a drip on the floor.
    The deformation of the seals is from the seals being compressed too much. The forward seal has actually split at the lip where it contacts the tube washer.
    The tubes were installed correctly as the highest part of the washer was flush with the cylinder base.
    It seems to me that the seals were rather soft when I put them on but I am basing that on the fact that the old ones were rock hard from 30 plus years of use and abuse.
    Somewhere I read that there should be a gap of three to four MM between the washer on the tubes and the cylinder base?
    This will be something I will attempt to fix over the winter as the temps here in Central Kentucky are already starting to drop and I have other motorcycles to ride.
    Removing the cylinders and making repairs is much easier on the BMW than it would ever be on other machines so I am encouraged to keep trying. I am just looking for guidance from members of this forum who have "been there and done that".
    I understand that this problem will arise after time just because of the engine design and the fact that air cooled engines do expand and contract with use but the deformed seals have me thinking that something is just not right. I can look at other bmw's out on the road and I seldom if ever see the kind of leaking that I am having.Maybe I just got bad seals???

  4. #19
    Liaison 20774's Avatar
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    I did my '78 R100/7 a few years ago...didn't have any problems but then I installed new Siebenrock cylinders as a replacement for the worn original cylinders. I still have my original cylinders. Just checked the location of the stop ring. On one cylinder, the high point of the stop ring is indeed level with the cylinder base. On the other cylinder, the stop ring is not quite as close, it appears to be maybe 1mm or so farther toward the head. I did play whack-a-mole with the stop rings over the years, so I guess I don't really know which is correct. Oak had very specific instructions in his manual for positioning and drawing the cylinder/head up to the engine case to avoid damaging the seals.

    I'm sure you saw that the seals have a proper orientation...the line points to the ground I believe. Plus there are seals for specific years as I recall. For my bike, the part number is 11 32 1 262 995.
    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!

  5. #20
    Thanks 20774,
    My bike is a 78 r100rs that I have kind of turned into a RT over the years. It has a luftmeister fairing and RT bars making it much more comfortable to ride. Also a corbin seat that is close to twenty years old but still looks like brand new. I will get the seals you suggested and try again.
    Has anyone here used Great stuff sealant ? or maybe a anaerobic like the one listed below
    https://www.permatex.com/products/ga...lange-sealant/
    I am glad you told me about the seals being different. I thought they were all the same.

  6. #21
    Liaison 20774's Avatar
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    Never heard about that Permatex product but Ultra Gray by Permatex is often a suggestion. Hylomar has been used in the past. Another that I recall is something called Yamabond as well as Driebond. Here's a couple of sites that discuss seal replacement:

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

    http://www.gunsmoke.com/motorcycling...bes/index.html
    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!

  7. #22
    I looked through the manual I got from Oak and I could not see any reference to pushrod tube height. Maybe I missed it but I looked several times and could not find it.
    I might have used the wrong seals because it was just too tight when I put the cylinders back on.

  8. #23
    Liaison 20774's Avatar
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    I looked at my manual a few days as well...didn't see it. I got that information from a diagram that Oak mentioned on the Airmail email list about 10 years ago. I asked him to send me a copy. Rather than reuse his "art work", I created my own. Nonetheless, the stop ring position that's been offered here is what he suggested.

    Where did you get the seals? What was the part number that you ordered them with?
    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!

  9. #24
    I believe I got the seals from a and s cycles when I ordered the stainless pushrod tubes

  10. #25
    Liaison 20774's Avatar
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    A&S is a good place. As I mentioned above, for the same year bike, my part number was 11 32 1 262 995. A cross reference for this number shows they're used all the way back to the /5. From the range of models, it looks like it covers virtually all Airhead bikes. Hard to understand how you might have gotten the wrong part.

    Pushrodseals.jpg
    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!

  11. #26
    The first time I re-seated an airhead cylinder, I used Hylomar about the base of the cylinder. Leaks reappear eventually. The most recent time (upgrade to Nikasil cylinders on /7) I used Hondabond (same as Yamabond); no leaks thus far.

    A friend with a /7 had persistent leaks from the set screws used in the drilled holes in the engine case for oil flow. Finally, he obtained some aluminum set screws from Re-Psycle BMW and installed these using Hondabond as a coating on the set screw threads. No more leaks. I believe that Matt Parkhouse was the one that recommended the Hondabond on the set screws.

  12. #27
    I will get some hondabond for the next round.
    It just seems to me that the pushrod tubes are in too far because they are really mashing the seals deforming them?
    Upon close inspection the oil seems to be coming from where the cylinder contacts the block. I might have gotten impatient upon reassembly and put them together too quickly.
    I could do the baby powder trick to be sure.

  13. #28
    I just had a thought and a question. If I remember correctly is there a air valve kinda like a crankcase breather valve on top of the block that lets the pressure inside the crankcase out through one of the carbs? If this is blocked wouldn't the pressure inside the crankcase force oil out through the seals and gaskets???
    Just asking?
    Dave

  14. #29
    Liaison 20774's Avatar
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    Dave -

    You're right...without the crankcase breather, that air has to go somewhere. It will find paths of least resistance, so that means seals such as the pushrod (which you can see the results) and the rear main seal (where you can't readily see the leak until it gets too big).
    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!

  15. #30
    Rally Rat 1074's Avatar
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    part numbers

    Actually not exactly right on the seals. /5s and /6s up to around 8 of 1975 use p/n 11 32 1 250 267. There was a change to the diameter of the tubes at that time (larger) that required a different seal (995) that was used thru the rest of airhead production.
    Boxerbruce

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