Pushrod seals replacement

Discussion in 'Airheads' started by bikecat, Nov 3, 2010.

  1. sigpe57

    sigpe57 Been here awhile

    Joined:
    Oct 11, 2005
    Oddometer:
    349
    Few questions about a push rod seal replacement.

    -No Silicone on the push rod seal replacement job at all?

    -Can I put back the head without using the H-alignment piece?

    -Some owner leave the piston ring and the head and remove the connecting rod instead. What's the reason? I found remove the piston from the housing is easier.

    Thank you for the reply,

    TT
    #41
  2. bmwrench

    bmwrench Long timer

    Joined:
    Nov 10, 2006
    Oddometer:
    3,536
    The reason for keeping the head on the cylinder is to save the price of a head gasket. Hardly worth it in my opinion. It is a good idea to leave the piston in the cylinder so as not to disturb the rings, but if you had you would have not seen that broken ring. Since the late wristpins use external snap rings, I remove the cylinder complete with the piston and remove the piston on the workbench. When reassembling I find it much easier to get the piston and rings into the cylinder on the bench.

    It's not surprising that the bike ran well with a broken ring; you just had a second gap in that one!
    #42
  3. Gillus

    Gillus High Desert Rat

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    In a former life when starting an engine with a new cam and/or lifters it was highly recommended to raise the RPM well above idle ASAP as it supposedly would decrease the load on the lifter face and get it spinning to avoid the initial "first minutes" wear for both the lifter and cam lobe.

    Preset everything, valve adjustments, ignition timing, fluids etc etc and double check everything. Engine starts and runs, gets oil pressure, no fluids spraying out or other immediate problems then rev it up a bit and hold it. I think we used to try for 2000 rpm for 20 minutes. However a running airhead will not stay cool so a few minutes may have to be good enough.
    #43
  4. wirewrkr

    wirewrkr the thread-killer

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    That's how I do it too. Seems like a better controlled situation for re-inserting rings in the jug.
    #44
  5. chasbmw

    chasbmw Long timer

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    When putting it together use Dreibond or Yamabond on the cylinder crankcase join.

    When you have the top end together, check oil flow to rockers by turning the engine over on the starter (plugs removed and grounded, rocker covers removed) and you will easily see that oil is getting to the rockers.
    #45
  6. Bluethumb

    Bluethumb Been here awhile

    Joined:
    Aug 7, 2012
    Oddometer:
    126
    Location:
    Texas Hill Country
    Your cylinders look great, at least in my limited experience. I've pulled the cylinders off maybe 4-5 airheads, and the cylinder walls have always looked like the picture you posted. What I've been told is that those "swirls" are the factory honing marks. Maybe someone else can jump in and tell me if that's true. I pulled the cylinders off my old RS with 100k and the cylinder walls looked brand new. I thought that was so impressive.

    I was always told to reassemble the pistons into the cylinders dry, but again, this was years go and someone with far more experience may want to jump in on reassembly. I did not hone the walls, simply installed new rings and put the pistons back into the cylinders and buttoned everything back up.

    What's great bout these motors is they are extremely easy to work on. Plus this forum helps to make it even easier.

    Just for fun, ask what kind of oil you should use..........just kidding! Starting a dreaded oil thread cn be dangerous!
    #46
  7. bmwhacker

    bmwhacker Still on 3 wheels

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    May 6, 2009
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    Anyone have any comments concerning the piston top wear / pattern?

    One of my R100S pistons had a similar minor "pitting", but not near as deep or rough as this.
    I rebuilt my top end and used the pistons with no issues yet.


    [​IMG]
    #47
  8. Horsehockey

    Horsehockey A GPS? Huh?

    Joined:
    Nov 17, 2010
    Oddometer:
    370
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    See post #33. BMWrench has provided the likely explantion.
    #48