Cracked nikasil barrel

Discussion in 'Airheads' started by carpetburn, Apr 30, 2012.

  1. carpetburn

    carpetburn Been here awhile

    Dec 11, 2009
    This is how it started, getting my matchless 550 twin cafe racer ready to register while work is very slow and it starts blowing lots of blue smoke out right side exhaust, swap over heads and valves fearing a worn valve guide but still smoking, problem eventually identified as an undersize oil ring.
    So i hop on my bitsa r75/6 and off i go in search of the "ring guy", couldnt find him and couldnt stop to look due to traffic so i continue on home, hop off bmw to open front gate and turn back to see bmw blowing lots of blue smoke out right exhaust, ride up drive cursing the bike[must have caught it off the matchless-lesson learned-dont park the bikes so close together!] and turn it off and the blue smoke casually falls out the right muffler. Let cool and pull off head-remove valves and push out inlet valve guide with finger, oil in inlet port is all below guide so i figure that is my leak, barrel is also full of/very oily above rings.
    I then remove r100 nikasil barrel and the rings are okay but the barrel is cracked inside at the front above the exhaust pushrod, crack direction is to front of bike and opposite flange face/crankcase but below the ring travel, the piston appears fine.
    My question is does this happen to others and why?
    I cant post photos[not terribly computer literate] but can email if required.
  2. Wirespokes

    Wirespokes Beemerholics Anonymous

    Jul 26, 2002
    Jackson's Bottom Oregon
    It's really difficult for me to picture this but I get the idea.

    If it's below the ring travel, I don't understand how the cylinder is getting filled unless the rings are shot.
  3. Beater

    Beater The Bavarian Butcher

    Sep 3, 2009
    Atlanta, GA, USA
    Do you know what year that Nikasil barrel was? The 81's had a bit of a manufacturing defect that rears it's head periodically. Can you post a pic of the crack? It it the coat that cracked or the whole barrel?

    PS - Email me the pic and I can post ... Txt it if you can't email ...

    Edit - Sounds like your guide is toasted. If the crack is entirely 'above' the ring / Piston, then that's probably not your problem (but it's certainly not helping). Is there any play in the valve? When was the last time the BMW was run / started / and given a good workout?