Guzzi beheaded (long)

Discussion in 'UK Motorcycles' started by Pip Luscher, Mar 10, 2007.

  1. Pip Luscher

    Pip Luscher Guest

    Took the LH head of the Quota this afternoon. Well, could be worse, I
    suppose.

    Had a few minor issues: to remove the fuel tank involved, not
    surprisingly, turning off the fuel taps. This involved a fruitless
    hunt for the Plus gas, liberal spraying of WD40, and finally the use
    of a spanner to hold the body of the LH petrol tap from rotating while
    I mangled the knurled ring with a pair of long-handled pliers.

    The next problem was that I very carefully undid the six head nuts in
    sequence, only to find the number five was actually a plug. Number six
    was a socket-headed bolt that lurks underneath it, so I hastily put
    four of the nuts back on to spread the load, and set to with a ruddy
    great Allen key (my Allen socket set wouldn't reach) with a tube
    jammed on the end. I then added more force, then finally hauled hard
    on the tube while beating the Allen key end with a hammer. It let go
    with a heart-stopping bang, then proceeded to creak and crack its way
    out, taking the stud with it.

    With some trepidation I lifted the head, to find... nothing untoward.
    I'd been expecting a piston crown looking something like the surface
    of the moon, or even with a ruddy great hole in it. It actually looked
    surprisingly pristine, well, apart from some oil and brown
    colouration. The head looked fine, as did the valves. I scratched my
    head. Err, the one on my neck.

    As the piston was at TDC (so as to close the valves) I turned the
    engine a bit and at first the bore looked absolutely fine. Lower,
    though, and I could see odd pale grey patches on the walls.

    Off came the barrel (I once got given a rubber mallet as a birthday
    present: I don't use it often, but it's bloody useful when I do need
    it).

    Ho hum, the piston's seized, but more-or-less on the sides of the
    piston where the gudgeon pin ends are. The rings have been pretty much
    immobilized.

    I'm a bit stumped as to how it happened, TBH. Judging by the spark
    plug, the other cylinder looks fine.

    Hmm. Having never seen a seized four-stroke, is this where they do go?

    The 'front' end of the gudgeon pin is roughly where the exhaust valve
    is. On two-strokes the exhaust side of the piston gets the hottest,
    maybe the same is true for four-strokes, and perhaps this caused the
    piston to spread along the line of the gudgeon pin?

    So did it just overheat? Certainly the piston crown, while hardly
    spotless, was a bit cleaner than I'd expect: usually there are thin
    crusty brown carbon deposits as well as on the head. Is this
    cleanliness normal for a Guzzi?

    I doubt that the ignition timing's out on that cylinder alone because
    AIUI it uses a common pickup on the clutch bell housing, and that
    bolts straight on; there's no adjustment. It could have run lean on
    the one pot, I suppose, but given that it's fuel injected, only a
    clogged injector would explain that.

    Or did I just thrash the poor old thing too hard? To be fair, there's
    a lot of bike to push along and I've been riding the old girl rather
    faster of late, but still mostly well below three figure speeds, so it
    seems unlikely.

    She did used to pink when WOT on warm days but I haven't really heard
    that since about the time I replaced the engine temperature sensor a
    few years ago, and anyway, it wasn't particularly warm that evening.

    As for fixing it, I imagine I can get the bore honed clean and a new
    piston etc. won't cost the Earth. I still need to know what caused it,
    though.

    In the meantime I've still got the Tuono for sunny days and this
    morning I've taken the TL off SORN. Trouble is, neither of these are
    great commuters because of their limited tank ranges.
     
    Pip Luscher, Mar 10, 2007
    #1
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  2. Pip Luscher

    JB Guest

    <snip>

    I'm sure that these are Nikasil bores on the Quota? I have seen this
    happeining before on LM3/LM1000 nikasil barrells. All three instances I've
    seen were from engines where the owner had used something other than fully
    syn oil. I'm sure you probably use fully synth though?
    What do the ring grooves look like, gummed up or clean?

    JB
     
    JB, Mar 10, 2007
    #2
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  3. Pip Luscher

    Pip Luscher Guest

    Hmm. I had been using a cheap brand oil for the last 6K miles, but it
    is, or claims to be, fully synthetic ACEA A3/B3 API SL (and CF for
    some reason). If it turns out that a cost cutting measure was to blame
    I'll be bloody annoyed with myself. Mind you, at least it's easy to
    prevent further recurrence.

    Can't say about the ring grooves: I'd have to lever the rings out.

    The bore itself is only slightly magnetic and not on the outside of
    the lower barrel, so I'm guessing that it's nickel plated. The manual
    doesn't say. There is no scoring or other bore damage other than the
    aluminium smeared on it.

    The only time I've ever had an engine seize was a race-tuned LC, and
    that wrote off the piston, barrel, head, crank and mildly damaged the
    cases, too, so this is a new experience!

    Do I take it from your comment then that you can't hone aluminium
    smears off a nickasil bore?
     
    Pip Luscher, Mar 10, 2007
    #3
  4. Pip Luscher

    JB Guest

    I wouldn't have thought even a cheap synthetic would be a problem. Old
    dino-mineral is known to be an issue with the older Guzzis though,
    especially if not changed often enough (1500-2000 miles max). Was the oil
    level low or low-ish at all?
    Definitely worth a look. especially the oil control rings.
    Indeed. I had a tuned X7 where pistons were 'service item'.
    You can but be careful. I'd use scotchbrite/wet&dry with paraffin as a
    lubricant rather than honing stones myself. That bloody nikasil is very
    hard but extremely fragile. Lock up or misalign a hone and it's fucked; No
    question about it. I've been spoilt I reckon. My Guzzis both have steel
    liners.

    JB
     
    JB, Mar 10, 2007
    #4
  5. Pip Luscher

    Andy Bonwick Guest

    On Sat, 10 Mar 2007 17:05:39 GMT, Pip Luscher

    snip>
    You can hone them to remove debris but if you start to remove the
    coating you'll end up with problems.

    http://www.newmantools.com/flexhone/index.html

    Buy one of the flexible hones and use whatever pistol drill you've got
    lying around but run it at slow speed. Flood it with paraffin while
    you're doing it to flush away any debris and it'll be finished in 10
    minutes.

    The company in the link won't be the only supplier and I'm sure if you
    search a bit you'll pick one up for about £30.
     
    Andy Bonwick, Mar 10, 2007
    #5
  6. Pip Luscher

    Pip Luscher Guest

    OK, I'll get brutal with the piston. It's not as if I'll be using it
    again.
    Which reminds me: I *must* get a top-end service kit for the YZ.

    Ta.
     
    Pip Luscher, Mar 10, 2007
    #6
  7. Pip Luscher

    Pip Luscher Guest

    OK, Ta.

    I'll try Scotchbrite first and if that doesn't work, I'll try one of
    those hones.
     
    Pip Luscher, Mar 10, 2007
    #7
  8. Pip Luscher

    Pip Luscher Guest

    Nope, bang on the full mark. I check pretty regularly. I do stick to
    the 3000 mile service interval.
    Well, I did by dint of snapping a bit off the oil control ring. The
    groove looks like it was machined yesterday: utterly perfect. No signs
    of blow-by, no burnt oil on the underside of the piston (well, a hint
    of brown near the middle), no bloody clues at all apart from it having
    seized. In fact apart from the seized bits, the piston is in superb
    shape.

    It must have overheated, I think. Once I get the cylinder sorted then
    I can start trying to diagnose what happened. The injector's the prime
    suspect ATM, though I've just found that the airbox contains a lot of
    soapy oil.
     
    Pip Luscher, Mar 12, 2007
    #8
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