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What a dropped valve looks like...

Discussion in 'Technical and Troubleshooting Torque' started by Trevor G, Jan 17, 2008.

  1. Yup. Dropped valves. Get blamed for all sorts of problems but the truth is: if you have one your engine is unlikely to run at all.

    Here is a pic showing two dropped valves. The heads have come off the valves. They hit the piston and provided some extra ventilation to help get rid of the heat. ;-)


    This head is off a Moto Guzzi v twin, the V65 Lario, to be precise. They had a design flaw, well, two to be exact.

    The valves were a 2 piece design and they weakened at the join because the valve springs chosen by the factory were way to strong for their intended use.

    Here's the result of the 2 dropped valves:


    Another cause is when you over-rev and the valves bounce (usually due to weak springs) and contact the piston. Electronic ignition prevents that these days, unless you change down too soon or too many gears at once.

    This frequently results in a bent valve stem or a bent head.


    Trevor G
  2. Ouch - so hopefully not your bike?

    Thanks for the details, fingers crossed I never have to post up pics like that :shock:
  3. That's OK, I bought it like this so I could work out what to do to fix them properly. I have another one, not exploded yet, which was my rider until I realised that this one actually had one of the recommended cures, lighter valve springs

    Someone just never got around to replacing the valves! I have replaced the piston and am about to fit a spare head just to get it running. Then, the head overhauls begin...will continue the writeup I started in the Projects page some months ago.


    Trevor G
  4. haha lol,
  5. I just try and buy my bikes working :oops:

    All the best with it and look forward to the updates :cool:
  6. That just looks painful... was that the only problem with the bike?
  7. I hope so! :)

    I'm just putting it back together now. So far, there's a new (used) piston on the rod.

    It has (according to the paperwork I saw) a new clutch and gearbox overhaul.

    It has a leaking front tyre.

    It has the usual Lario issues which I will detail in the Mod and Proj section.


    Trevor G