Author Topic: Dragonfly cylinder heads  (Read 128 times)

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Offline cbranni

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Dragonfly cylinder heads
« on: 11 Aug 2019 at 20:13 »
Hello to all,
Both heads on my recently bought 1957 Dragonfly have cracks in, so I am looking to buy a pair heads in good condition, if anyone has any for sale please reply.
Many thanks
Colin


Offline eddie

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Re: Dragonfly cylinder heads
« Reply #1 on: 12 Aug 2019 at 06:24 »
Hi Colin,
              If your bike still runs OK, don't get over concerned about the cracks. My Dragonfly has a crack in the LH cylinder head (from the plug hole to the exhaust port) - it has been like it for at least the last 20,000 miles without getting much worse. In my opinion, the Dragonfly heads suffer from cracking due to a hot spot being generated around the spark plug due to the shielding from the through studs retaining the heads. Also, bear in mind that we now run on lead free fuel that generates more heat than was originally expected - to help keep the heat down, it pays to go up about 10 on the mainjet size.

  Regards,
                 Eddie.

Offline cbranni

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Re: Dragonfly cylinder heads
« Reply #2 on: 12 Aug 2019 at 07:23 »
Thanks for the informative reply Eddie, the bike was a non-runner when I bought it so I stripped and rebuilt the engine/box, I had a mate weld the heads and I machined them back, I feel happier now knowing yours have run with cracked heads but would like to a pair of un-cracked heads just incase.

Kind regards Colin

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