Author Topic: Question about my recently rebuilt Dragonfly  (Read 241 times)

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Offline cbranni

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Question about my recently rebuilt Dragonfly
« on: 23 Jun 2020 at 14:57 »
Hi to everyone,

Due to restrictions in Wales I have been unable to run my Dragonfly since it's rebuild, but I have today ridden it for about eight miles and it is a joy, it's smooth, handles fine and I really like it and want to use it but! there is always a but, I am leaving a plumes of blue smoke behind me  :(

The bores were standard size although worn, but I honed them and bought set of rings from Cox and Turner but as I thought it didn't fix it, so I have read up about fitting Honda CB250N pistons and rings and compared sizes but I have a few questions.

1. What is the Honda part number? is it 13101-442-004 this is for a std 62mm piston
2. The Honda piston is 5mm greater in height than the Douglas, any issues there?
3. I shall have to make a pair of small end bushes so could somebody tell me the correct spec material to use
4. The small end to top of piston seems ok , unless anyone knows different.
5. If I fail to find 62mm pistons how bigger can I go before the cylinder spigot gets too weak.

Thank you for reading this
Kind regards Colin
« Last Edit: 23 Jun 2020 at 16:20 by cbranni »

Offline cbranni

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My Dragonfly
« Reply #1 on: 23 Jun 2020 at 15:07 »
Sorry forgot to add a photo

Colin

Offline AndyMorgan

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Re: Question about my recently rebuilt Dragonfly
« Reply #2 on: 23 Jun 2020 at 17:25 »
I have just rebuilt my Dragonfly with 62.5 oversize 250N pistons, Although I haven't ridden the bike, it's still in bits, the engine runs fine and recently cured the smoking barrel by fitting the correct rings. I had the small end bushings made from Phosphor Bronze PB104 (CuSn8) and had an extra set made if you need them let me know by PM. Once fitted you need to drill through the oil way and then ream back to 15mm.

Cheers

Andy

Offline cbranni

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Re: Question about my recently rebuilt Dragonfly
« Reply #3 on: 23 Jun 2020 at 17:51 »
Thanks for the reply Andy, can you remember the Honda part number please for the piston set and did you use genuine  Honda parts or were they pattern.

Kind regards Colin

Offline AndyMorgan

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Re: Question about my recently rebuilt Dragonfly
« Reply #4 on: 23 Jun 2020 at 18:25 »
Pistons were AE Hepolite
The box says

" REF. 20355  +0.0197" +0.5mm
Suitable for BMW (with "Honda 250 S/D" penciled in)
Original bore 2.4409" /62mm
DB07 119"

Cheers
Andy


 

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