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Dave

2024-06-11, 20:02:05
Have you tried the new Drafts feature yet? I just lost a long message today and learned my lesson. It is a good idea to save a draft of any long post you are writing. You can then just keep writing and keep saving a draft, knowing you have a backup if there is a glitch. The draft is automatically deleted when you post the message.

Dave

2024-06-08, 18:30:04
For Sale
xman has two very nice 1950's machines available - a green 1950 mk4 and black 1951 mk5 - both in good condition and running well.

Dave

2024-06-07, 02:13:36

Dave

2024-06-03, 08:23:05
For Sale
Duncan has just listed his green and cream 1957 Dragonfly for sale with spares and documents.

Dave

2024-06-02, 08:34:05
Parts avalable
alistair still has parts available - barrels, carburettor, castings - see all listings.


Dave

2024-06-01, 18:33:27

Dave

2024-05-28, 00:09:46
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Fitting Japanese Pistons to a MK3

Started by Clive, 24 May 2007 at 04:33

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Clive

Hi Everyone ,


Has anyone fitted O/S Japanese pistons to a MK3, there seems to be a lot to choose from ie 62-63mm range
Honda Suzuki, Yamaha,which are the best ?  I have read write ups on T35s fitted with these pistons and the amounts to be machined off the cylinder and head to maintain the compression ratio . Has anyone done this conversion to a MK 3  which does not have such domed pistons .
What are the pit falls, i know the weakness of the cylinder near the base , but there dos,nt seem to be a lot of spare cylinders out there so this convertion seems a good way to get another life out of the old bits .
Regards
Clive

Alan Cun

Hello Clive, dont know if this is of any help but about 4 months ago I picked up a heap of mark Doug parts that were going to used for a historic racer. In among the parts were two barrels fitted with honda pistons and never used.     They are a 4 valve piston  one side gudgeon says Honda.    The other A25 (hole) /5 .  On top of piston by the reconditioner is 2.4398.    I bought the package from Kevin  Hodges Traverston via Gympie Qld , very experienced in old bikes, so reckon he knew what he was doing. I am sure others have had more results to pass on. regards Al

trevorp


Clive

Thank you for your replies , i was hoping for more detailed responce but never mind will have a go myself and then i can perhaps pass on a more detailed account of the convertion .
Regards
Clive

eddie

Clive,
          I have fitted Honda CB250N pistons in Dragonflies. All you have to do is change the small end bushes for specials with a 15mm bore and have the cylinders bored to the required size. Just to be on the safe side, I also filed a couple of flats on each piston to clear the valves, but I have heard of owners fitting the pistons without filing the flats. If you check the Honda pistons, you wil find they have the gudgeon pin slightly off centre. I ignored this and fitted both pistons with the exhaust cutaways to the bottom on both cylinders, and the engine ran fine. The resulting lower compression doesn't seem to be a bad thing with our modern unleaded fuel - it appears to give more torque without sacrificing too many revs.
                     Regards,
                                    Eddie

Clive

[Thanks Eddie,
Will acquire a couple of Honda pistons and have a go and thank you to everyone that replied to this Post

Regards
Clive

MRD

Clive
I also have CB250 pistons in my Mk. They have been in there for some 12 plus years and had no problems, at one point I had the barrels off and there was no sign of wear.
Regards......MRD