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Motorcycle Discussions => Identify these bikes! => Topic started by: Ralf89 on December 07, 2025, 07:16:51 AM

Title: Strange JAP cylinder
Post by: Ralf89 on December 07, 2025, 07:16:51 AM

Hi,
Has anyone every seen such a Roadster cylinder with seperate sparkplug hole like the SV sports engines K and U?
Furthermore this cylinder has very tiny but many cooling fins.
This cylinder was mounted on a 550cc Roadster engine from 1927 ( LY/I ). It has the original bore of 85,7mm and a stroke of 95mm, so it is a real 550 roadster barrel. But I haven't ever seen a roadster barrel with seperate sparkplug hole and such tiny fins.
In the pictures you can see this cylinder compared to a 500 roadster KY/W
Thanks
Regards
Ralf

Title: Re: Strange JAP cylinder
Post by: Rex on December 07, 2025, 12:58:56 PM

I nothing less than nothing about JAP engines other than they made many more industrial and stationary engines than bike engines, so maybe it's off something like that?