Strange JAP cylinder

[Ralf89]

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

[Rex]

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?

[R]

Ditto.

Rob Saward has written a little booklet about dating JAP engines,
additional to all the pneumatic palava, as research into aussie built versions.
He'd be the chap to ask, although his health may not assist here.

[cardan]

Hi Ralf,

JAP made a lot of engines, and as Rex points out not all of them went into motorcycles. By 1927, when your engine was built, there weren't many makers using the 500/550/600cc side valve singles. Possibly your engine came from a continental maker, rather than the UK.

Anyway, I don't really understand LY/I as a JAP prefix. The L is OK (85.7 bore) but Clew says that Y means twin port head, in which case I'd expect Y to be always accompanied by O (eg LOY) meaning ohv. Not to worry. LY probably means 550 sv. I after the / is unambiguously 1927.

Here are some sv engines form the 1927 JAP catalogue. Do either of them look like yours? Your photos don't show this side...

Cheers

Leon

[Ralf89]

Hello
Many thanks for your response!
You are absolutely right- I am from Austria and I found this engine also here in Austria. As far as I know the 550cc engines where very popular in Germany and maybe also here in Austria. According to my research the "Y" on SV engines stands for the cheaper "Roadster" or "Standard" version. They has smaller valves and no rotary breather than the sporty SV K and U engines.
So far so good. But my problem is as mentioned before the fact, that normally the KY and LY engines has the sparkplug located directly on the intake valve cap, but my engine has a seperate hole for the sparkplug like the sporty K and U SV engines. But with the small valves and tiny cooling fins.
Very confusing....
Maybe it is really a industrial engine...
Thank you.
Regards
Ralf

[cardan]

Hi Ralf,

The really unusual thing about your engine is that it doesn't have an "oil box" on the crankcase underneath the timing chest. JAP introduced the oil box in 1914 - it uses crankcase pressure and flapper valves to distribute oil around the engine. All large JAP engines after 1914 used the oil box, but not yours. Yet it has the "sports" style cylinder with the separate spark plug hole.

Without an oil box, my guess would be that the engine was for an industrial application (a trolley towing luggage on a railway platform, a concrete mixer, or whatever), but it could also have been supplied to order as a "cheap" motorcycle engine? Sorry I can't be more definitive.

Cheers

Leon

[cardan]

I had a random thought about this engine. /I usually means 1927, but it can also mean 1947. Speedway engines aside, JAP didn't build many motorcycle engine post-WW2. I don't think it's really likely, but could this be a 1947 engine used in a European bike? All sorts of things were being exported from the UK after the war.

Leon