harley 10/12

[purri]

You've stirred a memory mate. I reckon the HD models being 6/7 were 750cc, the 7/9 1000cc and the last 10/12 1200cc as stated. The formula from memory was from the Royal Automobile Club (Pommy) and was a fixed ratio between bore and stroke (swept volume). Naturally ON THAT PRINCIPLE an undersquare engine was preferentially taxed for rego purposes as it was assumed that an undersquare engine produced less horsepower per cc/cu.

[DaveAus]

I've heard U models also referred to as a 10 horse

[hairynob24]

I've heard U models also referred to as a 10 horse

G,day Dave,the reason i started this 10/12 question is an old mate of pasted a few years back,he was 75 years young,he would come over to my place and help with my brother 44 chief,it had a M88 on it no wounder it gave us trouble,but old mate got it sored.any way he had an old roller sitting under a sheet of corry in the back yard but no motor,i saw his wife a few weeks back and asked about the roller, thats when she said the old 10/12, i always through it was a wla anyway i am working on it but her boys dont want to sell it.Old mate was and still is a legend around here he brought his wla outfit in 1947 they still have it,and he rode it untill he pasted away,very cool

[Speeding Big Twin]

I spoke to two employees from the RAC here in Perth but they couldn’t add anything at this stage. One of them looks after the archives one or two days per week and he said he’d ring me if he found anything relevant.

I also contacted another member of the VMCC and he commented on the 10/12 and 6/7. He said for 10/12 that 10 was the rated horsepower, with 12 being a reference to the 1200cc range. And a similar thing applied for 6/7, with 6 being rated HP and 7 being a reference to the 700cc range. Obviously the 6/7 engine is closer to 750 than it is to 700 but apparently all the 7 in 6/7 does is indicate the range.

So if I apply similar thinking to the 7/9, 7 would be rated HP. And I’m wondering if 9 would be a reference to the 900cc range of certain F-head engines because although they are known as 1000cc I think they really only reach approximately 990cc in standard form.
Eric

[Friday]

Ive heard flat head BT referred to as 10/12 .used to be here in NZ too. Live to Ride mag had a few pics of a UL hauled out of a chook shed out Perth way . it lived in there for 40 odd years , apparently the chook paste preserved it.
I think it was hidden like so many vehicles to avoid Gov commandeering when war breaks out......Vietnam?? I dont know some of these Old guys ,once theyve been thru ww2 , they dont want a second go at it ,so they stash what theyve got.