i think it was a lot of different things that made HD ,as for the knuck it was a decent design but it had its flaws with the oiling of the top end that caused it to over heat ,thats one reason they stuck with the flat head in the military bikes (if the knuck would have been the better design it would have been no problem to fit the knuck right in the flat heads frame acording to my interchange book its a drop in swap . plus the flat head was also one of HD longest used designs it was used in servicars up until at least 73 with very few changes mostly in the charging system and electric start .but back to the point LVspringer that is a cool bike ! later,roaddawg4life
Great looking WW2 bike, looks really good, bet you get some looks riding it about, being in the UK I often go over to France for the day/weekend looking at WW2 sites and your bike would not look out of place, hope you enjoy it, ride safe, Bucket.