To associate the K with failure of any type as a design and actual motorcycle to me is pure baloney. Monday morning quarterbacks looking back 55 years. The Model K was the most beautiful motorcycle ever designed in many enthusiasts opinion, an all new design incorporating the best styling cues from H-Ds other models with new modern suspension, unit case and large brakes etc.
Ask anyone back in 1952 about this beauty. It was instantly loved by many around the world, motorcycle lovers took note! The K has evolved into the most successful model motorcycle ever in the H-D line up. My OP 52K went 20 years and almost 20,000 miles without a transmission problem or other major problem. Than the shifter spring broke inside. Sure any idiot can pop the tranny and cases drag racing or other abuse. Just like all these Hemi powered cars and Jeeps can rip the 904 w overdrive transmissions out in one abusive test drive. Operator error causes most failures attributed to bad designs. As for using the same part number for new parts, it makes perfect sense if the part is the same one with only minor modifications or improvements. Obviously the head numbers on heads are a bit off yes. As we know H-D usually added the -A, -B etc to identify them as a newer version of same part inless a major change occured than they would change the year suffix when that happened. Also they might change one number on the end for similar parts. Except in cases where production changes out paced the book writers or the foundry typesetters, and and an existing number was floated. There probably should have been -52, -52A, -54 & -54A numbers for suffixes. The Spare Part book does list the later heads as different numbers with last number one higher than -52# and with the -54 suffix for 54-56 KHK. It lists the -52 heads for 52-56 K, KK, & KH. The -59 Book. I think the 54KH had the newer style head but weak raised numbers, contradicting the book again. So the foundry or whoever presented the material to the foundry made that error in number 54 upgrade. Or we've just never seen a -54 head Early heads have stamped in numbers, the 54ish ones have weak raised numbers and the 55 56 have tall sharp raised numbers. Looking at the 32 heads I have. There are KK heads like Patrick mentioned. Deep relieved but not wide on intake valve. No polishing. Early heads have smaller chambers with shallower relief than newer ones definitely. I think it is .040" less on a K in the intake valve head area. More fun K "what's really going on thoughts.." Cheers folks and RIP to my Buddy Joe Leonard who we lost Thursday afternoon. He was a close friend and great fellow. I miss the 4-5 emails a day etc. He was so interesting and friendly besides the greatest racer ever. No one has matched Joe's Multiple Consecutive National Championships on Motorcycles and in Cars. Erik K