- Joined
- Oct 1, 2011
- Messages
- 719
Rob wrote: "When I switched to macs in the sport 40's, it was no contest. The mac 45 on a bad day would outpull the K&B 7.5 on its best day."For what its worth, I ran K&B 7.5's for years. Disk and drum. In hydro's and mono's and sport 40's.Disk engines of course made more power but were prone to breakage, drum engines were timed a bit tamer and required some mods to the closing timing. With that being said, when you got them screaming, the bearings would not hold up because of the very small balls in the big bearing and little front bearing. I found that I could get 3 great heat races and then they would start to go away. These are older technology from the 70's and early 80's. When I switched to macs in the sport 40's, it was no contest. The mac 45 on a bad day would outpull the K&B 7.5 on its best day.
I ran them untill I ran out of bearings and front ends. Great engines in their day.
Thanks Lohring,,yes,,I read about the great Bill Wisniewski designing the .40 size engine for pylon racing back in the day,,looks like the old 7.5 case is basically a bored out .40/6.5cc case,hence the smaller/shallow transfer passages and the same .750" stroke,,so the .40 is the better engine for what is was designed for,,,,Now that you mention it,,I havn't noticed many of the new 1 piece case 7.5s laying around,,probably has better transfer passages and I think .780" stroke and a smaller bore,,cheersK&B's engine designer was the great Bill Wisniewski. The older K&B design had a detachable front and rear on the crankcase. That design could use similar parts for a large variety of applications. It was not ridgid by today's standards. It used die cast parts. In 1998 that design was updated to a one piece investment cast crankcase. This was a much better engine in both inboard and outboard configurations. It is a lot harder to find.
Lohring Miller
View attachment 291597View attachment 291598
Interested in knowing what that is.015" stroked crankpin,
NormInterested in knowing what that is
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