2 b or not 2 b

[John (Taylor) Gabrowski]

Frank: Around here during stock outboard days 1950s to 1983 the Merc 20H crankshaft became a real sore spot due to breakage of the top throw or crankshaft neck with some people shedding the flywheels and some times breaking the crankcases when the crankshaft separated. I converted several Merc Mark 25 cranks to Merc 20H specs on the center main bearing and they lasted but who knows for how long as the frequency of racing declined over the years anyway. The last 20H crankshaft here that broke was in 1983.

Thanks for the info.

[Aeroliner]

The Mark 25 crank came in two versions. Some had the babbit center main and others were 20-H style. Has anyone tried the babbit bearing style in a looper. They are not cut down for the rollers. I have a couple cranks thought I might try it.

Alan

[John (Taylor) Gabrowski]

The versions we changed were the babbit Mark 25 cranks. We got them re-machined re-ground to Mark 20H specs. They were locally heat treated and used in the 20Hs. No breaknage since on any of them afterward when they were run. All still in the motors they were installed in. The heat treating looked weird as the crank was already re-ground and the heat treating left a crust on it that easily came off leaving the bearing surface a blue metal color and ready to use. Back then the re-gring was $30.00 and the heat treating was an additional $40.00 and that was in the early 1980s.