Noisy in Reverse . . . Atomic 4

[Jerry Magnuson]

The Admiral and I just launched our new 1979 c30 "Defiance" last weekend. So far she has been living up to her name. The Admiral says that Defiance did not want to leave warm Lake Powell to come to the cold of western Montana. But my check book said she had to !Atomic 4 purrs like a cat,until I shift intoreverse . . then this gawd-awful sound comes from the general area of the engine compartement. Boat backs up ok but the noise from the transmission reminds me of the old non synchronized manual transmissions. (Yes I am old enough to remember those.)I checked the archives and found several remarks by owners the indicate that the Atomic 4 transmission may be known to be noisy in reverse. What say all of you ?

 

[Rob Rich]

You got it bud...

The A-4's reverse gear is incredibly loud. Sounds like it is about to eat itself alive. I asked my surveyor about it and he confirmed it. That's just the way she sounds.I won't launch into a long explanation about it, but it has something to do with the fact that reverse gear is not directly engaged. I believe it has a planetary drive that actually revolves around the clutch coupling, reversing the direction of the shaft. For a better explanation, check out the link below, or subscribe to the e-mail list serv at sailnet.com - the list serve is extremely helpful. Enjoy your engine. Give it proper routine maintenance and you will really fall in love with it. RobThe below quote explains the reverse gear a little better:"REVERSE OPERATION: In reverse the shifting linkage both frees the clutch plates and thru the flat metal reversing bar (on the top starboard side) it tightens a Brake Band around the outside of the reverse gear case to prevent it from turning, this forces pinion gears to turn the tail shaft (and prop shaft) in the reverse direction. In reverse, the tail shaft rotates OPPOSITE to the crankshaft, but at only 75% of engine RPM (1.33:1). The reverse speed of your prop is only 75% of the forward speed for the same engine rpm's, which is why you have to use a lot higher RPM's in reverse to accomplish a similar response from the prop. You will not feel a Detente when shifting into reverse, the reverse adjustment determines how large a neutral zone you feel in the shift linkage before reverse gear engages. You do not want this zone to be excessively large as it might exceed the range of travel in your shift linkage. You can tell when reverse is engaged because it makes a loud whining sound, this is normal. "