Atomic 4 Transmission Slippage? - SailNet Community

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Old 08-22-2006
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Atomic 4 Transmission Slippage?

Hello All,

at the beginning of the season i replaced my ignition system, (coil, cap, plugs, etc.) to address problems with no/little power in forward and fine in reverse. i also replaced the carburetor and added a secondary fuel filter. i adusted the timing and was able to get up to about 4.5 - 5 knots max. whenever i would push the rpms to go faster the transmission would slip and rev very high. i would have to throttle down and then up in order for it to catch again. in mid july i let the boat sit for about 2 to 2.5 weeks and when i returned the max i was able to get was maybe 2.5 to 3 knots in forward. again reverse was/is fine. i took the boat out and reset the timing again but she still will give me very little power in forward and slips. a friend told me i may have stripped something in the transmission since i have had the boat for 3 years and have always sailed with the engine in neutral. i don't think there is anything on the prop. just before the season started i did a short haul had the bottom washed and new zincs installed.

Can anyone help with this issue.


BTW - i sent this question to Don Moyer earlier today.
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Old 02-07-2007
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Tranny can be adjusted. Behind the engine there is an access plate with 4 screws. Remove and there is a large dia nut with grooves in it. This is what needs tightening. It has been a while since I looked at mine so I dont recall specifics. This should get you started.

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Old 02-07-2007
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Scroll down on the link to find directions to adjust the trans on an Atomic 4. We did this as part of a two week crash rehab of an Ericson 29 we borrowed to cruise the Bahamas for the winter several years ago.
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Old 06-19-2007
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I know this thread is a few months old, but I thought the following would be helpful:

Refer to photo for description below.

The reversing gear on the Atomic 4, what many refer to as the transmission, is easily adjusted.

You will need only a few tools:

1/2" wrench
3/4" wrench
Large flathead screwdriver
Gasket (available from Moyer Marine HERE)
Permaflex gasket sealant

Before removing the cover plate, put the motor in neutral. You should be able to rotate the shaft at the coupling by hand. Once that is done, remove the cover plate.

The plate for the reversing gear cover is held in place with four half inch bolts, which are easily removed. Once the bolts are removed, the plate slides right off. When the plate is removed, you should see the assembly in the photo above.

The shaft should be spun so the lockscrew is positioned at the 12 o'clock position and visible as illustrated in the above photo. The lock screw and the adjusting collar (which is the gear the lockscrew secures) adjust the forward gear. The reverse adjusting screw adjusts, you guessed it, the reverse gear.

Adjust the forward gear first. This is adjusted by manipulating the adjusting collar. If the collar is moved to the right, it will tighten it. So, if your forward gear slips while engaged - which is common - you would move the collar to the right.

To move the collar, back out the lockscrew until it no longer engages the gear. IT IS CRITICALLY IMPORTANT THAT YOU DO NOT REMOVE THE LOCKSCREW FULLY. If it falls into the oil beneath the assembly, you're in for a long afternoon. Once the lockscrew is backed out, the collar will be able to move by hand. If it sticks a bit at first, apply steady, controlled pressure. You need to be able to monitor how much you adjust it. It typically requires only a notch or two to be sufficient.

When the collar is adjusted, simply back the lockscrew back down. It is important to be sure it fits securely into the teeth of the adjusting collar. Also, do not over-tighten the lockscrew.

The procedure for adjusting the reverse gear is equally straightforward. The gear is adjusted by a 3/4" inch bolt called the reverse adjusting screw, again see above photo. If you are slipping in reverse, tighten the bolt; if you cannot engage reverse fully, loosen the bolt slightly. Do not overtighten the bolt as the retaining plate can break.

Test your adjustments by engaging forward and reverse with your shift lever. The forward gear should engage firmly after passing through it's detente. The reverse gear does not have a detente, so just go by feel. You should be able to push your gear shift fully into the reverse position. If you cannot, then you need to readjust.

After this, simply replace the gasket and reinstall the cover plate.

TIP: You may want to go ahead and change your oil while the cover plate is off. The Atomic 4 is designed so the engine and the reversing gear share the same oil. Simply pump the oil out of the easily reached bottom of the reversing gear assembly. Not only is this far easier than sucking it out of the oil level tube, you can usually get more oil as you can reach lower into the assembly than the oil level tube will.
HDChopper and kmteed03 like this.

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