1984, 1985, 1986 Alpha Castle Nut Replacement
writes 05/14/03 :
I have a 1986 Larson DC215 with a 170
Mercruiser Alpha One out drive. The unit shifts fine in the drive way with the
ear-muffs on but tends to kick out immediately back into neutral when it is under
power. No particular speed. I've already replaced and adjusted the lower
shift cable. I was told that my clutch dog may be worn and needs to be replaced.
Sound familiar? If so, how big a job is it to replace the clutch or should I
leave it up to the pros? The boat is still in good shape but, we aren't going to
spend too much more money on it.
Thanks for any input. Jace Tuccio
Our reply was :
On 1984, 1985 & 1986
Alpha models, MerCruiser put the wrong heat treat on a small shifting nut in the
lower unit. If yours is worn down to far, you will never get the shift cable
adjusted properly. If you take it to the pros, they will sell you a new set of
gears and Lord only knows what else.
It is possible that the
clutch and gears are worn and need to be replaced but a lot of the time you
can get away with just turning the clutch around and replacing the small
castle nut located at the very inside end of the propeller shaft assembly.
If you remove
your drive from the boat, you can check to see if you have a bad castle nut without
having to disassemble the lower unit.
To check it with
the drive off the boat :
the propeller shaft in a counterclockwise direction while you turn the brass
shift lever on the outdrive in a clockwise direction until they both lock up.
Keep light tension on the prop shaft and see if you have any left to right
movement on the brass shifting lever. There should be very little. If you have a
lot of movement, the castle nut most likely needs to be replaced.
To replace it,
the upper and lower housings have to be separated and the lower needs to be
required are as follows :
Carrier Wrench # 0190
Tooth Vertical Drive Shaft Tool # 0220
Nut Tool For Under The Water Pump # 5500
small castle nut ( shown ) goes on the end of the shift cable spool assembly (
shown ). It is held in place with a cotter pin. In 1984, 1985 & 1986
MerCruiser only put a 10 rockwell on this nut. It was suppose to have at lease a
30 rockwell. The bottom shoulder of this nut, on some drives, will wear down as
much as 1/8 of an inch. This makes adjusting the lower shift cable impossible
because the cable has to move such a great distance before the shift spool even
starts to move the clutch.
We make our own
castle nuts with a 50 rockwell on them.
of 05/10/2019 we only have 1 left. We will no longer sell this separately.
Order # 6888