Will a lower unit from a '77 Merc 850 work on a '73 850?

[SCSJR]

I have a 1973 Merc 850(85hp-#3616811). The lower unit is bad. Will a lower unit from a 1977 Merc 850 (#4595979) fit and work?.

Thanks in advance

 

[emckelvy]

Re: Will a lower unit from a '77 Merc 850 work on a '73 850?

Yes, the newer lower unit will bolt right up to the older motor. Note that the newer lower unit may or may not have a preload pin at the end of the driveshaft, whereas your older motor, by the parts diagrams, is supposed to have one.

This feature is used in lower units with a tapered driveshaft bearing. Units without preload pin use a 'straight' driveshaft bearing and don't need the pin.

Whether the replacement is the type with a preload pin or not will have no effect on the motor's operation.

If the lower unit does have a preload pin, make sure the pin is free to move. You can easily check this by giving the end of the pin a stout rap with a small ball-peen or equivalent hammer. Use some penetrating oil to free-up the pin if it's stuck.

HTH...........ed

 

[SCSJR]

Re: Will a lower unit from a '77 Merc 850 work on a '73 850?

Thanks Again Ed...

I got a line on a '70 850 lu too (closer to home). I'll keep you posted how he project goes.

 

[SCSJR]

Re: Will a lower unit from a '77 Merc 850 work on a '73 850?

Well, after some shipping delay, got a L.U. from the '77 850. Checking it over and replacing water pump, seals, & shaft seals before bolting up. Looks like it's been sitting a while. Flushing fresh oil through the gear case too. No metal or water. Hope to bolt it up & test it later this week. Thanks to Ed for the great pointers on items to check.