mercruiser Lower gearcase spring loaded drive shaft

[ringmaster]

i have 2 outdrives one came off a mercruiser with a 225 and the other is from a 233. now what i dont understand is the one off the 225 doesnt have the spring loaded button on top of the lower unit driveshaft. the one from my 233 does. what is this button for and if i run the outdrive that doesnt have one what will it do to it?

 

[JustJason]

Re: mercruiser Lower gearcase spring loaded drive shaft

the button is the old way merc preloaded the driveshaft bearing. when you assemble certain gearcases 1 of the first steps is to set the rolling torque on certain bearings.
method 1, the old method, is to torque the driveshaft nut to a fixed torque setting and let the pin take care of the rest.
method 2, the newer method, is to slowly torque the nut and test the rolling torque with a spring gauge or a dial type torque wrench on the driveshaft.

as far as mixing and matching the lowers... i'd be a bit leary because even if it bolts up there may be more considerations. The upper gearcase driveshaft may or may not engage the lower driveshaft properly (ie~ the uppers may use 2 different size driveshafts)

I'd head over to mercruiserparts.com and do a part lookup by serial number. if the uppers of the original gearcase, and the other gearcase, are identical then go for it. If the uppers are not identical, they are not for a reason, and it's probably not best to bolt it up.

 

[rodbolt]

Re: mercruiser Lower gearcase spring loaded drive shaft

the difference is in the lower driveshaft bearing design.
on the style that uses a preload pin the race is below the bearing and the preload pin simply pushes down on the bearing to keep the shaft from bouncing up and down at low speeds, the design without the preload pin the race is above the bearing and is preloaded with a rolling torque and a spring loaded fixture. normal gear pushoff keeps the slack out when running.
the two cases can be interchanged with no worries.
however occasionally we see older cases that the preload pin is missing.
look at the top of the shaft,if there is a hole with 3 stake marks then most likly the pin is missing.
if not its most likly a later style MR type lower.

 

[ringmaster]

Re: mercruiser Lower gearcase spring loaded drive shaft

i did go talk to my local marine repair guy and it is a newer mr style so that is correct its the upper that is giving me issues the gearing is off he said to just put my origenal upper back on and the newr lower. in the end i should have just got my origenal lower fixed and would have been better off.