lower unit question

[mark abby]

1988 Mercury 150hp XR4 Magnum II

Lower Unit:

The upper drive shaft bearing was shot, so i removed it myself and will be replacing it soon. The lower bearing is fine.

The diagrams i look at show a shim under the bearing for backlash adjustments. However, there was no shim under the old bearing when removed. That being the case, can i install the new bearing without any regards to the shims that were never there?

Or, do i have to go thru all the backlash checks?

the bearing was the only issue with the unit...everything else is in perfect condition and since i have not changed any gears or disassembled any thing other than removing the prop shaft assembly, i should not have to be concerned with the shimming.

correct?

 

[Faztbullet]

Re: lower unit question

If you have the original small diameter housing replace the pinion bearing as it will fail as this was the weakness of the Xr4 housings and yes you will need to reshim and set preload.

 

[mark abby]

Re: lower unit question

If you have the original small diameter housing replace the pinion bearing as it will fail as this was the weakness of the Xr4 housings and yes you will need to reshim and set preload.

thanks.

not really what i wanted to hear, but, i guess if it has to be done, it has to be done.

i'm doing this myself and i don't really have all the special tools required in the manual, so i was hoping i could get lucky.

thanks again!!

 

[mark abby]

Re: lower unit question

another question comes up:

where are the or how do i find the serial numbers for the lower unit? i looked all over the housing but don't see any.

 

[Faztbullet]

Re: lower unit question

Serial number is on motor the casting number is on the housing , loo in the housing where exhaust exits from motor into lower unit.

 

[mark abby]

Re: lower unit question

found them!

thanks again!!!

and now it adds to the confusion. no wonder i'm having a hard time with the service manual diagrams.

my numbers are 1674-814247-c. looking that up on line says it's an XR6 lower unit, but, one place said it's an XR4.

can any one ID this for me for sure? i'd hate to do anything thinking it's one type while being the other...or, are they one in the same?

 

[Dukedog]

Re: lower unit question

Can be either. They used whatever when they were in mid block style change. A lot of tha later XR4's got tha XR6 gearcase. Both are tha small hub with 4 inlet holes. Trying ta remember but think tha XR4 there's a difference at tha tail end. Tha cavitation plate ends even with "snout" or "tailshaft", lower unit casting not tha exhaust, at tha very back. Tha XR6 looks like all tha rest. Tha cavitation plate extends a coupla inches past tha end of tha "snout" or "tailshaft". Both have a 4 1/4' hub.

This is tha 4 1/4" XR6 (mine). You can see how tha cav. plate extends out from tha "snout" or "tailshaft" , lower unit casting not tha exhaust, Tha XR4 cavitation plate ends flush or even with snout or tailshaft casting. On tha picture of tha complete motor (XR4, not mine) you can see how tha cav plate and "snout" or "tailshaft" or almost completely even............

 

[mark abby]

Re: lower unit question

thanks, dukedog.

then i guess i have the XR6 because mine is exactly like your first picture.

the replacement i got looks like the second picture, so it must be the XR4.

i appreciate all the help you guys are giving!!!!!!!

this being my first boat (1989 astro quickfire 18c bass boat) the only problem i've had was the seized upper driveshaft bearing..which i'm working on during the winter months.

 

[Dukedog]

Re: lower unit question

Just a note. If ya don't have tha right tools and knowledge ta set up tha gearcase I recommend ya have it done. Changin' that bearing is gonna change pinion height so shimming will probably be different. Some say they can just "feel" it but thats just bulls&!t...........JMO