Merc 650 lower unit repair (newbie)

[87racer]

Hi all , this is a great forum and thanks for letting me in!! my problem is i have a 1965 merc 650 that is slipping reverse. i removed the L.U. and started disassemble . i got the big aluminum nut off (behind the prop) with the spanner wrench and am now to the bearing housing. it has a small square key in the bottom. how does that come out?? does the bearing housing pull out or unscrew?? any help would be appreciated.
thanks in advance cory

 

[Moody Blue]

Re: Merc 650 lower unit repair (newbie)

Welcome to iBoats 87racer.

I'm in the middle of a LU rebuild myself. My motor is a 1971 Merc 800 with same slipping in reverse problem AND metal chips/slivers in the oil

You are doing good if you got the carrier nut off in one piece. The bearing carrier PULLS out with the propshaft, reverse gear and bearings as one unit. The driveshaft pinion gear and forward gear will remain in the housing.

I have removed the carriers from two LU and will be repairing the better of the two. I used a slide hammer with a custom adapter nut that screws onto both the prop shaft and the slide hammer. The first carrier pulled out easily with only 3-4 pulls but the second one was a beast. I ended up having to heat the housing around the rear of the carrier with a torch then use the slide hammer. It finally came out but reluctantly.

Turns out the cause of my problems was a badly worn shift cam that was preventing the reverse gear from fully engaging. All the slipping was chewing up the clutchdog and reverse gear dogs.

There is a good post here about the same problem of removing the carrier

http://forums.iboats.com/showthread.php?t=391064

 

[87racer]

Re: Merc 650 lower unit repair (newbie)

THANK YOU SO VERY MUCH!! i will try a slide hammer . good info to know. at least if i get that out i can try to diagnose the problem. appreciate the post!!

 

[87racer]

Re: Merc 650 lower unit repair (newbie)

WOW that is about as complete of a DIY thread as i have seen!! there is alot of knowledge on here!! thanks all!

 

[Wingedwheel]

Re: Merc 650 lower unit repair (newbie)

That carrier nut unscrews. If you don't have the proper tool, you may have to drill and collapse it to get it out. Then you go to work with the slide hammer.

 

[87racer]

Re: Merc 650 lower unit repair (newbie)

it appears by looking at the pics on posts that i can pull the shaft (slide hammer) with the housing or use a puller and pull against the shaft to get the housing out seperately. am i thinking correctly?? i have fabbed up some tools and will try it today. thanks

 

[Moody Blue]

Re: Merc 650 lower unit repair (newbie)

Slide hammer screws onto the prop shaft (will need to make an adapter nut between propshaft threads and slide hammer). Slide hammer does all the work, but you will need to clamp the LU down good. Be sure to pull STRAIGHT back on the slide hammer to avoid twisting the carrier in the housing as it slides out.

Puller will use the body of the LU to pry the carrier and prop shaft out of the housing. You can either attach to the prop shaft again or devise hooks to grab the back side of the exposed carrier. I've found using pullers in the past that it's best to put the parts under tension with the puller then smack the shaft (carefully) with a hammer to jarr the assy loose. Constant tension doesn't seem to work as effectively.

Just re-read your last post. You don't pull the carrier assy over the prop shaft, they come out as an assy no matter which way you go about it..

 

[87racer]

Re: Merc 650 lower unit repair (newbie)

ok, got the bearing assy out using a puller with 2 peices of chain cut to hook the bearing gusset area!, with heat and tapping. next question is how to get the vertical shaft out. i took the water pump assy out and the pinion nut off and it wont come out. i see a snap ring on the top side. any ideas??? thanks in advance

 

[Wingedwheel]

Re: Merc 650 lower unit repair (newbie)

If you've got the pinion nut off it should come out. Sometimes they are a little"stubborn".

 

[87racer]

Re: Merc 650 lower unit repair (newbie)

so after the pinion nut is off does it just pop out the top?? i couldnt see a way to hook up a puller

 

[87racer]

Re: Merc 650 lower unit repair (newbie)

ok i was looking into the L.U and noticed the reverse shift mechanism. is it a nub that pushes the shaft aft to make reverse?? if so if it is worn would it make reverse not fully engage or "slip" ??

 

[Moody Blue]

Re: Merc 650 lower unit repair (newbie)

so after the pinion nut is off does it just pop out the top?? i couldnt see a way to hook up a puller

That pinion gear is hard to get off the splined driveshaft end. I clamped the driveshaft in a vise (didn't care if it got damaged because I am replacing it) and using a 5 Ib hammer and piece of 2x4 I beat the lower unit off the driveshaft. I had to beat it pretty hard numerous times before it popped off.

As for the shift cam, yes, if it's really worn then it will not push the cam follower far enough to fully engage the dogs.

 

[87racer]

Re: Merc 650 lower unit repair (newbie)

great idea thanks. i will try it now. then i will assume i have to somehow remove the ring gear to expose the shift assy correct??....thanks again to all for your great comments!!

 

[Moody Blue]

Re: Merc 650 lower unit repair (newbie)

Nope, once the pinion gear is out of the way, the forward gear virtually falls out. It's a tapered bearing, so the race is pressed into the housing but the gear just lifts out.

The shift cam is loosely captured between two bosses and is a splined fit over the lower shift rod. Before removing it, pay attention to the orientation of it so you can get it back together right the first time .

One more thing that has not been mentioned. Keep track of the shims you find in different locations as you take things apart. You will need to re-use them for reassembly.

Question for you. What tools did you use to remove the pinion nut from the driveshaft?

 

[87racer]

Re: Merc 650 lower unit repair (newbie)

an old antique 3/4 wrench. i located the shift into fwd and marked it at the beginning

 

[87racer]

Re: Merc 650 lower unit repair (newbie)

hi, thanks for the wood block idea, it worked great! now i see some wear on the cam for the reverse .how do i know what is all worn in the drivetrain? i am also looking at wear on the 3 cogs on the reverse gear. does the shift rod just pull up??

 

[Moody Blue]

Re: Merc 650 lower unit repair (newbie)

Pretty hard to describe a good gear vs a worn gear. The wear points should be centered on the teeth and be eliptical in shape. The cogs that engage the clutchdog should have sharp edges, not angled or rounded.

The shift cam comes new with a "track" machined in it for the cam follower to ride in. A worn cam will have a wider and deeper track with varying depths. Check the cam follower for excess wear as well.

The lower shift shaft is captured in the lower unit by the shift shaft bushing. The bushing is screwed into the lower unit and requires a "special tool" to remove it. Once the bushing is removed, the shift shaft just lifts out from the top. The shift cam will then fall off the end of the shift shaft.

 

[87racer]

Re: Merc 650 lower unit repair (newbie)

thanks Moody! i made a tool and removed all parts. went to a local marine junk yard Twin Cities Outboard. they have it all!!! piles of stuff!! got new cam and used follower also shift shaft was bent. going to try and put it together now,,,thanks again

 

[87racer]

Re: Merc 650 lower unit repair (newbie)

ok one more question. i have it together and i found 1 o-ring (about the size of a quarter) laying on my bench. i fear it is suppose to be inside somewhere but cant find a pic with it in place. also it could be from one of my many auto fix it jobs. any ideas?? it seems to be the perfect size of the vertical shaft but i cant figure where it goes.......thanks

 

[Moody Blue]

Re: Merc 650 lower unit repair (newbie)

Only 0-ring inside the L/U is about 4" diameter.

The size as you described could be the o-ring from the top of the driveshaft, IF you motor uses one. Some do and some don't.

On some driveshafts, there is a grove just below the crankshaft splines for an o-ring. It is to help prevent water from entering the driveshaft/crankshaft splined joint and seizing the two together.