Reinstalling Lower Unit Mercruiser

"Hey guys, just ran into uniqu

"Hey guys, just ran into unique situation. My Boat is a 1984 Mercruiser. It had an Alpha Cased Lower Unit but had a preload pin on the upper drive shaft which they tell me was only done possibly during that year as they transitioned. I took my bad lower unit off and took it to a guy to tear down and rebuild with parts from another donor alpha ( type 1 ) unit but he said that the parts would not interchange because of the preload shaft etc...... SO I found an older style pre alpha lower unit with the preload pin ( used and not leaking, gears sound okay, oil looks fine and no metal residue ) that I am going to attempt to install. Is there any trick to installing them? It appears just getting the splines to line up and making sure the o-ring where the oil goes up the passage way to the upper part of the lower unit. I plan to replace the impeller as well. Does it make any difference what gear it is in - forward or reverse.

I did get to see the parts from my old unit and it had about 4 teeth gone on the forward ring gear. Of course there were damaged areas on the pinion gear but it was not terrible or chipped/broken.

Any tips would be appreciated.

thanks all,

Robert"

"Does it make any differen

"Does it make any difference what gear it is in? Both upper & lower halves need to be in forward.

"okay well, I think I had the

"okay well, I think I had the top and bottom in forward when I installed the lower unit. It was difficult to get lined up for sure.

Replacing the water pump was not too difficult. Old one didnt really look that bad.

So now for the bad news, when I put the shift lever in forward or reverse, the prop does not lock into gear, it just clicks when you turn the prop like a card in the bicycle spokes. It spins freely in neutral and is very quiet so it sounds like the bearings are good.

I did check and the metal mechanism under the lower unit moves the same distance as it did before I installed the lower unit so it is going from basically 12 oclock to about 3 oclock. when changing from forward - neutral then reverse.

So, what in the world did I do wrong or did I buy a defective used lower unit?

I was thinking when you put it into gear it would lock the prop not just click."

"[b]"I was thinking when y

""I was thinking when you put it into gear it would lock the prop not just click."

Ayuh,... It should Lock in 1 direction,+ Click in the other direction..."

"Make sure that when you put i

"Make sure that when you put it in gear it locks in one direction but free in the opposite direction and it will click as you turn it opposite of the gear you put it in. You may need to make small adjustments and I mean "small" because these outdrives have little play when goin from one gear to the other. Have a buddy with you when you do this, its easier. <Jim>"

"uhm, small adjustments to wha

"uhm, small adjustments to what? Sorry to have to ask so much about what to do, this is the first time for me to ever do anything like this because i couldn't find anyone in my area that would work on my boat because it is over 20 years old. I found a shade tree guy that didn't sound too reliable and then one dealer that I took my boat to flat out lied to me or maybe he was not familiar with lower units because he told me that a pre alpha drive and alpha gen one would not work on my boat. So here I am....."

any ideas what might need to b

any ideas what might need to be adjusted? Remove and reinstall or something?

"check in here
[url=""]http:

"check in here
http://www.boatfix.com/merc/Techbk/94/94hsa2.pdf"

"Here is a adjustment proceedu

"Here is a adjustment proceedure I wrote.



Trim out drive up 2 inches from all the way down.
Take keys out of ignition!!!!!!!!!!!
Have a second person stand at the prop.
You, remove the short shift cable from the shift bracket.
After the cable has been removed, push the plastic cable end all the way in and hold in place while prop is being spun C’Clockwise..
Have second person rotate prop counter clock wise until the prop is fully engaged and wont turn anymore. Maintain light effort on shift cable plastic end pushing it to keep forward engaged.

Measure the distance from the center of the brass trunion to the center of the round mounting hole in the plastic end. Adjust trunion to make that distance 6 inches. no more no less! In cases where the shift cable is old but still works well you can adjust this dimension to 5 15/16”. NO MORE.

Put shift control handle in forward FULL throttle position.
Remove the control shift cable from shift bracket at this time.

Install short shift cable back onto bracket at this time.

Take the shift control cable and adjust the trunion so it fits perfectly back into the shift bracket.
Before installing it turn the brass trunion 4 complete turns away from the plastic end and reinstall into shift bracket.

Now put shift control handle in the neutral position.
Have second person spin prop, it should spin freely.
Put shift control into the forward detent position at ~ 10:00 position. NO FUTHER.
Have the second person rotate the prop counter clockwise. You should have solid engagement with no ability to continue to turn the prop.

Now shift back into neutral. Prop should spin freely with no clacking or clunking.

Now shift to reverse to the 2:00 o’clock position detent NO FURTHER!!

Have the second person spin the prop clockwise.

If you have positive engagement with no clunking or jumping out of engagement, you are done.

If it does not fully engage into reverse than look at the shift bracket where the short shift cable mounts and there is a slot. Loosen the 7/16 hex that is touching the bracket and move the stud so you are pulling the short cable.

Try this and retest in water under load.



This should get you close if not rite on. If not you may need a new cable. (short shift cable)"

"I am headed to the Barn now &

"I am headed to the Barn now ( well after I eat my Wheaties ) to get to work on it, Thanks so much, stay tuned!!!!

Also if I can con my wife in to turning the prop."

"oh one more thing, i noticed

"oh one more thing, i noticed in these instructions when it is in forward you have the prop being spun CC, my prop spins C when going forward, are these instructions written for a C or CC lower unit.

Or when a prop is fully engaged in forward or reverse should it not turn in either direction?"

"okay I have news...... I didn

"okay I have news...... I didnt adjust anything yet, just lowered the unit to 2 inches above the ground, it engages in gear like you describe here, when I put the shift lever at 10 o'clock ( forward ) and attempt to spin the prop CC it locks and cannot be turned, if I turn it C it clicks. Maybe it is supposed to click going in the wrong direction ( stupid me ) I thought I should be trying to turn the prop in the direction it would be moving the boat. I get it now that the motor would be engaging it in the opposite direction - DOH!!!

When I put the shift lever in Reverse and attempt to turn the prop C it locks and cannot be turned if I try to turn it CC it is more difficult to turn than C in forward and doesnt click but is more of a thud type sound. I guess maybe it is okay and I should not be turning it against the grain.

This unit shifts so much easier than my old one and the 10 oclock and 2 oclock positions just click right into place my old unit was kind of like grinding into gear on my old tractor.

Is the moral of the story, don't turn the prop in the opposite direction, it should click?

It definately spins freely in neutral with no noises what so ever."

You are good to go!!

You are good to go!!

"Update.....I went ahead and w

"Update.....I went ahead and went through the adjustment settings because in the 10 o'clock detent in the shift lever for forward, it would sometimes not quite engage totally and click a couple times before engaging where you could not turn the prop CC.

The 6 inch measurement was right on the money, so I only had to rotate the Brass Trunion one full revolution and it now engages totally at the 10 o'clock position. Is quiet in both directions in the middle and engages perfect in reverse at the 2 o'clock detent in the shift handle.

Oh, by the way, you guys forgot to remind me when you are installing the lower unit not to forget to put the two center nuts in the housing before you get it too high because they will not fit in there over the studs once it is tightened down - HA!!! So I had to lower everything down, because I had these two lock nuts left over (hmmm, where do these go) then got the shift linkage selector out of position and so on.....I am sure next time it will be easier and I won't make that mistake again I hope.

So, now I need to clean out everything good before I put in new lower unit lubricant. I pulled the top cover off and it shows signs of contaminated oil residue from the bearings and gears going out of the lower unit.

Would diesel be okay to put in to flush things out, or gasoline, etc......

I thought I would just pull the 4 bolts off the top and flush everything out and let it run out the bottom hole where you fill the lower unit.

How about putting in new oil then put it in forward and reverse hooked up to the garden hose adapter with the engine idling, or is it not a good idea to put one in gear when its not in the water?

I was thinking about putting a bottle of oil in it then running it a bit then draining and putting in more new oil and calling it good.

Any recommendations?"

Just refill from the bottom wi

Just refill from the bottom with there HIGH PERFORMANCE gear lube and be done with it.

The outdrive uses ~36 oz.

If you can I would also pressure check the outdrive to 15 psi and it should hold it for 2 minutes.

so if I plug the bottom fill h

so if I plug the bottom fill hole and then stick some sort of air chuck in the top oil level check hole and then put air in from my air compressor woudl that work?

"Have a regulator in line and

"Have a regulator in line and set to a MAX of 15 psi. If you can install a shut off valve between the source and the guage so you can see it bleed down if there is a leak.


"

do i do the pressure test with

do i do the pressure test with oil in it or without

just wondered if i am testing

just wondered if i am testing for leaking air or leaking oil

No oil in outdrive and the air

No oil in outdrive and the air will show a leak.

A merc outdrive actually only produces approx 7-9 psi and they do NOT have a specification I am aware of. OMC does have a specification and it is/was 17 psi so I have adapted 15 psi for mercs.

This is what I test EVERY outdrive I service no matter what that service is.

If it has a leaky seal this will show it. Also you must be in a quiet area. Back ground noise will interfere with hearing where it is leaking if there is one

"""just wondered i

"""just wondered if i am testing for leaking air or leaking oil""

One reveals the other...................

"gotcha, i will isolate myself

"gotcha, i will isolate myself from noisy kids, dogs, and turn off the radio while listening, also can watch for reduction in pressure as I think i have an extra pressure gauge that is just sitting I can rig up when I test it.

hiss shoudl reveal where the bad seal is - Fingers, arms, legs, toes and EYEs crossed"