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TOPIC: Did I blow my lower unit ?

Did I blow my lower unit ? 2 years 1 month ago #127947

Title sounds provocative enough, hopefully get some good responses. Here we go; I have a 65 merc 1000 on my 67' 16 ft trihull. The current L/U is one I installed last season,it came of a 73 115. I run her pretty frequently, most weekends. The only issue ive had this season was with a trim cylinder which I replaced a few months ago. However ... I noticed the boat doing something odd at higher speeds. First noticed it while turninig pretty hard while going near plane speed,the engine revved up high, like it had come out of the water or something,which it had not. I noticed it do the same thing randomly at high speed a couple of other times, I just slowed down for a second and everything was fine. However a couple of days ago I was towing a large fella on the wake board and while we were at or near plane speed the same thing happened again however this time slowing down didnt help. I stopped and restarted the engine , when I attempted to put in gear it just kept revving up without fully engaging in gear. I checked it out after I got the boat home and the L/U and the control both seem ok. The prop spins freely in neutral, and locks into place when I shift into forward. I tried by hand to get it to disengage or pop out and it wouldnt. What could have caused this ? As always thanks for the help y'all

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Re:Did I blow my lower unit ? 2 years 1 month ago #127952

Put a mark on the end of your prop shaft and another mark on the body of your prop. Back into the boat launch, but keep the boat secured to the trailer, and start her up and shift into forward gear and attempt to accelerate. If the beast just revs up, stop, and see if the two marks still are aligned.
If not - your prop's rubber hub has failed.
doc

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Re:Did I blow my lower unit ? 2 years 1 month ago #127954

  • Dr.Go!
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That was my first thought. I too sometimes forget that if I want take down one of our old "decorative" props off of the prop "tree", I need to have the prop shop re-hub the older prop rubber since time, weather, sun and use will catch up to it eventually and cause it to spin on the hub. of course that is much better news than lower unit problems.

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Dr.Go!

Re:Did I blow my lower unit ? 2 years 1 month ago #127958

Thanks Doc, So the rubber hub is most likely my culprit ? Any other possibilities ? If it is the hub will I need to take it to a marine shop to get sorted ?

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Re:Did I blow my lower unit ? 2 years 1 month ago #127959

  • Robby321
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Bet the hub is shot...

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Re:Did I blow my lower unit ? 2 years 1 month ago #127970

I just replaced a prop for a guy with the very same problem and he was thinking his lower unit was shot.
First test is put the motor in reverse because that locks up the gearcase and wont ratchet like forward would. grab the prop and see if you can move it right or left against compression if it move at all the hub is cooked. Also second thing is pull the prop and look at the back of it and if the rubber is cracked or looks chewed up its shot. Very common problem.

Put on a spare prop to water test too. Send the prop to a prop repair shop and not through a dealer. Dealers charge more. Find a prop shop in your area.
Bob

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Re:Did I blow my lower unit ? 2 years 4 weeks ago #128003

Not the hub. Was sure it had to be. Instead of testing the way Doc recommended, I decided to put a different prop on. I had one laying around that I pulled from my old lower unit that I destroyed by not winterizing properly that year. Took it to the lake today,launched but kept the boat attached to the winch cable and tried to get her to into gear, she wouldnt have it, tried forward and reverse. It did seem to have a noise I havent noticed before...kind of rattling, more pronounced when rpms where higher as I tried to engage the lower. Although the engine started up and idled normally, she wouldnt budge the boat, I trimmed up the beast to see if there was any movement from the prop as I throttled up, which there was not. I secured her to the trailer and drove the hour and a half home wondering what it could be. My next guess would be something in the shift linkage. As I said it does rev up when the throttle is moved in any direction, just not engaging the gears. Any advice on what else could have gone ?

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Re:Did I blow my lower unit ? 2 years 4 weeks ago #128004

  • ed-mc
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Was it pumping water? One possibility, the worst, is that the crankshaft splines are stripped. If it was pumping water, that ain't it, 'cause the driveshaft would be turning.

Other possibility, it's not shifting into gear because of a problem in the remote control box. Easy enough to check, see if the shift cable is moving the shift arm as it should. If not, disconnect the shift cable at the motor and manually shift.

Note that the shift arm should move all the way to the rear of the shift guide "rack" when in Reverse.

You may need to pull the lower unit to check it out. I'd also pop the drain plug and see what the oil looks like.

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Re:Did I blow my lower unit ? 2 years 4 weeks ago #128021

Thanks master Ed. The water did not seem to be pumping normally. Kind of sporadic if I remember right. I will inspect the cable and remote box, but I dont feel like thats where my problem is. I may try to start it up in a barrel (instead of muffs) just to confirm that its not pumping. Side note : I did see a 85 horse merc of a similar vintage on craigslist for 2 hundo. Ad said it had been rebuilt , but was "missing a few parts". May be worth investigating. Is there any other possibilities besides the control box or crankshaft ?

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Did I blow my lower unit ? 1 year 6 months ago #131781

Hey fellas, I hope its ok that im posting in this thread instead of starting a new one, but Im still on the same topic, staying here keeps me from having to repeat the entire story. More importantly I hope for a few replys, which are hard to come by over at the "jegos place" forum, its like a ghost town over there sometimes....I guess all the cool kids are over here !

So yesterday I finally got around to pulling the lower unit off to check things out. From the outside everything appeared normal, as it did last time I tried to figure this out. The prop spins free with the remote set at neutral, and locks up (one direction) when I put it into first. Upon pulling the lower off most everything seems normal, no lose parts or anything. My only observation was that the top of the driveshaft splines had some caked grease in there, which I will clean off.

I really hate the daunting task of reinstalling the lower unit. Not only is it heavy and cumbersome, mine has a extension section to accommodate the long shaft, and the extension part that mates the shift shaft to the shifter splines at the bottom of the l/u. This thing is a HUGE PIA ! I struggle for hours with it everytime. Trying to get fingers or a screwdriver in the tiny slot to make sure the extension bit falls correctly on the shifter knob (while my wife tries to hold the l/u in place. ....Its a good time ! lol. If there was a issue with the remote or the cable, I dont think it would have locked up the prop when shifted. I am going to just re assemble, and hope that it was the shifter extension bit coming lose somehow...otherwise it must be the part inside the powerhead that mates to the top of the driveshaft ? No ?

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Did I blow my lower unit ? 1 year 6 months ago #131786

When you say, "The prop spins free with the remote set at neutral, and locks up (one direction) when I put it into first.", what direction are you rotating the shift shaft?
When looking down at the shift shaft in the lower unit, if you turned the shift shaft counter-clockwise, and held the drive shaft stationary, the prop shaft is not supposed to turn. Then if you rotate the drive shaft clockwise, the prop shaft should turn counter-clockwise (Reverse gear)
If you turn the shift shaft clockwise (2 detents when starting in Reverse gear), and hold the driveshaft stationary, and rotate the prop shaft clockwise, you should hear & feel a repeating 'click-click-click'. If you turn the drive shaft clockwise, the prop shaft should turn clockwise. This indicates Forward gear.
If it passes these trouble-shoots, the possibility that the failure is inside the gear case are reduced significantly.
But if you find one of the sequences don't work as described, there is still a possibility that the clutch dog, its external spring, or its cross pin might have failed. I don't think this is the case, since your shift one way results in not being able to rotate the prop shaft, but,...
If it passes these trouble-shoots, check to see if the shift cable in the port side of the engine pan is actually moving forward or aft when someone shifts the control box into Forward, and then Reverse.
(the lower unit does not need to be installed during any of these tests).
Also remove the gear oil drain plug, and check the magnet for metal. A little is expected, but excessive shavings in recently replaced gear oil could indicates something is wrong inside. It could also just indicate that the operator is shifting too slowly into gear from Neutral.
Take a good look at the male & female splines of the driveshaft extension stub shaft too.
If you have a spare drive shaft, or can borrow one from a dealership's junk pile, stick it up into the crankshaft, and see if you can turn it without the flywheel moving. If it seems to be turning the flywheel & with the ignition key turned OFF, put vise-grip pliers on the driveshaft (use several layers of shop rags or card board to keep from marking the driveshaft) then firmly hold the drive shaft stationary while someone attempts to turn the flywheel clockwise with a 15/16" socket on a ratchet or breaker bar.
If the flywheel turns, but you can keep the driveshaft from turning, the female splines in the crankshaft could be rusted away - or stripped.
Keep us posted.
doc
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Did I blow my lower unit ? 1 year 6 months ago #131803

If I am not mistaken he has a 5" extension. Instead os finding another driveshaft just remove the extension and trial fit the driveshaft into the crankshaft that way to check for blown out splines. Maybe getting another driveshaft to try (given the hassle of dancing with that gearbox) would be easier IDK. Just a thought.
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Stay calm. Move on.

Did I blow my lower unit ? 1 year 6 months ago #131807

Thanks Clyde ! Great advice.....Will do

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Did I blow my lower unit ? 1 year 5 months ago #132298

So I finally got around to trying to perform some of the tests doc outlined. However... I noticed as tried to move the shift knob, that the piece below it looked broken. The shifter spins freely also, no resistance, nor did it seem to change what gear was engaged. here are a few pics I took of what appears to be the broken part. It is probably safe to assume that something also broke inside the lower, Im guessing this all means I will need to find a used functioning lower somewhere..
Attachments:

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Did I blow my lower unit ? 1 year 5 months ago #132301

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The black part on the shift shaft is the reverse lockout cam. It shows some wear, but is not broken.

If things are assembled correctly, the lower unit is currently in Neutral. Have you tried to move the shift shaft in the C-C-W direction? Or does it just spin 360 degrees with no resistance at all?

Note that in the forward direction (Clockwise) the shaft will have about 270 degrees of free-play due to the design of the shift mechanism.

All the shifting to Neutral and Reverse are done with the shift shaft going Counterclockwise.

HTH........ed

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Did I blow my lower unit ? 1 year 5 months ago #132304

Thanks again ed, the shift shaft seems to spin 360 with no resistance. The lower is not in neutral either. It was when I pulled it, but not now. Am I screwed ?

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Did I blow my lower unit ? 1 year 5 months ago #132305

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discoboater wrote: Thanks again ed, the shift shaft seems to spin 360 with no resistance. The lower is not in neutral either. It was when I pulled it, but not now. Am I screwed ?


Sounds like the shift cam (or other parts associated with shifting) may be broken. The L/U would have to come apart for repairs.

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Did I blow my lower unit ? 1 year 5 months ago #132306

Passed em all Doc ! So I very carefully re read docs instructions ...and realized I had not been doing them correctly. I was turning the prop not the drive shaft. I repeated the tests only turning the driveshaft clockwise , then adjusting the shift shaft. I got it to engage forward , reverse and neutral as instructed. However havent tried the gearbox dance just yet. need a buddy to help with that one. Will keep you all updated, thanks for helping as always.

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Did I blow my lower unit ? 1 year 4 months ago #132404

Stuck again ! Spent over 3 hours trying to get her back on track yesterday ...no luck. First try, got everything back together, went to test the shifter, we could only get the lower to engage in reverse, that was with the lever in forward. Knew we messed up the shift shaft. Pulled it all back apart, re tested the lower (forward, neutral, reverse) all good. Went to reinstall the lower (in neutral). However when we went to pull the shift lever back to neutral it wouldnt budge, it is now stuck in full forward, and cant be moved ! I noticed the lever in the pan, where the shift shaft goes through, is pushed all the way against the bottom carb, and the shaft appears to be unseated and about a inch higher than where it should be. I was not able to move the lever in the pan in any direction, The tension on the lower (shift) cable is noticeable. Please help, I need to get this thing out of my parking lot and out on the water ! How do I get the tension off this cable so I can shift back into neutral ? Or do I install the lower in 1st then try to shift back ? I also wonder if the problem is in the control box. Should I disconnect both cables on the port side ? I did notice the plastic lever that sits on the end of the bottom (shifter) cable does not do anything, I cant remove it, but I can turn it either direction freely.
Thanks again for any help fellas

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Did I blow my lower unit ? 1 year 4 months ago #132405

I also wanted to mention that I did test the splines on the driveshaft/ flywheel. I noticed the flywheel turned easily, unless I had the driveshaft ALL the way up in there. The flywheel would spin even with 1/2 inch between the extension plate and mid section housing. I presume the tolerance is just very close. At any rate, I knew that once installed, the lower would be fully seated, so all should work fine.

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Did I blow my lower unit ? 1 year 4 months ago #132406

Tech Doc – Installing the lower unit (gear case)

If you are confident that the shift cable and throttle cable were adjusted correctly prior to disassembly - and you prefer to reassemble in Forward gear,...Simply have a pal shift the control box's main handle into Forward gear and slowly continue to move the main handle forward as he would to advance the throttle. 
When you (standing off the port side of the Merc) see that the shift cable has stopped moving and the throttle is beginning to move, you can tell him to stop.
Now you are ready to focus on the lower unit.
There is about 180+ degrees of rotation of the lower shift shaft that is all Forward gear.  What you will want to do is rotate the lower shift shaft counter-clockwise through this 180+ degree rotation, until you feel the lower shift shaft stop.  Further counter-clockwise rotation of the lower shift shaft would result in shifting into Neutral gear & you don't want to do that - you want to stop rotating at this point.  Now the lower unit is in Forward gear and the lower shift shaft is in the correct position for when you put the lower unit up into place.
Before you put the lower unit back on, be sure and liberally grease the driveshaft splines, the lower unit studs, the 'boot' that the exhaust tube will go into, the bottom end of the exhaust tube, & the splines on the lower shift shaft.
Also have a 15/16" socket and ratchet or flex-bar on the flywheel nut in case you need to rotate the crankshaft to align its splines with the driveshaft splines.
Also make sure that you have the alignment piece that sets up into the bottom end of the mid-housing and holds the upper shift shaft's female coupler properly aligned.  (your power trim may not have had this piece, but there should be one in a mid-housing from a non-power trim mid-housing that will fit and aid in assembly.
Make sure that the cap-screw or allen head cap-screw that secures the trim tab (anode) is in place before installing the lower unit.
 
There are three critical steps to be aware of when putting the lower unit back on.
 
#1) As the driveshaft goes up into the mid-housing be sure that the copper water tube aligns and goes into the plastic alignment tube you will have installed in the top of the water pump housing.
#2) The driveshaft will butt up against the crankshaft next and as you continue to firmly hold the gear case up so that you can feel it when the driveshaft goes into the crankshaft,...You begin to slowly rotate the crankshaft (clockwise only) with the 15/16" socket wrench until you feel the gear case move upward ever so slightly.  Don't let go or you may loose the alignment.
#3) Finally,...It is time to try and get the lower shift shaft to go into the upper shift shaft.  Ideally it will align and the gear case will go on up into place.  Realistically,...You will want to try and get one or two threads started on the two front side studs.  One or two threads will be about it until you get the shift shaft aligned, but it will help hold the weight of the gear case too.
Now, with the two front side nuts barely holding onto a very few threads, hold upward on the gear case and see if the upper shift shaft has lifted up a bit from its seat under the bottom carburetor.
If it has lifted a bit - it is not aligned yet.  You will need to slowly move the arm on the top end of the upper shift shaft back-n-forth a smidge until you feel the shift shaft drop onto the lower shift shaft.
Hang onto the gear case so it won't slide back down a smidge and loose the connection.
If the shift shaft has properly coupled together, you should be able to push the gear case up enough to put a few more threads into the two side nuts.
Then slowly continue adding threads to the two front side nuts.
When you have about 1/4" of the very front stud protruding above the casting - you can put one of the thick washers and the nut on the front stud.
Once you are positive you have some good threads into the front nut - you can remove the two front side nuts and put their flat washers in place - then put the nuts back on and give them a few turns.
You should have about 1/4" of gap between the mid-housing and the gear case now & the upper shift shaft should be setting down on its bushing.
Now start the 3/8"NC cap-screw (9/16" socket required) and washer that goes in from the underside at the opening for the trim tab (anode).
Once you know that you have a couple threads started on this aft cap-screw and the gap appears equal from front to back between the mid-housing and the gear case, you can slowly turn the flywheel (clockwise only)  via the ratchet & 15/16" socket and see if the prop shaft begins to turn with the crankshaft.  If the prop shaft turns with the crankshaft it is time to test and see if you also have Neutral.
Ask your pal to shift the control handle back to Neutral position.
Now the prop shaft should turn silently and freely in both directions.
Don't try Reverse just yet.
If with the controller shifted back to Neutral the prop shaft turns freely both ways - finish tightening all nuts and the cap-screw until the gear case is up against the mid-housing.
Check the upper shift shaft periodically to insure it is not being pushed upward as you bring the gear case up tight against the mid-housing.
When it is time to check for Reverse, remember to turn the prop shaft slowly as your pal attempts the shift or it might not want to shift into Reverse due to the square-cut gears and shift dogs that require some motion to allow the shift to be completed.
Let me know how it goes.
doc

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