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1990 4.3L alpha 1 Troubleshooting help

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steelersman224

Member
hello all,

I was looking for some pointers on how to trouble shoot my mercruiser. I've been an outboard guy my whole life and have been through them top to bottom and this is my first I/O. I was at the lake Saturday when I lost the ability to shift it into gear, the boat was in gear when it slipped out and there was a grinding noise and the RPM's jumped. I was noticing a chatter/whine coming from the lower unit earlier in the day as well as some smoke. I'm praying that its not the engine coupler, but what are some checks that I can do before going to the nuclear option? I understand that it could just be a shift cable and I can rule that out, but what are some other things I should rule out before asking to borrow my buddies engine hoist? if its the prop hub how to I diagnose that?
 
steelersman224 said:
hello all,

I was looking for some pointers on how to trouble shoot my mercruiser. I've been an outboard guy my whole life and have been through them top to bottom and this is my first I/O. I was at the lake Saturday when I lost the ability to shift it into gear, the boat was in gear when it slipped out and there was a grinding noise and the RPM's jumped. I was noticing a chatter/whine coming from the lower unit earlier in the day as well as some smoke. I'm praying that its not the engine coupler, but what are some checks that I can do before going to the nuclear option? I understand that it could just be a shift cable and I can rule that out, but what are some other things I should rule out before asking to borrow my buddies engine hoist? if its the prop hub how to I diagnose that?
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Drain the gear oil from and look for metal pieces. Pull the drive inspect the coupler from the transom, clanging may have been driveshaft splines and coupler splines shredding. Based off what you say would suspect coupler or upper gears in outdrive shredded. If coupler might be due to drive misalignment so check that before pulling the engine.

If metal comes out with drive oil pull top cap from drive and have a look. On a gen 1 drive with no lube bottle if the input shaft seal leaks into bellows upper gears run dry.

When you say there was smoke is that from inside the engine compartment?
 
Dieter said:
Drain the gear oil from and look for metal pieces. Pull the drive inspect the coupler from the transom, clanging may have been driveshaft splines and coupler splines shredding. Based off what you say would suspect coupler or upper gears in outdrive shredded. If coupler might be due to drive misalignment so check that before pulling the engine.

If metal comes out with drive oil pull top cap from drive and have a look. On a gen 1 drive with no lube bottle if the input shaft seal leaks into bellows upper gears run dry.

When you say there was smoke is that from inside the engine compartment?
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Not sure where the source of the smoke was coming from, just smelled and saw smoke when I would start the motor. The motor is a crate motor brand new from the dealer where I bought it, so I don't think its burning oil or anything like that. My lower unit is a gen one with no lube bottle. I'm not sure if it's typical of an I/O, but when I went to swamp the impeller right before this trip when I separated the skeg and prop part from the cavitation plate gear oil was leaking out.
 
steelersman224 said:
Not sure where the source of the smoke was coming from, just smelled and saw smoke when I would start the motor. The motor is a crate motor brand new from the dealer where I bought it, so I don't think its burning oil or anything like that. My lower unit is a gen one with no lube bottle. I'm not sure if it's typical of an I/O, but when I went to swamp the impeller right before this trip when I separated the skeg and prop part from the cavitation plate gear oil was leaking out.
Click to expand...

1. You should have included that YOU SWAPPED IMPELLER in your first post...ugh!!!

2. Of course gear oil leaks out when the upper and lower are seperated.. what would make you think otherwise?

3. Did you refill out drive with gear oil after swapping impeller?
If no, then you more than likely took out the upper cap bearing and possibly the upper gear set.

4. on trailer, not running, shift into forward gear, can you turn prop C'clockwise?
If you can (which should not happen) then either stripped gears or spun hub. Have someone watch to see if drive shaft is spinning when doing this at back of engine. If gears and coupler are good, you should not be able to spin prop by hand. If drive shaft spins freely at coupler, the coupler is toast.
 
steelersman224 said:
Not sure where the source of the smoke was coming from, just smelled and saw smoke when I would start the motor. The motor is a crate motor brand new from the dealer where I bought it, so I don't think its burning oil or anything like that. My lower unit is a gen one with no lube bottle. I'm not sure if it's typical of an I/O, but when I went to swamp the impeller right before this trip when I separated the skeg and prop part from the cavitation plate gear oil was leaking out.
Click to expand...
Smoke was inside or outside the boat ? If the engine was just installed was alignment checked? Normal some gear oil comes out when the halves of drive are separated. A lot will come out if it wasnt drained. You refilled after doing the water pump ?

between what Jack and I wrote you can figure out what is going on.
 
kghost said:
1. You should have included that YOU SWAPPED IMPELLER in your first post...ugh!!!

2. Of course gear oil leaks out when the upper and lower are seperated.. what would make you think otherwise?

3. Did you refill out drive with gear oil after swapping impeller?
If no, then you more than likely took out the upper cap bearing and possibly the upper gear set.

4. on trailer, not running, shift into forward gear, can you turn prop C'clockwise?
If you can (which should not happen) then either stripped gears or spun hub. Have someone watch to see if drive shaft is spinning when doing this at back of engine. If gears and coupler are good, you should not be able to spin prop by hand. If drive shaft spins freely at coupler, the coupler is toast.
Click to expand...
Thanks for your reply and insight. I replaced gear oil when doing the impeller. Like I said I’ve only ever owned outboards before this and I’ve never opened up an I/O before. Prop turns when in gear so I will troubleshoot the rest when I get time to go fuss with it.
 
Dieter said:
Smoke was inside or outside the boat ? If the engine was just installed was alignment checked? Normal some gear oil comes out when the halves of drive are separated. A lot will come out if it wasnt drained. You refilled after doing the water pump ?

between what Jack and I wrote you can figure out what is going on.
Click to expand...
Thanks for your reply and help. I think the smoke was on the outside. I will troubleshoot with what you guys have helped me with.
 
steelersman224 said:
Thanks for your reply and help. I think the smoke was on the outside. I will troubleshoot with what you guys have helped me with.
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Could be steam if upper gearcase got hot like one would expect with gears shredding. if the coupler was wrecked like would be likely if new engine went in and was not aligned you would smell burnt rubber
 
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