Need to replace lower unit Volvo Penta SX Cobra 3868389 1.66 t0810400

White90GT

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My lower unit is cracked around the propeller. The housing itself is missing a small chunk and has a crack that has started expanding (sorry no pic at the moment, boat is at my parents place). I'm pretty sure there is no way to repair it and started looking for a used replacement today.
The boat is a 97 Chris Craft 170 concept, 17'. Motor is the 4.3 Liter Vortec V6. Outdrive setup Volvo Penta SX Cobra 3868389 1.66 t0810400 are the numbers on the plate.

I have found a complete stern drive unit, ie upper/lower off a Four Winns with a 5.0 v8. I think it may be a 1.51 ratio, but I could be wrong. Here are the numbers on the tag for that unit 3868404, 4111537059, can't make out the ratio on the tag. It says SX-C1.

Will that complete drive unit work for me? What if it is indeed a lower gear ratio, will the 1.51 vs 1.66 make that big of a difference in performance? I just gave the boat a tune up and it runs great right now other than some noise from the lower unit (which I found/heard last time I took it out) and haven't been out since. Is there a way to just change the gears out and use my gears?

Just had the transom rebuilt on this boat and again did the tune up, but now the damn lower unit is the problem with a crack in the housing.
 

vwbugman69

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Re: Need to replace lower unit Volvo Penta SX Cobra 3868389 1.66 t0810400

Just use the lower from the new unit. The gearing is in the upper so the ratio becomes a non issue and should bolt right up.
 

White90GT

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Re: Need to replace lower unit Volvo Penta SX Cobra 3868389 1.66 t0810400

You think $2100 is a good buy for a used unit? It's at a boat salvage yard in Houston. Seems like all the others I've seen online are almost twice that for a rebuilt unit.
 

Augoose

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Re: Need to replace lower unit Volvo Penta SX Cobra 3868389 1.66 t0810400

I know on some of the mercruisers that the gear ratio is controlled by the upper gear unit of the overall lower unit, but do the VP's do the same or do they have gearing in the lower gear units as well?

I would recommend looking for a replacement lower gear unit vs a whole lower unit on craigslist or ebay - that will get you into the several hundred price range vs several thousand.

As far as your compatibility, unfortunately I can't help you there.
 
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vwbugman69

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Re: Need to replace lower unit Volvo Penta SX Cobra 3868389 1.66 t0810400

The gearing is in the upper on VP as well.
 

White90GT

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Bringing this back up. I haven't bought a unit yet, but found a complete out drive on craigslist cheap. Problem is he said it was behind a 3.0 liter 4 cylinder motor. I am waiting on him to send me pictures of the metal tag on the drive that has the product, serial, number and the gear ratio. Will that lower unit still work with my upper unit?
 

White90GT

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Re: Need to replace lower unit Volvo Penta SX Cobra 3868389 1.66 t0810400

The gearing is in the upper on VP as well.
Bringing this back up. I haven't bought a unit yet, but found a complete out drive on craigslist cheap. Problem is he said it was behind a 3.0 liter 4 cylinder motor. I am waiting on him to send me pictures of the metal tag on the drive that has the product, serial, number and the gear ratio. Will that lower unit still work with my upper unit?
 

White90GT

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OK, here is the info off the other unit I've found for cheap. 3868586 5x-ct2 1.97 ratio 4112042928 those are the numbers off the plate. I know the gearing is different, so I'm curious as to whether the lower unit will bolt up to my 1.66 upper unit. The guy is willing to take $400 for the complete upper, lower, prop, and I believe even the tilt/trim cylinders are still on it.
 

White90GT

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Keeping this up top I really need to know if this lower will work with my upper.
 

White90GT

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Back up top, I still need to know if this will work. Might be worth buying anyways since it is so cheap, then post it back online if it doesn't fit and make a few bucks off it.
 

White90GT

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No responses. I guess I will have to be a guinea pig and find out myself.
 

HalfFish5087

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As long as the drive is the same model, its my understanding that it should mate up. I may do a little inspection before buying. Such as draining some of drive oil and rake a good magnet through the oil to check for metal shavings; also would look hard for any cracks from any past impacts, take off the prop (if on) and check the splines and make sure they're straight all the way around (impact on the prop can bend the splines), rotate the input shaft or prop and make that it turns easily when the unit is in gear, and other obvious signs of damage... Good luck.
 

White90GT

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Thanks HalfFish, I'll look it over well. I know it has a small chunk missing from the skag itself, so I will be going over the case with a fine tooth comb.
 

White90GT

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I went ahead and bought the lower. The snag is bent quite a bit and a small chunk missing from it, but I'm hoping I can heat it slightly and bend it straight. The propellor shaft is very smooth with no play at all. The prop itself has some damage on the back ring but not the blades. They said the boat drifted into some rocks with the motor down.

I will post pics when I get back to a computer.
 

White90GT

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Success! The lower unit bolted right up to my upper. Turns out based on the year stamp inside the top of the lower unit, mine is a 96 model and the one I picked up is a 97 model. The part numbers stamped inside the case were exactly the same except the very last number, I want to say it was D1 vs D2. The shaft and everything was the same, so my prop went right on. One thing I did notice though inside the propeller housing there is a piece in there that wasn't on my drive. I don't know if it is because mine was rebuilt and had a different shaft housing or what, look at the pics and see what you think.
 

White90GT

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I went ahead and removed the "whale tail" for now, but I may put it back on to try it out at some point. I took the boat for a test ride Sunday morning and she drove perfectly normal. Topped out at 53-54 mph on the speedo (don't have a gps to compare). Now my tachometer was reading off for some reason. I know the motor wasn't zinging over 6k rpm as it sounded perfectly normal at speed, so I'm not sure what caused the tach to be off. I did a quick scuff and paint job since my upper had a lot of corrosion on it. I didn't do a lot of sanding as it was 97 degrees out and I had been outside all day Saturday. I may redo it at some point, but it should be fine for this summer. I painted it gunmetal grey metallic.
 

White90GT

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I went ahead and removed the "whale tail" for now, but I may put it back on to try it out at some point. I took the boat for a test ride Sunday morning and she drove perfectly normal. Topped out at 53-54 mph on the speedo (don't have a gps to compare). Now my tachometer was reading off for some reason. I know the motor wasn't zinging over 6k rpm as it sounded perfectly normal at speed, so I'm not sure what caused the tach to be off. I did a quick scuff and paint job since my upper had a lot of corrosion on it. I didn't do a lot of sanding as it was 97 degrees out and I had been outside all day Saturday. I may redo it at some point, but it should be fine for this summer. I painted it gunmetal grey metallic.
 

White90GT

Petty Officer 2nd Class
Joined
Jul 5, 2011
Messages
161
I went ahead and removed the "whale tail" for now, but I may put it back on to try it out at some point. I took the boat for a test ride Sunday morning and she drove perfectly normal. Topped out at 53-54 mph on the speedo (don't have a gps to compare). Now my tachometer was reading off for some reason. I know the motor wasn't zinging over 6k rpm as it sounded perfectly normal at speed, so I'm not sure what caused the tach to be off. I did a quick scuff and paint job since my upper had a lot of corrosion on it. I didn't do a lot of sanding as it was 97 degrees out and I had been outside all day Saturday. I may redo it at some point, but it should be fine for this summer. I painted it gunmetal grey metallic.
 
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