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5.8L OMC Cobra, Mid 90s, outdrive issues. Prop shaft bent, i
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Author:  kaczman [ Mon Jul 27, 2015 4:33 pm ]
Post subject:  5.8L OMC Cobra, Mid 90s, outdrive issues. Prop shaft bent, i
(Attn LouC)

Hi all,

I have a boat with a mid 90s 5.8L OMC Cobra engine and outdrive on it. I hit some rocks this weekend, and bent up the prop.

I replaced the prop, and inspected it. The outdrive appeared to be good, and ran fine for nearly a 2 hour trip. On the way home, the prop shaft let go.

I had my marina inspect it, and they don't do alot with OMC's. They put it up on dry dock, drained the fluid and saw some metal shavings in it. Im assuming when the prop got bent it bent the whole shaft, and as I used it, it got progressively worse.

The marina is asking if there is a way to inspect the upper, to see if I can just swap the lower unit. Boy are these things expensive. Any suggestions from anyone on this forum? Thanks in advance!
Author:  rpengr [ Mon Jul 27, 2015 5:03 pm ]
Post subject:  Re: 5.8L OMC Cobra, Mid 90s, outdrive issues. Prop shaft ben
Assuming this is an OMC Cobra, and not a King Cobra:

There is not a lot of "stuff" in the upper unit, since the shifting mechanism is a "dog-clutch" in the lower unit. The upper unit is mostly just the bevel gears that transfer the rotation from horizontal to vertical, shafts, bearings and seals. There is also the gear and shaft that powers the raw water pump on the back of the upper unit.

Depending on the severity of the metal shavings, you may be lucky in that 2 hours may not have provided much time for the oil in the lower unit to co-mingle with the oil in the upper unit. I would remove the plastic cover over the water pump (3 bolts) followed by the top cap of the upper unit (4 bolts) where you can see the main bevel gears at the top. If there is no signs of metal shavings up there, and no signs of galling or burning of the gear teeth, then you should be OK. If I recall, there was also a magnet on the dipstick that can be checked for shavings.

Ray
Author:  LouC [ Mon Jul 27, 2015 5:27 pm ]
Post subject:  Re: 5.8L OMC Cobra, Mid 90s, outdrive issues. Prop shaft ben
It really depends on what year your engine package is. Mid 90s could be the joint venture OMC Cobra which is a Volvo SX in OMC paint. Cone clutch shifting in the upper gear housing. Find out exactly what year the engine/drive are or post a good pic here I'll be able to tell you more then.
When you say the prop shaft let go what do you mean? Oil seal failed let out all the oil, lost power to the prop, boat would not move, etc? A bent prop shaft and bent up prop causes severe vibrations and continued use will damage the prop shaft bearings. But a hard strike can fracture a gear which may fail later and the chip will come loose and jam up the drive. What actually happened?
Author:  Graham R [ Tue Jul 28, 2015 8:34 am ]
Post subject:  Re: 5.8L OMC Cobra, Mid 90s, outdrive issues. Prop shaft ben
kaczman wrote:
(Attn LouC)

Hi all,

I have a boat with a mid 90s 5.8L OMC Cobra engine and outdrive on it. I hit some rocks this weekend, and bent up the prop.

I replaced the prop, and inspected it. The outdrive appeared to be good, and ran fine for nearly a 2 hour trip. On the way home, the prop shaft let go.

I had my marina inspect it, and they don't do alot with OMC's. They put it up on dry dock, drained the fluid and saw some metal shavings in it. Im assuming when the prop got bent it bent the whole shaft, and as I used it, it got progressively worse.

The marina is asking if there is a way to inspect the upper, to see if I can just swap the lower unit. Boy are these things expensive. Any suggestions from anyone on this forum? Thanks in advance!


There's a complete Cobra drive on Ebay UK, if that's the type you need.
Author:  rpengr [ Tue Jul 28, 2015 9:12 am ]
Post subject:  Re: 5.8L OMC Cobra, Mid 90s, outdrive issues. Prop shaft ben
Also curious what type of prop?
Author:  Technologic80 [ Sun Aug 09, 2015 11:04 pm ]
Post subject:  Re: 5.8L OMC Cobra, Mid 90s, outdrive issues. Prop shaft ben
kaczman wrote:
The marina is asking if there is a way to inspect the upper, to see if I can just swap the lower unit. Boy are these things expensive. Any suggestions from anyone on this forum? Thanks in advance!


The marina is asking YOU if there is a way to inspect the upper?!? Find a new marina, STAT.

Having owned an OMC Cobra, which expeditiously chewed its dog clutch up (fun stuff right there), and a KING Cobra, which was a completely trouble-free unit, I can tell you that WHEN I had service done, I used only the absolute most experienced and knowledgeable OMC mechanic I could find. I suggest you do the same.
Author:  rpengr [ Sun Aug 09, 2015 11:51 pm ]
Post subject:  Re: 5.8L OMC Cobra, Mid 90s, outdrive issues. Prop shaft ben
Another thread where the OP posted his question then never returned...

Sigh :roll:
Author:  Graham R [ Tue Aug 11, 2015 4:56 pm ]
Post subject:  Re: 5.8L OMC Cobra, Mid 90s, outdrive issues. Prop shaft ben
rpengr wrote:
Another thread where the OP posted his question then never returned...

Sigh :roll:


Yes, sad. I feel guilty, he posted on a UK forum, I suggested he posted here due to the extensive OMC experience here( LouC et al !). He never posted on the UK forum again either.
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