omc cobra 5.0 H.O. engine & 4.3 sterndrive?

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Jaysad

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First timer please help?
I have a 1990 Chris Craft w/5.0 H.O. engine with a 4.3 strendrive. I found this out when I had to replace the lower unit. A new lower unit was put on the 4.3 upper unit, and I was told the 4.3 and 5.0 were the same. Got one summer and the lower unit goes out again. Does the 5.0 engine & 4.3 sterndrive have any thing to do with the lower unit going out???:confused:
 

Gary H NC

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Re: omc cobra 5.0 H.O. engine & 4.3 sterndrive?

Not sure but the gear ratios were different between some of the 5.0 and 5.7 drives.
Our Member Boatin Bob could tell you..
 

Don S

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Re: omc cobra 5.0 H.O. engine & 4.3 sterndrive?

I'm not sure if the Cobra drives use different gears in the lower or it's all done in the upper like Merc, but one thing is common, if your idle rpm is 1000 or higher, the lower isn't going to last very long.
 

180shabah

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Re: omc cobra 5.0 H.O. engine & 4.3 sterndrive?

Cobras are VERY sensitive to shift cable adjustment. A stretched or misadjusted cable chews gears.
 

Boatin Bob

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Re: omc cobra 5.0 H.O. engine & 4.3 sterndrive?

Not sure if I can help or just confuse things more? First of all as Don pointed out the gearing is done in the upper like Mercs, the lower's are all the same (except for the small models and the 7.5's)

The 5.0 should have 21:18 gears in it and the 4.3 should have 21:19 gears (the exception would be if the drive was built for high altitude) then the gears are a little different. In 1990 the overall ratio for the 5.0 is 1.59:1 and the 4.3 was 1.68:1, they are close and maybe you can get by with a prop change to work reasonably well.

ps...this is assuming the upper is from 1990 if it came from a 1988 or earlier the gears are different again so the only true way to tell what you have would be to pull the top cover and count.
 

Jaysad

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Re: omc cobra 5.0 H.O. engine & 4.3 sterndrive?

Gentelmen,
Thanks for the info. I had the local boat guy do the work for me becouse his is the Jasper dealer in town and a freind. After I hit something he installed a new lower unit, and a new SS prop to make up for the 4.3 & 5.0 differance. Took it out, it was starting to overheat, so I stopped it went back and he said the inlet water tub seal came off while installing the new lower unit, so he fixed it. After 6 GREAT weekends of boating with the family, BOOM lower unit out again. I didn't hit anything. My guy said it may have been just a bad unit from Jasper. ????? We love the boat and would like to keep it, this lower unit thing is killing me. What about the upper unit. Should it be rebuilt.
 

a70eliminator

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Re: omc cobra 5.0 H.O. engine & 4.3 sterndrive?

Did you re-ckeck the drive oil level after the first run on the initial fill? I guess thats a critical step on those drives, If you measured in the 64oz that would be ok, did it seize up or anything other than BOOM.
 

Jaysad

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Re: omc cobra 5.0 H.O. engine & 4.3 sterndrive?

No it was BOOM!! I pull the lower drain plug and metal peaces not shaving came out. One thing I forgot, he told me the shift cable was waaay out of adjustment when he put the frist one in. The RPM is lower than 1000 at idle with it in gear. I run the boat between 4000 and 5500/ 35 to 45 MPH.
 

Boatin Bob

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Re: omc cobra 5.0 H.O. engine & 4.3 sterndrive?

If you've got metal on the drain plug then you've to tear down the upper as well since the metal will migrate throughout the entire drive.
 

Gary H NC

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Re: omc cobra 5.0 H.O. engine & 4.3 sterndrive?

If the shift cable was that far out of adjustment then it needed replaced.
The Cobra drive has very critical adjustment steps and must be followed to the letter.
Ask your mechanic if he has that info.
It is several pages in the original OEM service manual.
It would not hurt to invest in the manual if you plan on keeping the boat.

http://cgi.ebay.com/ebaymotors/_Man..._W0QQitemZ200264459424QQadiZ2872QQadnZManuals
 

Jaysad

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Re: omc cobra 5.0 H.O. engine & 4.3 sterndrive?

If the shift cable was that far out of adjustment then it needed replaced.
The Cobra drive has very critical adjustment steps and must be followed to the letter.
Ask your mechanic if he has that info.
It is several pages in the original OEM service manual.
It would not hurt to invest in the manual if you plan on keeping the boat.

http://cgi.ebay.com/ebaymotors/_Man..._W0QQitemZ200264459424QQadiZ2872QQadnZManuals

Yes,
Gcboat with the hastings site was a good one! I'll put a new cable and study all the info. on the adjustment of the system this winter. Thanks man!
 

Jaysad

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Re: omc cobra 5.0 H.O. engine & 4.3 sterndrive?

Thanks to all,
After reading the comments and going to all the sites we are going to be replacing the shift cable, and study all the info. on the adjustments of the system.
Is there any up grades for this system, or is stock the way to go?
I plan on pulling the unit on servicing the upper and u joints any suggestions?
After getting the drive right. I'll get started on the engine!:D
 

mthieme

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Re: omc cobra 5.0 H.O. engine & 4.3 sterndrive?

The gear ratios are different.
If my wife sees fit to afford me a little time this weekend:), I'll try to see if I can pin this down a little better for you in the manual.
 

a70eliminator

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Re: omc cobra 5.0 H.O. engine & 4.3 sterndrive?

Im wondering why, if your shift cable was that far out of adjustment to blow out the drive, did you not mention any shifting issues, if you were able to make decent shifts to neutral and reverse the adjustment couldn't have been that bad? I don't know it just seems odd.
 

Jaysad

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Re: omc cobra 5.0 H.O. engine & 4.3 sterndrive?

Any info. is welcome.
Now the wife saids that with she is unloading and loading the boat off the trailer, it sometimes makes a clucking sound before it goes in gear. So thats when she gas it a little more and I scream not so damn much. Once I get in it runs fine. It sometimes is hard to get in neutral. It like it's stiff, and well go passed the detent.
 
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