weak valve springs

PGATOO

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Aug 14, 2018
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had a complete rebuild done on my 1989 Bayliner Ciera with an OMC 5.7, they did everything except replace the Valve springs. The original reason for the rebuild was I wasn't getting proper WOT and low top end speed. WOT = 3800 and top speed 27 mph. After rebuild still same problem. Someone suggested to me that weak valve springs would cause the lack of power and low WOT. Can someone confirm this before I pull the motor again and replace the valve springs? Thanks for all the help on this forum. Although I am not a frequent poster I learn a lot just reading the threads.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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most likely your low on power for fuel system reasons. look in the stickies for reasons of low WOT.

if you were to float the valves, you would hear it. every good machine shop will measure the spring force during a rebuild. I seriously doubt you have weak valve springs unless the rebuild was done at toothless joes back-alley discount rebuild shop.
 

alldodge

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suggested to me that weak valve springs would cause the lack of power and low WOT.

Yes and No, weak springs can cause reduced power, but along with reduced power you also would be getting misfires from the valves not being closed. So right now I would not think this would be the initial problem

Start with the basics and verify all are correct
Timing, plugs, gap, compression
 

PGATOO

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Aug 14, 2018
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I guess I should have been more thorough on my initial post. I have read all the posts and went through the list on the sticky and that is why I asked the question regarding the springs. I will list below actions I have taken with no success but first some history.

the original equipment was 5.7 OMC with a cobra outdrive 15 x 15 3 blade prop
outdrive failed so was recommended to put a King Cobra (don't know the ratio right now but will ask mechanic)
went to 15 x 15 4 blade
worked OK but never seemed to be able to get the WOT over 4k and more than 28 mph
last year boat seemed more sluggish than ever, about 500 hrs on the motor so decided to re-build. the beginning of season boat acting exact same as the end of last year before the rebuild struggles to get up on plane and no top end. Started reading and trying to troubleshoot.


troubleshooting;

Fuel-related;

cleaned carb
changed separator
converted ignition to electronic
used 5 gallon outboard motor tank with fresh gas

mechanical;

changed prop from 15 x 15 to 16 x 12 (worked somewhat but not near enough)
another prop 16 x 13 ( not enough)
double check cam (mechanic says it is correct)
some other minor things but nothing seems to make a difference
 

Horigan

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Jun 12, 2016
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A couple of questions/thoughts come to mind.

Did you confirm with a compression test that you needed a rebuild?

If the ratio of the newer drive is significantly different than the original drive, that could be part of the problem, even with the prop changes.
 

alldodge

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For a motor to run correctly with full power it needs
The correct amount of fuel and air
Spark at the correct time (which includes amount of advance)
Correct amount of compression

So your old motor is doing the same thing as your new motor. This says that at least one of the three has not changed.

Carb was cleaned but was it cleaned sufficiently and adjusted correctly?
Does the motor have compression on all cylinders within 10% highest to lowest, and is it at least 130 psi?
Is the timing set correctly (8 BTDC), does it advance at least 20 degrees?
 

PGATOO

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Aug 14, 2018
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Horigan no it was not confirmed it was only assumed as the hours were over 500 and it seemed sluggish. I am starting to think the whole issue was caused when we changed from a cobra outdrive to a King cobra. If the Ratio is significantly different between the two drives what needs to be changed or adjusted?

AllDodge I will bring these 3 things up and confirm with my Mechanic

Thank you guys for the advice and all the good information, this site is a wealth of information and I will update after I speak with my mechanic this weekend
 

Bondo

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[I am starting to think the whole issue was caused when we changed from a cobra outdrive to a King cobra. If the Ratio is significantly different between the two drives what needs to be changed or adjusted?

Ayuh,...... Welcome Aboard,..... There ain't no "Adjustments",.....

Ya need the Right drive,......
 

kpg7121

Petty Officer 2nd Class
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Aug 25, 2018
Messages
174
I guess I should have been more thorough on my initial post. I have read all the posts and went through the list on the sticky and that is why I asked the question regarding the springs. I will list below actions I have taken with no success but first some history.

the original equipment was 5.7 OMC with a cobra outdrive 15 x 15 3 blade prop
outdrive failed so was recommended to put a King Cobra (don't know the ratio right now but will ask mechanic)
went to 15 x 15 4 blade
worked OK but never seemed to be able to get the WOT over 4k and more than 28 mph
last year boat seemed more sluggish than ever, about 500 hrs on the motor so decided to re-build. the beginning of season boat acting exact same as the end of last year before the rebuild struggles to get up on plane and no top end. Started reading and trying to troubleshoot.


troubleshooting;

Fuel-related;

cleaned carb
changed separator
converted ignition to electronic
used 5 gallon outboard motor tank with fresh gas

mechanical;

changed prop from 15 x 15 to 16 x 12 (worked somewhat but not near enough)
another prop 16 x 13 ( not enough)
double check cam (mechanic says it is correct)
some other minor things but nothing seems to make a difference
Whoever told you to drop a KC in that Bayliner is an idiot.
 

boobie

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Nov 5, 2009
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20,826
What kind of results do you get when you do a cylinder leak down test ??
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Jul 23, 2011
Messages
47,309
I guess I should have been more thorough on my initial post. I have read all the posts and went through the list on the sticky and that is why I asked the question regarding the springs. I will list below actions I have taken with no success but first some history.

the original equipment was 5.7 OMC with a cobra outdrive 15 x 15 3 blade prop
outdrive failed so was recommended to put a King Cobra (don't know the ratio right now but will ask mechanic)
went to 15 x 15 4 blade
worked OK but never seemed to be able to get the WOT over 4k and more than 28 mph
last year boat seemed more sluggish than ever, about 500 hrs on the motor so decided to re-build. the beginning of season boat acting exact same as the end of last year before the rebuild struggles to get up on plane and no top end. Started reading and trying to troubleshoot.


troubleshooting;

Fuel-related;

cleaned carb
changed separator
converted ignition to electronic
used 5 gallon outboard motor tank with fresh gas

mechanical;

changed prop from 15 x 15 to 16 x 12 (worked somewhat but not near enough)
another prop 16 x 13 ( not enough)
double check cam (mechanic says it is correct)
some other minor things but nothing seems to make a difference

a few things

at 500 hours, unless that motor was abused, beaten, and neglected, it would not need a rebuild. I have pulled apart many 500 - 1000 hour boat motors and most still have cross-hatching in the cylinders. so what testing and conclusion lead you to assume your motor needed a rebuild at 500 hours?

if the wrong ratio drive was put on the back, it would bring the motor to its knees and there isnt a prop small enough to make up for the wrong ratio

going to the same pitch and diameter, however adding a 4th blade to the prop, crippled your motor further and took out any remaining hope for the motor to push your boat. if you add a prop blade, you drop pitch by 2" or you go up in power by 30hp to keep the same RPM

fire your "mechanic" he is toothless joe's back-alley discount engine builder if he is also the one that sold you the wrong drive.
 

kpg7121

Petty Officer 2nd Class
Joined
Aug 25, 2018
Messages
174
a few things

at 500 hours, unless that motor was abused, beaten, and neglected, it would not need a rebuild. I have pulled apart many 500 - 1000 hour boat motors and most still have cross-hatching in the cylinders. so what testing and conclusion lead you to assume your motor needed a rebuild at 500 hours?

if the wrong ratio drive was put on the back, it would bring the motor to its knees and there isnt a prop small enough to make up for the wrong ratio

going to the same pitch and diameter, however adding a 4th blade to the prop, crippled your motor further and took out any remaining hope for the motor to push your boat. if you add a prop blade, you drop pitch by 2" or you go up in power by 30hp to keep the same RPM

fire your "mechanic" he is toothless joe's back-alley discount engine builder if he is also the one that sold you the wrong drive.
It's too late now but what decent mechanic would recommend to a customer to hang a King Cobra on anything? I feel bad for the OP when he needs parts for that King.
 

PGATOO

Cadet
Joined
Aug 14, 2018
Messages
12
so after much troubleshooting with no success, I am now convinced it is the outdrive (Cobra 985690 on top/ baby King on the lower.)
Question, if I split the outdrive and find out that it is the wrong gear ratio, can I put new gears with the right ratio in the baby king lower unit that will match the Cobra 985690 upper unit? or, should I swap the whole bottom unit out and go back to a regular cobra? My understand the swap was to stop that big of a boat (2655 wide beam) from chewing up the gears on the smaller Cobra
 
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