Need Engine

mad dwarf

Cadet
Joined
Aug 28, 2011
Messages
17
Looking to replace my 5.7 OMC cobra engine, has anyone bought from usengines.com? Bought the boat, it had sat for 7 years, after having the carb. rebuilt and replacing exhaust manifold gaskets, put it in the water for a test run. Would not go above 3800 rpm, brought it back out of the water was going to start troubleshooting by replacing spark plugs then run it again and adjust the carb. When we pulled the plugs two of the ports had water flowing out, however the oil level had not gone up nor did it look milky. Is this definately a cracked block and useless motor?
 

wire2

Lieutenant Commander
Joined
Jun 25, 2007
Messages
1,584
Re: Need Engine

Water from spark plug holes tends to indicate a blown head gasket. Both on 1 side? Also, if your dipstick tube is connected to the pan drain, it will appear clean, while the pan may have oil/water.
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Re: Need Engine

Looking to replace my 5.7 OMC cobra engine, has anyone bought from usengines.com? Bought the boat, it had sat for 7 years, after having the carb. rebuilt and replacing exhaust manifold gaskets, put it in the water for a test run. Would not go above 3800 rpm, brought it back out of the water was going to start troubleshooting by replacing spark plugs then run it again and adjust the carb. When we pulled the plugs two of the ports had water flowing out, however the oil level had not gone up nor did it look milky. Is this definately a cracked block and useless motor?

Howdy,

Salt-water or fresh? raw water cooled or closed?


Did you inspect and test the exhaust manifolds and risers? Check the riser gaskets?

You might also pressure test the cooling system.

I have only replaced 1 engine that came from USENGINE (a 3.0L Mercruiser about 3 years ago) Everything went well and the owner is still happy with it.


If you suspect a bad head gasket, get yourself a compression gage and check it.


Regards,


Rick
 

mad dwarf

Cadet
Joined
Aug 28, 2011
Messages
17
Re: Need Engine

Thank you for the replies

Yes, water was on the same side of the motor, not sure where the dipstick is connected, havent looked that much into it, noticed it runs from starboard side under engine to the port side.

It is fresh water, I pulled the exhaust manifolds leaving the risers connected yesterday, water was sitting in the exhaust manifold, but not sure if that is from the manifold leaking or if the cylinders are completely shot and the cavity was just that full of water. Trying to figure it out without having to pull the motor and tear it down, if I go through all that might as well purchase a new motor.

Tested the manifolds but not sure if I tested them right. What I did was put a cap on the end of the riser and took a water hose to the water side of the manifold, water came pouring out once the cavity was full, but started reading more into it and found that as it exits the riser the water side meets up with the exhaust, so having it plugged off completely would cause the water to come back into the cylinder side of the exhaust.

Going to try replacing the manifolds and risers, they are atleast 7 years old maybe more and pitted so either way they should be replaced. I plan on doing a compression test with the manifolds off. If the compression test turns out ok, should I just put the new manifolds on and run the engine again and see what happens? Pretty sure i got the water out of the heads, turned the motor over with the plugs out and sprayed wd-40.
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Re: Need Engine

Water in the exhaust area is most frequently a manifold, riser or manifold-riser gasket leak either due to the gasket itself or cracks in either the manifold or riser.

If you suspect manifold or riser leaks, you can test them.

Have a look at the following thread.
[h=1]MUST HAVE Technical Information for DIYers.[/h]
Check it all out, but have a look at #14 first!


Cheers,


Rick
 

mad dwarf

Cadet
Joined
Aug 28, 2011
Messages
17
Re: Need Engine

Rick, I re-tested the exhaust manifolds per how it is explained in the link you sent, thank you. Test did show a leak in the exhaust manifold. Also did a compression test, readings were #1 cylinder=92,#2=90,#3-8=87. readings seem a little low but not having a big difference across all cylinders is a good indication of no internal cracks just worn cylinders or rings correct?
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Re: Need Engine

Low compression readings are not related to internal cracks because when a block cracks it almost never cracks into a cyl.

If you have cyl compressions well below 100 PSI, I wouldn't call it "a little low". I would call that a LOT low!

Low compression readings indicate worn pistons, rings and intake/exhaust valve leaks, and possibly a leaky head gasket....
OR all of the above!
 
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