Mercruiser 7.4 V8 Bravo Seized. Help Please.


Old 07-12-04, 04:38 PM
Tony Booth
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Thumbs down Mercruiser 7.4 V8 Bravo Seized. Help Please.

Engine fitted in Rinker 23.6 seized because it has not been used for 5 years. Fully rebuilt 1996 & winterized after. Starter ok. Can anyone offer any assistance please ?
Tony, Liverpool, UK.

Last edited by Tony Booth; 07-12-04 at 04:42 PM. Reason: Spelling mistake
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Old 07-14-04, 08:25 AM
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Hello: Tony

Any number of possible problems may have developed as a result of a seized engine. Reason why must first be known. Overheated? Or lack of engine lube? Meaning the water pump was the cause or the oil pump, etc.

A mild seizure caused by overheating caught in time may not have caused too much internal engine damage but it will cause a shortened engine service life. As will the exact location of the seizure.

If the engine does crank and the cause was the water pump, replace the pump and try again. Best bet may be to replace that pump and crank the engine without allowing it to actually start. Disconnect and ground the ignition wire(s).

Intent is only to verify engine will crank without futher seizing, hearing feeling noises, binding or engine cranking difficulties. Engine must crank as it normally would and cooling water must flow freely.

Be sure engine thermostat is opening or replace it too while changing out the water pump, etc. Especially, if overheating was the cause.

More detailed and specific information would be helpful. Kindly use the reply button to add any additional detailed and specific information, etc. to this thread. Using the reply button method also moves the topic back up to the top of the daily list automatically.

The diy resident boat service & repair professionals will have additional helpful information, suggestions and advice. Check back on your question several times for additional replies.

Regards, Good Luck & Safe Boating.
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Old 07-14-04, 03:32 PM
Tony Booth
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Mercruiser 7.4 V8 Bravo seized.

Hello - thanks for your reply. Further info - the engine was rebuilt professionally in 1996/7 and has only been run for 7 hours since. Laid up for last 5 years, had been fully winterized and drained of water. The engine is not turning over at present - brand new Heavy duty battery just fitted, the starter motor which was also new can be heard moving into fly wheel/start position. The engine does not turn over. There was no overheating or lack of lube when running last. Seems that laying up has caused the problem. Any suggestions would be appreciated - this was an expensive rebuild.
Old 07-15-04, 05:48 AM
Join Date: Sep 2003
Location: cny
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try to turn it over by putting a socket on the crank & turning it by hand. pour some marvel mystery oil into each cyl. & let is sit for a couple days. then again try to turn it over using the crank. good luck.
Old 07-30-04, 04:26 PM
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I secound the last reply

I have used this marvel mystery oil and had good luck unstiking the engine with a breaker bar use plenty of marvel oil and let it seap down from the spark plug holes thru the block and dont be in a hurry. ps I also have the 7.4 in my slickcraft 23. a real power house of a engine. good luck to you and let everybody know how you made out.
Old 07-30-04, 05:00 PM
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Location: Mountain Williams Missouri
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Im thinking rust with the rings.5 years and it just said oil it and let it set could add WD 40. Also plugs out try by hand on the shaft. I see here for a Re Manufactured long block 7.4L $4250.00 US$ Mercruiser


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