What happened now?

[craig newton]

96 Mercruiser 4.3 L 4bb V-6 Vortec with Alpha One outdrive.
Put in new plugs, plug wires, dist. cap and rotor. It backfired once starting it but then started and went to a smooth idle. Sounded good. I let it run for 4-5 minutes to loosen up the oil to make it easier to extract through the dip stick tube.
Today because of the backfire, I replaced the coil. Went to start it and in less than a second the engine slammed shut, locked up. Best way I can describe it. I put a socket on the front pulley and tried turning it with a wrench by hand. Counter clockwise at first and everything turned for a few inches so I stopped and turned it Clockwise. It turned up to the point where I started the counter clockwise turn and stopped. It won't go any further. So what happened now?

 

[racerone]

Did the gearcase lock up?----Step #1 is to look at gear oil.

 

[Scott06]

Agreed either drive is locked up or water in cylinder , pull plugs see if it is hydro locked. If not hydrolocked pull drive see if it turns. you Pulled the oil did you refill?

why would you replace the coil because it backfired?

 

[craig newton]

Thank you guys
The crankcase oil and the gear oil in the out drive are both full.
I'll pull the plugs and see if it's hydro locked.
Do I need to drop the lower unit and manually try to turn the drive shaft to see if the gear case is locked?
The old coil had some corrosion at the plug and I was told that could cause it to miss or back fire.

 

[crazy charlie]

96 Mercruiser 4.3 L 4bb V-6 Vortec with Alpha One outdrive.
Put in new plugs, plug wires, dist. cap and rotor. It backfired once starting it but then started and went to a smooth idle. Sounded good. I let it run for 4-5 minutes to loosen up the oil to make it easier to extract through the dip stick tube.
Today because of the backfire, I replaced the coil. Went to start it and in less than a second the engine slammed shut, locked up. Best way I can describe it. I put a socket on the front pulley and tried turning it with a wrench by hand. Counter clockwise at first and everything turned for a few inches so I stopped and turned it Clockwise. It turned up to the point where I started the counter clockwise turn and stopped. It won't go any further. So what happened now?

How was it running prior to the tuneup parts change? any reason to prompt the tuneup? Any history?? Charlie

 

[racerone]

Was it running on muffs?----Water shut off when engine was stopped?

 

[ROY WILLIAMS]

THE TIMING IGNITION 2 DEG ATDC 600-700 RPM. THE GASOLINE OF THE WATER OF THE FILTER.

 

[Scott06]

Thank you guys
The crankcase oil and the gear oil in the out drive are both full.
I'll pull the plugs and see if it's hydro locked.
Do I need to drop the lower unit and manually try to turn the drive shaft to see if the gear case is locked?
The old coil had some corrosion at the plug and I was told that could cause it to miss or back fire.

If you end up pulling the drive pull it in one piece . You want to narrow down if the engine is locked up or drive, gimbal bearing etc.

start with the plugs and see what’s in there . Time is of the essence if there is water in the engine , if so need to get it out bet it running to drive off moisture

 

[Lou C]

A ‘96 would have those batwing exhaust manifolds, they can be prone to leaking water back into a cylinder & you could have water in a cylinder causing a hydrolock. In addition if water has been leaking into a cyl it can cause valves to stick and in this case a sticking intake valve can cause a backfire thri the intake/carb….

 

[Scott Danforth]

Never turn a Chevy motor from the crank bolt. You will usually strip the threads from the crank before budging the motor. Always use the flywheel or pull the damper and use a crank socket


Pull the drive, pull the plugs, see if it turns over from the starter

If it does, check the drive if it's locked up

If it doesn't turn over with the drive off and plugs out. Pull the motor

 

[Lou C]

Why I say this….so my engine had an overheat in 2013, and the head gaskets started leaking noticeably in Aug of ‘16. But at the first start up in April ‘16, it backfired thru the carb, never did that before…a harbinger of things to come….

 

[Lou C]

Agreed on the crank bolt. Only safe way to do it might be to remove all the plugs so there’s no compression to provide resistance….