Engine cut out while slowing down....

[Mtl-Diesel]

1984 Mercruiser 140. S/N 6777639
Was out today and then slowed from being on plane to a no wake zone. Slowed very gradually. Started to hear what I would describe as valve clatter that grew more pronounced and then the engine died. Would not restart. Turns over like crazy but nothing.
After about 45 minutes of paddling the police showed up and towed me to nearest marina. No services at this marina.

It has a converted EST ignition (Thunderbolt). New coil, wires, plugs, etc. I did some preliminary testing and when I throttle forward, I can see fuel dump into the carb. It has a mechanical fuel pump. If it was to go bad, would fuel still be sent to carb upon throttle?

Looked at all 4 plugs. They are dry and whiteish. Any ideas out there?

Thanks!
Rod

 

[alldodge]

If its EST its not Thunderbolt, or the other way. If distributor has 2 connector plugs on one side its EST. If it has 2 to 3 wires only coming from distributor then its TB

If fuel comes from the carb then its not the fuel pump

How new are the plugs?
Reason for asking, if they have only a few hours of runtime then they would be white. If they have several hours on them and they are still white then they might be running lean or there getting steam cleaned

 

[Mtl-Diesel]

If its EST its not Thunderbolt, or the other way. If distributor has 2 connector plugs on one side its EST. If it has 2 to 3 wires only coming from distributor then its TB

If fuel comes from the carb then its not the fuel pump

How new are the plugs?
Reason for asking, if they have only a few hours of runtime then they would be white. If they have several hours on them and they are still white then they might be running lean or there getting steam cleaned

Gotcha. It is definitely EST. My bad.

Plugs are new this year with likely 25-30 hours on them.

What has me perplexed is the sudden clattering just before the engine cut out. Like I said, it won't start now. Turns over like a champ but nada.

Where does the fuel come from if the engine is not turning over? I just had my son push the throttle forward to "pump the gas" to see if any fuel made its way into the carb. This was done WITHOUT turning the key.

Is it possible the mechanical fuel pump failed?

 

[alldodge]

Carb has fuel in the bowl until it is pumped out by the throttle or evaporates over time. If you have fuel pumping now, then its not the pump

 

[Mtl-Diesel]

Carb has fuel in the bowl until it is pumped out by the throttle or evaporates over time. If you have fuel pumping now, then its not the pump

OK. Makes sense. I'm heading out to check and see if I'm getting spark. What else should I check? Boat is 45 minutes away. :-(

 

[Scott Danforth]

1984 Mercruiser 140. S/N 6777639
Was out today and then slowed from being on plane to a no wake zone. Slowed very gradually. Started to hear what I would describe as valve clatter that grew more pronounced and then the engine died. Would not restart. Turns over like crazy but nothing.

check your compression

 

[alldodge]

Agree, compression

 

[Mtl-Diesel]

check your compression

yup. got my guage. I'll report back soon.

 

[Mtl-Diesel]

So...got all the way there only to realize I forgot the boat keys at home. Doh!! Heading back early morning and will report back.

 

[Mtl-Diesel]

Just wanted to mention my ignition system is new as of last year. AC Delco Voyager kit. EST. In case it helps.

Thanks!

 

[Mtl-Diesel]

Hey guys. So here’s the update.

Checked the compression: 2 cylinders at 0 (zero) & 2 cylinders at 40. Not good.

anyone want to guess what I might find when I open her up? What I should look for first?

 

[alldodge]

Tuliped valves

 

[Mtl-Diesel]

Tuliped valves

OK. Loaded question here. Is it going to be worth repairing this motor or should I look at a new one? Looking for cost comparison if possible. Will likely do the work myself.

 

[alldodge]

If you need a set of valves that would be about $60, then maybe another $100 for the head work. Add gaskets and your back in business

If it is tuliped valves then need to work on carb and timing

 

[Mtl-Diesel]

If you need a set of valves that would be about $60, then maybe another $100 for the head work. Add gaskets and your back in business

If it is tuliped valves then need to work on carb and timing

OK. Finally got around to getting some work done on the boat.

Took the valve cover off and the head. Here are some pics to show what I found. To my eye, nothing looks out of the ordinary. Disconnected fuel and coil and turned over, all cylinders move up and down as they should? No noises.

Reminder that I had 40,0,0,40 for compression. Head gasket is in great shape.

What should I do next?

 

[alldodge]

Look at your last pic and note between the middle cylinders is shinny

This points to the location that for me it appears the head gasket blew

 

[Mtl-Diesel]

Look at your last pic and note between the middle cylinders is shinny

This points to the location that for me it appears the head gasket blew

View attachment 327576

But the gasket is still intact. Slightly discolored but intact. I thought a blown gasket was ripped through? I appreciate your quick response btw!!! ;-)

 

[alldodge]

While it can get ripped thru, most are not, the head warps just enough to let gasses pass

 

[Mtl-Diesel]

So is my next step to bring the head in to be worked? Would this potentially cause both middle cylinders to have zero compression and the two outside ones down to 40? Just

 

[Rick Stephens]

The hard part is knowing where the compression was leaking now that the head is off. With it on you can do a leak down and figure it for sure - as you pressurize a cylinder through the plug hole you listen for where the air is escaping. If though the crankcase vent, it's rings, if through the cylinder next over, it is a head gasket or crack in the head. And so on. Without having done that you are down to inspecting everything. A machine shop will help a lot. They can check flatness pretty easily. And they'll know what to think about valve issues.