Slow crank won’t start after running great at WOT

[Dallas214Stars]

So I got a new mercury 1979 115hp yesterday and it was running great. We took it out and it was running at wide-open throttle back to 0 mph easily no problem. Did a few trim adjustments and kept going with no issues for about 25 min. Out of no where we are cruising at WOT and it just immediately slows it’s self down and shuts off. I troubleshooted for hours trying to figure out what had gone wrong before having to be towed in. Now when I turn the engine over it slow cranks won’t start like the starter is bad but I can’t imagine a starter going bad in the middle of driving would cause the motor to shut down. The ignition was hanging in the dash as this was a test drive of the motor and I hadn’t fully installed everything yet. I’m wondering if it made contact with something and shorted out what I would think would be the kill switch. Can’t seem to locate it on this motor any one know where it’s at? Now when we crank it it’s like it’s not receiving very much power. Jumped the starter as well and it’s continuing to do the slow crank won’t start. Gonna try to test compression today(it was 120 in all cylinders when I tested it before buying). Know that this motor was sitting for a few years was but fully serviced before it sat. We cleaned all the gas and fluids out and added sea foam to the gas it was using when we were testing. Any help is much appreciated this thing was running like a champ I really hope it’s not toast and we can get it back on the water

 

[alldodge]

Out of no where we are cruising at WOT and it just immediately slows it’s self down and shuts off.
slow crank

I'm thinking scored pistons and/or bearings

 

[racerone]

A new motor to you always needs a new water pump impeller.----And you were mixing gas / oil at 50:1 mixture I hope !-----I would say do a compression test on it 5 cylinders at least .----The bottom one is harder to get at.----Post your numbers.

 

[Dallas214Stars]

A new motor to you always needs a new water pump impeller.----And you were mixing gas / oil at 50:1 mixture I hope !-----I would say do a compression test on it 5 cylinders at least .----The bottom one is harder to get at.----Post your numbers.

Ya that’s what I was thinking about the water pump might as well change it since I’ll be keeping it. Definitely mixing the gas to the right ratio. It’s a inline 4 so super easy to test compression I’m about to do that and see what it says. I’m thinking the starter shot up when we were at WOT slowed down the motor then burned out the starter at the same time.

 

[Dallas214Stars]

A new motor to you always needs a new water pump impeller.----And you were mixing gas / oil at 50:1 mixture I hope !-----I would say do a compression test on it 5 cylinders at least .----The bottom one is harder to get at.----Post your numbers.

Bad news compression is at 120 on top and bottom. 60 on the second and 15 on the 3rd. I know that leaves me fucked what’s the next step? Is this motor salvageable or is it a goner?

 

[racerone]

????----A 1979 model 115 would be a 6 cylinder inline.----So I do not know what you have here.------Posting pictures will help.-------Maybe it is an 80 HP 4 cylinder but who knows without being able to look at it / touch it !!----If you ca rebuild it yourself there might be hope.------Paying a shop is likely very expensive and better off to find a running motor.

 

[Dallas214Stars]

[No message]

 

[Texasmark]

Er ah sir that's a Chrysler 4 cyl. Either your thermostat stuck shut and didn't allow water to circulate through your engine or your water pump impeller (propeller) was worn to the point that it couldn't pump adequate water to keep the engine cool at that rpm for that period of time. All due respect, I'd opt for another engine.

I bought a Chrysler 3 cylinder 85 hp new in 1971. I know what they look like.

I bought a used 70 hp Evinrude of 1975 vintage and had a similar WOT problem as yours, but it locked up tight in half a second, didn't slow down and quit, and I thought I'd have to dig my teeth out of the windshield it stopped the boat so fast. That engine did have the thermostat stuck shut. This was in around the 1985 time frame and I did all the work except for the machine work on the block which was boring and oversized pistons and rings.....parts cost was $1k and that was back then with me doing most of the work as mentioned.

 

[Dallas214Stars]

Er ah sir that's a Chrysler 4 cyl. Either your thermostat stuck shut and didn't allow water to circulate through your engine or your water pump impeller (propeller) was worn to the point that it couldn't pump adequate water to keep the engine cool at that rpm for that period of time. All due respect, I'd opt for another engine.

I bought a Chrysler 3 cylinder 85 hp new in 1971. I know what they look like.

I bought a used 70 hp Evinrude of 1975 vintage and had a similar WOT problem as yours, but it locked up tight in half a second, didn't slow down and quit, and I thought I'd have to dig my teeth out of the windshield it stopped the boat so fast. That engine did have the thermostat stuck shut. This was in around the 1985 time frame and I did all the work except for the machine work on the block which was boring and oversized pistons and rings.....parts cost was $1k and that was back then with me doing most of the work as mentioned.

Oh **** I just realized I put mercury lol its definitely a Chrysler my buddy and I have been working on his merc and I guess I brain farted and put merc not Chrysler

 

[Texasmark]

Oh **** I just realized I put mercury lol its definitely a Chrysler my buddy and I have been working on his merc and I guess I brain farted and put merc not Chrysler

At 78 they are getting more frequent with me!

 

[racerone]

It appears that there is a bolt missing on the propshaft bearing housing in your pictures.

 

[Dallas214Stars]

It appears that there is a bolt missing on the propshaft bearing housing in your pictures.

Can you send me a picture of where you’re referring to

 

[racerone]

A closer look says that maybe the screw is a " socket head cap screw " and all is well in the land.