57 35hp over-rev then no spark

[mntcman]

I had my 57 big twin out this week. Mounted on 1956 Lyman 15 foot. Running at full throttle motor suddenly over reved, continued running for several seconds then died. Would not restart after this. Rowed back to shore!!!!!! Checked for spark back at shore and no spark. Found broken wire at mercury switch. repaired wire still no spark. Has new plugs. What could have caused over rev? Where to start looking for no spark problem? Thanks for any and all relies.

 

[lindy46]

Re: 57 35hp over-rev then no spark

The mercury switch would have nothing to do with engine spark. It just prevents the starter from working if the throttle is advanced too far. You may have spun the prop hub, causing the over-rev condition. The cut-out switch would then cut the spark to the bottom cylinder, causing the motor to stop running. However, once the motor has stopped, you should have spark again to both cylinders. Does your motor have a key switch, allowing the motor to stop when you turn off the key? Or is it set up with just choke to stop? In 1957, the motor came with no kill circuit - only a start button and choke button. If someone has added a kill circuit, one of the wires could be shorting, causing the no spark situation.

 

[mntcman]

Re: 57 35hp over-rev then no spark

No kill switch. No key switch, just choke to stop. On further investigation, looks like prop nut lost cotter pin and backed of a turn or two. Would that cause "spun prop hub"? Exactly what is that?

 

[lindy46]

Re: 57 35hp over-rev then no spark

The prop hub has a rubber bushing which is designed to slip when you hit an underwater obstruction. Once it slips, the prop needs to be re-hubbed. On these 50+ year old motors, the bushing can just dry up and wear out and start slipping without hitting anything. But if your prop nut backed off, it's possible the drive pin was not engaging causing the slipping. Remove the prop and check the drive pin. If it's okay, re-install the prop, properly tightened down and with a new cotter pin. That may be all that was wrong. That still doesn't explain the "no spark". I'd be looking under the flywheel at the coils and points next.

 

[mntcman]

Re: 57 35hp over-rev then no spark

spun prop hub for sure. I can turn the prop without the prop nut turning. Are these still available?

 

[lindy46]

Re: 57 35hp over-rev then no spark

Prop shop can re-hub it, or take it to a Johnnyrude dealer - they can have it re-hubbed. Probably about $40-50.

 

[mntcman]

Re: 57 35hp over-rev then no spark

Sent prop out for re-hub but still can't figure out why no spark. Have not removed flywheel yet but everything looks fairly new thru point window. Checked cut out switch, seems ok. tested for spark, nada. checked what wires I could see, all ok. Any suggestions?

 

[freddyray21]

Re: 57 35hp over-rev then no spark

see if there are two black wires coming out from under the mag plate. If so those are kill wires. Find out where they go to and unhook them then see if you have spark.

 

[lindy46]

Re: 57 35hp over-rev then no spark

If it's just choke button to stop, it wouldn't have a kill circuit. I think you're going to have to break down and pull the flywheel and see what's going on underneath.

 

[freddyray21]

Re: 57 35hp over-rev then no spark

If it's just choke button to stop, it wouldn't have a kill circuit. I think you're going to have to break down and pull the flywheel and see what's going on underneath.

electric start 35's had a kill circuit. It may not be hooked up, but it had one. check first for the kill wires. It can also be a sheared flywheel key.

 

[lindy46]

Re: 57 35hp over-rev then no spark

electric start 35's had a kill circuit. It may not be hooked up, but it had one. check first for the kill wires. It can also be a sheared flywheel key.

Not in 1957 - 1958 was the first year with a key switch and kill circuit. Even the '57 Lark, which was the deluxe model, had a choke to kill button only.

 

[mntcman]

Re: 57 35hp over-rev then no spark

I think the electric start was added. When it died after over reving, it did so in a gradual manner, meaning over a period of about ten seconds it gradually stopped running. I cant see any kill wires. I think I will pull the flywheel. Ive done just about everything I can without pulling. Anything I should be looking for when I remove flywheel? Manual is on its way from Marine Engine.

 

[lindy46]

Re: 57 35hp over-rev then no spark

Points clean and not corroded, and set to .020" when at the high spot on the cam. Coils should have no cracks or blisters. Post a pic if you can so we can see what you have.

 

[freddyray21]

Re: 57 35hp over-rev then no spark

Not in 1957 - 1958 was the first year with a key switch and kill circuit. Even the '57 Lark, which was the deluxe model, had a choke to kill button only.

57 factory installed electric start did have a kill switch. I've owned several.

 

[mntcman]

Re: 57 35hp over-rev then no spark

I'll pull flywheel tomorrow and post more pics. Thanks for the help.

 

[Chinewalker]

Re: 57 35hp over-rev then no spark

I'm betting that when it over-revved you sheared the flywheel key....

 

[mntcman]

Re: 57 35hp over-rev then no spark

And the winner is....sheared flywheel key. Everything under flywheel is new. I'm thinking whoever replaced parts did not torque flywheel nut down. It came off too easy. Posting some pics of flywheel damage. I think with a couple of careful strokes with a suitable file and some emery cloth it might be ok. Any thoughts?View attachment 107305View attachment 107306View attachment 107307

 

[AlTn]

Re: 57 35hp over-rev then no spark

link to attachments isn't working

 

[mntcman]

Re: 57 35hp over-rev then no spark

Try this again.

 

[Chinewalker]

Re: 57 35hp over-rev then no spark

I like to lap the flywheel to the crank if it's buggered up a little. Some light valve grinding compound will work...