79 thunderbolt 500 blue 50hp starter not engaging flywheel

[Mack43432]

G'day

Took the boat out last week and it didn't want to start. Battery was fully charged.

Starter would spin hard but not go up.

Looked under the cover and seen a badly corroded wire from the starter motor to the solenoid, played with it and off she went.

Replaced the wire and now she's not starting. It does what it was doing initially, starter spins but its not going up.

I am now thinking it was just luck it started after i tweaked the wire.

Whats the best way to troubleshoot this ?

 

[Mack43432]

Re: 79 thunderbolt 500 blue 50hp starter not engaging flywheel

G'day

I worked out that the internal harness was buggered.

While my mate held the key, i played with the wiring harness (just behind the main plug) and got no power, then it spun but wouldnt go up, then bang she started.

I went out and got a new harness, installed it, tested it at home and she cranked 3 times in a row.

So now im thinking i've fixed the job myself, time for a fish.

Get on the water and shes not engaging the flywheel once again.

Any help would be much appreciated.

Mack

 

[ajgraz]

Re: 79 thunderbolt 500 blue 50hp starter not engaging flywheel

Are you saying that the Bendix drive (the part with the teeth on it, probably 10 teeth I'd guess) is not going up to meet the flywheel? Not going up AT ALL, or not going up with enough force to mesh with the flywheel?

 

[Texasmark]

Re: 79 thunderbolt 500 blue 50hp starter not engaging flywheel

It takes around 150 amperes of current to start your 50 hp engine. Doing the Ohms law thing with a 12v battery and requiring 150 amperes out of it you are talking about 0.08 Ohms of resistance in the circuit max to drop the 12v.....that is the total drop, has nothing to do with the voltage you need to the starter. But you need voltage at the starter, like at least 10v to get the bendix to spin up and connect to the flywheel and then turn the engine.

So now we are looking at 12v-10v = 2v of drop with 150 amperes needed to do the job. Bringing in Ohms Law again, that means that the most resistance you can have in the circuit from the battery to the engine starting circuit is 2/150 =0.013 Ohms. In case you are non technical, that's nothing.....i.e a short circuit.

So sir to do the starting job you need adequate sized wire and clean terminals, not outside, but inside where the current flows...clean and bright and tight.

If you get all that cleaned up and still have a problem then take a pair of common pliers and jump across your starting solenoid large terminals...switch and if it works, get a new one...starting solenoid.

If you need more info, come back.

Mark

 

[Texasmark]

Re: 79 thunderbolt 500 blue 50hp starter not engaging flywheel

Are you saying that the Bendix drive (the part with the teeth on it, probably 10 teeth I'd guess) is not going up to meet the flywheel? Not going up AT ALL, or not going up with enough force to mesh with the flywheel?

You need enough current to spin the starter fast enough to run the bendix gear up to engage the flywheel. But that's not the high current requrement. The high current comes into play when you need enough volt-amps to spin the flywheel at a couple hundred rpm to get the engine to light off.

Mark

 

[Mack43432]

Re: 79 thunderbolt 500 blue 50hp starter not engaging flywheel

G'day Texasmark

I've replaced the starter soleniod and now she's spinning the flywheel.

Thanks.

But shes not starting.

Sounds like she wants to start, might just be flooded.

Any ideas ?

Thanks again

Mack

 

[Texasmark]

Re: 79 thunderbolt 500 blue 50hp starter not engaging flywheel

G'day Texasmark

I've replaced the starter soleniod and now she's spinning the flywheel.

Thanks.

But shes not starting.

Sounds like she wants to start, might just be flooded.

Any ideas ?

Thanks again

Mack

My experience is just the opposite....fuel starved.

You didn't say what your experience with this engine was.

Fresh fuel mix. Set the engine at or near vertical. Squeeze the bulb till firm. Activate the choke. Run starter for 10-15 seconds. If no go, firm up the bulb. Do it again. If no go pull the plugs and see if they are wet. If dry fuel starvation. Possible cause idle screw not set right (ROUGHLY 1 1/2 turns open...depends on a lot of things, may only need 1 1/4 turn), carb float valve stuck shut.

If plugs are wet, ignition problem. but my experience is that almost firing and not catching is inadequate fuel. Might check compression just for grins.

Mark

 

[Mack43432]

Re: 79 thunderbolt 500 blue 50hp starter not engaging flywheel

G'day.

I've had the engine for about a year now and shes never let me down until now. She usually starts well, no strange noises or knocks.

I went through your starting guide she didn't start, pulled the plugs and its an ignition problem, got no spark.

When I changed the starter solenoid i changed the dizzy aswell (they were connected) but now im back on the original starter solenoid and dizzy and shes engaging and engaging fast, but wont fire due to no spark.

I'm now thinking it was the bendix that was stuck originally, really greased her up and not a problem.

Before i was unable to lift the cog by hand, now i can do it easily.

Mack

 

[Maxz695]

Re: 79 thunderbolt 500 blue 50hp starter not engaging flywheel

do not take this as fact but as a suggestion test te switchbox as I fear damge has been done to the electrical system.

 

[Texasmark]

Re: 79 thunderbolt 500 blue 50hp starter not engaging flywheel

G'day.


When I changed the starter solenoid i changed the dizzy aswell (they were connected) but now im back on the original starter solenoid and dizzy and shes engaging and engaging fast, but wont fire due to no spark.

What is the "dizzy"?

 

[Mack43432]

Re: 79 thunderbolt 500 blue 50hp starter not engaging flywheel

G'day texasmark

The dizzy is aussie slang for distributor.

Checked all terminals are clean again but no action yet.

How can I check if the switchbox is damaged ?

Mack

 

[Texasmark]

Re: 79 thunderbolt 500 blue 50hp starter not engaging flywheel

"Okaye" on the dizzy. Grin.

You can buy or subscribe to a maintenance manual on this site. Seloc makes an excellent manual. Actually I have both OEM and Seloc for my current engine and I prefer the Seloc. Rather than buy the whole thing, I just online subscribe for a period of time and pull down what I need. Fast and cheap.

Mark

 

[Mack43432]

Re: 79 thunderbolt 500 blue 50hp starter not engaging flywheel

G'day mate

What I was referring to was the power pack, not the distributor.

Took it to my mechanic and he tested it out.

Got the motor started, she starts now but wont turn off.

He said to take it to an auto electrician.

He tested the box out and said that it was fine, it must be something not right in the electrics.

What would cause the engine to start but not turn off ?

Could a killswitch installed fix this ?

I've been looking around on ebay and bookstores for a book manual for my boat, not a fan of the digital manuals/printing out etc..

Picking up the boat tonight, will know abit more.

Thanks Mack


Mack

 

[ajgraz]

Re: 79 thunderbolt 500 blue 50hp starter not engaging flywheel

You saying it won't turn off when you turn the key to "off"? If so, either there's something wrong with the ignition switch, or the kill wire (orange, possibly yellow/black on your year) under the cowling is not attached at the switchbox.