Chrysler 45 running wild

[pbiwolski]

I "inherited" a early 70's 45hp Chrysler last year from a guy who said it "ran great." It did well for the first few trips (short runs to a fishing spot) and then it went nuts. The best way to descibe it is that while running full throttle on mild(ish) water the sound of the motor would race into a high-winding pitch (like a chainsaw or something). I quickly would back off of the throttle and baby it for awhile. (I can't say that it lost thrust until I back off.) The problem occurred several times so I asked around for advice.

This advice led me to taking the L/U off to find the gears in terrific shape. It was resealed and reinstalled. It ran strong and then...rrrwwwaaaahhh - running wild again!

It seems when the river's flat, I can ease up to full throttle and it runs stong. When I hit choppy water, off it went again.

Any thoughts? I'm afraid of causing (more?) damage if it continues.

 

[Frank Acampora]

Re: Chrysler 45 running wild



This engine is mounted with the anti-ventilation plate one inch above the apex of the hull vee. because of the angle it looks greater.

A couple of photos of the engine and transom would not hurt--specifically the lower end, bottom of the hull and prop.

It sounds like the engine MAY be mounted too high on the transom leading to propeller ventilation under certain conditions. There is also the slight possibility that the rubber hub inside the prop is slipping but this is usually rapidly progressive to the point where you would not even be able to get forward motion at idle. That is not what you are describing.

The anti-ventilation plate (cavitation plate) is usually set from about even with the hull bottom to about one inch above it. Lower increases drag and higher usually leads to ventilating the prop--at speed, the propeller sucks in surface air.

 

[jerryjerry05]

Re: Chrysler 45 running wild

Spun propeller hub?

 

[pbiwolski]

Re: Chrysler 45 running wild

You're initial diagnosis is the best thought I've heard yet. At a glance the cavitation plate appears to be slightly below the keel. The keel runs the length of the V, but stops about 18" short of the back (making it appear to be at least 2 inches below the hull).

One thing to add to the scenario, the boat tends to lean to the right as the drivers seat/console is located there. I do try to level it out and even kneel in the middle while steering at times. I cannot say with certainty that the only time it runs wild is when the boat is leaning, but I'm definetely considering it and will be watching for it (hopefully this weekend!).