1973 Chrysler 45 hp prop replacement?

[pbiwolski]

I've been having an issue with reaching top speed over the last two years. I've posted about it in the past, but never found the solution. The motor seemed to go out of gear ? at about 3/4 speed. A 2-cycle genious of a friend, but not a marine mechanic at all, was trying to assist me. He thought that the rubber bushing inside the prop is wore out and is probably slipping under load. So he took it off, put it in a vice, put a screwdriver through the pin holes, and spun it a bit before breaking the screwdriver (cheap)! He's convinced I need a new prop.
If that's so, what are my options? It is a Michigan pr 132 that looks to be about 10 inches in diameter. Don't know about pitch. I have a 15 ft (some kind of V) fishing boat. I don't need crazy performance, but I would like to get it full throttle without is going nuts on me.

 

[Frank Acampora]

Re: 1973 Chrysler 45 hp prop replacement?

Well, It depends upon what you consider top speed. That engine on a 15 foot fiberglass boat would only deliver about 25 MPH. It is also really important to know what RPM the engine is turning. RPM at wide open throttle would be around 5000 for that engine

That said, slipping or popping out of gear can be due to a worn prop bushing or it can be due to a worn dog clutch. It could also be something as simple as a linkage alignment. However, if the engine seems to race at 3/4 throttle and the boat goes no-where, then yes, it most likely is a bad rubber bushing in the prop. If this is the case, the prop can be "pinned." See photo

If the engine seems to pop out of gear and thumps loudly at 3/4 or above, then it would most likely be worn clutch dogs.

PA is a big state. Where are you located? I have a number of stock props as well as bronze props that would fit that engine.

Stock props can be purchased new here at iboats or almost any marine supply. You would look for props for a Force 50, 1984 through 1992. They come in nominal 10 inch diameter (10 3/8) with 11 1/2, 12 1/2, and 13 1/2 pitch. Other pitches can be found used by searching the auctions

 

[pbiwolski]

Re: 1973 Chrysler 45 hp prop replacement?

Hi Frank, thanks for the reply. I'm in York County and I boat on the Susquehanna River. Can't be too awful far from your location!?

No loud thumps you described. The boat is aluminum if that matters, and I'd be happy with 25 mph!

Looking closer at the prop, the hub seems to sit slightly off centered. I'm assuming "pinning" is out of the question in this case? Tell me more about your props and/or what you recommend. Money is an option for me, and any advice is welcome. Thanks again.

 

[Frank Acampora]

Re: 1973 Chrysler 45 hp prop replacement?

I am located in West Chester, about an hour from York. Occasionally I go down to Conowingo and boat on the Chesapeake. It takes me about 1 1/2 hours to get there.

Assuming the engine runs well, and no loud thumping, then if you are losing thrust at over 3/4 throttle, it is likely that the prop is "spun."

However, it is also likely that the engine is losing fuel at over 3/4 throttle and going "flat." A simple fuel pump diaphragm change will fix that condition. If your buddy bent a screwdriver trying to make the rubber hub slip, this may be the problem.

At any rate, if you want to explore getting a new prop send me a private message with your email address and I will send my email address. Then I can send you photos of the props I have on hand.

And no, a crooked or off center hub does not necessarily mean you can't pin the prop. You could wedge it straight then drill and tap. The screws will hold the hub properly centered.

 

[pbiwolski]

Re: 1973 Chrysler 45 hp prop replacement?

The engine races more than anything when this problem occurs (usually at 3/4 or so throttle). It will sometimes to do it at 1/2 throttle after that. I'm forced to baby it until I reach the dock in such cases.

As to the diaphragm...Once in a while it will drop out, almost shutting off, while at decent throttle. At which case, by the time I shift to neutral, it is back to purring and I get on it slowly again. Does that sound relevant to what you're suggesting there?

As to the pinning, is there a trick to getting it back to center, or is eyeballing as good as I can expect?

 

[Frank Acampora]

Re: 1973 Chrysler 45 hp prop replacement?

Spin the shaft with the prop on it. If the prop wobbles then the hub is not centered correctly. If the prop does not wobble, then the hub does not need to be re-centered. Now, there is a bit of clearance between the shaft and the prop hub AND the thrust pin will let the prop wiggle a bit under no load conditions. Don't let this confuse you. An off-center hub will allow far more movement.

In any case, you can wedge shims between the prop and hub to center it and test for wobble before pinning. Drill three 3/16 holes from inside to out at a slight downward angle. Use the notches in the prop to space them evenly. Use a new drill bit as the bronze hub is difficult to drill. Tap the holes 1/4-20. Use three 3/4 inch long stainless set screws. locktite is not necessary.

The other problem could be an intermittent clog in hoses, fittings or carb, partially obscured screen in the pump inlet, a hardened diaphragm, or any combination. Thus, completely check the fuel system from tank to carb.

Just be aware that the Sussquehanna is a rocky river and pinning the hub will negate any slight protection a rubber hub will afford the engine in the event of a strike.