Non-thru hub vs thru hub on a '89 125HP Force

[dmas]

my question is, would it make any difference if I use a thru-hub exhaust propeller on my non-thru hub exhaust motor?

 

[jay_merrill]

Re: Non-thru hub vs thru hub on a '89 125HP Force

Assuming that you can get one to fit the motor in question, I would think that the hub diameter wouldn't match the diameter of the "hump" in the gearbox. This would probably cause drag and turbulence, which might lead to cavitation.

All of these thoughts are "WAGs", so I guess the best thing to do is just to try the idea.

All of this said, why do you want to do this? Is it because you can't find a particular diameter/pitch prop for your Force motor?

PS: I just 'image googled" a 1989 125hp Force engine and the pic I am looking at is a thru the hub exhaust engine. I really don't know these motors very well, but are you sure of the year of your motor?

 

[dmas]

Re: Non-thru hub vs thru hub on a '89 125HP Force

Hi Jay

the difference between a thru hub exhaust propeller and non-thru hub exhaust propeller is that the thu hub one has large open exhaust ports around the shaft and the other does not. the hub diameter is the same on both.

and I'm asking this question cause I bought one thru-hub exhaust propeller for my non-thru hub exhaust motor, it fits fine, but, my concern is if those open holes on it will affect the motor performance in any way.

here's a pic of a non-thru hub (top) and a thru hub exhaust (bottom)

 

[Frank Acampora]

Re: Non-thru hub vs thru hub on a '89 125HP Force

On an 89 single exhaust lower unit, it makes absolutely no difference. Performance will be the same with either. Currently, I am using an open hub Michigan stainless prop on the engine in my avatar. It drives a 21 foot cuddy at 38 MPH. Not too shabby.

In fact, When Chrysler first developed that one piece lower unit, it was one inch shorter than the two piece lower it replaced. There were ventilation/cavitation prioblems. So, Chrysler made the black plastic "Flare Washer". It fit behind the prop nut and made the prop look very much like a thru-hub exhaust prop.

At any rate, anything will be better than the P.O.S. stock, black aluminum, semi-cleaver prop some Forces came with. And, of course, a dual exhaust lower unit requires the use of an open hub prop.

However, on your engine, the only caveat is that you must use the correct sized hub. I forget the exact size but for example, while Force used a 4 1/4 inch gearcase, Merc and OMC used a 4 1/2 gearcase. The splines on their props are the same but the hub will not fit into the gearcase recess.

You must also be careful if you buy an after-market prop. For example, the Vortex advertises that the prop will fit Force engines. They don't know or won't tell you that the internal prop webs will interfere with the anode on the gearcase behind the prop. Use of this prop requires removing or drastically reducing the height of the anode. Then there will be plenty of clearance. YES: I have a Vortex. It is the exact same prop and part number as the small gearcase Mercury and will fit when the Force anode is removed. Before you ask: YES! Some Merc engines had a smaller diameter gearcase.

So, in short, use any style prop you want to as long as the hub diameter is correct.

 

[jay_merrill]

Re: Non-thru hub vs thru hub on a '89 125HP Force

I understand the difference between the prop types, but take Frank's advice. He knows the Chrysler and Chrysler derivative motors better than just about anyone around here, so you can take his word for it on this subject.

 

[dmas]

Re: Non-thru hub vs thru hub on a '89 125HP Force

thank you guys for your help, I have 2 propellers now, one is an aluminum Michigan 13 3/4 x 17 that I have been running for while without any problem, my concern was (as explained on another post) that I wasn't getting the factory recommended RPM at WOT.

So I bought a 13 1/2 x 15 repaired Michigan that came out of a Honda outboard, but the shaft is the same 15 tooth spline , the only difference without this 2 propellers and the one that came with the boat is that this two props are flat on the back when they meet with the anode while the factory one has big rubber O'ring where it meets the anode, but I haven't noted any difference besides the way they sit.

I will post pics of both factory and the others ones tomorrow so you guys can see what I'm talking about.

 

[jay_merrill]

Re: Non-thru hub vs thru hub on a '89 125HP Force

If Frank says this is OK, I'll take his word for it, but I do have one question - what holds the prop in place from the front? On OMC motors that use thru the hub exhaust type props, there is a thrust bushing to keep the hub of the prop fron contacting the hub on the gearbox. I know that many Chrysler derivitive motors make use of both splines and a pin, and that the purpose of the pin is to hold the prop in place rather than to drive it, but does this work with the thru the hub prop?

 

[dmas]

Re: Non-thru hub vs thru hub on a '89 125HP Force

Hi Jay in my case, the prop is hold by a big nut, then theres a washer, the prop and the anode on the back..here's a pic.

and this is what I was talking about, first pic is the factory prop. and has big O'ring around the hub and the second one is the one I got, it does not have any rubber on it, it's just flat.

 

[jay_merrill]

Re: Non-thru hub vs thru hub on a '89 125HP Force

Can you post a pic of the prop shaft, minus the prop, showing the anode?

 

[Frank Acampora]

Re: Non-thru hub vs thru hub on a '89 125HP Force

On the first prop, you are seeing the rubber hub that cushions the prop during a hard strike. It is not an O ring but a rubber sleeve that runs most of the way through the prop. This and the bronze splined hub it is glued to are pressed into the center of the prop.

In the second photo, you are seeing the thrust washer stuck into the aluminum hub. If this thrust washer fits your shaft taper, use it and do not use the one already on the shaft. If you remove it the prop will look similar to the other, unless it is attached to a removable urethane hub like a Vortex prop.

It would be a good idea to tap it out with a hammer and screwdriver or drift pin. If it is not part of a urethane hub, clean the corrosion holding it into the prop hub. Then coat the inside of the aluminum hub and the outside of the thrust weasher with anti-seize.

RE-examining the photos. if the prop is the one installed in the very first photo, it looks like it has proper clearance from the gearcase. Since the thrust washer seems to have a much larger hole than the prop shaft, perhaps it is designed to be used with the existing thrust washer. Explain how you mounted the propeller because it seems that that thrust washer would allow the prop to slide too far down the shaft. Did you change thrust washers? Did you use both? Did you remove the stock one?

I suspect that you need to remove the thrust washer from the new prop and install the stock one and hopefully it will fit the aluminum center.

I also hate to be the bearer of bad news, but (don't you hate that little word?) The prop in the second photo does not look like it will plug into the gearcase--only a photo and I could be wrong. But notice the difference in the machined flange on the original prop and the new one. If they indeed are the same diameter, then the new prop will fit. If the new prop has a slightly larger diameter at this flange, then it will not fit. However, I doo seem to remember that with some aftermarket props, Honda did have the same part number, so you may be good.

 

[dmas]

Re: Non-thru hub vs thru hub on a '89 125HP Force

Hi Jay, here a pic of the shaft without the prop and the other pic shows what's in front of the prop.

Frank, thanks for clarifying the rubber seal on the prop. the second prop fits fine, but I'm not gonna use it, that one is being returned, I bought it off ebay from a seller that listed it as NEW but it was actually repaired, I'm getting a used one in good cond 15 pitch from a Force motor.

here's also a pic of the one I have (17 pitch) and it actually shows what you said, I used the thrust washer that I had from the old one and as you can see in the pic it clears the gearcase just fine with it and I always use anti-seize on the shaft.

thanks again guys for your help.