1985 85 hp force prop question

[timdan94]

I have a 1985 85 hp force that I can only get about 4800 rpm out of with just me in the boat with 2 other people I get only about 4200-4400 rpm. the wot range is supposed to be between 4500 and 5500 rpm. it came with a 12.7 x17 4 blade comprop on the boat. I'd like to go back to an aluminum 3 blade prop but have no idea what size to get. I don't know how fast I was going because I don't have a speedometer. I just put a 20 pole tachometer in the boat and I am not sure that it reading right because the engine sounds like it is really revved up.
any help is greatly appreciated.

Thanks

 

[steelespike]

Re: 1985 85 hp force prop question

Unfortunately without the speed we really can't tell anything.Especially with the possibility of an inaccurate tach. Perhaps you can borrow a gps or have a friend with a gps go for a ride.What size/type of boat?weight?If you give us make model and year we may be able to find weight.
In the mean time you might check the setup.If you have no ventilation problems the motor is probably too low.Antivent plate(just above prop) even with the bottom of the boat is considered a starting point.Is the motor well tuned,good compression?Is the throttle opening all the way?Prop in good shape?

 

[timdan94]

Re: 1985 85 hp force prop question

the tach is brand new and is supposed to be calibrated with in 3% from the factory. its a 15ft 1986 mfb caprice the hull is supposed to be 650 lbs, the engine 250 lbs the prop is in excellent shape. I think I have it to the point where if I go out from the transom to another position that it will porpoise because with just me in it with little waves it already starts to but then smooths out. when you get past the waves.

 

[Frank Acampora]

Re: 1985 85 hp force prop question

The Comprop IS your problem. Get yourself a nice Michigan three blade 13 3/8 X 17 pitch aluminum and you will most likely see the rpm increase a couple of hundred. These props were 13 3/8 inch diameter but sometimes are listed as 13 inch--so either is acceptable.

Comprop is great when you boat around rocks because the blades either flex or break off. But, that's the only positive to them. They are good as an emergency prop.

If you are flush with cash and boat in clean, deep water, and it is not common to "customize" the prop with rocks, buy a three blade Michigan stainless cupped 13 X 17 prop.

And, BTW: The smaller boat is going to be sensitive to load. As you put more people in it it will slow down moreso than a larger boat having the same amount of people increasingly loading it.

 

[timdan94]

Re: 1985 85 hp force prop question

"And, BTW: The smaller boat is going to be sensitive to load. As you put more people in it it will slow down moreso than a larger boat having the same amount of people increasingly loading it."

Thats why I'm trying to get around the 5500 rpm mark with just me and fishing gear in it.

"The Comprop IS your problem. Get yourself a nice Michigan three blade 13 3/8 X 17 pitch aluminum and you will most likely see the rpm increase a couple of hundred. These props were 13 3/8 inch diameter but sometimes are listed as 13 inch--so either is acceptable.

Comprop is great when you boat around rocks because the blades either flex or break off. But, that's the only positive to them. They are good as an emergency prop.

If you are flush with cash and boat in clean, deep water, and it is not common to "customize" the prop with rocks, buy a three blade Michigan stainless cupped 13 X 17 prop."

unfortunately I mostly boat the Susquehanna river in pa so a lot of the water is 20ft or less usually about 7 ft... I launch in about 3-4 ft.

 

[timdan94]

Re: 1985 85 hp force prop question

Has anyone run propco props? I see them in one of my catalogs here and they are one of the few that sell them for force outboards.

 

[timdan94]

Re: 1985 85 hp force prop question

Do you have to get new tachometers calibrated. Because mine says that my boat is idling about 1000-1100 rpms and only gets to about 4800 wot with just me in it but it sounds like it is screaming.

Thanks

 

[steelespike]

Re: 1985 85 hp force prop question

Turn the idle down to about 700 in gear moving.If it seems to run good at that speed then the tach is probably accurate.By the way if the motor really is at 1,000 that is hard on the shift dogs when you shift and can cause premature wear.Would be good to get her idled down.
If we knew your speed at max rpm we could tell better if the tach is accurate and the prop produceing the proper speed for the rpm.Then we can
tell better what pitch change is in order.

 

[timdan94]

Re: 1985 85 hp force prop question

I had to remachine the clutch dogs a few weeks after I got the boat so I think thats why it had to be done... I'm gonna have to wait til spring to idle it down. I did notice that when in no wake zones the boat is going pretty good and throwing a pretty good sized wake.

 

[Matthew A.]

Re: 1985 85 hp force prop question

So far every tach I have ever used with my 85hp Force refuses to show a reading below 1100 or 1000 rpm even when it's obvious the motor is idling at a much lower rpm. Also, while the tach is showing 1000 rpm or so at idle the needle will be jumping around a hundred or so rpms in either direction. However, the same tach reinstalled on a friends boat with the same year Force engine and the tach reads as it should. Which leads me to believe that it may not be a tach issue persay but possibly a quality control issue. Perhaps something to do with the windings of each individual stator and the manner in which the windings may have been wrapped around the core at the factory.

 

[timdan94]

Re: 1985 85 hp force prop question

mine holds steady. it even sounds like the engine is idling high

 

[timdan94]

Re: 1985 85 hp force prop question

I got this prop for $50. it was remanufactured. it looks good. it is a 13X17 he told me that the 13X17 comprop 4 blade that I was using was causing a lot of problems with loss of rpms because it didn't slip enough. he said that the 13X17 three blade would help a lot.

 

[timdan94]

Re: 1985 85 hp force prop question

Well after getting rid of the comprop and adding trim and tilt it no longer kicks out of gear and I'm now running 5200+rpms. thanks for the help guys

 

[Frank Acampora]

Re: 1985 85 hp force prop question

I told you!

BTW: that looks like a Michigan manufactured closed hub Chrysler prop. Chrysler and Force engines seem to like that blade profile and seem to run better with that design prop.

AS a remanufactured prop or repaired , they did a good job. most times they grind the leading edge and change the blade profile.

 

[timdan94]

Re: 1985 85 hp force prop question

It used to slip out of gear when I'd throw the hammer down. with the power trim and the new prop it doesn't even kick out when I stand on it from a stand still I think the comprop was too hard on the drive line.

 

[timdan94]

Re: 1985 85 hp force prop question

I have another question. Now that it is running good and I have trim should I raise the motor? here is the situation: I had me, my fiance, gear and 12 gallons of gas in the boat I could trim all the way out and start tilting without the prop blowing out and without porpoising.

 

[Frank Acampora]

Re: 1985 85 hp force prop question

With the Force, assuming the lower bolts are in the upper two clamp holes. you only have the option of going up one inch without re-drilling the holes for the lower mounting bolts.

If the ventilation/cavitation plate right now is even with the V in the transom or slightly below it, then try going up that one inch. I won't give you a remarkable increase in speed but you may gain some. You may also find that with that full inch ventilation will now be a problem and you will need to tuck trim all the way in until the boat is on plane. Ventilation may also be objectionable in turns.

But raising that engine is easy: You don't need to disconnect anything. Loosen the top clamps a bit--not all the way, just enough so the clamps will slide up.-- then remove the bottom bolts. Use a crowbar or tire iron to wedge up the transom clamps on each side and block them with wood scraps. Then center the engine again again and reinstall the lower bolts with plenty of RTV silicone. Less than 1/2 hour of work--even if you need to re-drill the lower holes.

 

[timdan94]

Re: 1985 85 hp force prop question

thanks again Frank. I'm new to this and trying to get the most out of what I have.