Question on prop compatability Johnson 25hp-85hp

[chazz11bravo]

I have an at risk teen I'm mentoring on the weekends. This kid is wanting to use my 85hp prop to go on his 25hp. I'm pretty sure it wont work. He seems to think he can get it to fit. I don't want the kid to waist his time. We're restoring an old Larsen Lapline and the transom needs some timely TLC.

Thank you in advance.

Chazz

 

[steelespike]

Re: Question on prop compatability Johnson 25hp-85hp

Even if it would fit ,which it won't, the performance would be worse. The bigger the prop (diameter) and the higher the pitch the harder for the motor to turn the prop. Prop size is given in inches. Diameter X pitch.
A mid range 25 hp prop would be about 10 3/10" x 12" a mid range 85 hp prop would be 13 3/4" X 17".
A big prop on the 25 would be about 10" X 14" A big prop on the 85 would be about 13 1/4" X 23".
As you increase pitch its like putting the motor in a higher and higher gear. Imagine putting a car into overdrive and trying to do everything in that gear.He's trying to put the 25 into triple overdrive.
If you read the stickys at the top of the prop forum or the helps at the prop store page it may help you understand prop technology better. Feel free to ask any questions.If you have the 25 on a boat we will be glad to help get the most out of it.

 

[Frank Acampora]

Re: Question on prop compatability Johnson 25hp-85hp

The kid wants to get the performance of an 85 simply by changing the prop. Unfortunately he doesn't have the knowledge. The prop itself will not fit--there is no doubt about that. It can not be re-hubbed to make it fit, the inside diameter is different. However, explain to him that different engines are designed for different props. Show him these replys and let him study other information in the prop forum. THEN, let him try-- he won't waste more than a couple of minutes and you won't be stifling his creativity. It will be part of a learning curve for him.

 

[chazz11bravo]

Re: Question on prop compatability Johnson 25hp-85hp

Thank you for the answers. I sure there'd be more than just an issue involving whether it would fit or not. The kid needs a new prop and is trying to save some pennies. I was trying to save him something that he doesn't realize at his age is far more valuable time wasted. Like most kids is grasping at straws. If there's even the slightest glimmer of hope of getting "it" now they don't want to take no for an answer. I was the same way growing up in a bad environment. I probably wouldn't have glanced at the long run possibilities and burned up my motor if by sheer chance the prop fit.

Again thanks for the input. I'll look at my Adult to teen language translator and hope I get the pronunciation correct. And if I get it right I'll take "cliff notes" for those of you dealing with kids with classic ptsd i.e. bad memory, ADD like symptoms, etc. etc. Or just those with kids in general. If there we're only a remedy/drug that would give kids the foresight that experience gives you with out lessening their spirit per se. One with out a 200 word list of potentially ill, painful, and deadly side effects

Sincerely Chazz

PS I'll be back with more questions I'm sure.

 

[steelespike]

Re: Question on prop compatability Johnson 25hp-85hp

As far as the prop he has; It may be able to be repaired for less than new.Though in that size new may be the better choice.
Also a prop shop or dealer may have a used prop that would be less. Sometimes they have a repaired prop that was never picked up.
If you let us know about the size of the boat the 25 is on we may be able e to suggest a size.
If performance is adequate the same size prop should work.What year is the motor?
Prop size should be near the base of the blades or under the prop nut.

 

[chazz11bravo]

Re: Question on prop compatability Johnson 25hp-85hp

I took it too a local reputable Marine shop. The owner and the manager are pretty good guys. The kids trading yard work for store credit. Win win well for me. This kid has to told a few times and shown a few times to get things right. That's after you get him toshut up and listen. I'm too old and grumpy to be able to take it for very long. Now I know why I was always told as a kid to "Go work on that over there" all the time.

Next time around I'll look up the serial numbers and have my sh@# together. I imagine that makes things easier for you all to answer these type of questions. Been working on that for the better part of 40 years. I'll understand if you send me to ask questions on another thread .

Thanks again for your patience and informative answers.

 

[Jim311]

Re: Question on prop compatability Johnson 25hp-85hp

Keep up the good work brother, you're doing a great thing.

Edit: Stock prop on a Johnny 25 should be 10x12, if that helps anything.

 

[chazz11bravo]

Re: Question on prop compatability Johnson 25hp-85hp

Keep up the good work brother, you're doing a great thing.

Edit: Stock prop on a Johnny 25 should be 10x12, if that helps anything.

Keep up the good work brother, you're doing a great thing.

Edit: Stock prop on a Johnny 25 should be 10x12, if that helps anything.

Thank you Jim. That means a lot. That thought helps me keep my patience with them. I was floored last night to find out the quiet one's mom died a year or ago. I'm getting to come out of his shell. He's clean now though. It's hard to get a kid to realize that drugs only hide the pain. Unfortunately he's perma fried and has no self esteem. He's a good kid though. Again thanks all.

I'll be in the "Mariner section to see if a motor I bought is a good that I can find parts for. Or a hard to find parts for one my friend that owns Lynnwood Marine told me about. See y'all over there.

PS My typos and grammar aren't so good thanks all the d's. ADD PTSD etc. etc. Sometimes you have to look at it like a fill in the blank puzzle.