new prop

[geoff69]

.Problem.Fitted new prop to replace one damaged by a careless rock.
Motor:1976 75hp Johnson stinger.
Boat;1971 Wescraft 17.
Dealer looked in magic book,said 12/17standard for this motor,however,when fitted and tested yesterday OK at low speed but can not get out of the hole and starts cavitating at about 2/3 revs.It seems smaller than the damaged prop which unfortunately had no identifiyng marks of any kind on it.
Suggestions/advice greatly appreciated.
Geoff69

 

[walleyehed]

Re: new prop

Dealer's book is magic alright....there is no "magic" book, and there is no "STD" prop for that engine.
Sounds like he jumped a step-up in pitch...maybe dropped diameter..depends on the Make of prop.
With the prop off, there should be a P/N and/or size right under the nut and washer.

 

[geoff69]

Re: new prop

Took it back in today,dealer said he must have read it wrong and has ordered another 13 !/4/17 wich he says is the listed size so I guess we wait and see.Thanks for the response.Have a good day.
Geoff69

 

[walleyehed]

Re: new prop

We got a problem here....
Did you give him a wide open throttle rpm with the old prop?
Does he know the pitch of the old prop?
What are you/he referencing to order the new prop?

Now...your dealer may be thinking this engine uses the small diameter props of the early years, ie the 12X17, when it should have been the 13.25X17, which is fine "IF" thats a match to what pitch and the same make you had before.
Keep us posted on how the newer one works.

 

[Dhadley]

Re: new prop

I bet he looked at the page in the parts book for a 15" 75hp. They had the smaller gearcase and used the smaller diameter props. If yours is a 20" model it takes the larger diameter props.

"Back in the day" a prop came with every motor. The installing dealer was supposed to swap it out for the correct pitch, which rarely happened. The prop shipped with the motor said "std" in the parts book. It still confuses dealers today. Obviously.

 

[geoff69]

Re: new prop

We got a problem here....
Did you give him a wide open throttle rpm with the old prop?
Does he know the pitch of the old prop?
What are you/he referencing to order the new prop?

Now...your dealer may be thinking this engine uses the small diameter props of the early years, ie the 12X17, when it should have been the 13.25X17, which is fine "IF" thats a match to what pitch and the same make you had before.
Keep us posted on how the newer one works.

OK, here's the deal.I have managed,by dintof a lot of scraping and emery work ,to uncover some marks on the damaged prop.They don't convey anything to me but someone may understand them.
Under the nut it says MICHIGAN PJ 89 CUP.With michigan at the top and the rest on oppsite side going counter clockwise.Does this mean anything to anyone? Is it a manufacturers code? Any takers.
Geoff69.