Mercruiser prop

[cdt785]

Hi. I have a 1997 3.0 mercruiser with a alpha one Sterndrive. this morning when i was bringing it in, my prop hit what seams to be a rock or concrete. The prop has a few gouges and nicks in it. My question is this,how much free play should be in the prop....in and out.....and are there bearings or anything that would break when this happens. It still engages in gear and I noticed the prop does spin. Thank you for any advice in advance.`

 

[Barnacle_Bill]

Re: Mercruiser prop

Maybe 1/8 to 1/4 inch. I would get the prop rebuilt. You don't want to get stranded due to a spun hub plus if it is out of balance which is probably is, it can affect seals after a while.

 

[Texasmark]

Re: Mercruiser prop

Maybe 1/8 to 1/4 inch. I would get the prop rebuilt. You don't want to get stranded due to a spun hub plus if it is out of balance which is probably is, it can affect seals after a while.

Ditto.

The slack is required for the "over revving" feature of the lower unit to work. Upon deceleration, like you are blasting away at 40 mph and decide to cut the throttle and let the boat sink off plane, the prop is a screw in the somewhat solid water environment so it screws it's way down to the new rpm the engine is putting out; but the engine rpm responded immediately to your cutting the throttle. That means it has to slip while that happens (like an overrun clutch on an old Ford 8n to keep your mower from driving you into the neighbor's fence.)

Mark

 

[cdt785]

Re: Mercruiser prop

TYhank you both for your comments. I checked the shaft and there's about 1/8 inch movement,so i guess i'll be fine. I'm planing on switching to a 4 blade prop for towing a tube,and faster planeing time. We only go about 25-30 mph, so i'm not concerned about losing speed at WOT. I'm thing a 19 degree prop will be best. any comments on what degree prop would be best for my situation? Thanks again.

 

[steelespike]

Re: Mercruiser prop

Pitch is measured in inches.
If we're going to do some prop selection we'll need more info about your present setup.
If you read "read this first" at the top of the page and get us as much info as possible
we can get you going.A 4 blade should inprove low to mid range performance but pitch will be determined by your previous performance.

 

[ufm82]

Re: Mercruiser prop

The slack is not there for the prop to slip when you suddenly slow down. That's handled by the clutch dog in the L/U. They are spring loaded and reside in the nose of the bullet.

 

[Texasmark]

Re: Mercruiser prop

The slack is not there for the prop to slip when you suddenly slow down. That's handled by the clutch dog in the L/U. They are spring loaded and reside in the nose of the bullet.

If you will watch the prop as you rotate the prop CW in F gear you will notice it move forward slightly as F gear walks over the high points of the dog and then it moves aft slightly as you fall in the low points. Seems the spring keeps it in the low points for whatever difference that makes. Spent a lot of time in this area in adapting a peculiar prop to my engine and had to build a spacer bushing and the dimensions had to be right.

Additionally, to ensure that my lower unit was in proper order and my slop was in spec, I went to a Merc dealer and went to several similar hp new engines sitting on boats in the yard and pushed on their props and all responded as mine...went in about 1/8" and popped back when released.

Mark

 

[cdt785]

Re: Mercruiser prop

Thank you for explaining your experience Mark. I feel alot better about my Prop. Thank you all who replied . This really is a great forum. First year with my own boat. Learning as I go. Sorry that the boating season is comming to an end here. Thanks again all.