yet another slippage question

[Commander_47]

Last year, I had trouble with my prop and ended up buying a new one. Old one was 14 inch 18 pitch. I replaced it with a 14.2 in Solas Amita 3, 21 pitch.

First time out this year, had all the grand kids, and we were treated to the disintegration of the engine coupler. Not fun, but another family story for Thanksgiving.

I spent all summer, and prime boating season, pulling the motor and doing a ton of work.

Boat is a 24 foot cruiser, with 5.7 Mercruiser alpha 1 gen 1. It is an older boat but I like it because it still has teak wood trim, and teak swim platform.

I went ahead and put in a new coupler. It is the older triangle shaped type without the grease fitting. While I was at it jobs included the power assist steering, exahaust, new rubber etc etc.

I also redid the stringers and put in new engine mounts. I was careful to align the motor and gimbal using the store bought alignment tool. I adjusted the motor until the tool slipped in easily, and the sterndrive also slipped in easily.

One small issue arose when I went to put the cables back on. The shifter on the stern never did face exactly straight forward until after this last replacement of the impeller. Now it faces directly forward for forward gear.

This seemed to alter the cable alignment somewhat as I had to lengthen the remote cable on the motor to achieve first gear and reverse.....withe the reverse setting in the upper most position.

Having said all that, my wife and I took the boat out for the first time yesterday and everything was awesome. Cruising at 3500-3800 at 25-30 mph was just fine. I decided to check out WOT and began easing up the 4000 and suddenly the engine was spinning with no apparent gear connected.

I immediately shut down, and eased it back up on plane again with no problem running at 3500. Whenever I tried to push it up the motor spun out of gear at around 4000.

Since I have a new prop, new coupler, and newly aligned motor mounts I am at a total loss.

I just can't believe a new coupler would spin out after only about 15 minutes of running time.

I'm wondering if I may have too much prop. Would cavitation cause such a thing?

Any and all advice sought and welcome. thanks.

 

[Bondo]

Ayuh,...... Welcome Aboard,...... Any chance you were carrin' a buncha weeds on the prop/ drive,..??

 

[TurtleTamer]

Curious, why'd you go from an 18P to a 21P? I'd've thought a 19P the next natural step if you were over-revving

 

[wellcraft-classic210]

Are you installing brand new parts or used //If used that could be the issue // If new you might want to try another prop that's close to what your boat had in it when new // Prop cavitation is rare but a possible // cruisers tend to run larger diameter low pitch props in many cases

 

[Commander_47]

The coupler is new old stock. I did not get any burning, smoke or other indications.

It shifts wonderfully. Better than ever. I was able to go from forward to reverse smooth as a caddy, and it was good and strong in reverse. In fact, i was able to back into my slip!!!! That was a first. Normally the wife has to do her little dance to get us secured.

I was hesitant to go with the bigger prop, but it was all the marina had!!!!! I got the closest one to the size I need. Even Solas doesn't seem to have one the original 14 X 18 my size.

I actually thought the V8 would have no problem with it. Neither did the marina.

Do you think a 14.5 X19 would be a better fit?

This 21 sure does get my boat up on plane faster.

 

[wellcraft-classic210]

Are you sure about the diameter on the old prop being 14 inch ? . My 26 cruiser uses a 16 inch dia on an alpha but yours may differ.

Can you find out what your boat came with originally ?

Otherwise a lot of trial and error can be had --and most importantly the top WOT rpms need to be in a certain rpm range or the engine can get damaged

Pretty sure its 4400 to 4800 for your engine.

 

[wellcraft-classic210]

A few added thoughts

Lots of variables hare -- the key is narrowing them down.

Was the prop new and does it have a removable square hub or pressed in hub.// The ones with integral hub are pressed into rubber and can slip under heavy load.

If you can borrow & try another prop that may provide a lot of info. with not much labor // Might want to verify your trim is working and the drive is going down as well.

 

[Commander_47]

I really appreciate all your info, and I'm going to check it all out.

I did the prop research and it appears that my boat should have something in the 14.5-15 range around 19 pitch.

I'm sure the prop was original. I got the boat with only 40 hours on the engine and it had been sitting unused for over 20 years!!!! I had to replace all the rubber as it was dry rotted.

The prop I bought is a Solas Amita 3. Pressed in rubber hub. All reviews say this is a great prop.

I went ahead and orderd a replacement Solas Amita 3, 14.5 X 19 prop. It was cheap enough on here and seems to be closer to the recommended size. I figure I can always use a spare and I can always sell one if I need to.

to fit that 21 pitch, I had to grind out the anode to make room for it!!!. So that had to be the wrong size.

After I get the new prop and double check the coupler I'll post again.