Coupler or prop?
aero3113
Member Posts: 8,812 ✭✭✭✭✭
We were heading out for an overnight to one of our favorite spots. When I went to get up on plane I noticed it was taking a while to get up over the hump. Once I did I could only get the engine up to 4200 RPM. Once on plane all was fine. Got to a no wake zone and idled through. Once out of the 5 MPH zone the boat hoped up a lot quicker and got on plane, cruised for about 30 minutes then the RPM's shot up, I powered back and now all I get is about 1500-2000 before the coupler or prop starts to spin? I'm able to putt around at 3-5 knots and the engine temp is good. We ended up docking at our spot for the night, I looked at the coupler and no sighns of rubber dust or burning rubber smell. I tried to look at the prop but couldn't see much. What do you guys think?
Comments
PC BYC, Holland, MI
I have an alpha one attached to a 5.7 Merc.
Mine behaved just like that last month when my coupler failed but your boat comes out of the water either way and it'll be easy to know. Mine only had 300hrs but the drive alignment was horribly wrong and although I'd been told it was checked, it obviously wasn't.
My guess/hope is a prop hub which is pretty painle$$. On the other hand having just changed the coupler in our '04 270 I barely saw any rubber debris and never smelled any burnt smell. After the coupler came out I found the slightest amount of ground rubber around the outer edge of the hub so I think I solved my issue. The irony of having an ear for odd mechanical sounds is you catch problems almost instantly, well before it destroys itself making it obvious whats wrong.
Hope that isn't your issue but considering what you do for a living, pulling this motor is like turning on a light switch. I'd say getting all the ground wires reconnected on top of the bell housing underneath the PS ram was the hardest part. A coupler is pricey but amazingly basic engineering.
Here's my weekend project and a $300 OEM hub from Ebay. I was glad I pulled it if not just to service everything underneath that I couldn't get to later.... and to fix the OD alignment before it toasted my $8k drive. Mike
It was the prop hub!
I replaced my 3 blade 18-16436-14 with a 4 blade 14-1/2-17 but could only get 3200 RPM's ( I was getting 4600 with the old prop) Did the guy at the marine store set me up with the wrong prop? He used a little computer to calculate for the correct prop. I plan on using the old prop as a spare when I get it fixed.
OH if it was the coupler you would know sounds like a junk yard grinding metal and very un healthy to your wallet believe me I know glad it was just the hub
Aero - in my opinion 3200 rpm is no good for your engine you will kill it fast at those rpm. It will not be falling in its wot band and you will be lugging it. Even 4600 rpm is the middle of your wot range which, unless I am misinformed, should be 4400-4800.....but 3200 - bad! :-( MT
I agree MT, I only used the new prop to get us home. I would like to figure out what 4 blade prop would replace my 3 blade. I'm going to go to a couple of shops tomorrow, hopefully they can help me out.
Hey areo - stupid question maybe, but why do you want a 4 blade? If you were within the proper wot specs for your engine with your 3 blade what did you seek to accomplish with a 4 blade? I'm looking to be educated here :-) I thought, technically speaking, unless you go down in diameter, the 4 blade would give you more bottom end pull but less top end rpm. If your boat is already at 4600 rpm with a 3 blade my guess is that you will need a much smaller diameter 4 blade - which will then give you less pull. In my opinion one will cancel the other and you'd be right back to where you were with the original 3 blade. In my opinion you can go from a 3 blade to a 4 or 5 if your engine has the big torque and/or you drop diameter....but in your case I don't know why the 4 blade? Most Rinkers have been propped by long standing experience and unless you are looking for a hole shot for water sports (and know you will over rev at the top end) etc. changing the blades often (imo) accomplishes less than desired. MT
MT, I was hoping to get a better hole shot to get me over the hump quicker(no water sports). I know I would lose a little on the top end but now I'm thinking I might just stay with the 3 blade.
I took the boat to the marina today and we ended up installing a new 16 X 14P prop (same as what was on there when the hub failed). They said it wasn't worth re-hubing my old one because it was old and the newer style hubs are better, plus my old one needed to be reconditioned. Below is a pic of the new 3 blade.