Over propped & engine damage????

[BeerBarge]

I was reading through some old 2 cycle oil threads debating the usual. I came across one that stated "not even good oil can save an overpropped engine". I just bought a 24ft. toon with a new 115 Merc. The dealer put a 15 pitch prop on it. Last weekend I finally opened up the motor and could only get 4800 RPM out of the motor. My understaning that WOT on this engine is around 5300 RPM. Is the fact I cannot run 5200-5300 hurting my new motor. This is my first outboard. Any tips on how it should be set up would be greatly appreciated.

 

[Down South]

Re: Over propped & engine damage????

Hi beerBarge,<br />I have somewhat of the same problem if it's really a problem, I have a couple 24' bardges. My latest would only turn 4600 with a 17 pitch prop running a Johnson 88 SPL. I put a 15 pitch prop on it and have it up to 4850 rpm which is in the manual for WOT. My WOT should be between 4500 and 5500 rpm so I'm in the ball park. Look in your manual and see what the min WOT is, not just the top side. Even though I would think you should get more out of that 115 on a 24 footer.<br /><br />Good luck

 

[DJ]

Re: Over propped & engine damage????

Beerbarge,<br /><br />Downsouth is right, there is a minimum and maximum range for WOT. Check your manual to see if you are in that range.

 

[Down South]

Re: Over propped & engine damage????

Hey BeerBarge, <br />By the way I like the handel. Sounds a lot like me. <br />I was just thinking, If your motor is new and you just opened it up for the first time. You may still be running a double oil mixture for break-in. If so, the motor will pick up some rpm when you stop mixing double.

 

[wayne c.]

Re: Over propped & engine damage????

Yo Beerbarge, Have a 20' Bennington pontoon with '02 90 hp 4-stroke Merc.. WOT is 5000-6000 rpm. Dealer and I went round and round about what prop to use--he wanted 11" pitch, I wanted a 13". I ended up w/both. With 13" I can turn approx. 5400 rpm. Keep in mind thats with 3 adults, full cooler of "beverages", and all the other stuff the little woman thinks we should haul around. Took 11" off before engine was broke in, not sure what WOT would be with it. A 13" would likely bring your rpm up 200-300 rpm GOOD LUCK.

 

[rickdb1boat]

Re: Over propped & engine damage????

Don't know if this relates to your Merc, but I have had 24'Toons with 70HP and 88HP(Johnsons)on them, and I have always run with 14"x13" pitch props on them. 11" is just too underpropped! 15" dropped RPM's with any kinda of a load! 13" just seem to be the best all around preformers on these Barges! Both boat ran well with a decent load, with the 13" prop, at about 5500RPM's. Just my thoughts! <br /><br />Rick

 

[wayne c.]

Re: Over propped & engine damage????

I agree with Rick--had a 80 hp Yammy 4-stroke on 21' party barge ( traded original 2-stroke)before the new Bennington. Ran 15" prop--never could turn more than 4800 rpm, wot was suppose to be 5000-6000. Was about to go to 13" when boat went to bottom of lake in a storm. Once again, I believe wt. , trim, etc. are important factors when it comes to WOT..