can't plane after engine swap. does reach 5000 rpm's

[onebadbusa]

I relaced my 5.7 260hp vortek with a new long block 325 hp. Timing is correct sounds great but only reaches 18 mph at 5000 rpm's. Really stumped. Also put new flappers in while apart. Tries different props also. It's a 1996 25' Larson. Any idea's would be much appreciated if not any recommendations for a wrench that could look at it first thing April. Thanks

 

[hottoddie]

Re: can't plane after engine swap. does reach 5000 rpm's

Maybe a bad engine coupler or spun hub on the prop

 

[Bondo]

Re: can't plane after engine swap. does reach 5000 rpm's

I relaced my 5.7 260hp vortek with a new long block 325 hp. Timing is correct sounds great but only reaches 18 mph at 5000 rpm's. Really stumped. Also put new flappers in while apart. Tries different props also. It's a 1996 25' Larson. Any idea's would be much appreciated if not any recommendations for a wrench that could look at it first thing April. Thanks

Ayuh,... Welcome Aboard,.... By the sounds of it, the crankshaft ain't connectin' to the prop, hardly at All...

Ya left the trailer in the parkin' lot, 'n not hooked to the boat, Right,..??

Ya swapped props,.... that sorta counts it out,...

The Coupler can do that, but it usually slips abit, 'n then Nothin'...

What drive is on the boat,..?? Do ya Know it worked well before the swap,..??

 

[Don S]

Re: can't plane after engine swap. does reach 5000 rpm's

Will the engine go faster than 5000 rpm, or is that where it tops out at WOT (wide open throttle). Does the engine sound like it's going that rpm? It's not the tach is it???

If the coupler rubber hub spun, you would smell the burning rubber, and the engine would rev and the boat would slow down even more. So that doesn't seem to be what you describe. If the splines were stripped out, you wouldn't move at all.

So you change the prop, did the exact same thing happen with two props? If so, then that won't be the problem.

That leaves the drive itself. It has a cone clutch that could slip. Have you checked the gear lube for metal, and is it full of gear lube?

Put the drive in gear, you should be able to turn the drive one direction, but not the other. Does that happen? shift the other direction and the direction the prop turns should change also.

 

[sharkin95]

Re: can't plane after engine swap. does reach 5000 rpm's

check the valve adjustment valves could be torqued too tight.you could lose 500-800 rpms

 

[Bondo]

Re: can't plane after engine swap. does reach 5000 rpm's

check the valve adjustment valves could be torqued too tight.you could lose 500-800 rpms

Ayuh,... Did you even read the thread,..??

The motor is turnin' 5000 rpms Now....

Timing is correct sounds great but only reaches 18 mph at 5000 rpm's.

 

[onebadbusa]

Re: can't plane after engine swap. does reach 5000 rpm's

Same problem with different props. no smell of and rubber WOT only 5000 yes. On trailer Prop only turns one way. Drive is fine Alpha one with gear oil. The only thing I did was swap motors. Engine sound like it's running at the proper rpm's. I plan on dropping the boots and checking the flappers when it warms up in April. Should it tach over 5000 WOT? I double checked all conections wires and nuts & bolts. No water leaks oil leaks etc. Thanks for all the suggestions keeep them coming please?

 

[achris]

Re: can't plane after engine swap. does reach 5000 rpm's

How'd it perform before the engine swap?

 

[onebadbusa]

Re: can't plane after engine swap. does reach 5000 rpm's

How'd it perform before the engine swap?

32 mph @ 5000 rpm's all day long with 5 or 6 people on board.

 

[Tail_Gunner]

Re: can't plane after engine swap. does reach 5000 rpm's

Well if the engine turn 5000 and still work's....You need to have a peak at your coupler and drive....somewhere there's a lot of heat being generated i would not run it any longer

 

[Don S]

Re: can't plane after engine swap. does reach 5000 rpm's

32 mph @ 5000 rpm's all day long with 5 or 6 people on board.

If the coupler is good and the drive is good, then you have problems with your engine.

Do a compression test, What ignition system are you using?

OR, your speedometer is wrong. At 18 mph in a 25 ft boat, you wouldn't be up on plane, are you on plane? Are you only going by the speedometer? Does it feel like 18 and not 35?

 

[onebadbusa]

Re: can't plane after engine swap. does reach 5000 rpm's

If the coupler is good and the drive is good, then you have problems with your engine.

Do a compression test, What ignition system are you using?

OR, your speedometer is wrong. At 18 mph in a 25 ft boat, you wouldn't be up on plane, are you on plane? Are you only going by the speedometer? Does it feel like 18 and not 35?

Even if it's a brand new Merc long block? oniginal ignition manifold and carb. Won't go on plane until at least 20mph and using GPS for speed check. Tach is correct WOT at 5000 rpm's GPS reads 18 mph.

 

[Bondo]

Re: can't plane after engine swap. does reach 5000 rpm's

Even if it's a brand new Merc long block? oniginal ignition manifold and carb. Won't go on plane until at least 20mph and using GPS for speed check. Tach is correct WOT at 5000 rpm's GPS reads 18 mph.

Ayuh,.... Ya answered a couple of questions, but many more have been asked....

It's soundin' more like a Hull issue....

Who did the transplant,..??
Alignment checked,..??
Drive serviced,..??

 

[Don S]

Re: can't plane after engine swap. does reach 5000 rpm's

If you have a good engine, the coupler is good, the drive is good, and the prop is good, and if nothing has changed on the hull, then I would have to suspect you aren’t trimming the drive correctly.

You aren’t by some chance trimming by what the gauge says are you? If so, forget the gauge and trim the drive up after you get to 18 mph and see if the speed picks up and the bow of the boat lifts. You could be plowing through the water in a bow down position.

The extra HP could very well be allowing you to get to 5000 rpm. You may have to up prop pitch if the rpm’s go any higher as you trim up.

Or maybe you are trimming the drive correctly but you have trim tabs and they are holding the bow down causing the boat to plow.

 

[Tail_Gunner]

Re: can't plane after engine swap. does reach 5000 rpm's

25" boat....bowrider or cuddy with a 300hp v8 under full power and 18 mph. If the prop was hooking up it could not reach 5000 rpm unless it was a 12p prop or something crazy. You cannot be mechanically hooked up...But it could blow out and that would indicate tremendous drag on the hull's part...Your leg does lineup straight up and down to the transom does it not.

 

[onebadbusa]

Re: can't plane after engine swap. does reach 5000 rpm's

If you have a good engine, the coupler is good, the drive is good, and the prop is good, and if nothing has changed on the hull, then I would have to suspect you aren?t trimming the drive correctly.

You aren?t by some chance trimming by what the gauge says are you? If so, forget the gauge and trim the drive up after you get to 18 mph and see if the speed picks up and the bow of the boat lifts. You could be plowing through the water in a bow down position.

The extra HP could very well be allowing you to get to 5000 rpm. You may have to up prop pitch if the rpm?s go any higher as you trim up.

Or maybe you are trimming the drive correctly but you have trim tabs and they are holding the bow down causing the boat to plow.

I will check once in water all these things. I have the trim tabs at up position. Hull is clean. I will have a professional double check my timing. Thank you all for all your input and help. Will update all with finding once fixed.

 

[Hoosmatroos]

Re: can't plane after engine swap. does reach 5000 rpm's

Boat very heavy due to water in the hull?

 

[NHGuy]

Re: can't plane after engine swap. does reach 5000 rpm's

You can check the final drive ratio by turning the motor over while it's in gear and counting the prop rotations. Most 5.7's are 1.5:1.

 

[onebadbusa]

Re: can't plane after engine swap. does reach 5000 rpm's

My take, if you are getting to 5000 RPM there is nothing wrong with the engine and I wouldn't waste another minute going over it. I'll caution one more time, do NOT trust the boats built in tach to make that determination!!!

Assuming the engine is doing what it should the problem has to be in the drive line or in the boats attitude, bow down and can't lift as needed, but I doubt even that would keep you from eventually getting on plane with 335 ponies pushing you. I just have to believe that for some reason all those ponies are not getting to the prop. or for what ever reason the prop. is cavitating something horrible and all you are doing is making lots of air bubbles. (Trim)

One more off the wall thought and I only mention it because I seen it happen once. You had someone change the engine, to do that they pulled the outdrive off and stored it somewhere while they did the engine work. It may sound weird but if they were working on more than one boat they may have put the wrong drive back on. Like I said, I seen it happen once and the drive ratio was all wrong and was set up for a small four cyclinder and the boat had a V-8 and it spun like mad going no where. The owner of the boat smacked his forehead and said, "I never even looked at the drive, if I had I would have known it wasn't mine". Hey, stuff happens even in the best of shops.

The drive was never removed. I did the swap with a mechanic friend of mine. The thing went in without a hitch. Thanks for all the suggestions

 

[Don S]

Re: can't plane after engine swap. does reach 5000 rpm's

The drive was never removed. I did the swap with a mechanic friend of mine. The thing went in without a hitch. Thanks for all the suggestions

No it didn't, you lost all your speed but you have rpm.

Something is wrong with the engine, the tach, both, or how it's being operated.

The drive was never removed.

Then how did you align the new engine.