twin 300s one breaks loose after it was serviced

[1fastski]

story on the boat , its a commercial boat that always ran great its been in use many years now . this spring { i am the shop mechanic here } i went to put water pumps in , well the shafts were stuck in the gear up top , after a small fight we got Suzuki to cover some of the bill and we dropped the boat off to the dealer they did the work . { shafts , gear housings up top ect and put in the update that they say fixes the problem { a grease fitting } so now the problem at about 3k rpm the stb engine seems to break loose or pick up about 1k but not go anywhere . not all the time . it will break loose then go back. the mechanic that did the work said first he might have forgot a part in the lower that could do that , now it changed to no nothing they did could do that . so i am fishing for some ideas ? things it will not be { mounting , props , or anything on the bottom of the boat } thanks for any info

[Bamahemi]

Only thing I can think of that would slip like that is the prop! And that is saying nothing has changed on the boat and there has never been any cavitation before. Swap props on the motors and see if the other motor does it and nothing now on the one that had the issue.

[ChrigelKarrer]

I see 3 scenarios:
1° ding/nick/bent the propeller or not the original (your) mounted propeller
2° propeller hub is spinning out
3° some protrusion in front o the stbd lower unit creating turbulence leading to ventilation.
4° change in weight distribution may lead to ventilation

First: check with 2 different propellers and check the propeller hub
Second: check if there is no transducer/truhull/antifouling drops in front or near of the stbd lower unit

Suzuki engines ventilate very quickly and just a small imperfection can lead to ventilation.

Chris

[1fastski]

we have done the props , even got a extra set , the only thing that was changed was both powerheads were removed and lowers rebuilt . then on the way home from the the shop that did the work it was breaking loose and has seemed to do so now after 3k all season just not all the time but most .

[Bamahemi]

If the props are ruled out and you had the lowers rebuilt then I would say swap the lowers, if the same lower breaks loose then there's a problem with that lower and make the shop fix it!

[Solarman]

You say "breaks loose", but does nothing? Is the motor jumping out of gear, like into neutral? Or, while in gear rpms run much higher as if it is cavitating?

If cavitating, check if there is a gap between the prop and the hub? If a gap, a spacer may be in wrong place, the gap may allow exhaust to interfere with prop.

If acting like jumping in and out of neutral, something in the work done is not quite right? Are these motors electric shift?

How high do rpms go when it does this? Does this happen when running wot, or just around 3k? Possibly a shift switch acting up? Out of adjustment?

Good luck.

[1fastski]

at about 3k it will rev up but not push { cavitation}

[1fastski]

Boat owner says it will go from 3k to 4500 then back again .

[Bamahemi]

If nothing else has changed on the boat since the work on the lowers, my money is a problem with the rebuild of the lower in question. Swap the lower to the other motor and if it happens on that motor then you have your answer. He's checked the props, obviously he hasn't added anything that would create turbulence, the prop pitch size didn't change.

[1fastski]

its going to the dealer next week , will update when i know what it was . first thing is swapping lowers .

[Bamahemi]

Soooooooo what was the fix?

[1fastski]

so it seems when they lifted the boat they or it must have twisted just enough to where the engine had to be lowered . working fine now . it is a alum framed boat .