Strange Spun Prop? or 2 problems at the same time. Need help to diagnose.

[BootMachine]

I think I spun my prop but at first I thought there was something wrong with my motor and now Im totally confused.

1999 Johnson 70 HP 3 Cyl. 2-Stroke

Here are the exact symptoms in order of occurrence:

- Was running at WOT with no issues
- Suddenly power loss similar to running out of fuel but engine was still running slowly at WOT
- Reduced to idle... engine idled fine
- WOT again and still no power to get up on plane... Engine wont rev up.
- Shut everything down and checked what I could on the water.. fuel ok, engine didnt feel hot, could put my hand on the side of the block. It was very warm but not burning hot.
- Started back up and all of a sudden no problem
- Hit WOT again and everything seemed fine and then all of a sudden no thrust and racing RPM. Felt like the prop was slipping or cavitating. Like when it has weeds on it
- Reduced RPM and prop seemed to bite in again
- Slowly increased RPM and prop would slip
- Found the max speed I could go without the prop "slipping" ...or whatever was happening... and made it back to shore.




Ok so to me it seems like I spun the hub of my prop. Most of the symptoms seem exactly like a spun hub.

EXCEPT...

Why did I lose power all of a sudden at WOT and then not have enough power to get back up on plane?

Could I have 2 problems that happened at the exact same time?

Could it be the temp sensor limiting RPM? The engine didn't feel hot and I checked to make sure the water pump was pissing a stream out the side.

Could a spun prob be binding some how? Maybe when the hub let go, rubber came out and bound up the shaft? Just a guess.



Any and all information is welcome especially if you recognize these symptoms.

Thank you kindly...

 

[phillnjack2]

No Title

ok first off the loss of power with throttle still in wot position....this is an over heat protection that sounds pretty normal.
if the engine has for any reason got a touch warm the S.L.O.W feature jumps in and puts the engine into a limp mode.
Now this can happen for a number of reason, it could of been lack of oil if your still using it as vro, (vro is bad idea)
or could of been an obstruction like a plastic bag covering the water pump inlets etc.
Anything like that can cause a sudden over heat and the S.L.O.W will come in and not go until the engine has cooled down and stopped and re-started,

Now the slippage, this again seems to be stemming from the same effect of a plastic bag or weeds around the propeller !!! this could of also been the over heat
problem that caused the slow function to jump in and send into limp mode.

first thing I would do is take off the vro pipes and run the engine on premix to see if the over heat stops !!!
if it does then don't waste a fortune on vro pump just go get a small old style fuel pump and do it the safe and trusted way 50 to 1 in the tank.

My engine did not feel excessively hot when the S.L.O.W function came in, but it only takes a few seconds to coll if water is getting through again !!
the slow function comes in fast, but takes a while to go back out again, its a safety feature.

to check for a spun prop just get some nail varnish and paint a line going through the nut and the hub of the prop, ive done the same
here is a pic of prop with red line to check if it had a spun hub..

Just my opinion but had exactly the same things happen to me and I also have the later type 56 cu in 3 cylinder engine.

 

[BootMachine]

phillnjack2

Thanks so much for the reply.

First thing I did when I shut it down was lift the motor, go to the back of my boat and check that there was nothing wrapped around my prop and then check the water inlets. Nothing on the prop and plenty of water flow.

Also, VRO has been disabled on my engine and I run pre-mix in the gas tank. I dont trust VRO.

I will pull the prop off and see what there is to see. I will post what I find.

Im not near water (30 mins) so I will have to do most of my testing with water muffs on.

With the engine off Im going to put it in gear and try and turn the prop and see if it slips or if I can turn the motor over.

 

[jakedaawg]

phillnjack2



Im not near water (30 mins) so I will have to do most of my testing with water muffs on.

With the engine off Im going to put it in gear and try and turn the prop and see if it slips or if I can turn the motor over.

This will not tell you if you have a spun hub.

 

[jrttoday]

for what it's worth - a powerhead saved and other major inconveniences....; plus you no longer have to wrench your neck and take your eyes off of where you're going
http://www.iboats.com/Faria-Chesape...953415--session_id.629740577--view_id.1243029

 

[BootMachine]

jakedaawg Yes you are correct. I tried my technique and it took very little torque to turn the engine over. Less than the holding torque of my assumed spun prop.

I did what phillnjack2 recommended (the line method) and put the prop back on to test in water. I will post back with results after I do my test in a few days.

Thanks for the info!

 

[BootMachine]

jrttoday what is your opinion of installing a head temp sensor rather than a water pressure sensor as you recommended?

 

[ondarvr]

jrttoday what is your opinion of installing a head temp sensor rather than a water pressure sensor as you recommended?

They tell you different things, both can be useful.

 

[BootMachine]

****UPDATE****


This morning did some testing. Here are my results.

- Drained the bottom end lubricant. Lots of good lube in there and no metal shavings on the magnet. No water in there either.

- Tried to see if the prop hub was slipping by turning the prop with the engine off and in gear but it was too easy to turn the engine over...which tells me nothing. I did the line method and Im awaiting a water test to see if the hub slips.

- Did a compression test on all 3cyls and got approx 140PSI on each.

- I took the plugs out and read them for info. All looked good, nice tan colour, good clean burn and the plugs are almost new so I checked the gaps, cleaned with a wire brush and re-installed.

- Started the engine with the muffs on and let it come up to temp and there were no obvious signs of anything. Starts perfect, runs smooth, sounds good, smells good, revs up clean and settles back down into a smooth idle without issue. Lots of water pumping through the head.




SO...

I will be doing an on-water test to see if my prop is slipping. Which I think is part of the problem. Hopefully the prop is slipping and I can replace the hub and be finished with the 1 issue.

I will also be installing some gauges so I can see whats going on in terms of RPM and head temp. Why did I experience sudden power loss I dont know. If it was the SLOW system kicking in, why was the engine overheating? 40:1 mix in the tank, no VRO, water pump working???



QUESTIONS...

Should I install a head temp gauge or water pressure gauge?

Can anyone provide a link of how to replace a prop hub? Im assuming its pressed in using a shop press?


Thanks to everyone who replied...

 

[jrttoday]

what "I" think isn't as important as what "you" do... I just discovered two weeks ago that my temp horn in the remote is toast; new horn or gauge or idiot light? hmmmm.. I like gauges. Gauges keep you informed. Gauges and sensors aren't the same in my book. Mechanical gauge vs a sensor that sends an electrical current to a gauge is crap.

I do a lot at home, pressing in a hub is not one of them - local prop shop. I've seen tutorials on U tube but haven't the equipment

 

[BootMachine]

Just following up on this thread in case someone happens to be reading it for information on a similar problem.

Prop had spun the hub. Replaced prop and the slipping stopped.

Carbs were not tuned properly. I bought a carb rebuild kit and tore them all apart and cleaned and rebuilt them back to brand new. Took my time and chased all the tiny holes out with thin wire, then carb cleaner and finally compressed air.

After the carbs were back on I did a link and sync as per the manual and tried the boat out. Much improvement but engine was lacking power.

I changed the spark plugs and tuned the carbs with the air screw in the side and now everything works perfect.

The procedures I used on the carbs were straight out of the Johnson FSM so I would recommend picking one of those up.

I also installed a digital temp gauge just to keep an eye on things.

For reference, my engine runs at 160F when trolling and 140F when running wide open

 

[82rude]

Wish more people would follow up as you did ,it can be very informative.

 

[GA_Boater]

Absolutely! Thanks for the followup. It may help some one in the future. :thumb: