what causes the thump thump thump???

[jigmister]

A couple time now in last month or so when I start up my outboard and put it in forward gear it THUMPS. back in "N" and it stops.
sounds like the prop is hitting a piece of wood or somthing.
running on top end is normal. idling is normal.

It only did this twice now in about 4 fishing trips so it could be a piece of a tree branch or somthing in the water.
Not really sure though. dose this sympton jump out at you as a well known common problem??
I suspect maybe its not engaging all the way into gear???


1986 mercury outboard 175 HP.
serial# 0A960011
model# (according to the merc site) 1175726

 

[walleyehed]

Re: what causes the thump thump thump???

Does this engine use the flo-torq multi-piece hub system for the prop?

 

[jigmister]

Re: what causes the thump thump thump???

what is that?
The prop comes off all in one piece..............

 

[walleyehed]

Re: what causes the thump thump thump???

It either has a solid rubber hub pressed in during the manufacturing process or it uses a flo-torq hub which you slide the black plastic piece inside the hub, slide the prop on the shaft, install aft piece of hub insert, then the nut/washer system.
Some engines "knock" slightly from back-lash in the shift-dogs, and only does it at Idle In gear.
It "could" be something else, but I would guess that is the noise you are hearing.

 

[gss036]

Re: what causes the thump thump thump???

I think I would be draining the lube from the lower unit checking for metal shavings. Sounds like the grears are now meshing right.

 

[walleyehed]

Re: what causes the thump thump thump???

And if you have "fuzzy" steel on the plug magnet, unless it looks like a small dogs head..it's normal.

 

[jigmister]

Re: what causes the thump thump thump???

It either has a solid rubber hub pressed in during the manufacturing process or it uses a flo-torq hub which you slide the black plastic piece inside the hub, slide the prop on the shaft, install aft piece of hub insert, then the nut/washer system.
Some engines "knock" slightly from back-lash in the shift-dogs, and only does it at Idle In gear.
It "could" be something else, but I would guess that is the noise you are hearing.

this is like somthing is definaly wrong. it is just like the prop is hitting a piece of wood or somthing like that. you can feel it and hear it. the motor jumps around. it definalty is alarming.

like I said though, it only did it a couple time and I cant get it to repeat.

I will check the lower end gear oil. might be a problem there...........

the prop is not flo torq

 

[jigmister]

Re: what causes the thump thump thump???

well the problem came back today. I am also noticing that it is getting harder to push the throtle into forward gear.
seems like a cable or somthing is binding.

Could it be that the cable just needs adjusting?

I had a friend operate the throttle while I watched the cables on the outboard
(on trailer engine off)

when it goes into forward gear, the cable for the shift shaft moves some.
then it moves MORE when the throttle for the carbs start to move.

shifting to reverse I see no troubles.

I wonder if there is a problem down inside the lower end.
how do I trouble shoot?

thanks

 

[Texasmark]

Re: what causes the thump thump thump???

SWAG: Sounds like the thump is caused by the fact that the control box single lever control is binding. You shift into gear, but it doesn't go all the way. You advance the throttle thinking you are in gear and as you do, the control box then allows the shifter cable to move to the position that it should have been in initially putting the engine fully in F gear.

This causes your rpm's to be excessive when the shift finally occurs and you get the thump. The thump would be a lot worse if you didn't have the rubber slip hub in the prop ("the prop comes off in one piece" you said).

It's intermittent because you don't shift exactly the same every time I'd assume for varying reasons including having your mind on other things when you are trying to maneuver your boat out of the dock, or launching area.

I think it's time to tear your control box apart and clean and lube the moving parts.

If you can get some lube in your shift cable do that too. Also lube up your shift/throttle slides in the engine. While it's all apart, cables disconnected and all, move everything separately (box, cables, engine levers) and insure that everything is free and not binding.

I think this problem is solvable with a little lube and some time on your part.

Mark

 

[Alpinegold]

Re: what causes the thump thump thump???

I am having the exact same problem with my 94 135. The only difference is it happens "every time" I go from neutral to forward. When I shift into forward it goes thump thump thump and then I plane up and no issues at all till I come out of neutral again. I have noticed some shavings in my lower unit lube. Also my gears do not feel like they are not in any kind of bind.

Is there a test to see if my cables need some kind of adjustment so that they mesh properly in gear?

 

[old-gubbins]

Re: what causes the thump thump thump???

Re:
"I had a friend operate the throttle while I watched the cables on the outboard
(on trailer engine off)

when it goes into forward gear, the cable for the shift shaft moves some.
then it moves MORE when the throttle for the carbs start to move.

shifting to reverse I see no troubles."

This is probably not the answer, but could be part of it. As Texasmark says, but before tearing down the control box, I would try adjusting the cable length inside the motor casing, to see if you can get the gear shift to be set a little more towards f, without being put under tension when throttle lever is opened. If the cable is standard Merc. stuff, you just unfasten the adjustable barrel, (which is just inside the bottom casing on a Merc 4cyl 50) and rotate it once or twice to adjust the length. From memory (several years ago now), I think you would turn the barrell clockwise, looking from the front, to get more 'forward' movement, and correspondingly slightly less reverse.

hth

o-g

 

[jigmister]

Re: what causes the thump thump thump???

thanks for all the advise people!!
I will give cable adjusting a try. I really thing that is what the trouble is.
because trimming the motor up and back down seems to have an affect. (cables are being moved around)

I will let you know what happens
thanks again. This site ROCKS

Jim

 

[Texasmark]

Re: what causes the thump thump thump???

Old-gubbins, that is exactly what I am talking about. Fix that and you fixed your problem.

Mark

 

[old-gubbins]

Re: what causes the thump thump thump???

Hi Texasmark,

I think you are a step ahead of me, and right.

Given the description of "when it goes into forward gear, the cable for the shift shaft moves some, then it moves MORE when the throttle for the carbs start to move.", my suggestion is a "quick fix" which might work, but is probably not a true solution.

It seems likely that the cams/settings in the control box have slipped for the throttle cable to move before the gear cable has stopped moving, and a tear down will be needed to get that right, as you say, with a good clean and lube.

O-G

 

[jigmister]

Re: what causes the thump thump thump???

well I adjusted the cable at the outboard.
fired it up on the muffs and shifted in and out of gears many times without a single problem.
Time will tell if I need to get into the control box.
are control boxes specific to the engine or boat?

 

[Texasmark]

Re: what causes the thump thump thump???

No. Years ago I had a 3000 Quicksilver control box and didn't like it because it had the button on it that you push in to disconnect the throttle from the shifter to obtain "fast idle" for starting.

I wanted the lift lever type like I had on my OMC back in '72. Went to the Merc dealer and bought the kind with the lift lever (2000 I think), installed that baby with my current cables and that was that.

Now, when you say different, I'd think you need to stay in the brand, not try to use an OMC control box with Merc (Quicksilver) cables.

Once you get your box apart, you might find that wear is causing your problem and obviously that will require a new box.

Mark

 

[CharlieB]

Re: what causes the thump thump thump???

How old is that cable?

It could be that the cable housing is worn inside making the cable difficult to pull.

While you have that box apart also disconnect the cable from the motor and check its movement from the control box end, is it stiffer on way moreso than the other? Replace it.

 

[jigmister]

Re: what causes the thump thump thump???

cables are about 2 years old. what had happen is a bit differnt.

I bought the bought from a handicaped gentleman. He had the control box located to the center of the boat because he could not operate it with his right arm.
frist thing I did when I bought the boat was have the shop tune it up and put the control box back in its factory location. when they did this new cable were installed.

 

[Texasmark]

Re: what causes the thump thump thump???

Well that's all hunkey dorey as long as they didn't kink your cables or put them in a bind when they moved the box and installed them. You can only kink a cable once and never get the kink out. A kink could also cause your problem.

Mark

 

[jigmister]

Re: what causes the thump thump thump???

hmmmmmm
I suspected that they may have caused the problem.
thanks for letting me know about the one time kink!


Jim