1999 mariner 40hp 2 stroke pull start engine into gear thud.

[tommyturbo]

Hello new to boating and this forum. After a bit of advice.

Just purchased a boat with the about engine and it runs well apart from the thud when putting into gear. Is this normal as it sounds bad for it. My old johnson 50 didnt do this. Any help would be appreciated.

 

[Texasmark]

Re: 1999 mariner 40hp 2 stroke pull start engine into gear thud.

Thud usually means your idle is set too high. If you don't have a tach, remove your engine cover and move your throttle linkage while looking at the moving parts. When the throttle is set to the lowest point....idle, you should see a spring loaded screw that hits a stop. Move the throttle linkage and it moves off the stop. This is your idle set. Back the screw off until you can shift without the thud. Idle rpm is just under 700 rpm. You need enough rpms to keep the engine running when you shift, but not so much so as to cause a thud when shifting. If the engine dies, you either set it too low or your carb low speed jets may need to be opened a tad till it won't die.

HTH,
Mark

 

[tommyturbo]

Re: 1999 mariner 40hp 2 stroke pull start engine into gear thud.

Thanks mark. Ok I've extended the linkage so the carb is at it lowest point without it stalling. (It did a few times so up it) the thud/crunching is less but still does it. Does this mean the gearbox is damaged? My old Johnson 50 from 1980 didn't crunch at all.

 

[Texasmark]

Re: 1999 mariner 40hp 2 stroke pull start engine into gear thud.

I'd find a buddy with another prop first. But if it does it too, you may have a problem in the lower unit. Clutch dog in there to me would be the first suspect.

Mark

 

[tommyturbo]

Re: 1999 mariner 40hp 2 stroke pull start engine into gear thud.

I'd find a buddy with another prop first. But if it does it too, you may have a problem in the lower unit. Clutch dog in there to me would be the first suspect.

Mark

Why would the prop cause that? Have noticed the prop does not have a crown nut and split pin but a nylock nut. What should I look for? Thanks again.

 

[Texasmark]

Re: 1999 mariner 40hp 2 stroke pull start engine into gear thud.

Shouldn't. The prop should be tight on the shaft. Actually for my 90 hp the torque is 55 ft-lbs. For yours, maybe 45-50....50 is not a lot....you can get that holding onto the prop while turning the nut till you can't hold onto the prop any longer. If the prop is loose, there is your smoking gun.

On the prop shaft of my engine is first a thrust washer, tapered inside to fit the taper on the shaft. Then the prop. Then a big washer with tab slots in it. Then a SS sheet metal tab with 6 ears on it, then the nylon inserted nut. The process is to install all that and as you are tightening the nut, align 3 of the tabs with 3 slots in the washer while also holding the washer against the back of the nut so that the hex detent in the tab fits around the hexagon shape of the nut. I put my knee against the prop and use one had to guide the tab'd washer. Then torque her down and as you are, stop when you get 3 tabs and slots to line up....at the torqued value and bend them down to lock the nut.

On smaller engines like yours, you MAY not have the additional locking feature of the tabs......but you do want the nut tight.

I was thinking about this thread last night on the way to sleep and one thing occurred to me. When you shift out of N, how far do you advance the handle? Since the handle is dual purpose, if you push it too far too fast, you will increase your rpms before you want to. Doing that can cause a thud.

HTH,
Mark

 

[tommyturbo]

Re: 1999 mariner 40hp 2 stroke pull start engine into gear thud.

Shouldn't. The prop should be tight on the shaft. Actually for my 90 hp the torque is 55 ft-lbs. For yours, maybe 45-50....50 is not a lot....you can get that holding onto the prop while turning the nut till you can't hold onto the prop any longer. If the prop is loose, there is your smoking gun.

On the prop shaft of my engine is first a thrust washer, tapered inside to fit the taper on the shaft. Then the prop. Then a big washer with tab slots in it. Then a SS sheet metal tab with 6 ears on it, then the nylon inserted nut. The process is to install all that and as you are tightening the nut, align 3 of the tabs with 3 slots in the washer while also holding the washer against the back of the nut so that the hex detent in the tab fits around the hexagon shape of the nut. I put my knee against the prop and use one had to guide the tab'd washer. Then torque her down and as you are, stop when you get 3 tabs and slots to line up....at the torqued value and bend them down to lock the nut.

On smaller engines like yours, you MAY not have the additional locking feature of the tabs......but you do want the nut tight.

I was thinking about this thread last night on the way to sleep and one thing occurred to me. When you shift out of N, how far do you advance the handle? Since the handle is dual purpose, if you push it too far too fast, you will increase your rpms before you want to. Doing that can cause a thud.

HTH,
Mark

Been away for a few days on the boat and the issues are no longer with the gearbox, its now the engine itself lol.

Just want to say thanks for your help, and i think it was just me being over worried about it. There is no rev increase before the gears have been selected so the cruch/thud is less now. I guess this was down to lowering the idle speed.


As of saturday the new issues are, it will just cut out while idling and then be very hard to start. it got worse as the days boating continued to the point that at 1/4 throttle it would just cut... Once i nused it home, i got it started out of the water and it was doing a big missfire every 30 sec on idle followed by a puff of smoke from the exhaust. Ive just purchased some new plugs in the hope its a broken one. The joys of boats haha...