thumping when put in forward gear

[scotssandy]

please help, i have a 1978 50ph 4cyl mercuy, when cold and put in forward gear the engine judders and thumps for a few mins before setteling down it sounds bad , the gears dont sound like they are grinding , anyone got any idea what the cause of this could be ??

 

[Rabbitdawghunter]

Re: thumping when put in forward gear

Pull the Lower unit off and run the engine with a water hose on the water tube that was inserted into the water pump on the L/U. If the thumping is still there you know it is the engine and not the L/U. Sounds can travel down/up the driveshaft and fool you as to the real source. The lack of load and backpressure may not allow the engine to display the symptom however. Its a starting point.

 

[mphsmaestro]

Re: thumping when put in forward gear

Have someone check to see if it is your "dog" gear. It is the gear that engages the prop spline. When the teeth get rounded it will "slip" and make a bumping noise. Forward progress is impaired.

 

[Texasmark]

Re: thumping when put in forward gear

I agree with maestro. Other thing I'd check is shift linkage. The shift dog is on the prop shaft (horizontal shaft) and sits between the forward and reverse gears.....slides back and forth to shift. Not a lot of room. If the remote linkage hookup to the engine is such that you are not properly engaging and disengaging the shifter, it could be a problem.<br /><br />You can spend a few minutes with your engine and remote and answer the question. 2 people makes it easier. Just move the control and "test" the prop and determine if neutral is in the center of the (movement) range of both the control and lower unit, and you get full and even forward and reverse movement. An adjustment may be in order.<br /><br />Other thing it could be is the prop. My Merc manual says that the prop (nut) should be torqued to 55 ft lbs. It should be good and tight. No movement at all between the prop and the shaft. Also you must use a thrust washer on the shaft in front of the prop so that you have something to torque the nut (prop) against.<br /><br />Good luck and Merry Christmas.

 

[scotssandy]

Re: thumping when put in forward gear

tks for the help guys i will check these things out and get back to yous

 

[scotssandy]

Re: thumping when put in forward gear

thanks for the help, i adjusted the gear linkage and it now seems to be fine,

 

[Texasmark]

Re: thumping when put in forward gear

Yeah!