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120 hp Johnson sudden thud at speed

M

mike dever

Guest
" I have a 1992 120hp Johnson

" I have a 1992 120hp Johnson which will be running along on plane just fine, then all of a sudden...THUD. It shakes the entire boat. At first you think you have struck an underwater log with the lower unit and you can physically see the motor quiver. However, there is no loss of power or motor performance. The motor& boat speed does not change at all. At first, this condition started off very infrequently now over time the frequency has increased. Now, its a very regular condition. It seems to happen every so many minutes while running +60% full throttel.

Would appreciate any input on the cause/fix for this mysterious condition.

Thanks,
mtd "
 
I would think that the shifte

I would think that the shifter dog is slipping out of gear and is cuasing the motor to shake. Check to see if your control cables are adjusted correctly. Let us know what happens.
 
also check the lower unit oil

also check the lower unit oil level.just went through mine with not enough oil and too much.when the oil ran out it made a thud and slowed had to about idle back to landing to keep lower unit cool.too much oil pushed the seal above the upper bearing out and lost all the oil.Jim King
 
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