thump sound

[badognobisc]

when in neutral, I can feel a thump when the motor is running also in gear with muffs. The thump is every 4 seconds then 8 seconds then 4 then 4 then 8 ( probably 4 seconds every time just not feeling it everytime..)

My thoughts would be one of these 1)gimbal bearing 2)u joints 3) mis aligned 4) clutch dog


I shut off engine and started searching but not finding anything that is matching.

What are your opinions, advice, best guess, and thoughts before I go to the parts store in the morning and spend all day working on the problem? It feels like a vibration just not every rotation. Almost like the engine is misfiring.
My idea was to remove the drive and run the engine only to see if it was a misfire and if the vibration was coming from the engine or the drive. The boat has only had 3 days of use due to horrible rain and stormy weather over the past 2 months. 14 inches in 2 days. I jsut want to make sure this is not some bad fuel and risk damage.

 

[badognobisc]

Re: thump sound

I do have a secondary water line that is pressurized to hook up to the water inlet on the lower unit to feed the motor that pushes 13 gallons per minute.

 

[Bondo]

Re: thump sound

Ayuh,.... Pullin' the drive should tell ya which end needs Attention,...

It don't take a Firehose to feed it either.....

 

[badognobisc]

Re: thump sound

THx for the advice bondo. Any idea if a u joint assembly or a gimbal would be making that noise. I am leaning on the coupler or the u joint. The vibration was almost in perfect timing.

How much damage ya figure if I let it ride over the weekend if it turns out to be a u joint problem?