Knock on deceleration, Force 50

[shindig888]

Ive got a 91 force 50 (ser?) When I rev the throttle (burp it) She has a pretty severe knock on deceleration... what causes this?

 

[12Footer]

Re: Knock on deceleration, Force 50

That doesn't sound good. It could be a worn wrist pin, cylinder wall, piston,crank, or lower unit problem, or any combination thereof..<br /><br />If it were mine, I'd run a compression test.<br />If it passed, I'd drop the l/u, crank it up briefly ,just long enough to see if the knock is still there.<br />If it is, and the compression is good, I'd pull the head,and inspect the jugs and crowns, and check clearences per the mamual.

 

[shindig888]

Re: Knock on deceleration, Force 50

I did a compression test both were 150 psi. Is this good ?

 

[shindig888]

Re: Knock on deceleration, Force 50

I did a compression test both were 150 psi. Is this good ?

 

[roscoe]

Re: Knock on deceleration, Force 50

150 is almost too good, better than most.

 

[12Footer]

Re: Knock on deceleration, Force 50

Yes, that really is better than spec.-- no problems there.<br />Try checking the flywheel for any play (if it wiggles, but the shaft does not).<br />If it does not have play at the flywheel shaft, but you still get some lateral wiggle or play, I would suspect the main crank bearings (under the flywheel, and a lower bearing on the bottom of the powerhead).<br />If it's tight, it could be a worn wrist pin or worn crank.<br />Is there anything you can do durring operation that changes it's tone, or gets it to stop knocking?<br />Something else that is common on these motors that may cause a noise (not allways a knock but--) check the starter worm gear. Insure that once the engine starts, the gear on the starter shaft disengages the flywheel, and stops.

 

[12Footer]

Re: Knock on deceleration, Force 50

Question: Does it only happen when you are underway, and pull the throttle back to idle?<br />If so, a clicking noise will be heard from the prop area. This is normal.