'89 100 hp johnson knocking

[dt]

Was going across the lake at 3/4 throttle and motor quit. Prop quit turning and the boat came to an immediate drift. I started the motor and it ran with no problem at wake speed all the way to slip at marina. Knocking sound existing now that wasn't there before. Motor will start and run with no other problems. Help with knowledge before I take it in so I don't get taken.<br />dthomasderrick@netscape.net<br /><br />------------------

 

[JB]

Re: '89 100 hp johnson knocking

Sounds like flywheel trouble, dt. Maybe threw a magnet or one has come loose. The only on-water failure I ever had with an OMC was a Johnny 100 that broke the flywheel.<br /><br />Hope it's simple. Good luck.<br />JB

 

[12Footer]

Re: '89 100 hp johnson knocking

Is it a steady knok? does it sound like it's comming from the prop or the engine?<br />Are the bolt tight on the transom?<br /><br />Does the motor shake when it knocks?<br /><br /><br /><br />------------------<br />Time to change my tagline

 

[dt]

Re: '89 100 hp johnson knocking

To JBC, what I need to know is did it end up becoming a spendy fix and was there a great degree of difficulty to have it done. (ie hrs in the shop---shop time?)<br /><br />To 12Footer, yes, it is a steady knock that's coming from the upper area of the motor. No prop difficulties, loose bolts, or shakiness going on.

 

[Paddling]

Re: '89 100 hp johnson knocking

It might be ignition components i.e. power pack that is failing. If some cylinders won't fire, you might not be able to get past idle speed and dead cylinders will sound like they knock because firing cylinders are in effect dragging them through the combustion cycle. I have had flywheel magnets come loose and every time the motor would not run at all. Check for fire at plugs and don't get shocked, it hurts.

 

[12Footer]

Re: '89 100 hp johnson knocking

It doesn't sound good. It could be ignition (cylinder not firing), but even if it is, it <br />should not "knock". It might have injested a reed,or have a rod bearing failing.or wrist pin about to break.<br /><br />I would run a compression test, and not run it until I found out for sure where that knock is comming from,as it could "unglue" on you doing major internal damage.

 

[JB]

Re: '89 100 hp johnson knocking

Yo, dt. My flywheel broke at the hub and locked the engine, but it knocked for about 10 seconds before it let go. I bought a used one for $20 and replaced it myself. That's 20 1980 dollars, by the way, so I guess it would run a couple hundred in 2001 bucks. <br /><br />Now don't get carried away by our guessing what might be the cause. Pull your cover and explore; turn the flywheel by hand (easier if you pull the plugs), shift it in and out of gear and see if you can turn the prop. Then you will know a lot more about your problem than any of us do so far. Share it with us and we can eventually diagnose your problem and forcast repair costs. <br /><br />Good luck.<br />JB

 

[Burhead]

Re: '89 100 hp johnson knocking

It wore out!

 

[Dhadley]

Re: '89 100 hp johnson knocking

Take compression first!<br /><br />Good luck!