force motor knocking noise

[crash0924]

I finally got to take the boat out and try the motor. Started up fine and idled fine. First I had it running this year. Fogged the motor at the end of the season. The motor ideled fine but when I throttled it up with out it in gear, up to about 2000 to 3000 rpms, something in the motor did not sound right, sounded like something loose in side. Never had the motor apart. Never heard this noise last year. After about 10 minutes. Still heard noise. Did not take the boat of the trailer just sat there and kept reving it up. everything was fine spitting water like it sould. after about 10 minutes the buzzer came on I take it for the temp. Any suggestions on what the noise could be and why the buzzer came on. Also could any thing in the lower unit be causing that noise and would the fogging oil do that.

 

[javsam]

Re: force motor knocking noise

take a compression test and do not run motor until you find out what it is.the last thing you want is a rod coming through the block.the buzzer is an alarm indicating overheating.<br />javsam

 

[crash0924]

Re: force motor knocking noise

I took a compression test and the top cyclinder was 120 middle was 110-115 and bottom was 130. there was now lose in the pressure in either cyclinder. Could the fogging oil cause knocking when first started back up and cause the temp. buzzer alarm to go off.

 

[eurolarva]

Re: force motor knocking noise

You failed to mention the model, HP and make of the motor. If this is a 120 HP motor at 3000 RPM strapped to the trailer you may have been cavitating so bad that the motor was sucking air bubbles instead of water. Do you have a trolling motor? If so take it off the trailer and play with it around the landing. See if the noise comes back.

 

[crash0924]

Re: force motor knocking noise

the motor is an 88 85 hp force. will this cause a knocking in the motor

 

[eurolarva]

Re: force motor knocking noise

Sorry I missed the part about the 3000 RPMs being out of gear. Is your gas properly mixed at 50 to 1? Does the knocking sound go faster with higher RPMs or stay constant?

 

[imported_LakeRunner]

Re: force motor knocking noise

Same problem I had, boat was running fine, took it out one day and it started knocking. By the time I started back it died on me leaving me stranded on the lake. Fortunately a benevolent boater came by and towed me back to the marina. You may be running lean. Have your fuel mixture checked.

 

[imported_LakeRunner]

Re: force motor knocking noise

The following is a quote from a good friend who helped me diagnose my problem, if the the mixture is correct then have the timing checked. Either way catch it before it gets you! "lean out any modern outboard of any design or allow it to overheat or allow the timing to vary outside its limits and the results are usually a detonated piston."

 

[crash0924]

Re: force motor knocking noise

thanks everyone the knocking sound stays the same just gets louder when you rev it up. I have not taking it off the trailer yet, I am also reving it up at the motor by the throttle, thanks again for the help. Went to try the motor again and pulled out of the lane where the boat was and knocked the skag off the lower unit. any help finding a new lowerer unit would be appreciated thanks again

 

[roscoe]

Re: force motor knocking noise

Ebay usually has lower units.<br /><br />You might just want to get the old skeg welded back on.<br />Or maybe get a skegguard and bolt it on.

 

[javsam]

Re: force motor knocking noise

any good welding shop can weld a skag back on,and should be around 50 to 100 bucks. like lake runner and eurolarva say, make sure your running a 50 to 1 oil mix(one pint to six gallons of gas) and get your timing checked. you might want to take your plugs out and see if you can see any detonation damage using a flashlight.<br />javsam

 

[Bry21317]

Re: force motor knocking noise

I also have a Force 125hp Engine, when I reve mine at throttle on the Carbs, it will make a knocking noise. From what I can tell, the reason is that it is not adjusting the Timing correctly when you do this. The timing tower only moves when you use the Throttle control at the drivers seat.<br /><br />Just put the boat in the water and see how she does, then see if you still have the noise.<br /><br />Hope this helps.<br /><br />Bryan

 

[RRitt]

Re: force motor knocking noise

I have an '88 85hp. It once made an very slight knocking noise at RPM. It was not a metal to metal knock though. It was more like the knocking noise that a car makes when you lug it at low rpm ... just faster because it happenned at 3000 to 3500. as per your description, "something did not sound right". Turned out that the mixture was running lean.

 

[RRitt]

Re: force motor knocking noise

you guys may want to check your reeds. in another thread lake runner blew his engine and his mechanic traced it to the reeds not working properly. <br /><br />cross-checking parts diagrams I discovered that mercury changed the reed design in 1991. further cross-checking revealed that they did not change the reed design in the 40/50 motors. <br /><br />A quick check of ebay auctions confirms that very few 40/50 motors are experiencing any problems. I could not find a single instance of a 40/50 being parted out due to detonation in the last 30 days. However, there were dozens of "runs great" 40/50 that were bought and sold.<br /><br />so it would appear that there is a very strong correlation between running lean, detonating pistons, and the mercury designed reed assembly. Maybe it's nothing but coincidence but it's still worth investigating if you own a 1991 or later engine of 70HP or greater. If your reeds are going bad, it looks like you can retrofit the original chrysler design if you can locate the parts. the bracket is NLA and the reeds are $10 per. the mercury design is only available as a block assembly at $95 per port.