Engine Banging?

[reb0707]

Hi All, New problem. I have a 1984 Johnson 115. I went out yesterday and on the way in it felt like the motor hit something. It did not. Then it happened again and again and again. every few seconds. The motor was jumping or banging. The motor itself was running smooth. I ended up ideling in to keep the motor from doing this. I think it has somthing to do w/ the lower unit. I am wondering if my drive shaft is sliping? How can this be corrected. Thank You.

 

[emoney]

Re: Engine Banging?

Well, you need to start with figuring out what's going on. It's sure sounds like there's a lower unit issue. Start by finding the inspection plug for the lower unit fluid and let's see what that oil looks like? Is it a milky, chocolate-brownish color? When you were "idling it in" was it still engaged and in gear? Need a little more info, I'd think.

 

[fireman57]

Re: Engine Banging?

Sounds like you might have a clutch dog that is bad. It will feel like you are hitting a log. Lower unit needs to come apart to fix.

 

[reb0707]

Re: Engine Banging?

Thanks guys for responding. This is what happened. I was out in the ocean going about 20 Knots and bam, like I hit something. This caused the engine to shutter as if I had hit something. The motor kept running well so I ignored it. Then it happened again and again. To the point where it was doing it every few seconds. I stopped it by bringing the engine idle to under 2k. I limped it home. The whole time though the motor ran smooth. No it didn't do this in neutral but I didn't rev it in neutral. No reason to. The oil in the lower unit was changed about 2 months ago. I have not looked at it yet. I was just guessing that the drive shaft might be slipping. Like the splines may have worn out. I don't know, just a guess.

 

[daselbee]

Re: Engine Banging?

Lower unit clutch dog is slipping a cog when under load. Has to come apart. I would do it now, not later, as you are now generating metal chips, I would think.

 

[reb0707]

Re: Engine Banging?

I have been trying to learn about this lower unit clutch dog and one of the posts I read said that this could cause my engine to go out of gear. This has not happened to me but it does feel like something is slipping and the motor jumps like i hit a log or something. Thank you, I am trying to learn all I can about this. Also I do not have any problem putting it forward or reverse when I give it gas under a load is when it starts happening. I have not tried putting it under a load in reverse.

 

[glengold]

Re: Engine Banging?

This happened to me a year ago. Same thing, like a bang every few seconds. I drained the lower unit oil and found metal chips. It was cheaper to purchase a rebuilt 55 hp with the other motor as a trade-in than have the LU rebuilt. For my 50 hp evinrude the rebuilt LU was about 1500 bucks here on iboats. it sucks.

 

[jrs_diesel]

Re: Engine Banging?

That is bacause there is more force on the dogs at high speed than at idle. Like someone else said, it's bad for the clutch dogs. And if you don't fix it soon, you may end up replacing the gears too.

 

[boobie]

Re: Engine Banging?

If it is the clutch dog you'll also have to replace the fwd gear. When you're done, check your shift linkage for any slop and proper adjustment.

 

[reb0707]

Re: Engine Banging?

About a month ago I ran the engine w/o water for 30 seconds to a minute. As preventive maintenance I took the boat to have a new pump wheel put on. The mechanic was unable to remove the lower unit. He said the drive shaft was rusted to the power head. My other mechanic said the first mechanic may mot have adjusted the shifter cable properly when he reassembled it. The second mechanic said I should disconnect the shifter linkage but the boat in the water and manually shift the boat into gear. He said if it doesn't pop out it was either a bad setting or worn out shifter cable. What do you guys think?

 

[emdsapmgr]

Re: Engine Banging?

You could have an adjustment problem with the shift cable under the cowling. That's fairly simple to adjust. If you had the water pump recently replaced, it is possible the mechanic changed the shift rod height-which will affect the clutch dog clearance when in gear. In any event, you need to resolve this quickly, as continued running will do more damage to the clutch dog and gear face.

 

[archcycle]

Re: Engine Banging?

About a month ago I ran the engine w/o water for 30 seconds to a minute. As preventive maintenance I took the boat to have a new pump wheel put on. The mechanic was unable to remove the lower unit. He said the drive shaft was rusted to the power head.

Can you clarify whether anyone ever got the lower unit off and changed the water pump? I don't know the qualifications of your mechanic but there are plenty of other good reasons for the LU not coming off. You may have a bolt hidden under the trim tab. He may not have unhooked the shift linkage (this is not the shift adjustment on the side of the motor that the next guy refers to!) If it were rusted he ought to have been able to do something about that. If nobody's replaced it yet then it really does need to be replaced.

My other mechanic said the first mechanic may mot have adjusted the shifter cable properly when he reassembled it.

There shouldn't be any shift cable adjustment involved in this job. Unless the second guy said "shift shaft" and you mixed them up, this shouldn't be your issue. Even then the only practical way he could have mis-adjusted your shift shaft would be to first drop the lower unit, then mis-adjust it. If guy #1 did adjust your shift cables then you need to find another mechanic!

The second mechanic said I should disconnect the shifter linkage but the boat in the water and manually shift the boat into gear. He said if it doesn't pop out it was either a bad setting or worn out shifter cable.

The shift linkage has very little throw to it and is very easy to adjust. Either google how to set it or consult your manual (see next comment). It is really easy. If your shift shaft is not connected to the shifter then you risk it banging around out of and near gears. This is something you'd want to avoid. Please don't do that. The only thing I can image this would tell you is whether it would ever engage F or R and you already know it will.

What do you guys think?

I think you need to forget about these two guys for now and get yourself a factory service manual and follow its troubleshooting steps. You'll be amazed at how easy this all is if you read every step, make sure you have every tool (the vast majority can be had at an auto store), and take pictures as you go. I say learn to do it yourself because it sounds like these two supposed outboard mechanics have done nothing but scratch their heads and stare at it.

I hope you didn't give them any money

 

[superdog8]

Re: Engine Banging?

Just had the exact same problem you describe with the banging on my 1981 Johnson 15hp. Used gears cost as much as a used LU! I managed to find a used LU for $275 so they're out there. Switched the units, runs great. If you do end up replacing the it, save the old one for parts (water pump, reverse gear etc). It was because of this thread that I was able to figure out what was wrong with the engine and not have to pay a mechanic to tell me the same thing. Thanks for the help guys!

 

[reb0707]

Re: Engine Banging?

Do you guys think the threads are still good in the power head on my 115?

 

[wilde1j]

Re: Engine Banging?

Do you guys think the threads are still good in the power head on my 115?

Do you mean driveshaft splines??? If they were shot, you wouldn't get any go power, just high RPM, no go. I'd go with clutch dog and fwd gear NG and needing replacement. Get an OEM shop manual if you're planning a DIY event here.

 

[reb0707]

Re: Engine Banging?

Wilde1j, No it's the spline in the drive shaft. I dropped the lower unit. I am probably going to have to remove the power head and check the splines on the crank.

 

[fireman57]

Re: Engine Banging?

rebo what are talking about? wilde just told you if they were bad you wouldn't have had any power to the lower unit to make things clunk. What exactly are you asking? Were there any metal shavings or signs of wear on the top of the drive shaft when you pulled it?