Clunking Sound from Johnson Motor

[adamhaskins]

1988 Cimmarro 15.5 ft w/ 40 hp Johnson VRO

Just put in brand new stringers, deck, carpet, new seats, $500 bow mount trolling motor $300 fish finder ect. The boat has been running perfect the last few days. All of sudden it wouldnt start. When we took the cover off the motor, all the wires were corroded, broke, ripped apart. When I bought the boat the VRO system was taken out and the guy said I could just mix the oil myself. Well since the boat wouldnt start, I thought it was an issue with all those wires being destroyed. I spent another $50 and re wired every single wire 1 by 1. Boat still didnt start.. Jiggled the key and it cranked right up.

We took the boat out in the water when it was super choppy out and we had the throttle fully open and the boat wouldnt plain out and it was going quite slow. We thought it was because of how choppy the lake was so we took the boat back home for the day. We woke up 5 am this morning and took the boat out to go fishing and it was still running sluggish. We shut off the motor to check for weeds ect in the prop. Everything looked good. We cranked it back up and hit full throttle again. This time the boat took of with no problem.. trimmed out and we was hauling tail for about 20 minutes straight. Then all of sudden the motor start to make a clunking clang sound that we could hardly hear.. but it was enough to wonder what was going on. Then it started to bog down even more like something was restricting the motor from going. The boat went from going full blast to fully stopped in about 1 minute.... even tho it was full throttle. We shut the motor off to inspect everything.. Everything looked good.. water pump was pumping good.. and it had plenty of oil mixed with the gas.

We tried to start it again and it started but was bogged down real bad with full throttle. We shut it off again and tried it one more time but the starter engaged and the motor was siezed. We gave it about 15 minutes and tried it again and it tried to crank... but now it wont start.

The clanking sound almost sounded like it was coming from the lower end.. but that wouldnt explain why the motor doesnt start now... or what could have possibly happened. Any ideas?

 

[witenite0560]

Re: Clunking Sound from Johnson Motor

Sorry, I'm not that familiar with that motor. But, sounds very much like it seized from lack of lube to me.

 

[Daviet]

Re: Clunking Sound from Johnson Motor

You need to start at the beginning and do some systems checks. Check the compression, and then check the spark, should be bright blue and jump a 7/16" gap. Is there any water in the lower unit? Does the power head look discolored (overheated)?
What is the model number of your engine?

 

[oldcatamount]

Re: Clunking Sound from Johnson Motor

Sounds to me like it may be a fuel delivery issue. Maybe the carb needs cleaning. Are you mixing the fuel at 50:1?

 

[adamhaskins]

Re: Clunking Sound from Johnson Motor

The power head looks fine. However, I'm not sure what normal really looks like. I just bought the boat about 4 months ago. We also noticed that the water pump was spitting water out of the holes that showed it was working properly.

I'm not sure what model the motor is. Is there a specific place I could find that?

All I know is its an older model Johnson 40 hp with the VRO oil system. Bought the boat for 1100. Put all kinds of money into it and this happens I know I started to get a buzzing sound from the throttle box and I looked it up and it said it could be warning sounds for either the VRO system not working or if it was over heating. I remember feeling the motor and it was cool enough to touch when all of this happened. So im guessing all the wiring we hooked up was for the VRO part and it was telling us it wasnt working. But we already knew that because we mix our own oil.

 

[adamhaskins]

Re: Clunking Sound from Johnson Motor

Sounds to me like it may be a fuel delivery issue. Maybe the carb needs cleaning. Are you mixing the fuel at 50:1?

Yes 50:1 is exactly what we are mixing it as. It doesnt seem like a fuel issue tbh because it happened so drastically and it had a wierd clunking sound that would make you want to shut the motor off.

However, Im wondering if us hooking up all the wiring that was corroded and ate up by rats or something, could cause this fuel issue. Would it make the motor clunk really bad if it was having a fuel issue? Maybe the VRO system trying to push oil into the motor when there is nothing hooked up?

 

[Daviet]

Re: Clunking Sound from Johnson Motor

Look on the transom clamps, there should be a model and serial number plate there. A constant warning horn would indicate an overheating problem. Do the tests I mentioned above and tell us the results.

 

[adamhaskins]

Re: Clunking Sound from Johnson Motor

Also this particular motor has 2 carbs. Im not sure if that is normal or what. Just wanted to add that in there

 

[adamhaskins]

Re: Clunking Sound from Johnson Motor

Look on the transom clamps, there should be a model and serial number plate there. A constant warning horn would indicate an overheating problem. Do the tests I mentioned above and tell us the results.

Yea the warning horns never worked until we hooked up all that wiring. After shutting off the key and turning it back on.. the sound wouldnt come back on. I will try to do these tests. I have no tools to do this so Ill have to try to find a compression tester.

So check compression.. get serial number.. and check for water in the lower unit. Ill try to reply by tomorrow with some results as Im very tired from traveling 5 hours across a huge lake with a trolling motor and very choppy waters. Thanks for all the advice.

 

[Daviet]

Re: Clunking Sound from Johnson Motor

Check compression and spark, the model number is the one we need.

 

[adamhaskins]

Re: Clunking Sound from Johnson Motor

model # J40TLCCS
Serial # G7724331

 

[adamhaskins]

Re: Clunking Sound from Johnson Motor

Also when i spin the motor by hand. It feels like its hitting a dead spot unlike a compression point. Its a dead stop like its hitting something internally. Im not sure if boat motors do this sort a thing or not. Im a car man 100% and I have no clue about 2 cycle motors or how they work. But the clanking sound we heard was low and got worse by the second until it was so bad we shut the motor off. Almost makes me think it blew a rod but once again. I have no clue.

 

[54fleetwin]

Re: Clunking Sound from Johnson Motor

you sieized it, not sure if it was from running lean, which it could have if the carb was dirty. You did clean the carbs right?
Or you didnt have enough oil.
When the piston started grabbing the cylinder wall it placed alot of stress on the connecting rod bearing, or what you are hearing is piston slap.
Either way, you need to tear her down.

 

[Daviet]

Re: Clunking Sound from Johnson Motor

You have a 1988 engine. Do the compression test, if you have a low cylinder pull the head and check the piston and cylinder for damage.

 

[adamhaskins]

Re: Clunking Sound from Johnson Motor

I figured it would be something serious. It was running perfect. We had a perfect mix of oil and it was being cooled properly. The carbs seems to be fine, but I do remember feeling like it would miss sometimes. It also had blue smoke coming from it on startup sometimes but would usually go away once it warmed up. Is there any way someone would have instructions on doing a tear down for this motor to check for the problem. I'm pretty good at doing mechanical work. Thanks for all the help.

 

[Daviet]

Re: Clunking Sound from Johnson Motor

If you have decided to tear it down and look for something the first thing you need is a manual, an OEM manual. It will have all of the information that you will need to maintain your engine.

 

[mrcj001]

Re: Clunking Sound from Johnson Motor

I would just repower. Quicker and probably cheaper.

Look on Criegs List in your area. You may find a good engine replacement.

If you do, take a compression tester with you and test the engine. All cylinders should have pretty much the same compression numbers. If it dont, dont buy it.

 

[beverly]

Re: Clunking Sound from Johnson Motor

You feel a dead spot while turn turning the motor!

Before hooking up the compression tester. Shove a solid stick down the spark plug hole, touching the top piston. You should see the stick move as well when you turn the the flywheel. Also look down the hole with a flash light for scoring while your at it (you won't know the full damage until you take it apart, if it is). If theres a chunk of the side wall missing. Then, well, ummm.

Does the prop turn when you turn the flywheel.. can you turn the flywheel with the prop in neutral? And many more to come.

You can also empty the lower unit oil out to check the color and maybe find bits of shaving come out.

 

[adamhaskins]

Re: Clunking Sound from Johnson Motor

I havent got into it yet as Im performing alot of maintenance on one of my cars. The prop does turn when I spin the motor by hand and doesnt when in nuetral. When spinning it.. it gets stuck around 12 o clock on the spin clockwise and counter clockwise. I will perform the above steps in a couple of days and get back to you. Thanks for the replys!

 

[Vanover]

Re: Clunking Sound from Johnson Motor

Maybe a broken driveshaft? I had a lower unit go out on a 89 rude that sounded like a constant clunking. The motor ran great though. Let me know what happens with it all.