Sharp Noises and Vibration from Power Head During Throttle Up

[HerbieJ]

Well, this is my 2nd used motor since last October that supposedly ?runs great!?. But after investing much time and several hundreds of $$$, it still looks like I?m not going to make it to the lake. Hoping someone on this site might have an idea of what is going on ? neither of the two ?mechanics? I had come to hear the motor were able to tell me very much.

I have 1994 Mercury, 60 hp, 3 cylinders. It had oil injection, but that has been disconnected, all lines plugged, and the pump drive shaft removed. (Drive gear still on crankshaft though.) New water pump works fine. Engine is on boat and currently runs in a big garbage can. It starts fine and idles okay, (a bit rough, but doesn?t nearly stall). Problem comes when accelerating. Above 1500 RPM there is a metallic clunking sound coming from the power head. It sounds as if there?s a piece of metal loose inside, bouncing around. Engine vibrates / shudders along with the sound ? not dramatically, but I can feel it as I am working the throttle by hand. Perhaps a couple of people hitting the engine block with hammers is a better way to describe the sound / vibration. None of this seems to affect engine power, nor does engine appear to be misfiring / breaking up. The clunks are louder as engine speed increases: I don?t dare go above 4000 RPM. There is no rhythmical sound to the clunks. Surprisingly, after more than two hours of combined run time for test purposes, there has been no noticeable change or deterioration in engine performance. I would think a bad bearing would have chewed up the crankshaft or connecting rod in that time.

So, anyone have an idea as to what is going on? The noise is definitely coming from the power head, and it's the same with the lower unit off the engine. One mechanic who heard it told me to launch the boat and try it in the lake, that under the load of a propeller, any ?sloppiness? in the motor might be absorbed and I may not hear it anymore. I tend to doubt that though, and the nearest lake isn?t all that near. Besides, just because I may not be able to hear it any longer doesn?t mean I won?t blow the engine out in the middle of the lake somewhere.

Anyone ever have a similar problem? Any thoughts on what might be causing it? All responses appreciated!

 

[daveswaves]

Re: Sharp Noises and Vibration from Power Head During Throttle Up

It sounds like one cyl is dropping out perhaps loose plug wire, bad plug, wire shorting to frame of motor. If you pull the plugs the one that was not firing will be oily/wet. Don,t run it in a garbage can or on muffs above 1500 rpm, 2 strokes can run away on you before you know it and the results are not pretty.

 

[CharlieB]

Re: Sharp Noises and Vibration from Power Head During Throttle Up

Do you have a timing light and a remote starter button?

Remove all the plugs, ground the plug wires, attach the timing light shift into Forward gear, WOT, crank the motor and observe the WOT Timing.

What is WOT Timing set at?

CAUTION: WATCH OUT for the turning prop, or better yet, remove the prop before conducting this test.

 

[HerbieJ]

Re: Sharp Noises and Vibration from Power Head During Throttle Up

Thanks, daveswaves and CharleB, for giving this a shot. Just got back in from rechecking your suggestions. I wish I had found something wrong, but, plugs and wires are brand new, timing is dead on @ TDC-2 (idle) and TDC+22 (WOT). No loose connections fould, but I'll run it briefly tonight and look for any wayward sparking. Re: spark plugs - checked them also and found them ALL wet and oily, but they have been been so every time (many!) I've pulled them. As a desparation move, I also pulled the flywheel, hoping to find damage or evidence of tampering there. Both stator and trigger are original and show no damage whatsoever. I casn usually think of things to try / look at, but this time I'm completely perplexed.

 

[CharlieB]

Re: Sharp Noises and Vibration from Power Head During Throttle Up

Next step is to remove the exhaust side and inspect the pistons, rings and cyl's, as far as possible.

 

[verado7]

Re: Sharp Noises and Vibration from Power Head During Throttle Up

has acompression test been done on this yet - i'm thinking worn cylinders /piston slap /wrist pins ?

 

[HerbieJ]

Re: Sharp Noises and Vibration from Power Head During Throttle Up

Thanks verado7 and CharlieB. Compression was checked cold weeks ago and was a pound or two away from 115 on all three cylinders. Rechecked it just yesterday with engine warm and got within a pound or two of 120 on all cylinders. Then I did something different. I checked each cylinder with the engine running. The 120 reading on each cylinder dropped steadily to about 60 PSI as it was tested. (Ran the RPMs up to 3000.) Is that normal? I wonder if it?s related to what I observed today, which was?

I hooked up the throttle cable and reinstalled all the covers and cowlings. I also put a prop on and hooked up the water muffs. This meant I would be running the motor from the console, instead of with my head right next to it. (Can you tell I?m getting braver / dumber / frustrated with this?) Anyway, I ran the motor up to about 2000 RPM. It sounded pretty good with all the cowlings on and from twelve feet away. In fact, I could only hear some unevenness in the exhaust, as if the engine had a phantom miss in it. Over 2000 RPM was a different story though. I held the throttle steady at 3000 RPM, but the motor stumbled and dropped 500 RPM. It did this twice and couldn?t recover. I got it back up to 3500 RPM and it continued doing it ? 3500; 3000;2500, 2000. Once back to around 2000 RPM, it smoothed out and ran fairly even ? but still with the phantom miss.

I can?t tell if the problem is mechanical or electrical / ignition related. I tend to lean toward the latter ? or maybe I?m just hoping for it to be the latter. I?m really not up to tearing this motor down. I?m still in search of leads / things to test or try, whether mechanical or electrical. Is there an electrical component that performs okay at or near idle, but could become suspect under load?

CharlieB ? What do I look for if I look into the exhaust ports? Both mechanics ruled out piston slap, and there shouldn?t be any scoring since compression is equal. If I moved the flywheel, would I be able to possibly observe bearing wear?

Hope you?ll stay with me on this!

 

[daveswaves]

Re: Sharp Noises and Vibration from Power Head During Throttle Up

Thanks verado7 and CharlieB. Compression was checked cold weeks ago and was a pound or two away from 115 on all three cylinders. Rechecked it just yesterday with engine warm and got within a pound or two of 120 on all cylinders. Then I did something different. I checked each cylinder with the engine running. The 120 reading on each cylinder dropped steadily to about 60 PSI as it was tested. (Ran the RPMs up to 3000.) Is that normal? I wonder if it?s related to what I observed today, which was?

I hooked up the throttle cable and reinstalled all the covers and cowlings. I also put a prop on and hooked up the water muffs. This meant I would be running the motor from the console, instead of with my head right next to it. (Can you tell I?m getting braver / dumber / frustrated with this?) Anyway, I ran the motor up to about 2000 RPM. It sounded pretty good with all the cowlings on and from twelve feet away. In fact, I could only hear some unevenness in the exhaust, as if the engine had a phantom miss in it. Over 2000 RPM was a different story though. I held the throttle steady at 3000 RPM, but the motor stumbled and dropped 500 RPM. It did this twice and couldn?t recover. I got it back up to 3500 RPM and it continued doing it ? 3500; 3000;2500, 2000. Once back to around 2000 RPM, it smoothed out and ran fairly even ? but still with the phantom miss.

I can?t tell if the problem is mechanical or electrical / ignition related. I tend to lean toward the latter ? or maybe I?m just hoping for it to be the latter. I?m really not up to tearing this motor down. I?m still in search of leads / things to test or try, whether mechanical or electrical. Is there an electrical component that performs okay at or near idle, but could become suspect under load?

CharlieB ? What do I look for if I look into the exhaust ports? Both mechanics ruled out piston slap, and there shouldn?t be any scoring since compression is equal. If I moved the flywheel, would I be able to possibly observe bearing wear?

Hope you?ll stay with me on this!

You can get a motor started and running on muffs, but you cannot, I repeat, CAN NOT simulate a loaded condition, which is how outboards are always operating. In my opinion, you could be creating the " problem/symptom". Running up to 3000 and 4000 RPM could be leaning out a cyl until it "snorts", causing your noise. You really need to get it to a lake or river and report the results based on a loaded run. You have eliminated most if not all of the obvious knocking sources.
I mentioned before, but running unloaded on a 2 stroke is dangerous territory.

 

[verado7]

Re: Sharp Noises and Vibration from Power Head During Throttle Up

so plugs are wet always right ? your never see a totally dry plug ?
trigger wires arent crossed up ?
mayber were overthinking this -has teh ignition been tested with a dva ? i'd like to see the results of that .maybe an intermittent firing from one of the components off idle .

 

[daveswaves]

Re: Sharp Noises and Vibration from Power Head During Throttle Up

so plugs are wet always right ? your never see a totally dry plug ?
trigger wires arent crossed up ?
mayber were overthinking this -has teh ignition been tested with a dva ? i'd like to see the results of that .maybe an intermittent firing from one of the components off idle .

If damp the coils "CAN" cross fire. It just does not feel that we have a good definition of the problem yet. Thats the challenge when you are trying to troubleshoot from a distance. It sure sounds like one cyl is dropping out.

 

[sschefer]

Re: Sharp Noises and Vibration from Power Head During Throttle Up

Not sure why the oil pump was removed but it could be that the crankshaft gear came apart or the bushing failed and is flying around in there.

In any case when you have noises like that comming from inside an engine, it's automatic to just split the case and fix the problem. Those little engines can be tore down in a day. You could either be back on the water in no time or be looking for another motor. 50/50 shot.