2002 Isalndia low RPS's

[jamepc]

My question is about idling. My 2002 2140 Merc Islandia has a very deep rumble (sounds like a lumpy cam in a hot rod) from idle to about 3000 RPS, once above 3000, the motor smooths out to a steady normal sounding 2 stroke. It's shakes the boat, not violently, but there's a definite difference once above 3000 rpm's. This happened on the original motor and now a fresh rebuilt motor, rebuilt by a reputable Mercury machinest that has done plenty of these motors and upgrades the weak points of the motor). It doesn't seem engine related, perhaps exhaust? Or perhaps that's just the nature of these motors?
Thanks for any help,
James

 

[Dr Honda]

It's hard to say from where I'm sitting. I've always thought that the 2.5l Merc engines were smooth for a 2 stroke. (my 96 XP feels like an old dirtbike)

The exhaust is basically hollow cans... so unless you can see a hole... I'd say it's probably not the issue. BUT... sometimes the hoses can de-laminate, and it could be "Fluttering" inside. AND, once the RPM's are high enough... it's pushed open.


I would be more inclined to think there is an issue in the pump. (if there is a problem) I know if I suck in a bag... there will be vibration, and some rumbling. So... you may want to look for some minor damage to a blade, or a bad gouge in the ring. Also... I know it's too late... but by any chance... did anyone try to turn the input shaft by hand, while the engine was out? I know that's the first thing I did... just to feel the gears, and bearings in the pump.

You can still get a feel on that. Pull out the spark plugs, and remove the top cover. Then... have a helper turn the engine. You can put a wrench on the flywheel bolt to make it easy... but don't use the starter. Then... get your ear down my the pump, and listen to the bearings, and gears. Also... put your finger on the stator in the pump, and FEEL for a vibration, or rough bearings.

 

[jamepc]

Thanks for the reply. Do you mind if I send a video of rumble? I don't know how well a deep rumble will sound on a smartphone video but maybe you can tell.

EDIT
I just remove the starboard exhaust can and looked in the pipes and they look OK. The can however has what sounds like pebbles in them. Maybe from reversing onto sand banks, although can't remember actually doing that.

Edit again
The rattling inside the mufflers were internal engine parts from when the rod came through the side of the block! However I doubt this explains the deep rumble I get at low RPM's

 

[Dr Honda]

It may be. it would be rattling around.

Post a pic of what you found. (lol)

 

[jamepc]

Here's what came out of the mufflers:




Here's the insides of the pipes. Doesn't look like an de-laminating went on. They hoses look like solid pieces of rubber and not like there's a laminated layer on the inside wall. Were laminated hoses used on '02 Merc 240's exhaust systems?

 

[Dr Honda]

Those look OK to me.


Looks like you have an ugly melt down. Those little pins are the bearings out of a wrist pin. And the chunks, are a piston. And that washer is the wrist pin shim.

 

[jamepc]

The alarm went off so I asked my friend to check the tank, he told me "it's full, keep going!". Trying to outrun a severe storm, I did. Moments later...boom! and it wasn't lightning. The oil left a blue tint on the oil tank so he thought it was full.

Those metal pieces aren't the source of the deep throaty rumbling. n I think that would be a completely different sound, plus it was like that before the rod came through the block.

The impeller and wear ring were replaced before the engine went (could be some damage since though)
Do you recommend checking the pump for roughness, bad bearings etc.?

 

[jamepc]

OK, so We turned the crank by hand looked and felt for any roughness, all seems tight and smooth. There's a slight play in what seems to be the beveled gears when turning the impeller shaft back and forth but it it very minimal.
I've search the web and found a few other posts describing the same roughness and thumping I feel at idle. Here's one thread:
http://www.jetboating.net/jetboating/common/forums/postview.aspx?postid=46498

Any other ideas what it could be?
Thanks,
James

 

[Dr Honda]

Yes... there will be some backlash in the gears... so that's normal.


Unfortunately... since I'm not there to listen... it's going to be hard to say. Are you sure it's not just the fiberglass deck beside the engine?? Mine rattles a bit, at low RPM's. Or... cables/wiring thumping around?


you can try to post a vid... but most camera's don't pickup the noises properly.

 

[jamepc]

I ran across this video on youtube. It's a Challanger with the 240. The sound recording quality is pretty decent but only appreciated when listened on my PC with the 2.1 speaker (2 speakers and a sub). You can hear the rumble up until about 1:38 into the video, then it's smooths out to the familiar 2 stroke purr. Dont know if it has the same shaking that the rumble produces on my Islandia though.
When I watched it on my PC without a sub, you can still hear the noise difference at 1:38 but not as well.
http://www.youtube.com/watch?v=Wk8qh0ftnes

 

[Dr Honda]

Like I said before... can't always tell from a vid. Besides... the tiny speakers on my laptop don't reproduce sounds well.

The rattling/thumping noise could have been anything rattling/bouncing around. It smoothed out because opened the throttle.


***EDIT**

Didn't mean for that to sound short... just didn't have an good answer.

 

[bhatch21]

jamepc, you might check the bolts at the rear of the jet pump. I had one of the long bolts work itself loose on mine and it made a rattle and vibration like running with my ladder down.