Engine Knock!

[jasoutside]

1990 Mercruiser 4.3 V6

I believe there is a troll living in my engine block. He is jacked up on Mt. Dew and has a hammer...

http://www.youtube.com/watch?v=ywszUpAFc5k&safety_mode=true&persist_safety_mode=1

This would be my first start on this set up since I bought it last winter.

So, what do you fellas think? Do I have a great big black anchor or do you guys think this is a fixable deal? Should I skip this whole boat building stuff and take up something that I might be a little more successful at - mall walking maybe?

 

[coheej]

Re: Engine Knock!

Listening to a video is not as good as being there, but it sounds like you have a major problem. Probably rod bearing. as loud as that knock is, I would not run it anymore. Your crank is most likely wore way past turning .010, .020, or .030 under.

 

[jerryjerry05]

Re: Engine Knock!

I hear you knockin!!! It's running,so start taking it apart.You might be able to salvage something.
A new marine short block could be a simple fix.J

 

[ziggy]

Re: Engine Knock!

So, what do you fellas think?

i'm not the one to be thinking really as i'm just a joe boater. but i think that when ya take it apart there will be clear evidence as to what is causing the knock.
ya could use your hearing hose to get the general location of the knock prior to disassembly. then ya could go right to where your hearing the knock to find the evidence of the failure..

 

[ussoldier_1984]

Re: Engine Knock!

That does not sound like a rod bearing, rod bearings have more of a clatter noise then a knock, that sounds like a broken rod, If it is a broken rod your cylinder wall is messed up pretty bad. you will probably need to bore out the engine to make the cylinder walls true. and at the least new pistons to match the bore. it might be cheeper to find a motor at a junk yard and swap the cam and heads to the donor block.

 

[jasoutside]

Re: Engine Knock!

Thanks a lot fellas for chipping in, appreciate it!

I will say (if it helps you guys) that it is clearly a knock as opposed to a clank/clatter sort of a deal, and it's loud too.

 

[Jeepster04]

Re: Engine Knock!

Do a compression test to which cylinder it is. After that I would take the valve cover off to check and make sure all of the rockers are rocking. Could be a valve hitting the piston. I wouldnt run it anymore till you figure out whats going on.

 

[6meter]

Re: Engine Knock!

Take the pan off and check the rod bearings. If it is one , you will be able to tell. Next I would take off the valve covers and watch the movement. Might even put finger on each rocker while running and feel for the valve hitting a piston. I would find the problem before I gave up on the motor. A little history might help also like what was it doing before it knocked. If you just changed plugs and now it knocks, you might have loosened a piece of carbon and that is what is making the niose. Sounds the same. Remove a plug wire one at a time. The knock changes its in that cylinder.

 

[jasoutside]

Re: Engine Knock!

OK, so I decided to chance it for a few more seconds and ran it while I pulled off each of the plug wires, one at a time. No difference at all.

Now, keep in mind my rookie status here, but....

If there was a rod issue of some sort, and I pulled that specific plug wire for that specific rod, the knocking would stop right?

Huh???

Have I got something else going on here maybe???

 

[Jeepster04]

Re: Engine Knock!

OK, so I decided to chance it for a few more seconds and ran it while I pulled off each of the plug wires, one at a time. No difference at all.

Now, keep in mind my rookie status here, but....

If there was a rod issue of some sort, and I pulled that specific plug wire for that specific rod, the knocking would stop right?

Huh???

Have I got something else going on here maybe???

It may or may not completely stop if its a rod.

You NEED to do a compression test as a START. THEN go from THERE. If you do not have any compression, I would just pull the head off and see whats up. Pulling a head off isn't a huge ordeal since the engine is sitting on a trailer.

 

[Bondo]

Re: Engine Knock!

Have I got something else going on here maybe???

Ayuh,.... It's Broken,... Really Bad....

Pull the motor, 'n start strippin' it to replace with a short block, or long block...

Whatever is knockin' will be plainly obvious when you pull the heads, +/ or the pan, 'n bearing caps...

 

[jtmarten]

Re: Engine Knock!

Put a stethoscope on it and pinpoint the noise. Even if it is a broken rod, a sleeve is much cheaper than replacing the block. If the other cylinders are nice enough to just be honed, bonus since you wouldn't have to bore and replace the pistons either. I'm sure good, used cranks and rods are plentiful.

 

[jasoutside]

Re: Engine Knock!

Thanks a bunch for helping me try a figure this, much appreciated!

Stopped and grabbed a tester to gain some more info. Here is what I found...

#1 155
#3 155
#5 145

#2 110
#4 130
#6 130

 

[a70eliminator]

Re: Engine Knock!

There isn't by chance a big dent in the pan, cause that almost sounds like a rod banging against the oil pan, or the flywheel ticking on sheetmetal somewhere, I've heard that sound before, it suddenly went quiet when it completely let go.

 

[coheej]

Re: Engine Knock!

Thanks a bunch for helping me try a figure this, much appreciated!

Stopped and grabbed a tester to gain some more info. here is what I found...

#1 155
#3 155
#5 145

#2 110
#4 130
#6 130

The only thing this tells you is that you don't have a broken rod. It's still knocking, so you might as well pull it. You be able to tell which one is bad.

 

[jasoutside]

Re: Engine Knock!

There isn't by chance a big dent in the pan, cause that almost sounds like a rod banging against the oil pan, or the flywheel ticking on sheetmetal somewhere, I've heard that sound before, it suddenly went quiet when it completely let go.

I handled the pan and didn't notice any damage or bends down there. It seems like a pretty solid knock. Maybe thicker/beefier that what a oil pan might sound like getting banged on.

The only thing this tells you is that you don't have a broken rod. It's still knocking, so you might as well pull it. You be able to tell which one is bad.

I am thinking that my hands cracking this open might be asking for more trouble. Hauling it over to the pro may be the ticket from here on.

Thanks again guys!

 

[jasoutside]

Re: Engine Knock!

Update....

OK, so I was turning by hand just a few minutes ago I am am all but certain what is ahappenin.

I was turning the motor by hand with my right and had my left on the oil pan underneath. Short of one revolution (maybe 3/4 of one full revolution) I can feel something bumping the oil pan out. It's happening right towards the front of the oil pan, so maybe #1 or #2.

I know a couple of you fellas mentioned the oil pan earlier, well, yur money!

OK, so what I need to do from here, eh? Might this here motor be fixable?

Drain, pull the motor, flip, take the oil pan off??

Thanks in advance guys!

 

[6meter]

Re: Engine Knock!

If you can feel something hitting the pan, pull it out. Easier to pull outdrive first though. Any history on this motor?

 

[jasoutside]

Re: Engine Knock!

If you can feel something hitting the pan, pull it out. Easier to pull outdrive first though. Any history on this motor?

Yah, outdrive is off already. I'll pull it out and grab an engine stand from Harbor Freight next time I go by there.

Well, I picked this up in the middle of last winter right off the marinas lot (owner stored it there). Didn't have them run it first (I know stupid you don't have to tell me). The marine tech told me that everything checked out and ran awesome. He had a fist full of receipts that provided info on the total rebuild and other maintenance that he completed on it. This dealer comes well regarded in this area.

Outside of that, what you see here on this thread is exactly what I have seen so far on this motor. Not good so far eh!

 

[a70eliminator]

Re: Engine Knock!

Boy you would sure be lucky to find the windage tray knocked loose dancing with one of the crank counterweights, I don't know what that pan has in it but I know my ford has a windage tray.