Diagnose a "knock"

[powrguy]

I've got a 1989 Merc. 2.0L 150HP motor, which runs, but has a "knock". I am not a mechanic and not real familiar with outboard work, but do I have to tear the whole thing apart to find the cause, or can I do some diagnostic stuff before that?

Where do I start?

thanks

[Superbender]

drop the lower unit first to make sure its not the gearcase,run for a few secs to see if noise is there or not with case off,check comp next

[j_martin]

One of these could help.

http://www.harborfreight.com/media/catalog/product/cache/1/image/370x/9df78eab33525d08d6e5fb8d27136e95/i/m/image_934.jpg

[baddjonny]

Even just a long thin screwdriver against your ear you can also use a small hose or hardwood dowl just poke around leaning it against the engine only other thing is loose flywheel magnets.

my 2 cents
jon b

[powrguy]

Well, I'll give the "listening" a try....I thought maybe somebody would say "pull the heads and check the bores". It runs, but it's a LOUD knocking, and I don't want to do more damage. The lower unit was rebuilt last year by a Certified Merc Mechanic, so I know it's in the mota.

Might just sell the WHOLE motor if I wimp out on doing major work.

thanks for the replies

(j_martin: When I first looked at your response, I thought the photo was a rectal thermometer! LOL)

[Capt.Insane-o]

Make sure the flywheel nut is tight.

[powrguy]

Make sure the flywheel nut is tight.


That would be GREAT if that's all it is !

I gotta get the mota from storage, and get it on my stand. Was hoping for tips on what to find without a total dismantling. The motor ran GREAT until the knock. Took it to "Certified Mercury Mechanic" and they went through the lower unit, told me it was fixed.....and the knock was not even addressed with that. $600 later, I still don't have a cause.

[Capt.Insane-o]

It's a best case scenerio. A guy called me just after thankgiving with a 260 he stuck all kinds of money into out of ignorance that started knocking, he would'nt take no for an answer and was so fed up and set on a new opti I bought the motor minus cowls and lower for a kick in the nuts. It took a $15 nut to fix it. :) But the easiest way is to pull the heads and intake and see whats going on, which even if your a noob won't take more than an hour.

[powrguy]

It's a best case scenerio. A guy called me just after thankgiving with a 260 he stuck all kinds of money into out of ignorance that started knocking, he would'nt take no for an answer and was so fed up and set on a new opti I bought the motor minus cowls and lower for a kick in the nuts. It took a $15 nut to fix it. :) But the easiest way is to pull the heads and intake and see whats going on, which even if your a noob won't take more than an hour.


I had the same kinda experience with a Mariner 150 Magnum II, where a guy had the motor on a stand for 10 years, intending to "rebuild it", then closed his shop and sold me the motor. I started disassembly to part it out (I bought it for the midsection and tilt/trim), and I found a broken stator wire. Compression was 120 across the board, and there were no other problems.

thanks

[Ron V]

I had the same kinda experience with a Mariner 150 Magnum II, where a guy had the motor on a stand for 10 years, intending to "rebuild it", then closed his shop and sold me the motor. I started disassembly to part it out (I bought it for the midsection and tilt/trim), and I found a broken stator wire. Compression was 120 across the board, and there were no other problems.

thanks

Not outboard related, but had that happen with a lawnmower. Like new, 21" MTD with a bagger, still had paint on the underside of the deck, but no blade. Was in some guy's garbage. As I was putting it in my truck he was telling me, "It still has some good parts on it". It ran but not well. A new diaphragm for the carburetor from Ace Hardware plus a blade and I was in business. It's basically a new mulcher/bagger with a Briggs (my favorite) for about $30.

[j_martin]

Well, I'll give the "listening" a try....I thought maybe somebody would say "pull the heads and check the bores". It runs, but it's a LOUD knocking, and I don't want to do more damage. The lower unit was rebuilt last year by a Certified Merc Mechanic, so I know it's in the mota.

Might just sell the WHOLE motor if I wimp out on doing major work.

thanks for the replies

(j_martin: When I first looked at your response, I thought the photo was a rectal thermometer! LOL)

Could be LOL. Just be sure your head is out of the way.:eek::D :leaving:

I bought an XR4 that was a real pig, had a knock, etc. The knock was in the LU. I had in my hand receipts for a LU seal job by a "certified" merc mechanic. I had my trusted Mercury man look into it and he found just about everything was out of adjustment, and the new seals had been damaged on install, as well as a couple of bearings. He showed me all the parts he replaced, and I was amazed it didn't put the pinion out the side when I ran it. Now is a fantastic LU. (small bore, high gearing, slippery and fast in the water.)

Pukey running was all misadjustments, wrong parts, etc, all done by the same "certified" mechanic. The original problem was crud in the fuel tank, which should have been a no-brainer. Just set up and tuned by the book, it now runs like a scalded dog. I had to go buy a steeper prop for it.

I'd pull the LU as advised. Also pull the flywheel and look underneath for signs of contact with the stator, and also tightness of the stator mounting. It should be a real grunt to get the flywheel nut loose. If it's easy, there's your problem.:D After that, pull the carbs and reed plate, and the heads, and ask here what to look for. Yer still at the shade tree level of mechanics at that point, and you can actually touch about every moving part in the engine except the wrist pins.

Unless yer a natural wrench turner, go get a set of cheap torque wrenches (1/4 and 3/8) for the reassembly. It'll save some heartache either at assembly or later. Borrowed torque wrenches work fine. When you're working with aluminum and gaskets, even and correct torque is the difference between no-sweat reliability, and trouble.

hope it helps
John

[powrguy]

Thanks, John. I actually was already on Ebay looking for the inch-pound (1/4 and 3/8 drive) torque wrenches. I thought that I'd pull the heads and look inside. Also, the flywheel/lower unit-dropping were two other ideas that I'm going to try, also. I know the LU was supposedly gone through to fix the knock, and the previous owner was told "it's fixed" ($600 later, which seems awful cheap for a LU job or ANY dealer-servicing), and when the motor was run, it still had the same knock in it. Anyway, the motor supposedly runs, with a knock, and that's how I bought it. I am picking it up this week, and will put it on the stand to start going over it. I am not sure I wanna even start the motor, on the stand, with the knock in it for fear of further damage. I don't know how far I wanna go with a 150HP project like this, as I really would like to replace my great-running 1988 Mariner 135HP 2.0 Marathon motor with a 200HP motor on my boat. My idea was maybe to get a backup 150HP, and/or maybe sell both and get a 200HP 2.4 or 2.5 Merc.