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Old 09-09-2020, 06:25 PM   #1
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Default 1996 Maxum 1900sr2 engine makes knocking noise and lost power

RElatively new boat owner who has leanred alot from this group and have actually been able to fix alot of issues based on advice here. So of course I got cocky and thought I knew boats.

Ill try to explain what happened:

casually driving boat in river for 30 mins then sat for an hour then ran 30 mins back to dock. On the way out, I did notice that the temp gauge went higher than normal, then it clicked back to regular, then it would occasionally get high again, then go back down (but it had never really done this before) -- still was running normal.

On way back in, ran it at full tilt for 10 mins and it ran great. upon slowing down and turning up to head to narrow channel, I started hearing a faint banging noise from engine compartment -- almost sounded like a heavy chain was sliding around in the compartment. I increase speed to see if it would change and it got louder and sounded more like a hammer hitting the engine. and the boat had much less power. I eased off and it was still making a softern noise. Like a fool, I increased poser to see if load noise would return. It did and boat was really dragging -- after a minute the engine shut off completely. I opened the compartment and there was smoke (or steam) -- still not sure of the source comping from all areas of the engine bay.

I turned the key and nothing. I waited 20 minutes and then the engine fired up after 1-3 seconds of cranking but sounded "off" and there was a lighter light banging sound still --- I ran it back to the slip at about 5 mph -- it ran like this for about 10 mins until we were back and then I just dhut it off and went home out of frustration.

Other than the temperature gauge acting a bit erratic, the gauge never sent over 200 or stayed high -- it would be up then go back to morman -- and the oil pressure the whole time running it was normal --

any ideas what happened -- there is no way I am taking it back out again, but want to prepare myself for the fisting I will probably take at the mechanics shop -- as it didnt sound good.

thanks for indulging in this long story and would love to hear your thoughts.
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Old 09-09-2020, 06:43 PM   #2
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Default sorry for all the typos -

I have one arm in a splint and am typing left handed
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Old 09-09-2020, 07:06 PM   #3
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Sorry to be brutal bit sounds like either big ends or rods.. I am not an expert though. I would suggest not to crank it to prevent further damage.

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Old 09-09-2020, 07:28 PM   #4
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What type of repair and what type of cost are we talking about if its the big ends or rods?
Also, how does that occur? Just through excessive use?
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Old 09-09-2020, 08:00 PM   #5
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Just for reference what engine; 3.0 or 4.3?

So the oil pressure is still normal? If so I doubt a main bearing failure but could be a connect rod. Either is a complete rebuild or replacement.
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Old 09-09-2020, 08:15 PM   #6
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"ran it at full tilt for 10 mins"..... WOT for 10 minutes. That would scare the hell out of me.
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Old 09-09-2020, 09:34 PM   #7
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its a 4.3 L

And when I say ran at full tilt, I mean I let her go for 5-10 minutes on the way home as the water was like glass and no one was out--- it was running fine at that point, there had been no issues prior to that and oil pressure was normal -- the noises did not start until after we slowed down and entered the channel

I did not run it full out after hearing or sensing anything -- I didnt go over 5 mph after it stalled -- just wanted to avoid waiting an hour for a tow and it seems "okay" at that low speed just to limp into the slip.
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Old 09-09-2020, 09:39 PM   #8
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....and if it is a complete rebuild, let me know if anyone is looking to buy a 1996 Maxum 1900 sr2 that needs a new engine! its in nice shape other than the engine now.
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Old 09-10-2020, 12:16 AM   #9
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Quote:
Originally Posted by MikeW View Post
its a 4.3 L

And when I say ran at full tilt, I mean I let her go for 5-10 minutes on the way home as the water was like glass and no one was out--- it was running fine at that point, there had been no issues prior to that and oil pressure was normal -- the noises did not start until after we slowed down and entered the channel

I did not run it full out after hearing or sensing anything -- I didnt go over 5 mph after it stalled -- just wanted to avoid waiting an hour for a tow and it seems "okay" at that low speed just to limp into the slip.
What rpm is full tilt? This engine is rate with a WOT of 4200-4800 rpm which should only be operated at for 2-3 minutes at a time else you can damage the engine. Can you post a video of the engine with a audio soundtrack of the noise?
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Old 09-10-2020, 12:20 AM   #10
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Quote:
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....and if it is a complete rebuild, let me know if anyone is looking to buy a 1996 Maxum 1900 sr2 that needs a new engine! its in nice shape other than the engine now.
Basically that would be a free boat as if one paid a mechanic the job would be ~$5K, half for the rebuild or rebuilt longblock and the rest for labor and odds and ends.
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Old 09-10-2020, 01:38 AM   #11
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I may have miscalculated the 10 mins comment.
Id say I ran it at 4300 rpm for 3-4 mins then ran it at 4500 for another minute.

I have no idea how many hours the engine has on itthe counter says 183, but it has never worked since Ive had it and i have no idea how long it had not worked before.
Ive never run the boat very long or very high rpm so I never really pushed it u til what I described above. The water was flat and only 2 people inboat so not sure if the damage was done during those 4-5 minutes or if it just aided the death of an older motor.

Any ideas on why the temp gauge was acting erratic on the way out when I was running it very tame?
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Old 09-10-2020, 11:40 AM   #12
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With no video we're left to our imagination as to what your engine sounds like. I think you are describing a heavier sound that is caused by piston vice valve. I would first check the oil to ensure it is at correct level, then drain a few ounces from drain hose to see if I get water or flakes. If oil is good, start engine and pull one wire at a time to isolate cylinder that is knocking.
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Old 09-10-2020, 11:52 AM   #13
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The temp gauge could have been erratic due to many things; electrical issue with it, thermostat acting up opening and closing, air in the cooling system is this closed or open cooled? How does the oil look? Jrsick is correct you can isolate it to a cylinder by removing one spark plug wire at a time and the noise will decrease when you find the cylinder that is bad.
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Old 09-11-2020, 11:17 AM   #14
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Thanks for all the feedback. Going to take it to marina nearby that specializes in MerCruisers to get a diagnosis. Will report the findings. Unfortunately, Im a glass half empty guy, so I fully expect to hear blown engine. We can fix it for $4,200.
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Old 09-11-2020, 11:21 AM   #15
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Quote:
Originally Posted by MikeW View Post
Thanks for all the feedback. Going to take it to marina nearby that specializes in MerCruisers to get a diagnosis. Will report the findings. Unfortunately, Im a glass half empty guy, so I fully expect to hear blown engine. We can fix it for $4,200.
Good luck!

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Old 09-11-2020, 05:04 PM   #16
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The glass is simply too big......
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Old 09-11-2020, 07:50 PM   #17
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Half empty = half full
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Old 09-23-2020, 05:22 PM   #18
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Mechanic did a diagnostic. Said 4 cylinders normal, cylinder 1 is at 110 and cly 5 is at 55.
Said he’s not sure where knock is coming from at higher revs. Assumes it’s a shaft.

Didn’t seem to want to speculate on whether it was fixable. Just said a remanufactured engine is $7k

Any sense in getting a second opinion or does the info about the 2 bad cylinders and the knock sound convincing enough to stop now and dump the boat?

I assume there are some things I could salvage and try to sell: Bimini, covers, trim hydraulic motor, alpha one out drive, 3 propellers, seats, trailer. Etc
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Old 09-23-2020, 11:53 PM   #19
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Could the knock be from detonation in cylinder #5? Not sure what he means by the knock coming from a shaft. I would next perform a leak down test to determine if the low cylinder pressure is from a valve or ring issue. $7K to install a long block with new exhaust is a little high by $1K but labor rates in you area may be higher or is he quoting other work such as rebuilding the transom assembly as well?
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Old 09-24-2020, 12:57 AM   #20
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In my years as a professional mechanic, when You pull a plug wire on an engine with a knock, if the knock goes away then that cylinder has a connecting rod bearing that is gone out. If the knock gets louder then it is a wristpin or a piston slap.
I had never got the opportunity to test that theory on an engine that has a bad piston but I can guarantee that it does work on the bad rod bearing and the noise goes away.
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