4.3l GM262 won't plane, knocking sound

[gbajramo]

This is for 1997 GM262 4.3LX(GEN+).

After idling though the channel for about 15 minutes I tried to get on the plane but the boat was plowing with bow up. I realized I didn't trim all the way down. Trim gauge and limit switch are not working so I don't know exactly how far up the drive was but it should have been right around the trim/tilt limit. I trimmed all the way down, prayed I didn't blow up something, and got on the plane. However the engine was louder and there was more vibration than normal. After few miles I was idling again and when I tried to get on the plane once more the boat would get some speed but before it could get on the plane the engine would rev up and boat would lose acceleration. I noticed that when engine revs up, the boat slows down.

I idled my way back and noticed distinct knocking sound. Here is the link to the video with the sound:

You can clearly hear the knocking at 0:24 and 0:54+
Sorry for the camera work, I was trying to get the knocking sound from different angles.

Let me know what you think. My understanding is that if the coupler was blown there would be no forward movement and engine would overheat. But I can still go forward and in reverse and engine temperature is fine. There is no smoke or bad smell from the engine.

 

[Bondo]

Re: 4.3l GM262 won't plane, knocking sound

Ayuh,.... Welcome Aboard,... What's the motor's oil look like,..??

How 'bout the Outdrive's oil,..??

I ain't hearin' yer knock,...

When was the fuel filter last changed,..??

Did you determine that the drive was Full Down, when tryin' to get on-plane,..??

How long has the boat been in the water,..??

How much sealife is livin' on the hull, drive, 'n prop,..??

 

[searay3]

Re: 4.3l GM262 won't plane, knocking sound

You may have a spun prop hub. To check you will have to pull the boat out of the water. Remove the prop nut and washers, scribe the hub and prop with a magic marker or pic, put the boat back in the water and try to get on plane. Remove the prop nut and see if the hub is still lined up with the prop. If not, take it to a prop shop or get another prop.

 

[bonzoscott]

Re: 4.3l GM262 won't plane, knocking sound

Just a guess, but you may have had the drive "WAY" up and smoked your U-joints. It idled out okay in that position but once you applied some torque to it, they failed. That's what the vibration tells me. BTW - Welcome to iboats...

 

[gbajramo]

Re: 4.3LX GM262 won't plane, knocking sound

Re: 4.3LX GM262 won't plane, knocking sound

Thanks for the warm welcome guys :joyous:

Yes, drive is full down. Outdrive oil level is normal. I haven't drained it yet.

Boat is in dry storage so the hull is uninhabited.

I've been having some problems with the fuel after boat has been sitting for a while. I've been changing the filter about every 15hrs or monthly hoping this will work itself out.

If you forward the video to 0:54 you can hear it. Knocking may not be the right description but it's some sort of klunk-like sound.

I removed the aluminum prop and inspected the hub. I didn't see any damage to the sleeve. Wouldn't the sleeve be chewed up if it failed? It's one of these hubs:

 

[bonzoscott]

Re: 4.3l GM262 won't plane, knocking sound

This is for 1997 GM262 4.3LX(GEN+).

After idling though the channel for about 15 minutes I tried to get on the plane but the boat was plowing with bow up. I realized I didn't trim all the way down. Trim gauge and limit switch are not working so I don't know exactly how far up the drive was but it should have been right around the trim/tilt limit. I trimmed all the way down, prayed I didn't blow up something, and got on the plane. However the engine was louder and there was more vibration than normal. After few miles I was idling again and when I tried to get on the plane once more the boat would get some speed but before it could get on the plane the engine would rev up and boat would lose acceleration. I noticed that when engine revs up, the boat slows down.

I idled my way back and noticed distinct knocking sound. Here is the link to the video with the sound:

You can clearly hear the knocking at 0:24 and 0:54+
Sorry for the camera work, I was trying to get the knocking sound from different angles.

Let me know what you think. My understanding is that if the coupler was blown there would be no forward movement and engine would overheat. But I can still go forward and in reverse and engine temperature is fine. There is no smoke or bad smell from the engine.

The way I read it, you tried to plane out not knowing where your drive was positioned. Not matter if you trimmed it down later. I heard the knocking. Bondo maybe didn't have his speakers turned on. This addresses only the knocking noise. Not sure if the Revving of the motor and losing drive power is related. I think the drive needs to come off and inspect. Loss of power could also be the coupler. You may want to have a shop check it out or follow up on iboats.

 

[Volphin]

Re: 4.3l GM262 won't plane, knocking sound

I hear it too. Sounds like U joints or coupler to me as well. It is not engine related as it is not consistent. I agree that the drive should be removed for an inspection asap.

 

[gbajramo]

Re: 4.3l GM262 won't plane, knocking sound

Here is an update: marina mechanic removed the outdrive and found no issues. He says coupler splines look great and since there is no overheating the rubber around the coupler is fine. He says gimbal bearing is smooth as butter and so is the u-joint. He says the clunkity sound is most likely coming from the exhaust system and it could be flappers. He changed distributor cap and thinks it's the fuel system issue.

Boat idles fine but hesitates and nearly shuts off when slowly increasing the RPMs.

Do you have recommendations on a good carb rebuild kit for the 4.3LX (GEN +) (2 BBL.) GM 262 V-6 1996-1997?

 

[dannys2004glastron175mx]

Re: 4.3l GM262 won't plane, knocking sound

sounds like a loose flywheel to me :ranger:

 

[MikDee]

Re: 4.3l GM262 won't plane, knocking sound

IMO, The rubber seal in the coupling has broke free, and the center hub is slipping.

 

[Fun Times]

Re: 4.3l GM262 won't plane, knocking sound

He says the clunkity sound is most likely coming from the exhaust system and it could be flappers.

That's what it sounds like to me. Pretty common really!!!

Good luck with it.

 

[bonzoscott]

Re: 4.3l GM262 won't plane, knocking sound

We may be getting confused here with two problems. The boat Revving Up and losing speed sounds like a spun prop hub. Did you ever check that out or point out to your mechanic. That problem would not cause a knocking noise so there may be two issues. Maybe get a prop and trial again on the water - isolate one problem at a time.

Boat idles fine but hesitates and nearly shuts off when slowly increasing the RPMs - could be a third issue, restriction in fuel flow, filter or anti-siphon valve on tank. Address those before carb rebuild.

 

[gbajramo]

Re: 4.3l GM262 won't plane, knocking sound

I'm going to look at tank and anti-siphon valve today.

I found this helpful:
http://www.justanswer.com/boat/492bp-97-mercury-v6-stroke-saltwater-series-ob-starts-fine.html

In the likely case I need to clean the tank, what material are these tanks made of? Is it polyethylene or something else? Which solvents or cleaners are safe to use without damaging the tank?

 

[Bondo]

Re: 4.3l GM262 won't plane, knocking sound

I'm going to look at tank and anti-siphon valve today.

I found this helpful:
http://www.justanswer.com/boat/492bp-97-mercury-v6-stroke-saltwater-series-ob-starts-fine.html

In the likely case I need to clean the tank, what material are these tanks made of? Is it polyethylene or something else? Which solvents or cleaners are safe to use without damaging the tank?

Ayuh,.... Ethanol gasoline is All the solvent ya need,....

 

[gbajramo]

Re: 4.3l GM262 won't plane, knocking sound

OK, here is the latest.

Carburetor was rebuilt and tuned. Engine works like a dream in neutral at all RPMs. But when I put it in gear it again hesitates about 1/3 of gas and it nearly shuts down. Weird thing is that it doesn't do that consistently. Sometimes it's fine, another time it stalls and nearly shuts down. Before it would usually backfire at the same time but it doesn't do that any longer. The vibration and clunkety noise are still there.

Not sure where to go from here. Look at the drive again? Shaft? Gears?

I noticed that manifolds don't run at constant temperature. I was measuring starboard manifold temperature on idle and it would variate from 100F to 128F in cycles. Is this normal or should it be fairly constant?

 

[dingdongs]

Re: 4.3l GM262 won't plane, knocking sound

try pulling the top cap off the drive and inspect the gears for missing teeth,
would suggest trying the engine with the drive removed to eliminate one or the other and did the mechanic prove this as would seem too good an opportunity to not try as the drive had already been off.fuel still sounds like the likely cause as more is required but the carb is failing to supply.was a carb rebuild kit used as the mechanic sounds as he hasn't diagnosed FA.

 

[leftcoast]

Re: 4.3l GM262 won't plane, knocking sound

I've got a 4.3L coupled to a Alpha 1 Gen 2 drive and hear the same 'clunking' sound at slow idle. The 'clunking' also has me worried, but aside from this she runs fine. I've pulled the drive and splines, u-joints, gimble bearing, gears are fine.
The clunking seems to be associated with a misfire (slight motor vibration), which I notice also in your video Makes me wonder if it is slack build up in the counter balance chain inside the engine.

I haven't run the motor with the drive removed but plan to soon to confirm it's not in the drive.

Does this sound plausible?

Jim

 

[gbajramo]

The planing and stalling issue was resolved by polishing the fuel. 3 gallons of water were filtered out.The stalling would occur when enough water accumulated in the carb and was worse on the way back because the fuel was agitated. Mechanic noted that O-ring on the gas cap was missing which could have allowed additional water intrusion. I can't believe it was running at all with so much water. 4.3L is the monster. Otherwise tank, hoses, and fittings were clean. As it turns the tank doesn't have an anti-siphon valve installed.

Another mechanic said that clunking is most likely exhaust flaps so I'll leave it at that.

I still have more vibration than before but I'll wait until next tuneup to see if there is improvement.