Very loud rattling/knocking noise under load

[cruiser83]

just purchased a 1980 Tahiti day cruiser inboard/outboard. It has a 95 vortec 5.7 converted to a carburetor and a first generation alpha outdrive. I just took it out for the first time and runs and drives fine except when I get up to around 3000rpms under a load it makes a loud knocking/chattering/pinging(?) noise. Sounds like a cracked or lose flexplate or the sound of a fan on a truck hitting the fan shroud. But I thought I ask before I pull motor. If I adjust trim up or down, it seems to effect how soon it makes the noise. And the slower I climb in rpms the longer it takes for the noise to come on. If I slowly ease into it the noise will not come in until close to 4k, that's with trim all the way down. And with trim up some it will come on as early as 2700 rpms. And the noise doesn't slowly come in. It's instant. And does not go away until I throttle down. Doesnt make the noise at all in neutral ethier. This is my first boat and it was my first time ever driving a boat lol. I've built lots of Chevy trucks from the ground up and know my way around a Chevy motor pretty well but never dealt with one in a boat or a boat all together. I live in northern AZ and it gets well below freezing so I can't just hook it to a hose without winterizing it Everytime.
​​And the local lake is way to cold to get wet and was frozen over last time I drove by there. So I gotta drive over 2 hours to test it on the lake....I'm just wondering does this sound like it could be a loose flywheel, or damper? Or cv or gimble bearing about to come apart? Next time I try it I'm goin to try and replace fuel pump, and fuel filter/water seperator. I'll have a timing light too so I can check timing and advance. I'm hoping it's just some detination and timeimg is off. I also just installed a pertronixs electronic ignition and removed the points. But I didn't drive it with the points or any time prior. It has a yl Mallory distributor. Is there a way to check the timing advance without running the motor and useing some type of tool and removing the cap? Thx

 

[kenny nunez]

You said it does not happen in neutral, is that when you rev it up to 2700 or above that the noise does not happen?
The first thing that I thought of was something in the adapter housing like a flat washer or a nut getting lifted from the air turbulence. The only way to find out is to pull the engine.

 

[cruiser83]

Yup only does it under a load cruising around 3k rpms, and in neutral it can be reved over 4k with no noises and sounding healthy

 

[cruiser83]

Would my set up have a damper plate?

 

[harringtondav]

You boat has had a lot of hands in it since 1980. New engine. Newer at some time out drive. Not sure, but probably some adapting at the transom for the new O/D. You can check timing with flush muffs and a garden hose to run the engine.

Your engine has a spline coupler bolted to the flywheel. The 'flexing" is in the rubber splined hub that couples with the outdrive yoke shaft. My knee jerk is your engine is fine. Something downstream needs help.

Dig in and keep us posted.

 

[tank1949]

Start with the easiest. Get steth-i-scope and pin-point noise. Or, pull OD and examine u-joint and gimbal bearing. Od is a lot easier to pull than motor.

 

[cruiser83]

That's what I'm thinking I bought the boat from a lady who said she put 10k into it but I think alot fo that was labor and the initial purchase of the boat..but the shop who she had replace bellows and seals on out drive said that they didn't install the motor...which I got a eery feeling about. And I'm thinking she knew about the issue and didn't wanna spend the money to fix it. I feel like it was all just put together. Too be sold. But I definitely will keep updated. Here's a pic of the fuel that I just poured out of my fuel filter

 

[altitude 411]

Yup only does it under a load cruising around 3k rpms, and in neutral it can be reved over 4k with no noises and sounding healthy

Is it possible it could be u-joints in the drive?

 

[cruiser83]

Ya if I can't fix it by adjusting timing and new fuel pump and filter, I'll check compression at the lake while it's wet. Then I'll pull out drive and check joints and bearing. I just watched a video on how to pull the drive. What's a good way to check gimble. Just try wiggle with my fingers?

 

[Scott Danforth]

first, in 1995, it was not a vortec engine (those are 1996 and later)
second, with the Mallory YL, why would you put a pertronix trigger in it vs simply one of the Mallory electronic triggers?
Third, what is your timing set to? if your suffering detonation, that is your motor eating itself.
Fourth, to check the gimble, you rotate it with your fingers, it should be as smooth as glass when rotating, any wiggle or brinelling and you replace the bearing.

Need more info - check the stickies

 

[Bondo]

Third, what is your timing set to? if your suffering detonation, that is your motor eating itself.

Ayuh,...... Agreed,..... A Lean condition could be another cause, especially considerin' it happens at higher rpms,....

 

[cruiser83]

See thats what I thought but I had a buddy say that "vortecs first came out in boats so it could be a vortec" but idk if he knew what he was talking about. Idk what the timing is because I didn't think of bringing a light with me to lake. And it had a points ignition in it. So I thought the pertronixs one would be better. I didn't know Mallory made a electronic ignition to drop in. It's a older Mallory distributor. I just said it was yl because after looking at all the pics on line that's the one the looked like it the most. The part numbers aren't Readable on it. I don't wanna bother checking the timing until I get it back to the lake so I don't have to flush the motor with antifreeze again.

 

[cruiser83]

Is there a way to check the mechanical timing advance without haveing the motor running?

 

[Scott Danforth]

Is there a way to check the mechanical timing advance without having the motor running?

with a sun distributor machine, yes without one, no.

however start with the basics. what is your base timing? anything more than 8* BTDC and you risk detonation

 

[Rick Stephens]

Feel for your problems. Tough part of this is both original poster needing to climb the steep learning curve on Mercruiser IOs and doing diagnosis in mid winter when the water testing options are an entire days effort.

First off, as much as possible needs to be accomplished in the driveway on muffs. Driving a couple hours for a quick test doesn't seem like a good way to approach this.

Second, 'winterizing' over and over is as simple as making sure you get the motor and outdrive empty of water each time. I do that all the time here in the northern Rockies. On a warm motor I just pull all the drains and make darn sure they all are open and the water comes out, and then lower the drive and make sure its drain holes are clear. At most a 15 minute job. I may do that a couple times a day and several times in a week just so I can either work on the boat or can fish when night time temps are well below freezing. That is the extent of 'winterizing' needed to work on the boat.

Third, a Chevy motor is a Chevy motor. Wrenching on it it is not hard. Learning where everything hooks up and how the Merc drive works is the task in front of you. First steps with the motor are to check timing, do a compression check and inspect the plugs to see if it has been running lean or timing issues going to cause it to eat itself.

Fourth, no new to you used boat should be assumed to have ANYTHING mechanically maintained. Don't care what the previous owner said. All maintenance needs doing before the boat gets dunked. Doing the maintenance will teach you more about boats and outdrives than anything else. Get the Mercruiser manual that matches your outdrive and go through everything before it ever gets wet again. Drain the drive oil, pull the drive, separate the halves, inspect the water pump and condition of the drive halves, look for any oil indicating a possible leak, turn the shafts on upper and lower to feel for bearing issues. Inspect the gimbal bearing and u-joints, look at all bellows carefully, check the shift cable for smooth operation. I would personally build a pressure tester (in the Adults Only information section on the forum) and pressure test the drive after reassembly and before refilling with oil. Only way to know for sure if the seals are still good and this is a new to you boat, find out now before it cost $$$ to fix. Inspect everything else! If you don't find a problem in the drive that would cause the noise, you may have to pull the motor. Easy as can be to do, but you'll have to know what you are looking for. So lots of questions here as you go.

I could go on. But that is the mindset you need. Old boat and new owner = always go through everything before getting it on the water.

Rick

 

[Scott Danforth]

See thats what I thought but I had a buddy say that "vortecs first came out in boats so it could be a vortec" but idk if he knew what he was talking about. Idk what the timing is because I didn't think of bringing a light with me to lake. And it had a points ignition in it. So I thought the pertronixs one would be better. I didn't know Mallory made a electronic ignition to drop in. It's a older Mallory distributor. I just said it was yl because after looking at all the pics on line that's the one the looked like it the most. The part numbers aren't Readable on it. I don't wanna bother checking the timing until I get it back to the lake so I don't have to flush the motor with antifreeze again.

the "vortec" name came out as marketing on older 4.3's starting in about 1985 and was scrawled across the engine vanity covers in about 1989. Marketing took the engineering name for the heads long before they went into production and decided to market it. however had nothing to do with vortec combustion chamber technology which started with the LT1 motors, then went into production in the 1996 model year on the SBC 5.0/5.7 and the 4.3 and even the L29 BBC. the same vortec head chamber then made it to the ATLAS line of engines

 

[Rick Stephens]

It is eminently possible to *build* a '95 block to having Vortec combustion chamber technology. And then, like my engine, you end up with a morphadite bastard motor that is lots more fun to buy parts for :^)

 

[Scott Danforth]

It is eminently possible to *build* a '95 block to having Vortec combustion chamber technology. And then, like my engine, you end up with a morphadite bastard motor that is lots more fun to buy parts for :^)

yes, and my 1988 motor even had vortec heads in it and a decent cam for about 5 years prior to going to BBC. the great thing about the SBC is its the "Mr Potato Head" of the automotive world.

 

[cruiser83]

Ya I've had the boat since October and rewired the entire boat up to the harness of the motor. Even put all new gauges, stereo system. Had all the seats out. Redid bases on seats. And went over everything possible. Just figured I give it a water test because I finished it all. And was pretty excited to take it out. These pics where taken before I cleaned it up and ziptied them

 

[Rick Stephens]

Ah, very pretty work! Nice.