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Bravo 3 Rattle under Load

S

shawnmd

New member
I have a 96 Chap with a 5.7lx and Bravo 3. I just put it in the water today. The boat ran great for the first hour at a slow speed (about 7 knots, 2000 rpm), then when I increased throttle to about 3000-3500 while pulling my son on tube, I began hearing a loud rattle (like marbles in a jar, not a nice sound). At first it sounded like a rocker arm rattle, but it was coming from the drive. I stopped, put it in neutral and revved the engine to 3500, and didn't hear any rattle, sounded perfect. I put it in gear again and went to 3500 under load and the rattle was back. I then trimmed the drive up a bit and the rattle stopped under load. Since a trimmed the boat that time, the rattle has for the most part stopped. I can still hear it very faintly under load.

Again, no noise in neutral, and trimming the drive seemed to have quieted the rattle some. Just before putting the boat in water, I changed drive fluid and greased the gimble bearing. Just last year, I replaced the drive bellows.

Does this sound like a gimble bearing going, or a universal?
 
Update......The ram anode was not the problem. I also pulled the drive and replaced the Gimball bearing. The universals looked perfect and turned freely. Put the boat back in the water, and the noise continues.

I should mention, before all of this, and simply for preventative maintenance, I just replaced the manifolds and risers this past spring. Could that work have created an issue?

So I have determined that lifting, lowering and turning does not affect the noise, and it only occurs under load, at about 2800 rpm and up. I have attached a video of the noise. Sorry about the wind noise at the beginning. You will notice that there is not rattle until i raise the rpms, right around the 16 sec mark.

https://youtu.be/xRLldix9kmE
 
Sounds like PINGING............

Bad gas or fuel/timing issue?

I suspect this is a carburetor engine?

When wwas the last time a tune up and the timing was checked?

What type of gas are you running?

More info on the motor specifics, size, ignition, etc etc.....

No noise in neutral means no load so no pinging.........

My opinion..........

Next time remove the engine cover so the noise can be heard better...............................................
 
kghost said:
Sounds like PINGING............

Bad gas or fuel/timing issue?

I suspect this is a carburetor engine?

When wwas the last time a tune up and the timing was checked?

What type of gas are you running?

More info on the motor specifics, size, ignition, etc etc.....

No noise in neutral means no load so no pinging.........

My opinion..........

Next time remove the engine cover so the noise can be heard better...............................................
Click to expand...


Engine is a 96 Mercruiser 5.7lx carbed, with Bravo III. Gas is 87 octane. Engine runs great otherwise, lots of power, starts right up, no miss. Carb was completely rebuilt professionly last year, cap-rotor-wires-plugs were all changed two years ago. Manifold and risers were just changed last month.
 
If you suspect ping or detonation simply retard the timing a bit and retest, turn the dist clockwise about a 1/4 to 3/8
 
Well if you have a knock sensor and it is faulty or not connected then yes it could be a cause.

The knock control feature helps provide protection
from harmful detonation. Knock control is handled by
the Knock Control Module. This module receives a
signal from a sensor that is mounted on the engine
block. The knock control module works in conjunction
with the ignition module to retard the timing if
spark knock is present.

The Knock Control Module (at distributor) (piggy backed on timing control module) contains solid state circuitry
which monitors the knock sensor’s AC voltage
signal and then supplies an 8-10 volt signal, if no
spark knock is present, to the Ignition Control Module.
If spark knock is present, the Knock module will
remove the 8-10 volt signal to the Ignition Control
Module.

Terminal “E” of the knock module is the signal line
from the knock sensor.



.Start engine and warm it up to normal operating
temperature.
2. Connect the positive (+) lead from the DVOM to
the PURPLE/WHITE timing terminal that comes
from the engine harness (see previous wiring diagram).
Connect the negative (–) lead from the
DVOM to a good engine ground (–). With the engine
running, there should be 8-10 volts on this
circuit. If voltage is not present, check to ensure
that there is 12 volts to the knock module (PURPLE
wire Terminal “B”).
3. Advance the throttle to approximately 1500 RPM.
4. Disconnect the harness connector (BLUE wire)
from the knock sensor. Connect the unpowered
test light to a positive (+) 12 volt source. To simulate
an AC voltage, rapidly tap the knock sensor
harness terminal with the test light. If knock module
and wiring is functioning properly, you should
see a voltage drop on the DVOM. If a voltage drop
is not seen, check the BLUE wire from the sensor
to the knock module for a short or open circuit. If
the circuit is functioning properly to this point, the
knock sensor may not be functioning. Proceed to
the following step.
5. Reconnect the knock sensor harness connector
to the sensor.
6. While still watching the DVOM, lightly and rapidly
tap on the engine block near the knock sensor
with a small hammer. If the knock sensor is functioning
properly, you should see the voltage decrease.
If a voltage drop is not seen, the knock
sensor is faulty.
 
How about simply checking the timing? If it's off a bunch, that's the problem. Takes only a few minutes.

Jeff
 
Well, we have a winner. Did a compression check on all cylinders, 6 were between 130 and 150 psi. However, cylinders 4 and 6 (next to each other) were 25 and 30 psi. Squirted a bit of oil in both, and didn't see any major difference in compression. Hoping it's just a head gasket......why it would be blown, I don't know. The boat never overheated.
 
shawnmd said:
Well, we have a winner. Did a compression check on all cylinders, 6 were between 130 and 150 psi. However, cylinders 4 and 6 (next to each other) were 25 and 30 psi. Squirted a bit of oil in both, and didn't see any major difference in compression. Hoping it's just a head gasket......why it would be blown, I don't know. The boat never overheated.
Click to expand...
You're welcome.

It happens.

Pull the heads and have them rebuilt. Possible tuliped valve. Rebuild the carb and go thru the complete fuel system.....
 
Docksidemarineservices said:
You're welcome.

It happens.

Pull the heads and have them rebuilt. Possible tuliped valve. Rebuild the carb and go thru the complete fuel system.....
Click to expand...


Thanks...The carb was professionally rebuilt last season and works great. Boat starts right up....I don't know why or how I would have a lean condition. Fuel filter is new this summer as well.
 
For your sake, I hope the block isn't 'fire gouged' where the leak was. (If so, the motor has to come out.)

That happened to me a few years ago with my Mopar 360 inboard. Be sure to take a really good look where the break occurred for, if there's gouging, the new gasket will blow out.

Got my fingers crossed for you!

Jeff
 
I know it's a twenty-odd year old engine and that shouldn't be a big issue but here's the thing...
Let's say that you go and pull the thing apart and have the head rebuilt and a new head gasket installed. What kind of money are we talking about for that? Couple thousand, no doubt if you're including labor. If you repair what you have, how much longer can you safely assume it won't develop another major problem? Exactly zero hours. If it were me, I think I would just go and have a remanufactured long block installed. The amount of work is actually less than a head redo. You just swap over the bolt-on parts like the intake manifold, exhaust and driven accessories. It's an afternoon versus who knows how long for the head to go to the shop and back.
You get a warranted engine, and the cost is not that much more especially if you do it yourself. A quick search on the web finds LOTS of choices for roughly $2200 with no tax and free shipping. A gasket set is about $100. Kinda what you would call a no-brainer.
 
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shawnmd said:
Thanks...The carb was professionally rebuilt last season and works great. Boat starts right up....I don't know why or how I would have a lean condition. Fuel filter is new this summer as well.
Click to expand...
The carb was rebuilt for a reason. The damage was probably already started and finally gave way.

As far as repairing your engine, before you pull it apart, Leak down the rest of the cylinders and see if it is worth a repair. If you should need to replace it, do not shop for the most inexpensive long block. NOTHING OUT OF FLORIDA......... I only install Mercruiser long blocks. 3 year warranty. Figure in the cost of new exhaust.
 
o2batsea said:
I know it's a twenty-odd year old engine and that shouldn't be a big issue but here's the thing...
Let's say that you go and pull the thing apart and have the head rebuilt and a new head gasket installed. What kind of money are we talking about for that? Couple thousand, no doubt if you're including labor. If you repair what you have, how much longer can you safely assume it won't develop another major problem? Exactly zero hours. If it were me, I think I would just go and have a remanufactured long block installed. The amount of work is actually less than a head redo. You just swap over the bolt-on parts like the intake manifold, exhaust and driven accessories. It's an afternoon versus who knows how long for the head to go to the shop and back.
You get a warranted engine, and the cost is not that much more especially if you do it yourself. A quick search on the web finds LOTS of choices for roughly $2200 with no tax and free shipping. A gasket set is about $100. Kinda what you would call a no-brainer.
Click to expand...


I agree a new or re manufactured block the way to go and possible cost with labor for head work/replacement could be equal but I have to disagree on the time it takes to replace a engine.

A head job/gasket etc. would be a several hours (4 plus) on both ends, disassembly and reassembly. (not including down time for heads to be refurbished)

To replace a complete long block you are talking a least two 8 hour days worth of work and possibly more.

I recently did a upper rebuild on a 350 inboard, Cracked heads etc.

Replaced the heads with known good heads from junkyard 60,000 mile auto ( I chased them down and delivered/picked up to machine shop), had heads checked for any issues at reputable machine shop and had any issues addressed.
Block cleaning and prep, all new gaskets etc.

Reassembly and initial timing etc.

Job took me 4.5 days part time in my drive way (work a full time job so worked on it in the afternoons and evenings) So I had at least 10 hrs into the boat in labor maybe more.

Lots of labor involved in both but engine replacement is at least twice the time/labor.
 
Maybe cz my engine is so out in the open I can get it out of the boat in about an hour and a half. I use the loader bucket on the tractor. Get the wiring and plumbing undone, take off the motor mount fixings and woooop, out it comes. Drive's already off so I'm cheating it a little.
Gotta do this again soon cz I have a big block and a B3 to install in it(yay).
For the OP, you should ask yourself whether this boat is worth the effort. A mid 90s Chaparral (you don't say what model but I'm guessing it's a bowrider or something under 20 feet) might be worth 4 or maybe 5K in running condition. Are you sure that you want to spend basically the entire worth of the boat on a repair? Maybe you would be better served if you put this one on Craigslist and see if you can get a couple thousand for it with the wonky engine. Then take the proceeds from that, along with what you would have spent on repairs, and look for the next SS Shawnmd.
 
o2batsea said:
Maybe cz my engine is so out in the open I can get it out of the boat in about an hour and a half. I use the loader bucket on the tractor. Get the wiring and plumbing undone, take off the motor mount fixings and woooop, out it comes. Drive's already off so I'm cheating it a little.
Gotta do this again soon cz I have a big block and a B3 to install in it(yay).
For the OP, you should ask yourself whether this boat is worth the effort. A mid 90s Chaparral (you don't say what model but I'm guessing it's a bowrider or something under 20 feet) might be worth 4 or maybe 5K in running condition. Are you sure that you want to spend basically the entire worth of the boat on a repair? Maybe you would be better served if you put this one on Craigslist and see if you can get a couple thousand for it with the wonky engine. Then take the proceeds from that, along with what you would have spent on repairs, and look for the next SS Shawnmd.
Click to expand...


It's actually a 25 Signature aft cabin cruiser. The boat is in excellent shape otherwise. It's in Canada and it's value is at 15-20 grand (cdn), so its well worth a rebuild or replacement. The engine has 650 hrs on it.

I'm hoping for a repair over a replacement of the engine (she's in there deep!).

The carb was actually cleaned and rebuilt due to what I percieve as running rich (gassy smell, black haze on stern)..
 
AN aft cabin? Oh Lord! There are a nightmare to change engines in. Saw it done once: They slide the long block down the stairs covered with planks. then dropped it in with a homemade A-frame deal.

More than ever you need to think repair in place. But if the block is fire gouged (as I explained above) you have no choice but yank her out.

Good luck!

Jeff
 
Strangely, I have a connection with these boats...the B3 and big block I have were pulled out of one. We did ugly things to the hull with saws and a forklift, but I do recall that the cockpit did open up nicely once you get all the "lifestyle" gear out of the way. Engine access is not bad. There's a big fuel tank that presents a challenge but I think once you get the engine on a crane you can wiggle it out without too much trouble. Getting to the rear engine mounts requires contortions that my body was reluctant to agree to, so the transom came out with.
It's not really an aft cabin in the sense that there is an actual cabin in the stern. Your typical bleach bottle weekender.
 
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Good after noon , quick question I recently have been going through my 97 7.4l 454 bravo 1 with TB V ignition just replaced ICM with the new updated module from mercury which was 625 dollars . I am replacing ignition sensor in distributor since oem sensor has some corrosion . The new sensor has a ground wire instead of the two wire from old sensor. Were does that ground wire need to be attached,?
 
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