Please check my diagnosis

[Gallf1]

Hi:
2000 SR380DA with Mercruiser 454MAG MPI's, V-Drives......engines running strong, new oil and fuel filter change, clean bottom, always run non-ethanol.

Since I have owned the boat (2 years now) the STBD engine has had a "rattle when idling in neutral or in gear at idle speed. Rattle disappears at around 1000-1200rpm when in gear.

I have checked:
Spark Plugs
Spark Plug wires
Coil
Distributor cap
Compression
Serviced all fuel injectors
Timing checked and set to spec (with computer)
Idle checked and set to spec (with computer)
Coupling is tight
Prop is tight
Cutlass bearing in strut does not have any slop
Transmission fluid is red, no burnt smell and at the right cold/hot levels
Transmission shifts F-N-R no issues, runs at cruising rpm's no issues

I am thinking it is the drive plate (as this is a known issue with V-drives....am I correct?

If so, can the transmission be separated from the engine to replace the drive plate while in the water?
Is their a better drive plate or just stick to OEM?

I have heard that even replacing the drive plate is no guarantee that the new drive plate wont rattle?

Thx!

 

[carterchapman]

Galf1 - you say you "checked" plugs. Did you change them? Seems like a lot of gassers with boats like yours +/- have had success with that. I can no longer remember if I ever had the problem on my 340 or not (a mind is a terrible thing to lose!), but changing plugs seems to work...

 

[Gallf1]

Galf1 - you say you "checked" plugs. Did you change them? Seems like a lot of gassers with boats like yours +/- have had success with that. I can no longer remember if I ever had the problem on my 340 or not (a mind is a terrible thing to lose!), but changing plugs seems to work...

Brand new plugs, checked and gapped to spec before install

 

[carterchapman]

Brand new plugs, checked and gapped to spec before install

Thanks. Hopefully someone else will chime in...

 

[hottoddie]

Could just be the springs in the damper plate are worn causing the rattle at low rpm. What is your idle rpm set at? If it's set really low (600-650 in gear) maybe bumping up the rpm 50-75 rpm would reduce or eliminate the rattle.

 

[techmitch]

Ignition wires are more suspect than the plugs. You can ohm them out all day long and it doesn't mean chit.

 

[Gallf1]

Idle set by computer to 800rpm.

Ignition wires?.....blue ones (Sierra?) where on the engine when I bought it two years ago. Seeing as how I pretty much replaced and/or eliminated other parts I will throw a new set of OEM wires at it and see if it does anything.

I agree with Mitch about ohm testing as I have done this on other parts/systems on the boat and it wont reveal intermittent faults due to vibration or temperature.

Thx all

 

[Phasma]

7.4 and 8.1 both are known for going thru plug wires

 

[Gallf1]

7.4 and 8.1 both are known for going thru plug wires

Thx....new wires it is then

 

[mquiet]

The V drive has a known "noise" from the pressure plate. If you hear a rattle when in gear and at idle, but goes away as you add throttle, then this is the known rattle. Super common. I had a 340 with 7.4's and it did the same thing for 800 hours.

 

[Gallf1]

The V drive has a known "noise" from the pressure plate. If you hear a rattle when in gear and at idle, but goes away as you add throttle, then this is the known rattle. Super common. I had a 340 with 7.4's and it did the same thing for 800 hours.

Thx....what you described is exactly what is happening....but I will still change the plug wires as I dont know how old they are and since I did a major tune up (and didn't change them out), they most likely are due....doubt new wires will eliminate the rattle but cheap enough to do.

Thx

 

[dtfeld]

Its the damper plate. As Mquiet says, super common. They are installed to dampen out the power impulse from engines at low rpm. Are inexpensive, but a PITA to get to.

For a V-drive, the shaft has to be slid back and the transmission separated from the engine. I would think much easier on land!! I dont hear too many people replacing unless they are in there doing something else.

 

[Gallf1]

Its the damper plate. As Mquiet says, super common. They are installed to dampen out the power impulse from engines at low rpm. Are inexpensive, but a PITA to get to.

For a V-drive, the shaft has to be slid back and the transmission separated from the engine. I would think much easier on land!! I dont hear too many people replacing unless they are in there doing something else.

Thx David....
Seeing as I how I hauled out recently for bottom paint and underwater lights.....I may wait until the next haul out and do it along with replacing the seals (preventative only) on my dripless shaft seals and replacing the bronze engine seawater intake strainer (one of the "ribs" is missing).

I wish a manufacturer had come up with a "mod" to take care of this issue as it appears to be quite common.....
Thx

 

[sbw1]

I agree with the damper plate Dx. It is common and it is harmless. One bad plug can bring it on and more commonly low idle rpms. Chances are, bumping the rpms up 50-100 will eliminate the issue. I would not go above 900. Technically I believe the owner manual advises you to not shift into or out of gear at more than 1000rpms to avoid possible transmission damage. If your tranny sounds crisp and solid when you shift, that is a better indicator of how things stand than a little rattle, especially if the fluid is red and has no burnt smell to it. Stay on top of fluid and filter changes and you will be fine. Many people tend to ignore fluid and filter changes on transmissions because they are so reliable. Go by the owner manual and avoid high rpm shifts and you will never have an issue.

 

[dtfeld]

Thx David....
Seeing as I how I hauled out recently for bottom paint and underwater lights.....I may wait until the next haul out and do it along with replacing the seals (preventative only) on my dripless shaft seals and replacing the bronze engine seawater intake strainer (one of the "ribs" is missing).

I wish a manufacturer had come up with a "mod" to take care of this issue as it appears to be quite common.....
Thx

They do wear out, but its something that can wait a while unless it actually fails (you find a spring or spring parts coming out)>

Dave

 

[Phasma]

I had the same problem. At idle speed I would year a rattle or knock. It ended up being the slap plate but it was due to a bad cylinder in my starboard. It was a miss in the engine that only became audible at idle.