2000 7.4 Horizon rattle in tranny in neutral at idle

[Nauti 97]

I have a 2000 Searay 380 with 7.4 Hoizons with Hurth HSW 630 trannys.
My question is. When the engines are running they have a rattling noise when in neutral at idle speed. The rattle appears to be in the tranny and happens on both engines.
When you throttle up the noise goes away or when you engage forward or reverse the noise goes away. Is this normal and is it harming the trannys.

 

[Nauti 97]

Anyone else have this issue? Is it a problem?

 

[Windjammer]

Can't speak for the 7.4's, but on the 8.1's when the transmission "chatters" especially when backing into the slip, a change of the spark plugs usually clears this up.

 

[Nauti 97]

Can't speak for the 7.4's, but on the 8.1's when the transmission "chatters" especially when backing into the slip, a change of the spark plugs clears this up.

It’s only when in neutral at Idle speed

 

[Creekwood]

Like @Windjammer said, you should try a tune up (plugs and wires). The plates in the v-Drive transmissions can rattle when the engine is not idling perfectly smoothly. And these bigblocks can seem like they are smooth even when two cylinders are not firing. As an example, every spring the first trip from the launch to my slip would make you think I have imminent failure. But its just storage fogging oil burning off after the first start up. By the time I take it out on a good fast run to burn it all off and get the plugs hot, it goes away until the next spring.

 

[Nauti 97]

Is that hurting anything when they are rattling

 

[Golfman25]

So I was looking at a boat a year or two ago. And when we started her up, there was that "rattle." Now I had heard that can happen. However, after looking at several boats the past year, this was the only one that did it. Browsing the interweb gives you many answers from "completely normal" to "you're engine will blow up any day now." So the question becomes is it something new or has it been like that from the start?

 

[Nauti 97]

So I was looking at a boat a year or two ago. And when we started her up, there was that "rattle." Now I had heard that can happen. However, after looking at several boats the past year, this was the only one that did it. Browsing the interweb gives you many answers from "completely normal" to "you're engine will blow up any day now." So the question becomes is it something new or has it been like that from the start?

I just Bought
The boat a month ago.
Both engines have the rattle so I find it hard to believe that the engine is going
To blow on both at the same time.

 

[HardHead]

I have a 2000 Searay 380 with 7.4 Hoizons with Hurth HSW 630 trannys.
My question is. When the engines are running they have a rattling noise when in neutral at idle speed. The rattle appears to be in the tranny and happens on both engines.
When you throttle up the noise goes away or when you engage forward or reverse the noise goes away. Is this normal and is it harming the trannys.

I had same issue when I purchased my 370. Make sure the idle is correct, I believe 750rpm. Mine was to low, so I turned it up to 750 and the clatter went away.

 

[Golfman25]

I just Bought
The boat a month ago.
Both engines have the rattle so I find it hard to believe that the engine is going
To blow on both at the same time.

So was it addressed when you looked at the boat? Did the owner mention how long it’s been going on? It’s most likely no big deal.

 

[Nauti 97]

So was it addressed when you looked at the boat? Did the owner mention how long it’s been going on? It’s most likely no big deal.

Didn’t here it at Sea trial or survey.
Ran it at 3400 RPM for about 8 hrs. The engines performed flawlessly. Haven’t ran them for about 3 weeks. This last weekend I started the engines and can here the rattling. In Neutral. When I throttle up a little still in Neutral the nrattle goes away

I had same issue when I purchased my 370. Make sure the idle is correct, I believe 750rpm. Mine was to low, so I turned it up to 750 and the clatter went away.

how do you turn it up?

 

[HardHead]

Didn’t here it at Sea trial or survey.
Ran it at 3400 RPM for about 8 hrs. The engines performed flawlessly. Haven’t ran them for about 3 weeks. This last weekend I started the engines and can here the rattling. In Neutral. When I throttle up a little still in Neutral the nrattle goes away

how do you turn it up?

I have carbs. Either way there should be an idle screw at the engine end of the throttle cable. Just adjust the throttle ever so slightly to see if it goes away.

 

[Golfman25]

Didn’t here it at Sea trial or survey.
Ran it at 3400 RPM for about 8 hrs. The engines performed flawlessly. Haven’t ran them for about 3 weeks. This last weekend I started the engines and can here the rattling. In Neutral. When I throttle up a little still in Neutral the nrattle goes away

how do you turn it up?

So it sounds like something changed. So search for it. Maybe a tune up -- new plugs, wires, idle adjust, etc.? Or get a stethascope and listen to the transmission to see if you can isolate where the noise is comming from. Probably a damper plate.

 

[Nauti 97]

So it sounds like something changed. So search for it. Maybe a tune up -- new plugs, wires, idle adjust, etc.? Or get a stethascope and listen to the transmission to see if you can isolate where the noise is comming from. Probably a damper plate.

How do you adjust the Idle?

 

[Creekwood]

Don't adjust the idle out of spec just to stop the rattle. If the idle is too high, its hard on the transmissions shifting in and out of gear. Just set it to the specs for your engine/transmission. I think mine is 650.

Check if it is both transmissions or just one. If its both, that seems strange, but it could be something like bad gas from a marina or water in the gas. I assume you didn't hit anything while underway? Didn't shift while at speed?
Also check the fluid level in them. Make sure its at the right level and not low or high. It shouldn't look or smell burnt. You could change the fluid if you don't know how old it is, and make sure its the proper fluid type for your model transmission.

 

[Chris-380]

Is that hurting anything when they are rattling

I agree, my 7.4 horizons idle at 650rpm also

 

[hottoddie]

I agree, my 7.4 horizons idle at 650rpm also

Is that 650 in neutral or in gear at operating temp? 650 in neutral would be very low IMO. Most transmission manuals specify not to shift into gear if rpms are 1000 or above. I idle my 454's with BW transmissions at 850 in neutral. The 390 needs some extra torque when docking.

BTW the rattle is harmless if it goes away when in gear or when the rpms are slightly increased.

 

[PlayDate]

You have a 21 year old boat. The flex plate on the transmissions have springs to counter shock to the transmission from a prop strike or higher than idle transmission shift. The springs rattle on most boats of that vintage....some worse than others. There is nothing to be worried about.

 

[Nauti 97]

Is that 650 in neutral or in gear at operating temp? 650 in neutral would be very low IMO. Most transmission manuals specify not to shift into gear if rpms are 1000 or above. I idle my 454's with BW transmissions at 850 in neutral. The 390 needs some extra torque when docking.

BTW the rattle is harmless if it goes away when in gear or when the rpms are slightly increased.

According to the manual Idle for the Horizon is 600RPM. (See below)
The more I thought about it, there wouldn’t be an adjustment. The idle would be computer controlled.

Models

7.4L MPI

454 Mag MPI

Propshaft Horsepower

(SAV1 Rating)

3101

(2752)

3851

Propshaft Kilowatts

(SAV1 Rating)

2311
(2052)

2871

Displacement

454 cid (7.4 l)

Maximum rpm @ WOT3

4200-4600 rpm

4600-5000 rpm

Idle rpm in NEUTRAL3

600 rpm6

Oil Pressure @ 2000 rpm

30-70 psi (207-483 kPa)

Min. Oil Pressure @ Idle

4 psi (28 kPa)

Thermostat

160° F (71° C)

Timing @ Idle rpm4

8° BTDC

Firing Order

1-8-4-3-6-5-7-2

Electrical System

12-Volt Negative (-) Ground

Alternator Rating – Cold

Operating Amps

65 Amps

Alternator Rating – Hot

Operating Amps

72 Amps

Recommended

Battery

Rating

Minimum 650 cca/825mca/150 Ah

 

[Nauti 97]

You have a 21 year old boat. The flex plate on the transmissions have springs to counter shock to the transmission from a prop strike or higher than idle transmission shift. The springs rattle on most boats of that vintage....some worse than others. There is nothing to be worried about.

John,
Thanks for that Info. I feel a lot better now.
I know as soon as you move the throttle off of idle the rattle went away so I didn’t think I had tranny issue yet especially on both Transmissions at the same time. Just wanted to make sure that I wasn’t causing any damage.