1994 8V92TA rattle noise

[Charles K.]

I have a rattle noise at the rear starboard side near the turbo of my 8v92. It sounds like a rocker arm rattling loose on top the head, but I am not having any issues with it running and the noise does not get worse with increased rpm. I'm an old Chevy small block guy and I've never torn down a Detroit, so I'm assuming it has rocker arms on top the heads and intake/exhaust valves too; I know it's a two stroke engine, so maybe the cylinders are ported instead and a loose rocker arm isn't possible? I have checked the turbo and it rotates freely without any play in the shaft and seems to be the same as the other turbo's; I checked them all thinking it was a bad shaft bearing on the turbo. I've tried placing a metal rod to spots all around the area and my ear, but I am not hearing anything to pinpoint the noise. The noise is not real loud and could have been there a while, but I recently noticed the noise while checking the raw water intake strainers after I cleaned them, something I do everytime I crank up afterwards. When I heard the noise I moved to the port engine and could not hear the same noise on it, but I could still hear the noise coming from the starboard engine, so I know it's not normal. I did take the boat out and ran it at normal cruising speed to check temp readings with my infrared thermometer all around the engine, but most all reading were a little cooler on the starboard engine as compared to the port engine, so that didn't point to anything either. As I said the noise doesn't get louder with higher rpm and the engine runs good as ever, so I'm lost as what this noise could be. Anyone out there have any clues?

 

[jgmo]

Hi,

I'm old and it's been forever since I worked on a Detroit but there's no reason to for you to be intimidated about pulling a valve cover and taking a look. No spring loaded "gotchyas" under there.

Yes, these have rocker arms...3 per cylinder. 1 for the injector and 2 for each set of exhaust valves.

There are no intake valves. Air is forced into the cylinder via ports at the bottom of the piston liner
So, nothing to be concerned about there.

There are 4 valves per cylinder....all exhaust valves.

Those.valves are in sets of two.

Each set is opened by a single rocker that pushes down on a "bridge" that sets on top of the valve stems. Two valves are opened by 1 rocker arm.

Sometimes, those valve bridges come loose because they are adjustable.

Sometimes the bridge will even pop off.

While losing the operation of two valves would definitely affect combustion, you might not get a detected misfire because there are still two other valves working for that cylinder.

This does sound as if it COULD be a valve bridge came loose or off.

Pull the cover and take a look.

While in there, look closely at all valve springs and injectors too.

Good luck.

 

[Charles K.]

jgmo, thank you for the advice, I did pull the valve cover and fortunately found everything intact. I even ran the engine with the cover removed and determined the noise is not from anything on the head, it all ran/functioned perfectly. Even better it doesn't spray oil everywhere like Chevy small block, ha! However, I did find that the rattle noise is coming from both engines, it was more noticeable from the port engine since I was in the engine room upon cold start up. I think the noise is on the exhaust side of the blowers for the turbo and I am hoping it has been there all along I just wasn't in-tuned to hearing it before. For now I will keep a close ear out and see if the noise remains the same or worsens, or I may pull the exhaust tube off the blower and inspect that end just for good measure. I appreciate the education you gave me as I now know much more about the topside of my engines, which I love my 892's.

Till next time, take care and thanks to Marine Engine for the forum!

Charles K.

 

[jgmo]

Hi Charles,

Well, just as a "point of order" as they say....
....the blower actually "exhausts" into the engine "blower box".

At any rate, you think that you hear the noise from the blower's intake housing from the turbos.

I know you said that you had a look in there already but if you're hearing a "tink"....tink........tink...
.....tink intermittent small bell noise, that still might be one or more of the wheels "tinking" against the housing(s).

If it gets louder, look at the wheel blade edges and the housing where they ride for signs of fresh metal....meaning contact. If you see that, it's turbo time.

Good luck.