Yanmar 3GM30F – Tapping/Ticking/Knock Noise at Idle

[Scubaseas]

Your prechambers might be perfectly fine. Or they might not be. I'd start with a stethoscope or long screw driver held to my ear. If the noise is most pronounced around the injector base then the theory of loose or broken prechamber is much more probable. Before I pulled the injectors I'd take the valve cover off and run it while pressing down on the rocker at the pushrod end to see if you can vary the noise. This might help isolate any lifter issue. With the motor off, I'd also check the clearances and see what kind of valve spring pressures you have and if there is any play obvious in the guides.

When the fuel is cut by cracking open the injector or the compression lowered by opening the decompression lever and the noise goes away that points a lot to wrist pin or piston slap. It could also point to a bad bearing (but not after 200 hours running). If there are no other symptoms like smoking, using coolant, eating tons of oil, blowby, etc. and it runs OK I'd be tempted to just turn up the stereo. But not my boat. You do you.

Unfortunately to verify a wrist pin or slap issue you would need to pull the piston.

[SY Harmony]

Random though

Before getting to deep into this. Get some playdough and measure the clearance between the rocker and the compression release cam in the valve cover. When the lever is in the run position.

[Scubaseas]

or just run it with the cover off?

[SY Harmony]

Messy

[kenbo]

Originally Posted by SY Harmony

Random though

Before getting to deep into this. Get some playdough and measure the clearance between the rocker and the compression release cam in the valve cover. When the lever is in the run position.

Very good thought

[Scubaseas]

Originally Posted by SY Harmony

Messy

For 3 to 5 seconds? Really? Even with a cloth over the rockers?

Not anywhere near as messy as running it and pushing down on the end of the push rod end of the rocker. That's truly going to be messy.

[JonathanC]

Originally Posted by SY Harmony

Messy

I know... Messy. However it's not off my list yet. My mechanic also mentioned this but he said "if you are up for it". I'd rather find an old 3GM30F valve cover (or bonnet as Yanmar says) and cut the top out (but would need to figure out a way to secure it). Back in the day I'd done with an old 289 ford to track down some valve noise. Unused small block valve covers were a bit easier to find I'm sure.

[Cheechako]

They do tend to tap at idle. Is it possible it's normal but when you omit cyl 3 it just changes the engine balance enough so it sounds different?

Another possibility is the dreaded 3GM cracked piston skirt issue. But you should have a bit of power loss with that, even though it will be smooth running when not at idle. (Compression test)

Worn valve guide in Cyl 3?

[Scubaseas]

Originally Posted by SY Harmony

Random though

Before getting to deep into this. Get some playdough and measure the clearance between the rocker and the compression release cam in the valve cover. When the lever is in the run position.

As opposed to taking off the head and taking the piston out? I don't disagree with ruling out excessive clearance due to decompression lever having insufficient clearance.

[JonathanC]

Originally Posted by Cheechako

They do tend to tap at idle. Is it possible it's normal but when you omit cyl 3 it just changes the engine balance enough so it sounds different?

Another possibility is the dreaded 3GM cracked piston skirt issue. But you should have a bit of power loss with that, even though it will be smooth running when not at idle. (Compression test)

Worn valve guide in Cyl 3?

Hey Cheechako-
I've been told by many I'm being to sensitive about the noise. It's just the fact that I can make it go away that keeps me looking. And this is coming from a guy who owns a Ford 6.0, those are noisy.

It would have to be a faulty valve guide as the engine has less that 900 hours on it. I don't think a valve guide would wear so quickly?

JC

[SY Harmony]

Originally Posted by Scubaseas

As opposed to taking off the head and taking the piston out? I don't disagree with ruling out excessive clearance due to decompression lever having insufficient clearance.

That engine has such great access I’d pull it out and take it home.
But yes, it’s less invasive to measure the clearance before taking things apart. Rule out the easy stuff first. That said, i’m willing to put money on that engine getting uncorked.

[skipperpete]

It looks like the youtube links are only missing for me .....on ios, visible on macbook but won’t open.
I can’t help but think its diesel knock but you already did the usual troubleshooting, if it was a delivery valve or a dripping injector your diesel tech would have noticed it as would he have spotted a phase and calibration error. A worn cam or collapsed follower would make the timing late so quieter rather than noisy. The fact that the noise disappears when you crack the fuel line sort of indicates a precombustion chamber issue but this is so rare that I’d just about dismiss it. Is your engine heat exchanger cooled or simply raw water through the block and head?If you suspect a bearing failure you can partially verify it by opening up the filter canister and inspecting the paper folds for shiny specks, messy but informative.
I’m really interested to know what you discover.

[JonathanC]

Originally Posted by skipperpete

It looks like the youtube links are only missing for me .....on ios, visible on macbook but won’t open.
I can’t help but think its diesel knock but you already did the usual troubleshooting, if it was a delivery valve or a dripping injector your diesel tech would have noticed it as would he have spotted a phase and calibration error. A worn cam or collapsed follower would make the timing late so quieter rather than noisy. The fact that the noise disappears when you crack the fuel line sort of indicates a precombustion chamber issue but this is so rare that I’d just about dismiss it. Is your engine heat exchanger cooled or simply raw water through the block and head?If you suspect a bearing failure you can partially verify it by opening up the filter canister and inspecting the paper folds for shiny specks, messy but informative.
I’m really interested to know what you discover.

Bummer about the YouTube links not working for you. I can send them again when I get to my office this morning.
We actually did an oil sample test and it came back with no indication of bearing failure.
JC

[Cheechako]

Originally Posted by JonathanC

Hey Cheechako-
I've been told by many I'm being to sensitive about the noise. It's just the fact that I can make it go away that keeps me looking. And this is coming from a guy who owns a Ford 6.0, those are noisy.

It would have to be a faulty valve guide as the engine has less that 900 hours on it. I don't think a valve guide would wear so quickly?

JC

Yeah, I often find myself thinking "does that sound right? Is there a problem?"
I think a valve guide would be a bit unusual for sure, to get bad enough to make noise it would have to be very bad I would think.
But the cracked piston skirt is always a possibility with that engine. In my cat one engine was replaced at about 550 hours under warranty. The other cracked the piston at 2300 hours IIRC.

[JonathanC]

Originally Posted by skipperpete

It looks like the youtube links are only missing for me .....on ios, visible on macbook but won’t open.
I can’t help but think its diesel knock but you already did the usual troubleshooting, if it was a delivery valve or a dripping injector your diesel tech would have noticed it as would he have spotted a phase and calibration error. A worn cam or collapsed follower would make the timing late so quieter rather than noisy. The fact that the noise disappears when you crack the fuel line sort of indicates a precombustion chamber issue but this is so rare that I’d just about dismiss it. Is your engine heat exchanger cooled or simply raw water through the block and head?If you suspect a bearing failure you can partially verify it by opening up the filter canister and inspecting the paper folds for shiny specks, messy but informative.
I’m really interested to know what you discover.

Skipperpete-
Here are the two video links on YouTube:
https://youtube.com/shorts/eNw3XFAm3fI?feature=share
https://youtube.com/shorts/iNnKngQaLSs?feature=share