Engine noise

Sailorjack · Oct 10, 2017

Kommy000 said:
Alright, I'm still new to working on marine engines and maintenance so be patient with me.
I posted before that my engine started making this weird noise. I ended up buying oil filter and other parts from local yanmar dealer.
For now I changed oil since it was absolutely black and oil filter. Used pump out evac unit I got on Amazon for the first time and it worked awesome.
Started the engine and the noise still there but it went away after about 20 seconds- I took a video of it with sound:

Waited about 5 minutes, made sure my new oil level is where it supposed to be and started again and waited 2 minutes and that noise never went away- video 2:

I still want to change the impeller on my next day off to see if that's what making noise.
Can anyone maybe give me some idea where that noise coming from?
I even thought maybe belt? It seems tight enough but I can move the alternator a little to make it tighter or even get a new belt.
Any ideas?
Thanks

Kommy , it sounds like metal touching metal. I'm not a mechanic but I would check the alternator belt tension. It could be too tight causing problems in the alternator. I had a similar noise when I overtightened the belt. To double check the alternator remove the belt and briefly run the engine. If the noise in gone then the alternator and/or belt is the problem. Re-install and adjust to spec by Yanmar. Approximately 3/8" deflection at mid point between crank and alternator pulleys. Also ensure none of the external rotating parts are touching anything they are not supposed to.

Charles Erwin · Oct 10, 2017

The screeching is likely a bearing or belt slippage - they can sound the same. As to belt slippage one way is spray the belt with H2O from a spritzer bottle and see if the noise changes. If so then belt(s) are glazed. As to bearings - alternator bearing or water pump bearings are the two most likely. As noted by Jack take the belt(s) off then put them back one at a time. Diagnose with all belt guards off the motor.

Charles

jviss · Oct 10, 2017

The water spritz will also quiet an alternator bearing (and that amount of water won't hurt the alternator. A good way to diagnose bearing and belt problems.

Removing belts, one can jiggle the pulleys to check for loose bearings. Water pump comes to mind.

SailormanDan · Oct 10, 2017

1GMs don't have separate water pumps, they are driven by a shaft off the engine, so no bearing to squeak, but try the other suggestions. Unfortunately, not a noise that mine has made, so I don't recognize it right off.

Benny17441 · Oct 10, 2017

Black oil in these old Yanmars is a usual condition. It is quite common to change the oil and have it turn black in just a few hours of engine operation. Dirty oil is not harmful to engines; it is the oil viscosity that we should be concerned with. The oil filter will remove the larger particles which could be harmful. That noise sounded to me like the valve train was not getting adequate lubrication at start up. That could be caused by using too thin of an oil that it totally drains down into the crankcase or oil that has lost its viscosity. It can also be the result of damage to the surfaces of the valve train components while the engine was ran with very little oil. It is hard to tell over the video where the noise is coming from and what I'm saying is just one possibility. Usually in this condition the noise abates when the engine is reved up and oil pressure increases. Definitely check the belt tension but that sounds like metal on metal.

njlarry · Oct 11, 2017

Easy trick to localize engine noise. ...take a long wooden dowel or one inch board about 2 to 4 foot long and hold it against any suspect part. With your ear placed against the other end you will very plainly know the point where the source of the sound is by moving the other end to each suspected part. Even a yard stick will do but slightly wider board is esier to place across your ear.
Good luck.

JamesG161 · Oct 11, 2017

Charles Erwin said:
The screeching is likely a bearing or belt slippage

Alternator bearing going out probably, making the belt flex. I see the belt flexing.
Jim...

kloudie1 · Oct 11, 2017

Agree.. belt is toast.. It should be wide enough to have the outer surface of the belt flush with the alternator pulley outer diameter.. If someone has changed it in the past, it may not be the correct width so don't just replace with another one like that one.. Yanmar Part # is 128170-77350
NAPA has some Yanmar belts that are probably better than Yanmar .. they may not have the 1GM belt, though.
This may be the one.. at NAPA: https://www.napaonline.com/en/p/NBG259290HD?interchange=1

jssailem · Oct 11, 2017

Changing a belt is cheap and never a bad idea. While off rotate/wiggle the pulley to see if there is grinding sound damaged bearing. It is a two for one action that may just solve your problem.

SEMPERAVANTI41 · Oct 11, 2017

Mechanic's Stethoscope $3.99 at Harbor Freight

jssailem · Oct 11, 2017

SEMPERAVANTI41 said:
Mechanic's Stethoscope $3.99 at Harbor Freight

That's almost as much as a customer 1by1.
Unless you can steal the 1inch diameter closet pole from the spouse.
Na... she would probably find out when she goes to the closet and finds here favorite clothes on the floor. Better not try that one.

Ron20324 · Oct 11, 2017

You didn't bend the pointer to set TDC for timing perhaps?

Capt jgw · Oct 11, 2017

On my Universal the alternator arm broke so I replaced it with a Balmar unit. The slot in the new arm is 3/8" but the bolt is 5/16". If I don't get it just right the alternator fan rubs on the arm making about the same noise. I just stick a flat screwdriver between the fan and arm when I tighten the bolt. For sure running the engine with the belt off will narrow it down.

SailormanDan · Oct 12, 2017

Good job! Glad to hear it was a relatively straightforward fix and didn't hassle you too much.

Charles Erwin · Oct 12, 2017

You can take belt to NAPA, O'Reilys or other and obtain shorter. The belts from Yanmar are made by MItsuboshi and the Yanmar dealer will have only the one size. A better option is Gates (Green Stripe) belts. Many size increments and overall probably a better choice. Get the notched version. They are more flexible so they run cooler and do not produce as much belt debris as the smooth (Yanmar/Mitsuboshi) version.

Charles