Normal sound?

[etpm]

A month or so ago I bought my first Yanmar. A YM2310. It was also my first diesel. To my ears it sounds like a typical diesel engine. but when starting it knocks pretty loudly. Not like rod knock though. Not like any kind of bearing knock that I've heard. The knock goes away quickly, probably less than 30 seconds, heck, probably less than 15 seconds. I almost follow the starting procedure outlined in the operating manual: transmissions in neutral, full throttle, crank until it starts and then immediately reduce throttle to 1500 RPM. Where I deviate from the manual involves the decompression knob. The manual says to pull the decompression knob and crank the engine until it starts. But it won't start with the decompression knob pulled out. I suspect that the manual is wrong, that the decompression knob should be pulled out and the engine cranked until it comes up to speed, then released and cranking continues until the engine starts. After reading here about starting the Yanmar engines this is the proper procedure. But back to my knocking noise question. Is it normal for a Yanmar diesel engine to have a fairly loud knocking/rattling noise when first started which goes away in less than 30 seconds?
Thanks,
Eric

 

[CoyPatton]

A month or so ago I bought my first Yanmar. It was also my first diesel. To my ears it sounds like a typical diesel engine. but when starting it knocks pretty loudly. Not like rod knock though. Not like any kind of bearing knock that I've heard. The knock goes away quickly, probably less than 30 seconds, beck, probably less than 15 seconds. I al!let follow the starting procedure outlined in the operating manual: transmissions in neutral, full throttle, crank until it starts and then immediately reduce throttle to 1500 RPM.

Does your Yanmar have a decompression lever. My is under the steering wheel slightly to my left of center. This slightly opens the exhaust valves releasing pressure as rpms and oil pressure builds. Typically once my oil pressure and rpms are up, I release the decompression lever and the engine fires in mere seconds, no knocks.
You did not mention a decompression in your start up procedure.

 

[Menagerie-Manor]

A month or so ago I bought my first Yanmar. A YM2310. It was also my first diesel. To my ears it sounds like a typical diesel engine. but when starting it knocks pretty loudly. Not like rod knock though. Not like any kind of bearing knock that I've heard. The knock goes away quickly, probably less than 30 seconds, heck, probably less than 15 seconds. I almost follow the starting procedure outlined in the operating manual: transmissions in neutral, full throttle, crank until it starts and then immediately reduce throttle to 1500 RPM. Where I deviate from the manual involves the decompression knob. The manual says to pull the decompression knob and crank the engine until it starts. But it won't start with the decompression knob pulled out. I suspect that the manual is wrong, that the decompression knob should be pulled out and the engine cranked until it comes up to speed, then released and cranking continues until the engine starts. After reading here about starting the Yanmar engines this is the proper procedure. But back to my knocking noise question. Is it normal for a Yanmar diesel engine to have a fairly loud knocking/rattling noise when first started which goes away in less than 30 seconds?
Thanks,
Eric

The instructions you quoted sound like the cold weather thermal start procedure, on my YM2310 in current temps I just pull the throttle back a bit and crank her over. She starts every time and I throttle right back to about 1K rpms while she warms up.

 

[ponytug]

You only need to have the decompression on to get the engine spinning. By using the decompression, you reduce the load on the starter (primarily) and the turning engine starts to get oil up into the engine, further reducing load (secondary). Diesels are very hard to turn past the initial compression, as I am sure you know, if you have ever needed to hand crank one.

But you need to turn the decompression off to get the engine to start. (So your instincts are right on the money!) So, as you suspected, decompression on, crank the engine up to speed, and push the knob in, and you are good to go.

If decompression is available, I think it is a useful part of the starting procedure for any diesel.

YMMV.

All the best,

Peter

 

[bmaverick]

A month or so ago I bought my first Yanmar. A YM2310. It was also my first diesel. To my ears it sounds like a typical diesel engine. but when starting it knocks pretty loudly. Not like rod knock though. Not like any kind of bearing knock that I've heard. The knock goes away quickly, probably less than 30 seconds, heck, probably less than 15 seconds. I almost follow the starting procedure outlined in the operating manual: transmissions in neutral, full throttle, crank until it starts and then immediately reduce throttle to 1500 RPM. Where I deviate from the manual involves the decompression knob. The manual says to pull the decompression knob and crank the engine until it starts. But it won't start with the decompression knob pulled out. I suspect that the manual is wrong, that the decompression knob should be pulled out and the engine cranked until it comes up to speed, then released and cranking continues until the engine starts. After reading here about starting the Yanmar engines this is the proper procedure. But back to my knocking noise question. Is it normal for a Yanmar diesel engine to have a fairly loud knocking/rattling noise when first started which goes away in less than 30 seconds?
Thanks,
Eric

Eric, What oil grade are you using? Too thick of an oil would offer loud starting knocking of the engine till it settles down. The American Iron tractors from years back used 15W40. These Japan tractors were never spec'ed to use that oil grade. Per the JIS (Japanese Industrial Standards), like our SAE standards, 10W30 diesel grade is to be used. Both Yanmar and John Deere have this in their OPS manuals for their YM and 50 Series tractors all made by Yanmar.

Getting the thicker oil pumped up to the upper part of a Japan made engine would create all that knocking for sure.