Engine knocking heavily on start-up

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JimC

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After a period of non-use my engine, a 2GM20, knocks heavily and shakes on its mounts for the first few seconds after starting. It then steadies down and runs sweetly. It sounds to me like the big ends are running dry of oil until the oil pump has had time to squirt some through which, if so, can't be good. It's not an old engine. I use 15w-40 mineral oil. I wonder would there be any benefit in using an oil additive such as STP which is supposed to leave a viscous film on the bearings?
 
Suspect it is diesel knock rather than big ends. Suggest if you are worried about oil circulation that you turn it over with the decompression levers up or the fuel stop pulled out for a couple of seconds before starting. The Yanmar does not have glow plugs so relies on a super rich mixture to start and often only one cylinder fires immediately causing the rough running until the second fires.
 
No benefit to be had from oil additive.
Big-ends won't cause your engine to shake. I'd guess that your engine isn't firing properly on both cylinders for the first few seconds.
Possibly a dicky injector if it's that bad.
Add; also agree with above, the 2GM20 isn't the smoothest of engines, and not the best starter from stone-cold.
 
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JimC said:
After a period of non-use my engine, a 2GM20, knocks heavily and shakes on its mounts for the first few seconds after starting. It then steadies down and runs sweetly. It sounds to me like the big ends are running dry of oil until the oil pump has had time to squirt some through which, if so, can't be good. It's not an old engine. I use 15w-40 mineral oil. I wonder would there be any benefit in using an oil additive such as STP which is supposed to leave a viscous film on the bearings?
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If you take any notice of Yanmar's stipulations, you'd not be using a multi-grade oil as you do.
It is possible that your engine is suffering from oil depletion on load-bearing surfaces - use as proposed an SAE 30, straight mineral oil, they tend to keep a more effective lubricant film on surfaces than modern synthetics.
SAE 30 CDI/SP. though an outdated description is the only one Yanmar offer.
All major oil producers have such oils in their range - unlikely to be on easy offer as the prices are too low to attract resellers.
It is possible that the injection pump timing is a little advanced.
Certainly do not consider adding another additive to your engine.
In the indirect cooled version, the 2GM is good for about 10K hours, as any Yanmar specialist will testify.
All horizontal twin engines are, basically, unbalanced, so you may have to live with the problem.
 
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My 3GM 30 does exactly the same. Give it a tiny bit of throttle in neutral when starting and there is no knocking. It's just that the hot engine tickover is a slightly lower throttle setting than is needed at start. Once the engine is running the neutral setting is perfectly OK, there is a little more friction when it is cold.
 
charles_reed said:
If you take any notice of Yanmar's stipulations, you'd not be using a multi-grade oil as you do.
It is possible that your engine is suffering from oil depletion on load-bearing surfaces - use as proposed an SAE 30, straight mineral oil, they tend to keep a more effective lubricant film on surfaces than modern synthetics.
SAE 30 CDI/SP. though an outdated description is the only one Yanmar offer.
All major oil producers have such oils in their range - unlikely to be on easy offer as the prices are too low to attract resellers.
It is possible that the injection pump timing is a little advanced.
Certainly do not consider adding another additive to your engine.
In the indirect cooled version, the 2GM is good for about 10K hours, as any Yanmar specialist will testify.
All horizontal twin engines are, basically, unbalanced, so you may have to live with the problem.
Click to expand...
Yanmar's current recommendation for the 1GM is 10W30 or 15w40

When you say 'straight' 30 are you talking monograde or without detergent? Either way it's advice from the dark ages.
 
vyv_cox said:
My 3GM 30 does exactly the same. Give it a tiny bit of throttle in neutral when starting and there is no knocking. It's just that the hot engine tickover is a slightly lower throttle setting than is needed at start. Once the engine is running the neutral setting is perfectly OK, there is a little more friction when it is cold.
Click to expand...

I think this is where I've been going wrong, starting the engine with the throttle at the idle setting. Now that I belatedly refer to the owners' manual I see it tells you to start the engine with the throttle open.

Thanks Vyv and all
 
vyv_cox said:
My 3GM 30 does exactly the same. Give it a tiny bit of throttle in neutral when starting and there is no knocking. It's just that the hot engine tickover is a slightly lower throttle setting than is needed at start. Once the engine is running the neutral setting is perfectly OK, there is a little more friction when it is cold.
Click to expand...
Same here.
A little bit of 'throttle' gives quicker starting without excessive revs when it starts. A bit of medium - fast idle before backing off and engaging gear.
If the engine's been left a long time since running, I sometimes crank over decompressed to get the oil around the motor.
 
charles_reed said:
If you take any notice of Yanmar's stipulations, you'd not be using a multi-grade oil as you do.
Click to expand...

1004972_l.jpg


In case you can't read it, under "Yanmar Genuine Diesel Engine Oil" it says "SAE 15W-40".
 
JimC said:
I think this is where I've been going wrong, starting the engine with the throttle at the idle setting. Now that I belatedly refer to the owners' manual I see it tells you to start the engine with the throttle open.
Click to expand...

Once it's warm my 1GM10 starts easily at idle; when it's cold it needs full throttle and then starts instantly. Not that it's about to be on eBay, oh dear me no.
 
On my 3 Gm 30 sea water cooled I always put the startup noise and vibration down to the water jacket being partial empty. Settled down as soon as the pump managed to fill all the water ways.
 
Given that it occurs after a period of non-use, it might just be a little air getting in to the fuel line at, for example, the fuel filter. Not enough to cause a non-start but just enough to make it run rough while the air is expelled via the injectors or return line. I agree though that the easiest way to clear it is to have the throttle partly open at start-up to speed it on its way. FWIW my Bukh (again no heaters) also needs a moment or two to sort itself out after a long period of rest.
 
Difficult to understand why anyone needed to post anything after #9. It is nothing to do with glow plugs, injectors, oil, air, water jackets or any other fanciful theory, it is simply that when the engine starts from cold it runs very slowly, less than 500 rpm unless the 'throttle' is opened a little. Diesels simply do not like to run as slowly as this and make knocking noises in protest.
 
JimC said:
I think this is where I've been going wrong, starting the engine with the throttle at the idle setting. Now that I belatedly refer to the owners' manual I see it tells you to start the engine with the throttle open.

Thanks Vyv and all
Click to expand...

You have it. It will start more readily as well.
 
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