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Old 03-07-2022, 09:06   #1
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What happens if valve lash not set correctly?

I had to remove the head on my 3GM30F to clear a stuck injector. I'm now putting it back together and I'm at the point where I'm adjusting the valve lash. I'm following the steps in the manual, which says the feeler gauge should just slip between the gap. This is something of a judgement (ie experience) call.

What would be the indications of a too tight or too loose gap?
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Old 03-07-2022, 09:11   #2
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Re: What happens if valve lash not set correctly?

Get a feel for it..

Drag a 0.030 through, and then a 0.035. You should be able to easily feel the difference.

If youhave to force it through and feel like you are scratching the surface of the feeler, it's too tight. If it slide through without any drag, it's too loose.

Don't sweat it. If you think it is right, you are surely close enough. This isn't a measurement you need to have right to within 0.0002"
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Old 03-07-2022, 09:28   #3
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Re: What happens if valve lash not set correctly?

If they're too tight, the valves won't seal correctly. That makes a real bad top end knock and will burn the valve faces over time. To loose and you'll get an annoying tapping sound and the timing could be a little off. As the valves wear, they get tighter (kind of counterintuitive) so better to have them a little loose than a little tight. Old timers (on cars) used to do it by sound and feel alone with the engine running, valve cover off. Loosen up till you hear the tapping then tighten a little. All the while oil spraying everywhere. Better to use the feeler gauge and engine off.
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Old 03-07-2022, 09:33   #4
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Re: What happens if valve lash not set correctly?

The old saying goes

slappy valves are happy valves

As said above, gentle drag with the feeler, err on the side of a little loose rather than a little tight.
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Old 03-07-2022, 09:56   #5
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Re: What happens if valve lash not set correctly?

When I adjust valves, I like to back them off a bit, stick the feeler gauge in, and then tighten them down to the feeler gauge. It’s a good way to get them just about perfect. Then you can do the microscopic adjustment, the gauge is already in there, and you can get it just right. So it drags just a little bit, but doesn’t feel like it’s getting caught up.
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Old 03-07-2022, 18:40   #6
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Re: What happens if valve lash not set correctly?

I'd like to add that you'll quickly get the "feel" for it. It's simple to learn. Chotu's method will teach you, and your fingers will "get it".

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Old 03-07-2022, 19:24   #7
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Re: What happens if valve lash not set correctly?

You can buy go/no go feeler guages specifically designed for valve lash adjustment.
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Old 03-07-2022, 19:57   #8
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Re: What happens if valve lash not set correctly?

All good advice upthread. The valve clearance for your 3GM30 is 8 thou. The 8 thou feeler gauge should just 'drag' slightly. A 9 thou gauge can be used as a 'nogo' gauge while a 7 thou gauge is a 'go' gauge.

Of course there is no reason to use feel gauges at all. Just back off the adjusting screw 58 degrees, easy enough as the hex locking nut has 60 degree faces.

From the 3GM30 service manual -
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Old 03-07-2022, 20:05   #9
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Re: What happens if valve lash not set correctly?

The fact that the above approximation is good enough for Yanmar reaffirms my long held belief that a few thousandths one way or the other isn't a big deal, so don't stress out too much about the job.

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Old 03-07-2022, 21:19   #10
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Re: What happens if valve lash not set correctly?

The critical thing is to retain some clearance as the engine heats up. If the valves are prevented from fully seating they will leak and eventually burn out.
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Old 03-07-2022, 21:40   #11
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Re: What happens if valve lash not set correctly?

Quote:
Originally Posted by Sailmonkey View Post
The old saying goes

slappy valves are happy valves


As said above, gentle drag with the feeler, err on the side of a little loose rather than a little tight.
And the other one "better to hear a valve than smell it" (again, encouraging to err loose).
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Old 04-07-2022, 18:14   #12
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Re: What happens if valve lash not set correctly?

Loose valve settings wear the rocker arm and valve stem top. So your valves go out of adjustment faster.
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Old 05-07-2022, 05:40   #13
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Re: What happens if valve lash not set correctly?

Loose valves will be noisy and give rough idle. Over tight will run poorly at high RPM's.

Learn how to locate the 'base circle' of the cam lobe for each valve and what the correct lash is. Google EOIC method.

With the lifter on the base circle, hold light pressure on top of the push rod side of the rocker arm and adjust until the feeler gauge has light friction. Good luck!
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Old 05-07-2022, 11:11   #14
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Re: What happens if valve lash not set correctly?

We havenít even talked about a cold engine vs a warm one :-)
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