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Old 14-02-2021, 15:30   #1
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Rebuilt engine throttle is light

So I just got done rebuilding our generator engine after hydrolocking it. Replaced just about everything but the crank shaft and connecting rods. New head, new pistons and sleeves, new seal on everything etc.

On thing that did stay was the fuel pump and governor.

Which is what's confusing me now. It's running at 1800 rpm which is what the generator calls for. It's putting out the right voltage at 60.4hz with about a 10% load. But it sounds a lot slower than it used to, and the throttle lever itself is maybe a third as advanced as it used to be.

Is there some reason it might have been at far higher rpm originally? It really seems to be running a lot slower than it used to, but I'm reading the rpm straight from the crank shaft, and the voltage/freq looks correct. I might be imagining it too, but it also seems to be making more 'diesel rattling' noise too.

The throttle thing just has me looking at it sideways. Should it be so much lower throttle to achieve the same rpm after a rebuild? It's a really new generator, 450 hours, the original setting was from the OEM that put the unit together. I'm a bit scared to put a full load on it in case I've done something stupid.
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Old 14-02-2021, 16:55   #2
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Re: Rebuilt engine throttle is light

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Originally Posted by Corvidae View Post
So I just got done rebuilding our generator engine after hydrolocking it. Replaced just about everything but the crank shaft and connecting rods. .
The only damage from corrosion? Seems strange not to replace the connecting rod.
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Old 14-02-2021, 17:19   #3
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Re: Rebuilt engine throttle is light

It locked while trying to start it, so the rods were never damaged. The pistons were just fused to the cylinder walls. There was also extensive corrosion on the head around all the valve seats and stems. It could have been repaired with new seats and valves etc, but the cost of machining was less than a hundred dollars difference to a whole new head.

After replacing the bearings top and bottom, the connecting rods had no off angle play.
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Old 14-02-2021, 18:59   #4
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Re: Rebuilt engine throttle is light

If you're making 60hz then the rpm is right. It's based on the windings in the generator. 50hz often uses the same generator and engine, it just runs at 1500 rpm.
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Old 14-02-2021, 20:18   #5
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Re: Rebuilt engine throttle is light

Maybe prior to the rebuild the compression was low and the governor had the fuel maxed out ? That could certainly account for it sounding different ? Sounds like it has good compression now, possibly there might have been a fuel timing change ?
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Old 14-02-2021, 20:47   #6
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Re: Rebuilt engine throttle is light

The fuel timing is more advanced. One of the shims was tore up during removal.
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Old 15-02-2021, 05:32   #7
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Re: Rebuilt engine throttle is light

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Originally Posted by Corvidae View Post
The fuel timing is more advanced. One of the shims was tore up during removal.


Well....youíve just answered your own question.

The more diesel knock sound youíre hearing is exactly that, more diesel knock. Depending on how far youíve advanced the timing you may be causing damage by completing combustion way too soon before tdc
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Old 15-02-2021, 12:47   #8
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Re: Rebuilt engine throttle is light

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The fuel timing is more advanced. One of the shims was tore up during removal.
There you go, inj more advsncedmeans means more diesel knock.
I don't lnow what engine this is, but I had two gm10 ns in a cat. Pne a goodstarter and not too noisy, the other a really bad starter and do f... Loud
I loosrnef yhe nuts that hold the pump a nit and. nothing. I hit the pump vateful so itv was really loose and the result was as rxpected. Sysrted right aesu, the heavy knock eas gone

Went to yhe yanmar shop and nought a liytle plastiv bag with some shims different sizrs
Cost, less than 10 euro
Less thsn 10 minutes work.
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Old 27-02-2021, 15:44   #9
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Re: Rebuilt engine throttle is light

So I added all the shims to put timing back to factory, couldn't start the motor. Took out one of the shims, and got it to start. The whole stack is supposed to be .75mm, I had it down to .3mm and right now it's back to .5mm. Got it started, seemed to be less knock, about the same rpm though. Ran for about 5 to 10 minutes and shut down, doesn't want to start again. It cranks, and kinda fires, but won't catch. Checked the oil and it seems very clear, going to let it cool and see what's going on with that.

Also it's a Kubota v-1505. 4 cylinder about 30hp.
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Old 27-02-2021, 16:18   #10
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Re: Rebuilt engine throttle is light

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Originally Posted by Corvidae View Post
So I added all the shims to put timing back to factory, couldn't start the motor. Took out one of the shims, and got it to start. The whole stack is supposed to be .75mm, I had it down to .3mm and right now it's back to .5mm. Got it started, seemed to be less knock, about the same rpm though. Ran for about 5 to 10 minutes and shut down, doesn't want to start again. It cranks, and kinda fires, but won't catch. Checked the oil and it seems very clear, going to let it cool and see what's going on with that.

Also it's a Kubota v-1505. 4 cylinder about 30hp.


You donít shim a fuel pump to any specific measurement, you shin it based on flow timing the point of injection. Or you guess and use artillery logic to pin down the right shim stack size.

Itís tedious and sucks, but itís the only way to get it right.

The shims are used to account for differences in pump, plunger and barrel bodies.
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