Blink
Recently I have ran into quite a few older nexus units (20kw) that exhibit a very weak crank, even with a brand new battery. I checked the battery cable connections and they seem fine. The units surprisingly start, but the crank is weak enough to cause concern. I use new Exide batteries, and this occurs even in the summer. What else could be causing this?
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Bassplayer1985
Valves adjusted properly? Make sure compression release is working. Maybe check the amperage draw and voltage drop while observing if the cables get warm

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Peddler
There is no compression release on any of the air cooled Generacs. The Nexis and newer units don't have as strong a starter as the older units had it seems to me. I would check the voltage at the starter motor (Starter motor side of the solenoid) during cranking and compare that to battery voltage at the battery during cranking they should be almost the same if the connections and solenoid are good.
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78buckshot
Starter would be the culprit if all else is up to snuff.
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MacL
When you say recently, that could mean since the onset of colder weather. And the full synthetic oil we use is like molasses when it's cold. Add that to the normal effects of cold temperatures on a battery, and you'll probably notice a slower crank speed.
State your problem, not your diagnosis.
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Cobranut
MacL;50392 wrote:
When you say recently, that could mean since the onset of colder weather. And the full synthetic oil we use is like molasses when it's cold. Add that to the normal effects of cold temperatures on a battery, and you'll probably notice a slower crank speed.


MacL: What kind of oil are you using?

Most synthetics exhibit a more stable viscosity over a wider temperature range than petroleum oils. This prevents them from thickening at cold temps or thinning out at high temps. This is actually one of the major benefits of synthetic oil, and it seems odd that your brand doesn't have this benefit.
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MacL
We use a 10W30 full synthetic
State your problem, not your diagnosis.
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nrp3
I've found a few bad battery cables. I take a set of jumper cables and bypass the frame ground and then the positive to see whether it improves.
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patmurphey
MacL;50394 wrote:
We use a 10W30 full synthetic called SuperSyn...


Isn't the spec for synthetic 5W30?
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Hodgy
patmurphey;50399 wrote:
Isn't the spec for synthetic 5W30?



I use 5W30.


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MacL
We're nearly in the tropics here, most oil recommendations come with a climate chart which is also taken into consideration.
State your problem, not your diagnosis.
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Canada_Guy
patmurphey;50399 wrote:
Isn't the spec for synthetic 5W30?


I was advised directly from Generac that synthetic 5W30 is the recommended oil for all their air-cooled engines.

I just lucked out and picked up 4-liter (a bit more than 1 US gallon) of Mobile1 for $23 CDN (about $17 US) at Walmart. It's typically about twice that up here.
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Blink
Thanks for all of the replies. I use Generac branded 5W30syn in all my generators. The generators experiencing the weak crank symptoms have been running this oil for years. I will check the cables and valves. Unless I'm wrong, I was under the impression that starter motors just die, they don't get "weak"...
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Birken Vogt
Blink;50424 wrote:
Thanks for all of the replies. I use Generac branded 5W30syn in all my generators. The generators experiencing the weak crank symptoms have been running this oil for years. I will check the cables and valves. Unless I'm wrong, I was under the impression that starter motors just die, they don't get "weak"...


I've had many starter motors get weak long before they die but it is very hard to distinguish between that and battery problems.
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BobCanuck
Birken Vogt;50425 wrote:
I've had many starter motors get weak long before they die but it is very hard to distinguish between that and battery problems.


That is where a battery load tester is useful. For casual use (home owner) you often can pick them up at Harbor Freight (Princess Auto, for my fellow Canucks) for around $20 on sale.

[url]https://www.harborfreight.com/100-amp-612v-battery-load-tester-61747.html[/url]
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Hodgy
BobCanuck;50431 wrote:
That is where a battery load tester is useful. For casual use (home owner) you often can pick them up at Harbor Freight (Princess Auto, for my fellow Canucks) for around $20 on sale.

[url]https://www.harborfreight.com/100-amp-612v-battery-load-tester-61747.html[/url]



Got that one at PA also.


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Blink
Circling back to this post. Same generator still exhibiting a very weak crank. Brand new starter, cables and battery. Valves adjusted to spec. 5W30 synthetic oil. I'm at a loss?
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UPS
Blink wrote:
Circling back to this post. Same generator still exhibiting a very weak crank. Brand new starter, cables and battery. Valves adjusted to spec. 5W30 synthetic oil. I'm at a loss?


You could try removing the plugs and see if cranking speed changes.
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BrianMartin
Have you checked the negative battery cable on the engine mount? If it's loose, you could be losing some cranking power.. 
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