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Can you run 1800 rpm Onans at 3600?

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Old 09-22-2017, 03:10:49 PM
Pete Spaco Pete Spaco is offline
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Default Can you run 1800 rpm Onans at 3600?

A friend wants to replace the Onan engine in his Case garden tractor and wonders if he could take the engine out of a 6.5 kw genset like a 6.5NH or 6.5NHE and run it at 3000 rpms or so.
Does anyone do this? I was thinking that, for those Onan engines to be run at 3000 or 3600, that they'd have to do some serious balancing, and who knows what all to get them to run well at those much faster speeds.

I don't even know if the crankcase castings would even mate up with whatever is on the garden tractor.

Any comments?

Pete Stanaitis
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Old 09-22-2017, 03:35:58 PM
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BRae BRae is offline
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Default Re: Can you run 1800 rpm Onans at 3600?

1. don't think those engines are designed to run faster than 1800rpm. some use different connecting rods.
2. it will need a crankshaft adaptor generators use a short tapered shaft.
3. I wouldn't run one that fast without a flack jacket.
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Old 09-22-2017, 03:37:30 PM
len k len k is offline
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Default Re: Can you run 1800 rpm Onans at 3600?

Would guess you could get engine up to 3600 by opening throttle , may have to use stiffer gov spring. Question is how long would it last. Centrifugal acceleration is proportional to Rw^2 so those forces would be quadrupled. I'm thinking more along lines of higher connecting rod and bearing forces, so wear may increase. Higher accelerations/forces in connecting rod too. Would guess gov balls will wear more , since higher forces on them.

Last edited by len k; 09-22-2017 at 06:21:48 PM.
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Old 09-22-2017, 03:56:41 PM
Tracy T Tracy T is online now
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Default Re: Can you run 1800 rpm Onans at 3600?

I don't think you are going to get there with a diesel, but some of the welder/ generators with on an engines do run up that fast. More than likely those Oman engines are built to run at higher speeds. Diesels don't peak at a certain rpm like a gas engine does, if you looked at a diesel on a dyno they tend to plateau over several rpm with torque and horse power pretty constant.
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Old 09-22-2017, 04:57:32 PM
YellowLister YellowLister is offline
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Default Re: Can you run 1800 rpm Onans at 3600?

No... not to mention you would need to make a adapter for the pump if it's hydrostatic.

The 3600 rpm units have a different cam lobe and cast iron connecting rods vs aluminum for the 1800 rpm units

Would be better finding a welder engine like said as they run 1800 for the generator side and 3600 for welding, but also have a tapered shaft
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