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Unsiezing a Onan Twin cylinder engine

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Steven Wood

07-14-2002 15:33:22




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I have an onan B series engine in a Gravely 818T, and it will not turn over. What could be causing this and how can I repair it?




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Steven Wood

07-15-2002 11:52:27




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 Re: unsiezing a Onan Twin cylinder engine in reply to Steven Wood, 07-14-2002 15:33:22  
The Gravely 818T was Gravely's last entry into the 800 series. It had a Onan B48M-GA018 engine mounted directly to the transmission. My transmission is working perfectly. I removed the spark plus and tried to turn over-no luck. Tried a prybar and no lunk. Believe I have a frozen engine. Need a rebuild kit.



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Farmer Gene (WI)

07-15-2002 06:10:06




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 Re: unsiezing a Onan Twin cylinder engine in reply to Steven Wood, 07-14-2002 15:33:22  
Just a thought, on alot of the horizontal piston engines if too much oil is put in crankcase and the engine sits for awhile, oil runs past the piston rings into the combustion chamber causing a liquid lock. Pull the sparkplugs and see if it will turn over.



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Medfarm

07-14-2002 21:41:42




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 Re: unsiezing a Onan Twin cylinder engine in reply to Steven Wood, 07-14-2002 15:33:22  
Steven
Is the Onan a model CCKB with horizontaly opposed cylinders? What is is driving? A clutch or pulley or drive shaft?
1) Remove output mechanism to isolate engine. Some of the Onans had a tapered shaft for use with a clutch (such as a two man railroad car) or a straight shaft.
2) Try to turn flywheel with a bar being careful not to break any cooling fins.
3)If engine will turn when the load is removed from the crankshaft, try to make engine run (Carb, plugs, points, sparkplugs, wires).
4) If electric starter or hand start will not turn over engine and the bar on flywheels fails to turn engine, the engine is froze up (either by mechanical failure or by moisture corrosion).
5) At any rate, you must first determine if engine or machine is froze up. If engine is stuck, remove engine from motor mount. The crankcase can be removed with 4 bolts, I believe, allowing you to see the crank and bottom end. Look for the obvious.
6) If the bottom end appears okay, remove the air shroulds and both heads. Again look for the obvious.
7) Parts and rebuild kits are still available for the Onans but they are not cheap. If the engine is a CCKB. I beleive the horsepower output is around 20 at 3200 to 3400 rpm. It has been several years since I rebuild an Onan but they are durable and relatively troublefree. If the engine has an belt driven alternator, the engine probably has ignition points located above the output crankshaft and 1 ignition coil with 2 plug wires.

Hope this helps. Ray Medley
California

PS What is an Gravely 818T?

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Medfarm - I forgot to tell you to

07-14-2002 21:48:09




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 Re: Re: unsiezing a Onan Twin cylinder engine in reply to Medfarm, 07-14-2002 21:41:42  
Steven

Remove the starter if you can not turn the engine over by using a bar. Sometimes the bendix can jam into the teeth of the flywhell causing a locked engine.

Good luck and let us know what you found out.



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