Flywheel GX270 vs. GX390

rkcarguy

New member
I acquired a electric start GX270 that has sat a long time and is stuck, and a good running GX390 off a dead pressure washer that is pull start and runs good. Both are early style mechanically governed engines. This will not be for a racing application I'm leaving the engine stock and governed to run a hydraulic setup.
I was looking up parts online for both engines, and it appears that the flywheel key, charging coils, ignition coil/plug wire, and many other parts are the same from the GX270 through GX390, but lists the flywheels as different parts. I would like to swap the electric start stuff(starter, flywheel, charging coils, key start box, etc) onto the 390 if possible?
I wouldn't be against having to re-key the flywheel if it wasn't the same, but if the taper is different on the crank I guess I'll have to keep looking for GX340-GX390 electric start parts.
 

rkcarguy

New member
I took a better look at my GX390 and the starter hole isn't machined, so I'm not going to bother trying to swap the parts over. It turns out, the GX270 had a pressure washer pump with a 2:1 gearbox on it that ran out of oil and one of the bearings was coming apart and had jammed metal into the gears. Once I removed the gearbox, the motor actually started up when I went to turn it over and surprised the crap out of me.
My main need is just for the GX390 to have a charging coil or alternator added, so I'll keep looking for those.
When I removed the pull starter and flywheel cover from both engines, they are different sizes, so while the taper on the crank may be the same, I'd bet the flywheel diameter is smaller on the 270.
 
The flywheel on the 270 is smaller as well ...the flywheel will not fit over the charging coils for the 390 and your ignition coil won't reach either ...you will need to do a lot of modifications to get that to work
 

WinstonSmith

New member
The flywheel on the 270 is smaller as well ...the flywheel will not fit over the charging coils for the 390 and your ignition coil won't reach either ...you will need to do a lot of modifications to get that to work
Thank you for this valuable information.
I am new to the big block
 

CarlsonMotorsports

Premium User
I took a better look at my GX390 and the starter hole isn't machined, so I'm not going to bother trying to swap the parts over. It turns out, the GX270 had a pressure washer pump with a 2:1 gearbox on it that ran out of oil and one of the bearings was coming apart and had jammed metal into the gears. Once I removed the gearbox, the motor actually started up when I went to turn it over and surprised the crap out of me.
My main need is just for the GX390 to have a charging coil or alternator added, so I'll keep looking for those.
When I removed the pull starter and flywheel cover from both engines, they are different sizes, so while the taper on the crank may be the same, I'd bet the flywheel diameter is smaller on the 270.

I probably have the stator and everything you need for the 390 -- new take-off stuff from big block UAS-type builds.
Give us a call at the shop:



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Carlson Racing Engines
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WinstonSmith

New member
Stupid question time,
Is the 390 flywheel heavier?
If it is what is involved in putting this heavier flywheel on a 270 or 240.

Ya you read that right I want heavier....
 

CarlsonMotorsports

Premium User
Yes, it is considerably heavier.
The biggest obstacle will be the larger diameter. You will need to make a bracket for the coil to mount and reach the larger OD.
 

WinstonSmith

New member
I don't have access to any of these parts.
I am still shopping for an engine to build ( budgets an all )
Do you have any of these parts you could photo for comparison to give me some idea what kind of circus I am considering get into?

I am building a replacement engine for a natural gas fuel stationary electric plant
My hands are free to build an engine specific to this task with the right balance of compression timing advance and heavy rotating mass for smooth flicker free performance.
 
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