Generac 15KW generator engine tear down

[pclausen]

I like the idea of making the 8kw unit portable and use as a backup! One year, before wiring it permanently into my house, I used it in a field for a party powering the lights and the live band. Worked great, but the 100lb bottles really started the sweat after a while, but genny just kept on running all night long (well, until about 4am or some when I, ahem, "checked out" )

 

[FairfaxStu]

My friend and his dad get these engines, and then discard everything but the block, crank and bare heads. Then they bore them out and put in larger pistons, valves, valve train, etc and set them up to run 15:1 compression on methanol. They also discard the OEM ignition coils and run dual Bosch blue coils with dial Mopar racing ignition boxes with individual crank triggers for each cylinder. Spin around 9500 rpm.

Yep, those dudes know their Generacs. I think they are actually getting about 120 HP. For the record, they do tractor pulling, not tractor racing. They finished in 2nd place at the Nationals 2 years ago (only time they went). Just to hear this thing run is amazing - it sounds exactly like a small block 350 when they hammer it. Great job Greg and Frank!

 

[pclausen]

Hey Stu. I edited my post to read tractor pulling.

In preparation for swapping engines, I went ahead and separated the generator from the engine.

First step was to remove the rear bearing carrier:

And then the stator:

Now I need to go get me a new bolt that matches my current rotor bolt and cut about 3" off the bolt head end, then slot it and screw it into the crankshaft. Then screw a M12x1.75 bolt into the rotor until I brake the taper. I'm sure that will be all kinds of fun.

 

[FairfaxStu]

Now I need to go get me a new bolt that matches my current rotor bolt and cut about 3" off the bolt head end, then slot it and screw it into the crankshaft. Then screw a M12x1.75 bolt into the rotor until I brake the taper. I'm sure that will be all kinds of fun.

Is this standard procedure for removing the rotor from the engine? I don't quite understand.

-Stu

 

[pclausen]

Yep, that's the procedure listed in the service manual. The rotor shaft is hollow and by screwing a long stud into the crank, and then screwing a larger bolt into the internally threaded rotor shaft, it will push against the stud, and force the rotor off the crank taper.

 

[FairfaxStu]

Yep, that's the procedure listed in the service manual. The rotor shaft is hollow and by screwing a long stud into the crank, and then screwing a larger bolt into the internally threaded rotor shaft, it will push against the stud, and force the rotor off the crank taper.

Can you take a pic of this while you are doing it? Seems like an odd process.

 

[pclausen]

Here's a shot right after I got the rotor shaft separated from the crank. Red arrow on the crank is where I screwed in the stud (also red arrow). I had to sacrifice one of my long Phillips screwdrivers for the task, see here supporting the bolt/shaft pieces. Even after letting the rotor/crankshaft taper soak overnight with PB Blaster, it still took a few blows with a rubber mallet to break it after tightening the bolt (yellow arrow) into the rotor real hard.

Here's the rotor after being removed. Red arrow is where the yellow arrow bolt from above pic was tightened into.

Close up of crank taper:

And some shots of the engine getting ready to be swapped out for a unit with only 12 hours on it. The bottom end on this failed one looks to be in real good shape. Once we pop the crank cover to steal the oil pump and pick up tube, I'll be sure to snap a few more shots to see what the internals look like.

My friend's dad that I'm getting the virtually brand new replacement from wouldn't give it to his son over the weekend. He insist on coming up himself to swap the oil pump to the new engine to ensure everything is done right. I'm quite confident that the replacement engine will be rock solid!

 

[FairfaxStu]

Cool beans, Peter. There is nothing like having somebody that has done it many times come up to swap out the parts for you. That way you are guaranteed that it will be done correctly. Any idea how soon he can come?

The rotor to crank seperation process makes sense now. The only thing that confuses me still is what is holding the rotor to the crank? I don't see a keyway in the crank so I am wondering how they prevent it from slipping. Is it just a pressure fit?

 

[pclausen]

Yep, just a pressure fit. The taper provides an incredible amount of surface friction, way more than the generator would ever be able to overcome, even at full load. There are no shock loads like, say a gearbox with a clutch could exert. You do have start up loads, like when an A/C compressor turns on, but you have the inertia of that heavy rotor spinning at 3600 rpm to absorb that.

Frank is coming up on August 9/10th to perform the swap.

 

[pclausen]

I split the crank case to see what the bottom end looks like.

Cover:

This image should make it pretty clear who manufactured this engine:

Closeup of rings on #1:

Closeup of rings on #2:

#1 cylinder wall:

#2 cylinder wall:

I'll still proceed with the engine swap, but from what I can tell, the bottom end on this engine is 100% perfect, the issue was all in the heads.