Generac Engine Replacement ; Briggs to Tecumseh

[Lapkritis]

Well...

I read some threads about 5yrs old on this topic. I decided now would be a good time to share my rebuild/engine replacement experience. I'm almost done but not quite... Here's some pics to show where we are at.

Generator was a gift from my dad. We've had this at the family compound since the 90's and just had it quit in the last year due to a rapping noise after lending it out for construction site work. Prior to the death by construction site, it served reliably as an emergency generator via 6 switch panel for a house in rural VT. Ice storms, blizzards, hurricanes etc would often take the house offline and this generator would faithfully serve until Green Mountain Power could restore service. I believe the longest served was about 2 consecutive weeks during a particularly bad ice event.

The rapping noise failure was reported and my parents couldn't be bothered with a rebuild. They had their satisfied use of the unit and simply bought a replacement as they need reliability. My wife and I have been gifted their tired equipment and gladly accept... I can wrench.

So here the pictures begin. A tired/noisy/dead generator that hasn't been used in a couple years. I tore right in:





Comes apart easily.


Lefty loosy righty tighty.


Expected to find a broken rod or smashed internals from the sound. Instead we found the exhaust valve was impacting the cover (non-ohv).

Began disassembly viewing genpack guts.

 

[Lapkritis]

The major challenge people encounter is separating the rotor from the crank. I had researched and knew the trick to get through this step before I started. I used a 12mm tap to put threads inside the rotor shaft and a metal rod to then be driven beneath a bolt on the new threads to drive the rotor off the taper shaft.

Things were a bit sticky due to light rust/taper fit. When it finally popped I thought the crankshaft had perhaps snapped due to the sound.

Anyway, on to unwrapping the new Tecumseh. I had found the valve impact inside the briggs and stratton a couple weeks before I bought the replacement Tecumseh engine. In the interests of complete disclosure I was ready to rebuild the briggs until I found the engine was aluminum coated bore showing wear at the bottom of the jug. A bottom of the barrel rebuild kit is $90 without machine work and then I would need to donate my labor... not worth it when you can score these Tecumseh engines on ebay so cheap as long as the Tecumseh work okay. The Tecumseh are iron sleeve which is superior for longevity and rebuilds if you ask me.

Looks great to me for the price.

 

[Lapkritis]

Research pays off - I can see the snout on the Tecumseh is the same dimension as the Briggs I'm replacing.

Here's the only shot I have showing the bolt I used to remove the generator rotor from the crankshaft. The knowledge of how to complete this step makes the job much easier... write this trick down if you plan the same.

VW lug bolt used on the new threads to drive the rotor off the crank taper;

In the first pic of this post above, the new crank side is visible; same bolt pattern to accept the generator pack as the briggs with the only difference being the inner bolt holes on the Tecumseh accepting the bolts and the outers without thread.

 

[Lapkritis]

No time to waste, washed up some of the genpack bits and moved straight to reassembly today:

Spacers to stand off slightly closer to briggs; just used washers.

Same engine mounts transfer:

 

[Lapkritis]

The Tecumseh is inches narrower than the briggs and stratton on the engine mount side of the engine. This was an easy fix by just measuring and drilling new holes for the mounts on the cart. Here's one done and the second half done; I drill first with a smaller diameter.

Then to reassemble, I set the engine and beginning of the generator pack assembly on a pillow; the cart then tips on without contact and things bolt back together the same.

Added a $4 fuel filter kit from Advance Auto Parts; don't want to deal with carb rebuilds ever as long as I remember the fuel stabilizer.

Used WD40, scrub pad and paper towels to get all dust/grease off remaining parts including the fuel tank.

It's about ready to start up. I cracked one ear on the alternator assembly when tightening things up... I may need to call in a favor for a friend to weld it to make it perfect. It's not completely broken but I can see the crack. Once that is done, it's a matter of fuel, plain old SAE 30 oil and it's ready to start. I plan to break-in on generic oil and switch to synthetic after a few hours to keep things clean. Generator service will be for the house here during emergencies. I plan to add a switch panel in the spring/summer but in the meantime using it in direct connect support.

Thanks for looking. More to come as the final details close up and we put gas to it to see how it does.

 

[cptn_zippy]

Nice work! I'd like for my dad to do a similar swap on his old snowblower... Repower with a new engine, save the hassle.

J

 

[txst]

Good job. One piece of advice is to double check the brush alignment on the slip rings of the alternator. When changing engine manufacturers, some of the tolerances may be different on the crankshaft taper or the mounting surface of the alternator (where you had to add washers). The brushes should be pretty much centered on the pervious grooves on the slip rings, otherwise you could have some weird wear or arcing.

 

[Lapkritis]

I do appreciate the advice with the slip rings/brushes. The rotor and stator are offset by the depth of the spacer which is about 3mm. The rotor is seated on the taper and there's no interference issues fortunately. On the other hand I do have a spacer planned for the same ~3mm under the rotor center bolt to ensure tension is maintained on the taper. The brush alignment isn't perfect with the Briggs and contact is decent. The brushes show plenty of life but will be riding the slip rings in a new contact area. I may opt to revisit the solution one more time. The spacers were required due to the center hole in the stator housing where the crank snout enters the alternator. The Tecumseh has a raised seal design that interferes with the hole on the alternator housing. I may be able to simply enlarge this hole to do away with the spacers and return the stator/rotor alignment to original... That's probably the right thing to do.