Looking to replace B & S engine on my Craftsman lawn tractor. It came with a 20 HP Model number 31P977-0635-E1. I was leaning toward a new, newer model B & S that would just bolt up in place of this one without much alteration. Frame, chassis, tires, wheels and rest of mower still in good shape. Any advice on what to replace it with and where to buy would be appreciated.
Since that has the 3 Amp charging system with AC lighting, make sure the new one has the same circuit for "plug & play".
Most any Briggs 31 or 33xxxx series engine should work. Just make sure the PTO stub dimensions are the same.
The 9A charging circuit is likely designed to handle keeping the battery charged along with running something such as an electromagnetic PTO clutch. The PTO clutches draw some amps, likely more than a 3A charger could keep up with. From deduction, your 3A system likely doesn't have the load that a 9A system would be required to handle. If your system has a voltage regulator to keep from overcharging the battery, it should handle the load the 3A system previously handled, it will just be regulated down from its max of 9A to what is needed. If there is no regulator(I'm not going to go read), then 9A might just be too much, and could cook the battery by overcharging.
As far as the HF vertical, it's new, but if it follows the performance of the other HF engines, should be a good candidate for a replacement engine. There might be some surgery required for exhaust and throttle linkage, along with making sure the PTO dimensions would match the B&S. I know zip about the mounting bolt positions, but have an idea the makers somehow agreed to a common layout.
If I were in the market I'd give it strong consideration. OTOH, the B&S v-twins are good engines, as are the Kohler series. All save the B&S would require some 'adjustment' to get things installed.
tom
The 9A charging circuit is likely designed to handle keeping the battery charged along with running something such as an electromagnetic PTO clutch. The PTO clutches draw some amps, likely more than a 3A charger could keep up with. From deduction, your 3A system likely doesn't have the load that a 9A system would be required to handle. If your system has a voltage regulator to keep from overcharging the battery, it should handle the load the 3A system previously handled, it will just be regulated down from its max of 9A to what is needed. If there is no regulator(I'm not going to go read), then 9A might just be too much, and could cook the battery by overcharging.............
The tractor is wired for the 3A charge w/AC lighting engine.
Going to a Regulated system means they would have to do electrical "surgery" with mismatched connectors etc.
They "could" get the engine mentioned and swap out the flywheel & stator and then have "plug & play" installation.
It's just SO MUCH easier to get an engine with the 3A system to begin with.
Unless the OP wants to swap flywheels & stators.....
Maybe they do?
You also seem to forget the regulator is PART of the ENGINE.
Thanks for the info Bill. Wasn't trying to be difficult. The least amount of surgery, the better. I understand what you said about staying with the 3 amp system and I looked up some of the 31 and 33xxxx engines and didn't see one that had a 3 amp system. I guess I didn't look hard enough. Thanks to all for the input it is greatly appreciated.
IF the 31/33 series with a VR system is noticeably cheaper, it may be worthwhile to pay a shop to do an alternator/flywheel swap?
Don't be "beholden" into getting exactly the same Horsepower.
A 31 is going to pretty much have the same torque as a 31 as 31.
A 33 will have about 6-7% more.
HP ratings are at 3600 RPM. Your engine is likely governed somewhere around 3100-3200ish, so it never has a chance to develop advertised HP anyway.
Knowing which Craftsman this was on, would allow one to know if this engine (Remote Choke) is what you need or avoid, or if you need a fuel pumped engine etc. 31R777-0003
Well, You don't want the remote choke.
I can't tell from Sears if your engine has a fuel pump or not, but you can look for that.
Just follow the fuel line back from the carb. If it goes into a device with 2 other hoses, that's the pump.
If the current engine doesn't have a fuel pump, I don't see a problem with getting an engine with one. If it does have a FP, make sure the new engine does too.
Thanks for everyones input, I appreciate it. I ended up buying a Hustler 42" Raptor ZTR only because I've been wanting one and they gave me $400 for my 8 year old Craftsman as a trade-in.
New engine in the Hustler, original old engine in the Craftsman, lol. $2,560 out the door.
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