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My Poulan Pro PP20VA46 B&S 20hp engine has died (40N877-0004-G1) and I'm looking to replace it with a B&S 20hp engine (40N777-0031-B5) . Can I presume they have the same mounting footprint so the engine holes will line up with the frame holes?

scottmarsc said:

My Poulan Pro PP20VA46 B&S 20hp engine has died (40N877-0004-G1) and I'm looking to replace it with a B&S 20hp engine (40N777-0031-B5) . Can I presume they have the same mounting footprint so the engine holes will line up with the frame holes?

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Mounting pattern is standard across engines of the same brand as well as other brands.. So a Kohler, Briggs, Kawasaki, Honda will have the same mounting pattern.

I've noticed when Poulan's name is involved you cannot assume anything.

Thanks all for the input! Since there are only 4- threaded mounting holes on the bottom of the block I will assume it is standard across the B&S 40N models.

scottmarsc said:

Thanks all for the input! Since there are only 4- threaded mounting holes on the bottom of the block I will assume it is standard across the B&S 40N models.

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Standard from at least the 28xxxx series up to 46xxxxx series. The 13xxxxx-25xxxxx and 54xxxxx-61xxxx may have the same footprint also.

Not hard to drill mounting hole.
I take cardboard and make a template when the old motor is off the tractor, (if no fit) trace the center hole onto the cardboard. cut out the center per the trace and then center it on the donor motor and mark the donor's mounting holes onto the cardboard. Take it too the tractor and drill.
What I really watch out for is the shaft sizes and lengths of the donor motor vs the other, especially if pulleys from the old motor cannot be used onto the donor motor.

Forest#2 said:

Not hard to drill mounting hole.
I take cardboard and make a template when the old motor is off the tractor, (if no fit) trace the center hole onto the cardboard. cut out the center per the trace and then center it on the donor motor and mark the donor's mounting holes onto the cardboard. Take it too the tractor and drill.
What I really watch out for is the shaft sizes and lengths of the donor motor vs the other, especially if pulleys from the old motor cannot be used onto the donor motor.

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Also, how does the exhaust fit, is the wiring a direct plug and play, throttle cable hook ups the same?

Tiger Small Engine said:

Also, how does the exhaust fit, is the wiring a direct plug and play, throttle cable hook ups the same?

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engine swaps even small lawn tractor engines for example can be time consuming. Murphy is waiting and watching close for you during such.
If electric PTO needed, will the donor engine have correct charging system.

If you don't think about such at first, well you know the time/sweat /cost that can be involved and may have to throw in the towel later instead of sooner.

Thanks for all the guidance & input! Swap was made, mounting holes lined up perfectly except the new motor mounting holes were not tapped. Ace Hardware to the rescue with 4 new mounting bolts/nuts. All connections were compatible, and it started right up! Replaced the deck and main drive belts since they were badly worn, and oil soaked. Have posted a new thread concerning the drive operation- once forward pedal is pushed, the tractor will not stop until the brake is depressed. Same with reverse. Drive belt need tension adjustment?

link to new thread???

Answered my own problem with a few more days work scouring the internet. There was a small chip of wood ( and other debris) under the variator levers causing the primary pulley to not fully open. General Transmission has a wonderful website with lots of troubleshooting videos specific to the RS 800 transmission.