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I have a 2004 Murray 40" cut mower (405000x8E model) i'm doing a engine swap on and had a question about compatibility

The engine i'm Replacing is a 13.5 hp briggs I/C Model: 21B807 Type: 0239E1 Code 040913ZA
The new engine is a 17.5 hp Briggs Powerbuilt Model: 31C707 Type:3346G1 Code: 100923D

Edit: new motor is from a poulan 42" cut model po17542lt

what question?

make sure it bolts to the frame well. and also use the stock pulley sized for your drive best and your deck drive belt.

There are a few problems you might run into, but none of them are really that bad. If the mounting holes don't match up, you can always drill new ones, just make sure to get the shaft in the same location as the original motor. If the wiring is different, making mods to the harness to connect to the new engine is a simple task, just make note what each wire does on the old motor and find the corresponding wire/connection on the new one. The throttle/choke cable/s may not work with the new motor, but longer/shorter replacement cables are relatively cheap. The gas line may have to be lengthened or shortened. There are only three issues I see that could cause some head scratching and/or having to buy new parts. If the shaft diameter is the same on both motors, then your golden. However, if they are different, then you'll have to get a new pulley set for the new motor. The muffler on the new motor may not work with the old mower frame and hood. I don't know if you have the screw in muffler that is above the frame or the under frame style muffler, but you may have to buy a new muffler or improvise. And lastly that new motor may not fit under the hood of your mower.

First check to make sure the shaft diameters are the same, and if not, can you get a replacement pulley set of the correct shaft size and pulley diameters. Then try to test fit the new motor on the frame by just setting it in the correct position and see if the hood will close. Next look at the muffler location and see if it will work with the hood closed. Once you get those three issues worked out, you're well on your way to getting that new motor installed.

Thanks for the help and input. Luckily the shaft diameter is the same for both motors, so i'm good there. Mounting dose not seem like it'll be a problem the sumps look the same and have the same part number and bolt pattern. The throttle cable dose not look like it'll be a problem, the placement looks same on both motors. I might need a longer or shorter cable though, but that I won't know until i'm on the home stretch. Not really worried about wiring there are 4 wires 2 go to the stator the other two are for the afterfire solenoid. If need be I can modify.

mullins87 said:

There are only three issues I see that could cause some head scratching and/or having to buy new parts. If the shaft diameter is the same on both motors, then your golden. However, if they are different, then you'll have to get a new pulley set for the new motor. The muffler on the new motor may not work with the old mower frame and hood. I don't know if you have the screw in muffler that is above the frame or the under frame style muffler, but you may have to buy a new muffler or improvise. And lastly that new motor may not fit under the hood of your mower.

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The only two minor problems that I might run into. One being the exhaust and the other hood fitment. The muffler that is on my 13.5hp motor is the round bolt through type, whereas the new one is a between the frame rails. I'll probably end up using the between the frame rail muffler unless the other one has the same exhaust port size\pattern. The 17.5hp engine is a little longer so I'm going to try and fabricate a extension (or spacer) for the hood hinge. Height and width are fine.

I'll keep yall posted, i'm probably going to start next weekend tearing down and taking ALOT of pictures of progress.

Well I did not make as much progress as I had hoped, but I did get my hood bracket fabricated & mocked up. Hopefully this weekend if the weather is good I can get the donor cleaned up and ready for teardown.

The donor





Old engine



New Engine



Hood bracket

richey88 said:

Well I did not make as much progress as I had hoped, but I did get my hood bracket fabricated & mocked up. Hopefully this weekend if the weather is good I can get the donor cleaned up and ready for teardown.

The donor

<img src="http://www.lawnmowerforum.com/attachment.php?attachmentid=19146"/>

<img src="http://www.lawnmowerforum.com/attachment.php?attachmentid=19147"/>

Old engine

<img src="http://www.lawnmowerforum.com/attachment.php?attachmentid=19148"/>

New Engine

<img src="http://www.lawnmowerforum.com/attachment.php?attachmentid=19149"/>

Hood bracket

<img src="http://www.lawnmowerforum.com/attachment.php?attachmentid=19150"/>

<img src="http://www.lawnmowerforum.com/attachment.php?attachmentid=19151"/>

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Going to use the old engines shroud? It's prettier

exotion said:

Going to use the old engines shroud? It's prettier

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Not sure I can the 17.5 hp engine is longer.

richey88 said:

Not sure I can the 17.5 hp engine is longer.

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Lame lol

I got both mowers cleaned up today and both engines degreased and ready for teardown. I also did a tune up on the 17.5 engine, and she runs great. I'm hoping this weekend I can get the swap done. I have all week off but i'll be watching the little one.





My murray

Well I am new to the site/forum as of today and saw this post. I am not sure where you got with the project but the one thing I don't see mentioned it the possible swap of the wiring harness. I was going to attempt a similar repair to an old Murray I had but decided against it when I discovered that the original ignition switch on the Murray did not have a 12V switched source to use to power the solenoid. I am not sure if this is the same in your case but hope you were able to complete the project.

whitejww said:

Well I am new to the site/forum as of today and saw this post. I am not sure where you got with the project but the one thing I don't see mentioned it the possible swap of the wiring harness. I was going to attempt a similar repair to an old Murray I had but decided against it when I discovered that the original ignition switch on the Murray did not have a 12V switched source to use to power the solenoid. I am not sure if this is the same in your case but hope you were able to complete the project.

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I did manage to get the swap completed with one minor complication. The wiring was not a problem, it was as easy as plug and play. The only item that I had to swap over was the throttle cable from the donor. Other than that everything was easy. I was actually surprised the exhaust worked out. I thought I was going to have to do some modifications, but it bolted on and fit between my hood brackets perfectly. If the weather permits tomorrow i'm going to try and take some pictures, and get em' posted on here.

Pictures of the finished product. I cant wait till mowin' season starts back!

richey88 said:

Pictures of the finished product. I cant wait till mowin' season starts back!

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Nice I wouldnt be able to stop my self from playing with those leaves see how the engine holds