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I've got several "F" engine lawnboy mowers, some say 4 hp, I have one that says 5 hp. Looking up parts on the Toro/Lawnboy site, the piston, rings, con-rod all appear the same part numbers. How did they get different horsepowers?

Phototone said:

I've got several "F" engine lawnboy mowers, some say 4 hp, I have one that says 5 hp. Looking up parts on the Toro/Lawnboy site, the piston, rings, con-rod all appear the same part numbers. How did they get different horsepowers?

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Are all of the carburetors the same?

Phototone said:

I've got several "F" engine lawnboy mowers, some say 4 hp, I have one that says 5 hp. Looking up parts on the Toro/Lawnboy site, the piston, rings, con-rod all appear the same part numbers. How did they get different horsepowers?

Click to expand...

All about the carburetor. The walbro with choke only were all 4.5 hp. later plastic modular with the primer on the carburetor was 5 hp. the early non compliant with the primer in the shroud plastic carburetor were 4 hp. All are the exact same as far as parts. The only difference in parts is you will see an M with a circle on outboard marine corp. LB with a box was Toro/Lawnboy after the toro takeover. all the same parts.

So, if I need to replace piston and con-rod, I can use generic "F" engine parts, regardless of the horsepower rating printed on the shroud. The horsepower rating was only achieved by different carbs?

if the part numbers are the same its going to work. I personally dont know because the engines i have been in have been complete and just needed to be cleaned and resealed. Like i said though i think all the parts are the same from 1978-1997. Some of the earlier model motors i have been in had a few different looking parts but nothing looked like you could not use it on another motor without problems. I personally think you will be ok as long as the parts are new.

Phototone said:

So, if I need to replace piston and con-rod, I can use generic "F" engine parts, regardless of the horsepower rating printed on the shroud. The horsepower rating was only achieved by different carbs?

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The only concern I'd have is quality and I haven't heard a single horror story about non-OEM parts on these mowers.

Two-Stroke said:

The only concern I'd have is quality and I haven't heard a single horror story about non-OEM parts on these mowers.

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Well, outside of new rings and gaskets, I was more thinking about taking salvage off an older "F" engine to rebuild the "F" engine on a newer, more delux mower. For example, the connecting rod.

Phototone said:

Well, outside of new rings and gaskets, I was more thinking about taking salvage off an older "F" engine to rebuild the "F" engine on a newer, more delux mower. For example, the connecting rod.

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That shouldn't be a problem.

turfboy1997 said:

All about the carburetor. The walbro with choke only were all 4.5 hp. later plastic modular with the primer on the carburetor was 5 hp. the early non compliant with the primer in the shroud plastic carburetor were 4 hp. All are the exact same as far as parts. The only difference in parts is you will see an M with a circle on outboard marine corp. LB with a box was Toro/Lawnboy after the toro takeover. all the same parts.

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When you change the carb you have to use the crankcase assy that goes with that carb.