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I've transplanted a 21hp briggs and stratton from a craftsman ltx1000 to a craftsman gt5000 with a blown kohler 25HP with an electric pto.
Everything matched up pretty well, other than a couple of electrical connections and the shaft pully set up.
The briggs and stratton has a 1" shaft vs the kohlers 1.25" shaft. Also, the kohler had an electric clutch. The briggs did not.
Now I am trying to retrofit a clutch onto the briggs 1" shaft, making sure to match the pulley sizes from the kohler.
Obviously, I can't use the kohler setup on the briggs because of the different shaft size.
But I am having to match up pulley size and location on shaft to ensure proper operation.
My question is can I install an electric clutch on this engine that previously did not have one? Any tips or tricks would be much appreciated!

Well what the model number from the serial number tag of the GT5000? Need it to see which PTO was used to try meet the specs.

The problems will be as you stated the shaft size and the charging system. You can put a sleeve over the crank shaft to make for the correct shaft size. The charging system will need to be probably a 10 amp system. https://www.amazon.com/small-engine-crankshaft-adapter/s?k=small+engine+crankshaft+adapter

StarTech said:

Well what the model number from the serial number tag of the GT5000? Need it to see which PTO was used to try meet the specs.

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hlw49 said:

The problems will be as you stated the shaft size and the charging system. You can put a sleeve over the crank shaft to make for the correct shaft size. The charging system will need to be probably a 10 amp system. https://www.amazon.com/small-engine-crankshaft-adapter/s?k=small+engine+crankshaft+adapter

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I didn't even think of the charging system! Thanks man.
How do I determine the Amp output of the briggs?

StarTech said:

Well what the model number from the serial number tag of the GT5000? Need it to see which PTO was used to try meet the specs.

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I only know it's a gt5000. 2011.

Does the Briggs have a regulator on it and if so how many wires does it have? Does it bolt on with one bolt in the center of the regulator or two on the ends?

hlw49 said:

Does the Briggs have a regulator on it and if so how many wires does it have? Does it bolt on with one bolt in the center of the regulator or two on the ends?

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I don't see a regulator. Just a black and red wire coming from the altenator.

Well that pretty kills it using a PTO clutch until the charging system is upgraded. A 3 amp just doesn't cut it.

Personally trying to use 21 hp with a 48"or larger deck is really pushing it anyway.

It is a 3 amp charging system and not enough to keep battery charge and run electric clutch. You can change it by putting the stator for the 10 regulated system and the 10-16 amp regulator on it.

StarTech said:

Well that pretty kills it using a PTO clutch until the charging system is upgraded. A 3 amp just doesn't cut it.

Personally trying to use 21 hp with a 48"or larger deck is really pushing it anyway.

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Well, that pretty much kills the dream! Lol ohh well. Thanks for your input. Sounds like I'll have to rebuild that kohler and save this briggs for a different tractor.
Thanks again y'all

I remeber when you got a 42 inch cut with an 11 hp Briggs on it. Now you have to have a 18 or 20 hp engine. Over Kill

hlw49 said:

I remeber when you got a 42 inch cut with an 11 hp Briggs on it. Now you have to have a 18 or 20 hp engine. Over Kill

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Yes I remember one those 11hp OHV with 42" that came into my shop that would not even grass if it was slightly over grown. Since it was brand new I had my customer to return it for one that had a decent engine on it.

Now the old L head had a better engine that had lower hp ratings. The old 12.5hp L head would cut rings around the 16.5-19.5 OHV engines.

I personally have a 42" MTD that was a gutless wonder with a 16.5 hp OHV on it but now it has 21 hp OHV and walks through most grass I throw at it. I however had to upgrade the deck belt to a 5/8" one as the mower keep burning up the 1/2 belt.

What's a L-head?

StarTech said:

Well that pretty kills it using a PTO clutch until the charging system is upgraded. A 3 amp just doesn't cut it.

Personally trying to use 21 hp with a 48"or larger deck is really pushing it anyway.

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Upgrading the stator and installing a rectifier will fix the problem?

Slimbonic said:

What's a L-head?

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A L-head is a side valve engine. They are engines with the valves mounted in the cylinder block instead of the cylinder head. Another old term is flat heads.

Slimbonic said:

Upgrading the stator and installing a rectifier will fix the problem?

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It will fix the electrical problem but it will not fix the lack of hp. 48" and 54" decks simply require more start up hp. So replacing an engine you should always go with the same hp or slightly larger. Most OEM will put the smallest engine that works with decks and some will even under power them. On top of that Kohler are rated closer to the true hp than Briggs. Even than most are rated at gross hp and not net hp.

Just my opinion but I would find at least another 25 hp engine. The 21 hp might start up the deck but it is going to struggle mowing heavy grass with the 48"+ deck.

StarTech said:

A L-head is a side valve engine. They are engines with the valves mounted in the cylinder block instead of the cylinder head. Another old term is flat heads.

It will fix the electrical problem but it will not fix the lack of hp. 48" and 54" decks simply require more start up hp. So replacing an engine you should always go with the same hp or slightly larger. Most OEM will put the smallest engine that works with decks and some will even under power them. On top of that Kohler are rated closer to the true hp than Briggs. Even than most are rated at gross hp and not net hp.

Just my opinion but I would find at least another 25 hp engine. The 21 hp might start up the deck but it is going to struggle mowing heavy grass with the 48"+ deck.

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OK, thanks again for all your help. I really do appreciate it. Saving me money, too!
I may just try and rebuild the kohler. A broken push rod sent the ball end of it into the cylinder. It punished the head and valves after pinging around inside the cylinder before it completely stopped.
Not sure if there is any further damage (crank, rod, bearings, etc.).
Do y'all think it's worth rebuilding?
Hopefully it's just the head, piston and valves.
Or maybe just replacing the push rod, since the damage seems minimal to the piston and valves.
What are the chances of this motor surviving this catastrophe?
Again, it's a 25HP kohler pro.