Replacement engine options for a 720K?

BrownCoat

Member
Joined
May 16, 2016
Threads
4
Messages
22
Hi, all. I'm working on my dads old 720K which has (I believe) a Kohler CH640. That engine is becoming more trouble than it's worth, so I was curious what different engines can swap in. Have any of you converted your 720 to a different engine?

Thanks
 

bertsmobile1

Lawn Royalty
Joined
Nov 29, 2014
Threads
64
Messages
24,647
If you want help form the forum you need to give us a ittle more to work with.
Now I will tank a wild stab and assume you are talking about a model 720 Grasshopper
Then again you could be talking about a 720 Kohler engine.

So start by telling us what engine you want to replace & why you want to replace it then you are likley to get some useful answers.
 

BrownCoat

Member
Joined
May 16, 2016
Threads
4
Messages
22
If you want help form the forum you need to give us a ittle more to work with.
Now I will tank a wild stab and assume you are talking about a model 720 Grasshopper
Then again you could be talking about a 720 Kohler engine.

So start by telling us what engine you want to replace & why you want to replace it then you are likley to get some useful answers.

I posted in the Grasshopper section so I thought it was clear, but I suppose not. It's a Grasshopper 720K with a Kohler Command 20 engine. I posted once before about it backing out the rocker studs and bending the pushrods etc.

This Kohler engine is just one thing after another. Every bolt I touch strips with almost no effort or breaks off even if I soak it in penetrating oil or apply heat. Now that I have new push rods and it actually starts its started gushing oil out of the breather. like, a whole lot. I've put a new filter in it, checked the reed, but honestly the amount of oil this thing spits so fast I can't see it being from the reed. It still has governor issues that I can't seem to solve no matter what I try.

That being said... I'm just wondering if a whole different engine might just be the way to go. I can throw parts and time at this thing but it just keeps fighting back. So, I was curious is anyone has found an engine replacement for the Grasshopper 720K, besides another Kohler.
 

BrownCoat

Member
Joined
May 16, 2016
Threads
4
Messages
22
I guess I should also mention that with the way the bolts all strip on this I'm a little hesitant to pull the heads off and see if there's a bad gasket. I would guess that the oil gushing is from tons of crank case pressure but I'm really not sure about pulling it apart without having a backup engine plan.
 

shiftsuper175607

Lawn Addict
Joined
Sep 11, 2013
Threads
10
Messages
1,000
I posted in the Grasshopper section so I thought it was clear, but I suppose not. It's a Grasshopper 720K with a Kohler Command 20 engine. I posted once before about it backing out the rocker studs and bending the pushrods etc.

This Kohler engine is just one thing after another. Every bolt I touch strips with almost no effort or breaks off even if I soak it in penetrating oil or apply heat. Now that I have new push rods and it actually starts its started gushing oil out of the breather. like, a whole lot. I've put a new filter in it, checked the reed, but honestly the amount of oil this thing spits so fast I can't see it being from the reed. It still has governor issues that I can't seem to solve no matter what I try.

That being said... I'm just wondering if a whole different engine might just be the way to go. I can throw parts and time at this thing but it just keeps fighting back. So, I was curious is anyone has found an engine replacement for the Grasshopper 720K, besides another Kohler.

http://www.smallenginewarehouse.com/Repower-Old-Equipment/Grass-Hopper-720K-Category/
 

Carscw

Lawn Pro
Joined
Aug 11, 2011
Threads
66
Messages
6,375
Man just find a engine you like and put it on there. Only thing to look at is the output shaft size. If the holes do not line up drill new ones.
Once you find a engine let us know. I can tell you how to wire it up.
 

BrownCoat

Member
Joined
May 16, 2016
Threads
4
Messages
22
Man just find a engine you like and put it on there. Only thing to look at is the output shaft size. If the holes do not line up drill new ones.
Once you find a engine let us know. I can tell you how to wire it up.

The tag is completely worn off on the side of the engine so I'm just going off the air cleaner sticker which says Command 20. The output shaft size is what I'm kinda foggy on and I've never bought a small engine like this so I'm pretty unfamiliar with what's good or bad. I mean, Harbor Freight has engines, but while I might buy a set of wrenches from them I'm not sure I'd trust an engine. Ya know.
 

bertsmobile1

Lawn Royalty
Joined
Nov 29, 2014
Threads
64
Messages
24,647
Look up the specs for your engine .
The only important things are the shaft size and the height from the base to the shaft.
You can pick any engine you like so troll through the lists and find one that is heavily discounted.
If all the threads on your motor are stripping out then the alloy has gone soft and that happens because it is getting too hot.
This is very common with Walkers where the engine sits in a confined space under the grass bin.
If your Hopper drives from the front then you are in luck as shaft size does not matter and your stud shaft will bolt onto any Kohler flywheel as the centres are common for just about every engine they have made in the past 30 years.
Remember that your old engine will be rated 10% bigger than new engines as the method of determining Hp has changed.
Engines with tapered or splined PTO shafts are usually really cheap as there is little demand for them.
Small engine Supplies
Small engine warehouse
The Surplus centre
I have bought engines from all of them with no problems , some discounted up to 75%.

If your hopper does have a flywheel PTO make sure you fit the blow out covers which your engine should have been fitted with.
If not buy a pair of them and cut the housing to fit them then most important, use them regularly to keep the cooling fins clean.
 

Carscw

Lawn Pro
Joined
Aug 11, 2011
Threads
66
Messages
6,375
I know you don't want to hear this but I like kohlor engines. I went threw 3 Kawasaki engines on a toro in less then 1000 hours. Went with a kohlor pro and after 500 hours put them on my other 3 mowers.
I have not liked Briggs since they stopped making the opposed twin.
 
Top