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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

Anyone?

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.

bertsmobile1 said:

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.

Click to expand...

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.

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.

BrownCoat said:

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.

Click to expand...

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

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.

Carscw said:

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.

Click to expand...

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.

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.

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.

bertsmobile1 said:

Look up the specs for your engine .
The only important things are the shaft size and the height from the base to the shaft.....
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.

Click to expand...

Gotcha. Ok, I'll check into that and what those places have to offer. I'm not sure what the "blow out covers" are. Mine has shrouds around the heads but I had to practically take the whole engine apart to get those off and clean the fins.
Thanks for your help.

Carscw said:

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.

Click to expand...

I don't have anything against them, really. I'm a little miffed at how much you have to disassemble to get simple stuff off and some funky component placement issues. My main problem with them at the moment is the cost to replace one. I just don't have $1500+ to drop on a 20+ yo mower that still needs work in other areas. Still though, my dad replaced it with a Hustler and we all hate that thing. We'd much rather have the Grasshopper rolling again.

Thanks for the help. I'll take some measurements as soon as I can and see what's available. I was hoping that someone would say "oh yeah. this one and that one are direct replacements"

part number 34 in the diagram below.
http://www.jackssmallengines.com/jacks-parts-lookup/manufacturer/kohler-engine/command-pro-twin-ch-cv17-25-ch-cv620-750/ch18/ch18-62653-walker-mfg-18-hp-13-4-kw/blower-housing-group-6-24-262-ch18-750

They go over holes cut in the blower housing ( not shown ) in front of the cylinder heads .
You can remove them then blow out the debris around the cooling fins without removing the whole cover which for front PTO fittings is near impossible to do so never gets done.
When ever I get a horizontal shaft , flywheel PTO engine in for service I fit a pair of them.
You would not believe what I find under the covers, dead reptiles, rhodents, bird- rat- mouse nests, grass, clay etc etc etc.
Engine can not cool properly whith all that crud in there so it overheats, alloy gets soft, threads start pulling, valve guides shift in the head etc,etc,etc.

These guys on this forum gives very good info. If I had to grade them I would put bertsmobile1 at the top. It would be hard to pick second as there are several who are extra good. I've owned a lot of different mower engines. Kohler is my favorite. I have a 26HP sv735 Kohler with 1775 hrs. that still runs very good.

brother has the Kohler on his CubCadet.less than 30hrs on the motor and it has a cracked block.he did use JB weld and so far it's held...russ

bertsmobile1 said:

part number 34 in the diagram below.
http://www.jackssmallengines.com/jacks-parts-lookup/manufacturer/kohler-engine/command-pro-twin-ch-cv17-25-ch-cv620-750/ch18/ch18-62653-walker-mfg-18-hp-13-4-kw/blower-housing-group-6-24-262-ch18-750

They go over holes cut in the blower housing ( not shown ) in front of the cylinder heads .
You can remove them then blow out the debris around the cooling fins without removing the whole cover which for front PTO fittings is near impossible to do so never gets done.
When ever I get a horizontal shaft , flywheel PTO engine in for service I fit a pair of them.
You would not believe what I find under the covers, dead reptiles, rhodents, bird- rat- mouse nests, grass, clay etc etc etc.
Engine can not cool properly whith all that crud in there so it overheats, alloy gets soft, threads start pulling, valve guides shift in the head etc,etc,etc.

Click to expand...

Oh, ok. I see. That's what I think happened to this. When I finally got the covers off there was some packed in grass and oil which was blocking some flow. I'd say maybe 20% flow blockage. It still overheated though. Now it's like you said... all the metal is soft and useless and everything is stripping. Oh well. What can ya do. I'll have to pull the clutch off and measure that shaft and see if I can find an engine to match like you said to. I guess it's a crap shoot with these engines from what I'm reading. I'm not partial to any particular brand. I just need to get it mowing again. FYI - those Hustlers ride insanely rough unless your yard is glassy smooth. It's intolerable for someone like myself with lower disc problems.

cambre said:

These guys on this forum gives very good info. If I had to grade them I would put bertsmobile1 at the top. It would be hard to pick second as there are several who are extra good. I've owned a lot of different mower engines. Kohler is my favorite. I have a 26HP sv735 Kohler with 1775 hrs. that still runs very good.

Click to expand...

173abn said:

brother has the Kohler on his CubCadet.less than 30hrs on the motor and it has a cracked block.he did use JB weld and so far it's held...russ

Click to expand...

Extremely helpful people here. I'm used to motorcycle forums where everyone bickers and fights. Way nicer here

I guess you either get a good one or a bad one. I wonder if different engines are made in different plants or locations. Maybe that has something to do with the inconsistencies.

BrownCoat said:

Oh, ok. I see. That's what I think happened to this. When I finally got the covers off there was some packed in grass and oil which was blocking some flow. I'd say maybe 20% flow blockage. It still overheated though. Now it's like you said... all the metal is soft and useless and everything is stripping. Oh well. What can ya do. I'll have to pull the clutch off and measure that shaft and see if I can find an engine to match like you said to. I guess it's a crap shoot with these engines from what I'm reading. I'm not partial to any particular brand. I just need to get it mowing again. FYI - those Hustlers ride insanely rough unless your yard is glassy smooth. It's intolerable for someone like myself with lower disc problems.

Click to expand...

It will either be a 1" or 1 & 1/8" and most likely the former.
Your only real problem will be the PTO height.
If you don't mind a bit of metal work you can get superceeded Briggs around that size for around $ 800 with a warranty .
Kohlers go about 20% more
Add another 20% for Kwaka and
Add 10% for a Vanguard

The biggest headache from changinf brands is finding a muffler to fit or modifing the existing one to fit.
These are specific to a particular mower and in many cases the only difference from one spec to another

173abn said:

brother has the Kohler on his CubCadet.less than 30hrs on the motor and it has a cracked block.he did use JB weld and so far it's held...russ

Click to expand...

Must be a Kohler Courage

NorthBama...spot on.Don't know why they named them courage.where's the courage if you can only do 30hrs...russ

Go to smallenginewarehouse.com, click on repower old equipment, click on Grasshopper, click on Grasshopper 720K to see their recommendations for repower.

173abn said:

NorthBama...spot on.Don't know why they named them courage.where's the courage if you can only do 30hrs...russ

Click to expand...

Have seen two one was on a nice Husqvarna machine with 60 hours

bertsmobile1 said:

It will either be a 1" or 1 & 1/8" and most likely the former.
Your only real problem will be the PTO height.
If you don't mind a bit of metal work you can get superceeded Briggs around that size for around $ 800 with a warranty .
Kohlers go about 20% more
Add another 20% for Kwaka and
Add 10% for a Vanguard

The biggest headache from changinf brands is finding a muffler to fit or modifing the existing one to fit.
These are specific to a particular mower and in many cases the only difference from one spec to another

Click to expand...

Since your mower is a 20yr old 720K it's a Command, not a Courage & it probably has the 1-1/8" diameter shaft x 3-11/16" long. The internal thread holding the PTO on is probably 7/16", but if it's 3/8" just change the bolt. Get another Command engine in the HP of your choice up through 27hp, all your accessories will exchange as long as the replacement engine has the same style air filter.
I just replaced a '95 718K engine w/1700hrs that was doing about the same as yours(leaking oil, running hot) with a rebuilt 2000 725cc 25hp Kohler with the flat air filter and an oil cooler from this guy http://wichita.craigslist.org/grd/5741213718.html for $800 plus the cost of the trip to pick it up.
It was a direct bolt-in, used my old muffler & heat guards, everything else came with the new engine since it was an actual Grasshopper engine. Contact the guy, he will ship, it's about a half price alternative to a new engine.

Browncoat, I am curious. What did you do/decide on?