Kohler Courage 22hp engine knocking.....

[bertsmobile1]

I have a 6 year old Cub with the 20hp Kohler Courage engine and at about 150 hours it developed a knock at lower speeds with no load, I tightened all of the mounting bolts and the noise still persisted until this last weekend....Half way thru my lawn mowing experience the noise got louder I shut it off checked to see that the oil was still full, no lights on, started mowing again, suddenly the noise got even louder. Before I could get it back to the garage it started losing power and oil was being sprayed everywhere. After it cooled down I did an autopsy only to find several bolts were loose on the top plate under the flywheel, the game changer came when i discovered a 4" crack from the area of the loose bolts down the exhaust side of the block and cylinder jug....It seems the most prudent repair was to order a new short block assembly for $400. plus a gasket set. I will let you know it it will live again to mow another day. Seems like a shame that if the top plate bolts coming loose at low hours would lead to this disaster that someone might notify the owners of the affected engines so it could be fixed before it is too late...

That is what we call the Kohler Krack and is very common.
Usually happens to owners who mow large areas regularly so the engine runs for long spells at a constant speed.
IMHO it is because the Courage is a downgraded version of the Command and has a much larger & heavier cast malleable iron crank comparred to the Commands lighter, thinner & stronger forged crank.
The crank can represent up to 1/2 the entire cost of making an engine and casting is the cheapest form of shaping metal, thus the cast crank.
I get 1 some times 2 a season and have had some success with drilling the root and using an epoxy filler like JB weld or Devcon, about 4 in 5 seem to be happy like this.
Check the counter weight very carefully as the crack is oft associated with a broken or loose bolt that holds the counter weight halves together,
If you are mechanically minded, a short block will be a better fix.
You can also get the cases welded.
Gas welding seems to work a lot better than arc welding.
I charge $ 200 ( AUS) to weld one as I can usually do it in situ without dissmanteling the engine.
Bogging is a $ 100 fix with no guarantee as there is a bit over an hour in it by the time I have checked the internals, bogged the crack & replaced the gasket.
If you take it to a welding shop they will need the bare case & top plate, should come to $ 40 to $ 100.

OTOH places like Small Engine Warehouse , Small Engine Supplies, Repower etc ( find them on the links section ) usually can do an equivalent engine for $ 400 to $ 600 .
Then you can either break down your old mower for parts, or keep some spares.
A piston, rod, alterantor, flywheel , rectifier, coil, starter & carb sold as parts can come to way more than an entire new engine.

 

[bertsmobile1]

After my first year & replacing 6 Kohlers I now check those top cover bolts as part of the routine service of customers mowers, supprising how many are loose a the cylinder base.

 

[dsanders]

Well last weekend I replaced my knocking problem with a new short block for about $400. plus gaskets. When I originally posted I said the engine had 150 hours on it, I read it wrong it was only 105 hours and had been knocking for some time. When I did the autopsy on it several of the top cover bolts had worked their way loose and one had backed out far enough to be hit by the flywheel and snapped off the threads in the block along with the catastrophic 4" crack down the case on the exhaust side of the cylinder jug. It runs fine now you can bet I will check the bolt torque after running for 20 hours or so. I did locktite all of the cover bolts and check all of the torque specs in the new engine (several were too loose or too tight). Lets see if I can get another 105 hours out of this one before it too needs a major tune up....

 

[bertsmobile1]

After you have 20 or so hours on it , recheck those top cover bolts.
If you locktite them it must be the high temp ( red ) locktite

 

[shootr56]

Would like to add some info on tightening engine mounting bolts for low rpm knocking. Bought a nice used Troy Bilt Bronco with the Kohler courage 18HP engine. It exhibited a loud knocking at idle, but was fine at full throttle. Ran across this older posting about tightening the engine mounting bolts. I had previously visually inspected same, and they looked and felt tight, with no visible witness marks on frame showing any bolt movement. The first bolt I retorqued did not budge. the rest moved about 7 to 10 degrees, with one a good bit more. After this, restarted engine and NO KNOCK! I was thrilled that this did the trick, so thanks to you guys for the tip! So even if they look and feel fine, try tightening them a bit more, and it may just do the trick.

 

[semimechanicman]

I will check them this weekend, it would be great if that's all that's wrong with it!! Will let you know what I find. Thanks.
Keith

had the same exact problem with the same exact engine. it didn’t knock when you turned it was running but when you started it it turned it off, it knocked but the bolts where slightly loose. so i tightened them and boom.

 

[EatPreyMow]

Most of the single cylinder Courage engine failures can be traced back to loose engine cover bolts. After the bolts loosen, the case cover and its bearings for the crank and cams lose stability and thus proper alignment of the internals is lost. At this point the case often cracks or the balancer will grenade.

I got lucky and caught my bolts loosening at low hours. After I applied threadlocker and torqued them down the engine has been a workhorse for over a decade.