Doc Sprocket
*********
Well... That was interesting.
The first time the governor failed on the crappy little 4hp Kohler clone powering the Kids' Kart was a matter of the governor gear shaft coming out of it's press-fit in the engine's side cover. It manifested itself by the engine idling waaay too fast, runaway-kart style. Not yet ready for the kids to run ungoverned, I epoxied the shaft back into place and all was well... For awhile.
A few riding hours later, the engine refused to idle again, and again, I noticed a bit of oil drooling out of that hole. Under my supervision, Garry tore the engine down this time. What I found was both revealing and scary. The governor had effectively detonated. There were two cracks in the plastic governor gear, which was sitting way out of place on the shaft. The pins that retain the flyweights were sitting in the bottom of the crankcase. So were the flyweights, and the button, too! Closer inspection revealed that the oil slinger was bent, and had scored the inside of the crankcase in one place! One flyweight was bent like a taco, so I think that's what hit the slinger. I tried to bend back the end of the slinger, and the last 1/4" broke off. No big deal, it's a very large slinger and there's still a lot of area left to it. I had a good, long look at the internals and it would appear that damage was minimal. Freaky- it's just a roll of the dice that all those parts were flying around the 'case and yet we avoided catastrophic engine failure! Whew!
So, a couple thoughts to go along with it all... First and foremost, this goes well in hand with what I have suggested for some time. Running well above 3600 with the governor intact is a risky proposition. I had long since removed the governor limit screw and we were running probably 4200-4300RPM. More than once, I had tweaked the throttle mechanisms to allow a few hundred more RPM. This included bending the metal tab that the limit screw sits in, to allow more arm travel, and altering spring tensions and strokes to push it further still.
In the end, it forced me to take my own advice and surgically remove the governor. Garry, my 12-year-old son (toystory2 on these forums) did the work himself, and I am very proud of his first engine work.
I regeared the kart from the original 12:1 to 7.5:1 to increase not only top speed, but the load on the engine for running safely ungoverned. The gearing worked out well. I clocked myself out at an average of 52Km/h@5450RPM (33MPH). Acceleration is decent, and the valves are not fluttering at full bore. For comparative purposes, bear in mind the kart weighs about 200lbs without rider, has 4hp, and 15" rear tires. And although it didn't add much, I also installed my homebrew Cherry Bomb muffler on it.
So once again, I caution DIY'ers against running too fast with the governor guts intact...
The first time the governor failed on the crappy little 4hp Kohler clone powering the Kids' Kart was a matter of the governor gear shaft coming out of it's press-fit in the engine's side cover. It manifested itself by the engine idling waaay too fast, runaway-kart style. Not yet ready for the kids to run ungoverned, I epoxied the shaft back into place and all was well... For awhile.
A few riding hours later, the engine refused to idle again, and again, I noticed a bit of oil drooling out of that hole. Under my supervision, Garry tore the engine down this time. What I found was both revealing and scary. The governor had effectively detonated. There were two cracks in the plastic governor gear, which was sitting way out of place on the shaft. The pins that retain the flyweights were sitting in the bottom of the crankcase. So were the flyweights, and the button, too! Closer inspection revealed that the oil slinger was bent, and had scored the inside of the crankcase in one place! One flyweight was bent like a taco, so I think that's what hit the slinger. I tried to bend back the end of the slinger, and the last 1/4" broke off. No big deal, it's a very large slinger and there's still a lot of area left to it. I had a good, long look at the internals and it would appear that damage was minimal. Freaky- it's just a roll of the dice that all those parts were flying around the 'case and yet we avoided catastrophic engine failure! Whew!
So, a couple thoughts to go along with it all... First and foremost, this goes well in hand with what I have suggested for some time. Running well above 3600 with the governor intact is a risky proposition. I had long since removed the governor limit screw and we were running probably 4200-4300RPM. More than once, I had tweaked the throttle mechanisms to allow a few hundred more RPM. This included bending the metal tab that the limit screw sits in, to allow more arm travel, and altering spring tensions and strokes to push it further still.
In the end, it forced me to take my own advice and surgically remove the governor. Garry, my 12-year-old son (toystory2 on these forums) did the work himself, and I am very proud of his first engine work.
I regeared the kart from the original 12:1 to 7.5:1 to increase not only top speed, but the load on the engine for running safely ungoverned. The gearing worked out well. I clocked myself out at an average of 52Km/h@5450RPM (33MPH). Acceleration is decent, and the valves are not fluttering at full bore. For comparative purposes, bear in mind the kart weighs about 200lbs without rider, has 4hp, and 15" rear tires. And although it didn't add much, I also installed my homebrew Cherry Bomb muffler on it.
So once again, I caution DIY'ers against running too fast with the governor guts intact...
