Help with engine and clutch

[Matthijs]

Some pictures of the clutch



The springs and clutch lining inside


Just for fun, picture of the go karts. As you can see we've got some thick rubber mats (behind the bug) made to look like kerbs to make cool tracks!


The PTO shaft. It's 5cm or about 2" long


The PTO is long enough to cover both bearings.
The springs indeed engage at around 900rpm
The engine is mounted on slots so it's easy to put tension on the belt

The clutchpulley diameter is around 75mm or 3"
The driven pulley diameter is around 180mm or 7"
The wheels are 300mm in diameter or 12"

Tonight was very frustrating. I had some trouble getting the go kart (let's say go kart A) I'm testing on to run properly. First I couldn't get it to start because the engine got flooded so I had to wait for it to dry. So I went to work on go kart B. I replaced the clutch with one I put new bearings in. I took the clutch lining and springs from go kart A to rule out other variables. With the tachometer I could get it to idle easily at around 750 rpm on the PTO. However it won't accelerate. The clutch was just making a bunch of noise (high tone). I checked if it was the belt slipping, it wasn't. I tried taking it for a little drive but the clutch started smoking after 20 seconds of running so I set this go kart aside to cool down.
After a while of working on other stuff I tried starting go kart A again and got it working. However it doesn't run great. The only way to start it is to increase the idle with the idle screw and then screw it back once it runs. I can get it to idle at around 900rpm but it runs irregularly, it surges at random moments to 2k rpm and then back after a while. So I think I have to do some work on this engine.

Anyway, with the rpm now in the 900rpm range I swapped out the springs for stronger ones and took it for a drive. After a few seconds of drivingit felt like the clutch was stuck and yup. The clutch lining was pulled between the weights and the drum and the springs are gone.

Here on the left you can see the broken clutch lining and spring. On the right is a normal one for comparison


I bent the sides of the clutch linings tighter so they wrap around the weights better
I wanted to try and put in some even stronger springs but I couldn't get the go kart to start again so I gave up. It's late anyway..

 

[Matthijs]

Thanks alot for helping out by the way!

 

[JimD]

I am amazed the inner weight with the pressure it is putting on the shoe to the drum can still advance and rip the shoe apart while it is locked up. Is the weight on the inside of the clutch metal on some other type of material? Back in the 60's and the 70's we use to use a mastic to hold the clutch material onto the steel stamping and then we would put in two rivets per shoe. You have nothing to lose. I think i would try and use two counter sunk flat head screws to hold the shoe to the weights so it cannot destroy the end of the shoe when it slips past and wrecks the springs. It is worth a try and I would contact the German company and verify what spring color you should be using for an 800 to 900 engagement and how many springs. The clutch is getting too hot to quick so the springs you are using have to be the wrong color or you need to use more springs per shoe. Some how the combination you are using is wrong which you have proven by the temperature the clutch is getting to so quickly.

Another company that makes a metric clutch in a pulley like you are using is Lehane Engineering out on Australia. You can contact them and find out the cost of the clutch but let them know the 800 to 900 engagement you need. Their clutch is heavy duty but the shipping will be a killer since the do weight a lot.

 

[Matthijs]

Hey Jim,
The weights are solid steel. I'll weigh them when I get the chance. Bolting the shoes to the weights is a great idea. I'll give that a shot.

The weird thing is though, the same combination works way better on kart A. on kart B it overheats after just 20 seconds of driving.

Next time I'm going to rough up both the drum and clutch surfaces and give them another good clean.

Buying another clutch is not really an option because I'd have to do it for all 9 go karts. I am thinking about maybe getting some new pulleys for the axle to increase the ratio. Right now it's 1:2,3 or, with the 1:2 reduction in the engine, 1:4,6
If I swap out the 7" pulley for a 9" I'd get a 1:6 reduction so the clutch would have to deliver so much torque and would, hopefully, slip less. Would that work? The top speed is pretty good and a lot of fun but I think it's too high for small tracks anyway.

I would have to change the frame a bit to accomodate a 9" pulley but that's alright.

 

[JimD]

If you are willing to toss the old stuff's I would switch to a 10 tooth sprocket for #420 or #41 chain which is roller chain in a half inch pitch. Don't switch to #428 chain because then you have to find the correct sprockets to match up to that chain. Give me the axle OD and I will look into getting you a quote on a sprocket carrier to match up. You could get by with a sprocket on the axle with less than 60 teeth since you already have the 2:1 gear reduction. You put a picture on showing 5cm length of the PTO shaft. This is just a little shy of 2" which I need to put pressure on the crankshaft NOT on the clutch. What is the keyway width? I could make you up what I think would be the perfect clutch but you would have to switch to chain. Also give me the bolt dimensions you are using so the spacer I make you would be long enough and the correct size hole in it. When is your next trip to the states? So you could all nine in your suit case and make the trip worth while.

 

[JimD]

When you put the clutch on the jackshaft when you tighten down the bolt holding on the clutch, the pressure should be on the PTO shaft NOT on the clutch. Make sure you at a little free play on the clutch so it has the ability to more in and out at least 1mm. Put some shims or a spacer in the clutch bore to achieve this. Trying to figure out why it destroys the shoes the way it did. All clutches have to float on the crankshaft to help self align with the rear sprocket or pulley which never run true, thus the float to correct this.

 

[pearl111]

Matthijs sorry I can't help you on your project, but the picture of all those go karts, look so cool. I guess if you get them all running together it looks like a mini nascar race.

 

[Matthijs]

Hey guys. Did some testing again. I turned down the clutch drum of kart B a few tenths to get the surface flat agian. This did work a bit but the karts are still not accelerating enough. So I've decided to go ahead and try a new clutch with a sprocket on it. Then run it with a 1:4 reduction so it's top speed is around 30km/h or 18.6mph which, I think, is sufficient for small tracks. I'd rather have the clutch engaged most of the time than have it slipping everytime you need to accelerate.

Reason I'm going with this solution is because I can't fit a big enough pulley on the rear axle. Since the original clutches are pretty expensive I hope I can break even by selling them.

Jim, I've never been to the states. I'd really love to go one day but I just don't have the money for it unfortunately. Thanks for the offer though, I appreciate it.

I'm thinking of just buying a cheap clutch with a z10 #40 sprocket off amazon. I think we have 08B-1 chain at work which I believe is that size. We've got a lasercutter at work so I'll cut some platewheels with either 41 or 37 teeth. We can do 3mm max so I might just get two and bolt them together.

Only thing I'm wondering is if the clutch will engage or not, with my engines having the internal 1:2 reduction. Might have to mess around with springs again...

Edit: read the chain size wrong. It's not 08B-1

 

[JimD]

Most of the clutches on Amazon use the #41 chain sprocket which is fine. The problem you will have with all of them is the engagement will be way higher than you want. You want the clutch to come in around 900rpm. Watch out for the chain size you buy. The #428 chain will NOT work on most of the clutches offered on Amazon because the rollers on the chain will prevent the chain from going all the way down into the valley of the sprocket. You want to get a 10 tooth sprocket. Let me know the clearance you have from the axle to the ground so I can tell you what size rear sprocket you should shoot for. Try and keep the thickness of the two plates as close to .227, if you get above that then you would have to use the #40 chain.

Not many people know how to laser cut their own sprockets, we hob all of ours but we don't make any flat rear sprockets to start with.

 

[Matthijs]

To lower the engagement, can I just put a bit of steel or copper wire between the two ends of the spring to make it a bit longer?
I was thinking of getting the 420 chain, what do you think?

The rear wheels are 12" in diameter so I the clearance is 6".

I can laser 1, 1.5, 2 and 3mm plate so I can do 2x2+1.5 = 5.5 which is almost .227
Otherwise I can do 2x3mm for the #40 chain.

The axles already have a little hub on it where the pulley is mounted so I can just laser in a few holes in the right place and use the hubs. I've lasered many sprockets (I'm a mechanical engineer and at work we use many plate sprockets) so that won't be a problem

 

[JimD]

The wire would not work. There is a single garter spring in the clutch which puts tension on the shoes when it is put into the grove to keep the shoes for touching the drum. If you extend the spring then the shoes will be rubbing against the drum and in less than a minute you would be able to cook your dinner on the clutch drum. The heat would be tremendous. The spring strength must be correct to start with-- our spring is 9.100" plus or minus one loop of the spring. The spring wire thickness and the tension of the wrap is what gives the spring the strength to determine the various engagements. The other variable for engagement is the weight of the shoes which in our case we offer two styles, standard shoe 46 grams and the wedge shoe at 62 grams. To fine tune we can mix the shoes BUT it has to be done evenly (balanced).

 

[Matthijs]

Might be worth trying to bolt a sprocket to the current clutches. Can't find any 900 rpm springs :/

 

[JimD]

The space between the shoe assembly and the pulley groove, is the a ball bearing in there or a bushing? Also how big a diameter is the bell holding the shoe assembly?