4 stroke clutch HS tapered shaft burning

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userix

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I have the skyhawk grubee 4G engine kit that came with the HS 142-f tapered shaft engine. The first clutch somehow got completely worn to the point I was riding metal to metal on the way back home. This is only after 50miles so far. I got a replacement clutch and notice it has already started slipping. I will open up the transmission tomorrow to see what it looks like inside, but I have a feeling the clutch is burned. I do notice that with the original clutch, the tire spins at idle when I pick up the rear of the bike. The cable and throttle trim are adjusted correctly so that the throttle goes all the way back to idle position.

As for the tapered shaft on my engine, how do I know I have put the clutch far enough on the shaft so it doesn't slip between clutch and shaft? I know the tapered shaft isn't keyed and work strictly by press fit friction. When installing the new clutch pack, I just used a deep socket and dead blow hammer to drive it back on the shaft. But I have no clue if I have driven it in far enough or tight enough so that it is not slipping. I did notice toward the end of my ride today with the new clutch, climbing up the hill towards my house, the speed dropped and the engine started revving higher gradually, a sure sign that something is slipping. Now I wonder if there is any possibility that the clutch is slipping on the shaft? Would there be a way to tell?
 
scotto-

scotto-

Custom 4-Stroke Bike Builder
Jun 3, 2010
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userix said:
I have the skyhawk grubee 4G engine kit that came with the HS 142-f tapered shaft engine. The first clutch somehow got completely worn to the point I was riding metal to metal on the way back home. This is only after 50miles so far. I got a replacement clutch and notice it has already started slipping. I will open up the transmission tomorrow to see what it looks like inside, but I have a feeling the clutch is burned. I do notice that with the original clutch, the tire spins at idle when I pick up the rear of the bike. The cable and throttle trim are adjusted correctly so that the throttle goes all the way back to idle position.

As for the tapered shaft on my engine, how do I know I have put the clutch far enough on the shaft so it doesn't slip between clutch and shaft? I know the tapered shaft isn't keyed and work strictly by press fit friction. When installing the new clutch pack, I just used a deep socket and dead blow hammer to drive it back on the shaft. But I have no clue if I have driven it in far enough or tight enough so that it is not slipping. I did notice toward the end of my ride today with the new clutch, climbing up the hill towards my house, the speed dropped and the engine started revving higher gradually, a sure sign that something is slipping. Now I wonder if there is any possibility that the clutch is slipping on the shaft? Would there be a way to tell?
Click to expand...
It's quite easy to tell.....just pull the tranny off and look. I just pulled my original clutch off today. The thing looks almost new and it has 9,000 miles on it. There wasn't an excessive amount of clutch dust either.....I can't believe how well this clutch has held up. I did have to use a puller to get it off of course, it was really on there tight as usuall.

I think it would be pretty hard to get the clutch to spin on the tapered shaft, but it is possible I suppose.

Here are a couple pics:









 
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userix

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Thanks for the pics. Ok, my pads are completely worn away to bare metal and I barely rode 50 miles on it. How does it wear out this fast? I initially had a 44T sprocket for the first clutch.
 
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The_Aleman

The_Aleman

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Jul 31, 2008
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You have a 4:1 4G (80T rear pulley), right? And what output sprocket? 26" wheel?

To begin with, a 44T is way too small for almost any 4G, especially on a 26". If you have a 80T rear pulley and 11T output, your clutch isn't going to lock until nearly 15MPH. That's about the same as my shifter 4G in top gear. Your engine wouldn't hit torque peak until 22MPH, and you'd be going 35MPH at the engine's HP peak. While that all sounds fine and dandy, that clutch is going to be working very hard at takeoff and the engine is going to be lugging at any speed under 18MPH. If you have a 12T output gear, then add about 9% to the problem.

So, you basically need to change your gearing if you want your clutch to last. Assuming you have 80T rear pulley and 11T output, a 52T would be ideal. If you have a 12T output, then 56T.
 
scotto-

scotto-

Custom 4-Stroke Bike Builder
Jun 3, 2010
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Here is an interesting note that will make you think.......my gearing set-up is the 5:1 (100t pulley) with an 11t output sprocket to a 44t final. I don't pedal on take-offs and have actually closer to 10,000mi. on that clutch and look at the wear.....very minimal and the clutch does slip alot on the big hills around here.

I have seen Pat burn one of the clutches out in less than 500 miles, right down to the metal.....housing full of dust. I don't know how some hold up well and others fail way prematurely. China?

dnut
 
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The_Aleman

The_Aleman

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Could be that there's variance in the clutch springs, of course. But I think it's more of a riding style versus gearing issue. If one gears their drivetrain for high speed, and has a centrifugal clutch, it's natural that the clutch will slip more at lower speed and thus wear out quicker if you spend most of the time at those speeds.

Scotto with your 5:1 4G and 11/44 gearing, that's a 20:1 overall ratio with a 26" wheel. That's 25% more reduction than what the OP may have with 4:1 11/44.
Indeed your ratio is near the same as my 2nd gear and his is more like my 3rd gear. I can take off in 2nd fine, but not 3rd.

I've heard it said that 18.75:1 is the "perfect" ratio for these, where you have the ideal mix between take-off and top speed.
 
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userix

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I believe my gearing is as follows: 20T:80T(Pulley wheel):10T(fixed drive sprocket):44T

According to the tables that is included with the engine kit, that should give me a top speed of 31mph.
How do you come out with the final drive:gear ratio (single number) from my numbers?
 
The_Aleman

The_Aleman

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Okay, with your gearing your reckoning is correct. 7000RPM is 31MPH. Since you have a 10T, that put your gearing at ~17.6:1.
That's actually only a little tall, not as much as I thought you were running.

You shouldn't be having clutch problems unless you ride slow and never pedal.
 
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userix

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The_Aleman said:
Okay, with your gearing your reckoning is correct. 7000RPM is 31MPH. Since you have a 10T, that put your gearing at ~17.6:1.
That's actually only a little tall, not as much as I thought you were running.

You shouldn't be having clutch problems unless you ride slow and never pedal.
Click to expand...
What's the formula for getting the ratio? And yes, I don't pedal at all.
 
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userix

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I finally got the replacement clutch pads installed and now the bike pulls much better than before. Hopefully these pads will last longer than the ones that came with the engine.

Now, when I go WOT up a hill and then release the throttle completely, sometimes the engine will stall out. I tried adjusting the idle screw to the best I can. Right now, if I pick up the rear wheel, the wheel will spin fairly fast while at idle. Is this bad, since when the bike isn't moving and the clutch is engaging at idle, I would be burning out the clutch faster? If I attempt to adjust the idle screw lower to the point the wheel doesn't spin when idling, the engine is more prone to stalling after WOT climb followed by immediate throttle release.
 
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scotto-

scotto-

Custom 4-Stroke Bike Builder
Jun 3, 2010
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Ridin' inSane Diego, CA.
Set your idle at approx. 2200-2500rpm and don't worry about what your rear wheel does when you pick it up off the ground at a stand still. As far as the immediate release of the throttle after a WOT climb......why? Just roll off the throttle gradually unless there's a stop sign at the top of every hill you climb. Sounds like you might have some debris in your carb if anything.

dnut
 
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