SkyHawk Engine will rarely turn over?

Mjpioneer · Jun 10, 2013

I have a SkyHawk 66/80cc engine on my bike that normally runs great, I had an issue the other day with the chain binding itself around the drive sprocket causing the bike to stall. After fixing the chain I went to start it up and it wont go. I will pedal and release the clutch and not much happens, the motor sounds like it is turning over once every 60-70ft. Oddly though if I pedal slowly it turns over a bit faster, but still does not fire.
I checked the keys on the sprockets they are still intact, the clutch is engaging, the pads seems to be okay. Were should I look next?

allen standley · Jun 10, 2013

I went to start it up and it wont go.

Do you mean It will not fire and start-up?

I will pedal and release the clutch and not much happens,
I would think the trauma of the chain lock-up has caused your clutch cable to slip a little in the retainer at the end of clutch arm. I'ld check that first. Properly adjusted your rear wheel should turn/spin freely while clutch is disengaged, lever squeezed button locked.

sounds like it is turning over once every 60-70ft.

Properly adjusted, pushing your bike with the clutch ENgaged released lever should go plunk plunk plunk as you try to push it and you should feel the resistance of the engines compression.
While your looking at things pull the gear side cover off and check the big slotted screw in the small gear. Be certain that's tight.
Doing these things as to allow you to rule out clutch

Mjpioneer · Jun 10, 2013

When I said it wont go I mean I release the clutch, it is harder to pedal, but the bike does not go "plunk plunk plunk".

I adjusted the clutch when I put the chain back on, it is working as per normal, rear wheel spins nice and smooth well clutch is engaged.

Pulled the cover off, the little gear is as tight as it can be.

My only guess now is that the clutch is slipping, but I'd like to figure out a way to test that theory before buying new pads.

allen standley · Jun 10, 2013

I adjusted the clutch when I put the chain back on, it is working as per normal, rear wheel spins nice and smooth well clutch is engaged.

When clutch is engaged, rear wheel should not spin nice and smooth.
when clutch is engaged that means drive from motor to wheel is uninterrupted.

when clutch is disengaged means drive from motor to wheel is interrupted. allows you to coast-stop-idle. search clutch adjustment on this forum for a better understanding. don't give up you will get it.

maniac57 · Jun 10, 2013

Check out the classic section for great clutch adjustment advice and instructions.
Sounds to me like your clutch is slipping. New pads are very seldom needed. Just adjust it properly. The HT's have been called "1k motors with 10k clutch"

DeNunzio · Jun 10, 2013

Sounds like the same problem I had when I blew up my first top end ,
I would look inside at piston. I say you blew your rings or cylinder or piston or all three I posted this exact problem and not one of these "forum Gurus" even thought to say well nube you blew up your top end.

BigBlue · Jun 11, 2013

DeNunzio said:
... not one of these "forum Gurus" even thought to say well nube you blew up your top end.

http://motorbicycling.com/attachment.php?attachmentid=60447&stc=1&d=1370935947

Chris
AKA: BigBlue

Toadmund · Jun 11, 2013

DeNunzio said:
Sounds like the same problem I had when I blew up my first top end ,
I would look inside at piston. I say you blew your rings or cylinder or piston or all three I posted this exact problem and not one of these "forum Gurus" even thought to say well nube you blew up your top end.

Well, really there is still not enough information to make a diagnoses either way.

When my engine ate the crank pin bearings, it would turn over, the clutch was not slipping, it would start and rev a bit at full throttle then quickly die when no throttle was applied.
But, while riding the junk did momentarily seize my motor causing me to drastically slow and I would imagine if it totally seized my chain would have bunched up into the drive gear and once freed it would not start properly any more due to compression loss.

But first we have to rule out the clutch, then we can make a diagnoses.

allen standley · Jun 11, 2013

Toadmund said:
Well, really there is still not enough information to make a diagnoses either way.

When my engine ate the crank pin bearings, it would turn over, the clutch was not slipping, it would start and rev a bit at full throttle then quickly die when no throttle was applied.
But, while riding the junk did momentarily seize my motor causing me to drastically slow and I would imagine if it totally seized my chain would have bunched up into the drive gear and once freed it would not start properly any more due to compression loss.

But first we have to rule out the clutch, then we can make a diagnoses.

OK, pull carb n muffler - pull off the head and jug then take a look. Tell us what you find. Let's rule out or determine it's the top end. Can't hurt nothing if your careful. If all is good use care lining up your ring splits with the pins in piston. (assuming the top end is good) and reassemble. :-||

If Top end blown - get your correct parts and before reassembly, turn engine upside down and flush well to remove any broken pieces.

Mjpioneer · Jun 11, 2013

Top end is fine, rings are good, dont even have anyscoring on the cylinder wall. Motor has 180psi of compression. Turns over fine with plug out but clutch slips when plug is in due to compression. Adjusted the clutch how the guide shows same problem. Going to manually lock the clutch plate to the basket and see if it will fire up, if it does I will replace the pads.

allen standley · Jun 11, 2013

All excellent news! 180 psi seems like lots comp which is a good thing! The answer is here, keep looking. Once again, excellent news nothing is harmed.
stick with it.

biknut · Jun 11, 2013

Chances are your clutch pads need to have their edges filed a little so they fit into the clutch gear looser. When they fit too tightly, they bind in the clutch gear and only make good contact on one pressure plate instead of on both sides.

mew905 · Jun 11, 2013

allen standley said:
All excellent news! 180 psi seems like lots comp which is a good thing! The answer is here, keep looking. Once again, excellent news nothing is harmed.
stick with it.

180 is tons of compression. Like... tons... I wish I could get that much on my bike, using a drill at 1800 RPM I read 90 with a puch Hi head. christ man what did you do? I heard 175 psi is the upper limit for most motors.

KCvale · Jun 11, 2013

Ran great.
Chain seized on back sprocket abruptly under power halting motor.
Drive train now won't engage.

I just repaired a bike with exact same problem and it took awhile to find it.
The left side sprocket sheered the key.
It looked like it was in and the gear bolt was tight and like yours it kinda wanted to try and hold but just flat wouldn't without the key.

Just look at the sprocket and shaft dead on, if the keyway's don't match that's your problem. Note it is a half moon woodruff key, what a pain in the butt simply because they made the groove with a circular saw and didn't just do the whole length of the shaft.

maniac57 · Jun 11, 2013

If you adjusted it according to Norm's instructions and it still slips, you might actually need pads. I'd try cleaning them and filing the sides so they fit right before replacing though...
sometimes they bind and don't all make full contact with the pressure plate.

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SkyHawk Engine will rarely turn over?

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