I scrape scrape pop

turnofftheradio

turnofftheradio

Member
Well, it's been almost 700 miles of fun. I was crusing at around 30 when I started to get a scrapy noise, then a loss sof power and symptoms of misfiring. I got home and my clutch cable snapped just to add to the problem.

Pulled the covers and I see this, and think thats great it just shook some screws loose.


So I put a new cable on, tighten up those screws and realise that the magnet and crank wobbles like a dreidel. My crank bearings are shot and will need replacement. Not sure yet if there is collateral damage.

Good news is that it made it home like this.
Anyone care to diagnose what may have caused the failure?
What else could have gone bad when this failed that I should look for?
I've been careful about premix, but I tend to run this on the high side of the throttle. My plug looked great, it's been quite reliable so far.
 
Man that sux turnofftheradio, only 700 miles.

The most common failure of bearings is either lack of lubrication or excessive heat. Also foreign material in your crank case like metal shavings from the manufacture process.

Could also be you crank was out of balance causing premature bearing failure. Or maybe you just got crappy bearings?
 
I did not clean out the case before using it, so foreign material is not out of the question, My premix and plug look spot on so lubrication seems ok, bad bearings maybe? idk but at least the parts are cheap...
hopefully once its back together it will get more miles before teardown. At least the money I saved on gas so far basically equals out, and the fun factor was worth it. While I will fix this and ride it, I'm leaning more towards getting a legit vintage moped for commuting purposes. I'll take some pics as I tear this down and repair it.
 
Are you certain the bearing is bad or is the wobble due to a bent crankshaft?
The crank is only about 5/16" diameter out there where the magnet rides. It can be bent by prying the magnet off using too much force on one side. I've seen this several times on engines returned to a vendor.
If the magneto coil came loose and the magnet hit it hard enough it might have bent the crank.

Tom
 
I second what Tom said here, could just be a bent crank if rotor was making contact with mag coil.
If you actually have slack in the bearings when you lift up and down on the rotor, then I would say you for sure have bearing issues.

Map
reddd
 
mapbike said:
I second what Tom said here, could just be a bent crank if rotor was making contact with mag coil.
If you actually have slack in the bearings when you lift up and down on the rotor, then I would say you for sure have bearing issues.

Map
reddd
Click to expand...

If I rock the bike back and forth there is a solid 1/8" of play in all directions on the mag rotor.

As far as the brand of engine goes, I'm just not sure, I got the kit locally from a craigslist importer, I should call and ask him. He has been pretty good as far as support goes.
 
2door said:
Are you certain the bearing is bad or is the wobble due to a bent crankshaft?
The crank is only about 5/16" diameter out there where the magnet rides. It can be bent by prying the magnet off using too much force on one side. I've seen this several times on engines returned to a vendor.
If the magneto coil came loose and the magnet hit it hard enough it might have bent the crank.

Tom
Click to expand...

Wonder what came first?
loose magneto bent shaft causing bearing to fail?
or
failed bearing pushed rotor into magneto knocking it senseless?
 
turnofftheradio said:
If I rock the bike back and forth there is a solid 1/8" of play in all directions on the mag rotor.

As far as the brand of engine goes, I'm just not sure, I got the kit locally from a craigslist importer, I should call and ask him. He has been pretty good as far as support goes.
Click to expand...

Yep you have a bad bearing for sure, id take that engine down and see what actually went wrong, if it is only and issue with the bearings I'd replace them with some high grade bearings, pop a couple new crank seals in it and you will be off and running again in no time, if you were to get another engine form the seller you spoke of you may be buying another one with the same bearings that could give you the same or maybe even worse grief down the road.

here is links to the bearings I have bought for mine and the crank seal set.

http://cgi.ebay.com/ws/eBayISAPI.dl...akeTrack=true&ssPageName=VIP:watchlink:top:en

http://www.ebay.com/itm/80cc-66cc-4...844?pt=LH_DefaultDomain_0&hash=item4ac7b1b404

Map
 
mapbike said:
Yep you have a bad bearing for sure, id take that engine down and see what actually went wrong, if it is only and issue with the bearings I'd replace them with some high grade bearings, pop a couple new crank seals in it and you will be off and running again in no time, if you were to get another engine form the seller you spoke of you may be buying another one with the same bearings that could give you the same or maybe even worse grief down the road.

here is links to the bearings I have bought for mine and the crank seal set.

http://cgi.ebay.com/ws/eBayISAPI.dl...akeTrack=true&ssPageName=VIP:watchlink:top:en

http://www.ebay.com/itm/80cc-66cc-4...844?pt=LH_DefaultDomain_0&hash=item4ac7b1b404

Map
Click to expand...

thanks for the links, I have a local place my buddy's family owns that I try to source my bearings from, but not sure If he can do the seals.

Ive read a few threads about the bearings and replacing them now,but any insight that may save me a screw up during the process is appreciated.

I went to take the engine off the bike last night, but i just gave it dirty looks and drank beer instead.
 
turnofftheradio said:
thanks for the links, I have a local place my buddy's family owns that I try to source my bearings from, but not sure If he can do the seals.

Ive read a few threads about the bearings and replacing them now,but any insight that may save me a screw up during the process is appreciated.

I went to take the engine off the bike last night, but i just gave it dirty looks and drank beer instead.
Click to expand...

The bearings are easy to find, the seal are another story, the seal under the mag rotor/flywheel is a very thin seal which if I remember right is only 3mm thick never found any of these anywhere else but through the kit vendors, the seal on the other side is 7.5mm thick if I remember right, these seals are odd ball so you'll be best off just to order them from a vendor of the kits probably, but if you do come up with another source on them please share because so far I never have been able to find another source for them.

as far as removing the bearings go, I would just make sure that the case half you're working on is on a good even surface, with a screwdriver I'd pop the seal out and then find a socket that has a very similar diameter as the bearing and then start off easy popping the socket with a hammer and increasing the wraps a little at a time until the bearing starts to move and then just gradually knock it on out, put the new bearings in the same way making sure you never hit them at all on the inner bearing race, that will damage the bearing.

Hope this helps.

Map
reddd
 


looked worse than I would expect at 700 miles, nothing ruined so far. Piston top has a few marks where something may have bounced around. the front side of the piston had more scoring than the rear, but not that bad.
I'll have more when I acquire the puller tool.


In the meantime to prove I'm not giving up, I've added a smaller crank gear to the bike to make starts easier. In the process, I've noticed my bottom bracket is self lubricating with 2 stroke mix. I'll have to find out why it seemed to have so much in there, maybe the grease was just broke down badly.


look at the pin thingy on this. wtf?
 
Moto said:
imo cylinder and piston look pretty much perfect. I have much worse on my bike and still pulls 40 mph so I dont think you have anything to worry about in that department. Would you consider just ordering a new bottom end off the 'bay? They are like 65-70$ and will save you a LOT of hassle

http://www.ebay.com/itm/80cc-bicycl...Cycling_Parts_Accessories&hash=item2c7084548d

just as long as you dont have a GT-5 engine the stroke should be exactly the same.
Click to expand...

I think I'll just replace the bearings and seals, no use wasting the energy on a new lower end till it's ruined. I try my best to repair anything I can vs. replacing even if the cost is a wash, It is greener to re-use what I have, and that does have an impact somewhere... Not that i'm a hippy or anything. However I still have not split the case, so who knows what I find in there, plenty of measuring to keep me busy.

The ports may very well be responsible for the light scoring on the piston, they are very poorly made, the edges are not up to par vs any 2 stroke I've seen in lawn equipment or motorcycles, but they work.
 
Last edited:
crassius said:
you'll probably want to order a case gasket too
Click to expand...

thanks for the tip, I'm planning on replacing the case, barrel, intake and exhaust gaskets.

no engine work last night, but did bet my bottom bracket installed. And I broke my chain breaker. My big one does not seem to work well with the standard bike chain. I've used a punch and hammer a few times before, so perhaps that is the answer if i don't make it out to the store.

Also, I plan to check out a local hardware store that sells minibikes/scooters and see If I can get any seals/pullers locally. It would be nice if there was a parts supply within a mile.
Thanks for the insight so far, more progress to come.

my original gear was a 44t
 
turnofftheradio said:
thanks for the tip, I'm planning on replacing the case, barrel, intake and exhaust gaskets.

no engine work last night, but did bet my bottom bracket installed. And I broke my chain breaker. My big one does not seem to work well with the standard bike chain. I've used a punch and hammer a few times before, so perhaps that is the answer if i don't make it out to the store.
Click to expand...


best chain breaker I have ever used, works every single time...
4.5+Grinder.jpg

87.jpg


Map
reddd
 
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