Monster Moto 80 crankshaft

[B_Bimmer]

Well, I picked up a cheap minibike at the pawn shop knowing it needed work, once I cracked the case I found the crankshaft snapped in half. It scuffed up the side of the rod and obviously there is no salvage to the crank, but otherwise looks like new. Parts are MIA, anyone know of a source? Alternatively what is the lowest price you can get the lifan harbor fright 79cc for? I'd really like to just throw a new crankshaft in it, but obviously it's not worth much. I set an LCT. engine in it just to see if it would be easy, but there really isn't much room.

 

[mckutzy]

For the almost same price, I'd get a 212.... Forget the 79cc

 

[B_Bimmer]

I know, and it looks like if you go with a clutch it is just about drop in. From what I read that would transform it from a fun toy for the kids to a fun toy for me, and I kinda already have that department covered. I liked the idea of a little lacking.

 

[chancer]

79cc are 89 bucks.
I never see them on sale like when the 212 is 99 bucks.

No coupons are valid on predators.

 

[ironman]

I get the 99 coupons for 212 and the 89 coupons for the 79cc every month in the mail its in the back of our local energy magazine


Sent from my iPhone using Tapatalk

 

[B_Bimmer]

The cost to value ratio is so screwy it's going to be hard to really consider anything small...

---------- Post added at 09:10 PM ---------- Previous post was at 08:56 PM ----------

Here is a picture of the carnage. I don't know how clear it is in the picture, but in real life it's clearly a bad casting. I am surprised it lasted as long as it did.

 

[ironbutt]

Just put the 212 on that bike. I just did the same thing with my Motovox which basically the same bike.

 

[B_Bimmer]

How does it handle, too much for younger kids or still tolerable? Also, what did you do with your old engine? Didn't happen to have a good crank and rod did it?

 

[ironbutt]

It runs great...lots of lowend power and gets up to 30 mph with everything stock.

It would be fine for an older child by setting the screw on the throttle linkage. You know the one everyone says to back out all the way.

I pulled the OEM 79cc unused and sold it on craigslist for $75.

 

[B_Bimmer]

Sounds like you did good. That's a pretty dang low net cost to you for a substantial upgrade.

It drives me crazy how everything is designed to be throw away today, I will keep this perfectly good engine that needs a part which I should be able to get for twenty bucks in a box on a shelf for the rest of my life. Even if my saved ebay search turns up what I need it'll probably be done years ago. I'll still buy it and make it run cause that's what I do, but if I ever get through the list of things I have to build, something that uses a 80cc engine is pretty low on the want to build list, plus my kids will be too big... Oh well, maybe grandkids.

Did you have to do anything other than the engine, new clutch and drill new mounting holes?

 

[OzFab]

Well, I picked up a cheap minibike at the pawn shop knowing it needed work, once I cracked the case I found the crankshaft snapped in half. It scuffed up the side of the rod and obviously there is no salvage to the crank

IMO, there's no salvaging the engine, it's junk...

If it was a multi piston engine, maybe but, being a single, there will be damage to the conrod & casing (as you mentioned), more than likely damage to the piston, bore, crank bearings, cam gears, cam shaft (when the crank broke, it would've been still spinning, either putting excess pressure on the cam gear, possibly bending the camshaft, or it lifted away from the cam gear, chewing up teeth)...

Yes, most of those parts can be replaced but, at what price &, if the bore is damaged, the cost of a rebore is likely more than a new engine...

 

[ironbutt]

Yes I had to buy a new clutch online because of the larger shaft size. But I kept the original #35 chain and length.

Of course the new engine had different mounting hole locations but it was easy to drill them out.

The bike was a deal or steal...found new in the box at a local Sears for only $199 marked down from $399!

So with selling the original motor and buying the new clutch I'm probably only in $300 for a new and upgraded mini.

Checkout some of my post for more info and videos.

 

[B_Bimmer]

IMO, there's no salvaging the engine, it's junk...

If it was a multi piston engine, maybe but, being a single, there will be damage to the conrod & casing (as you mentioned), more than likely damage to the piston, bore, crank bearings, cam gears, cam shaft (when the crank broke, it would've been still spinning, either putting excess pressure on the cam gear, possibly bending the camshaft, or it lifted away from the cam gear, chewing up teeth)...

Yes, most of those parts can be replaced but, at what price &, if the bore is damaged, the cost of a rebore is likely more than a new engine...

Nope, it's all like new other than the rod, which got chewed up on the side, and the crank which broke. Due to it's small size and value it's not worth fixing given the lack of parts, but it would be possible if they were as readily available as a Honda.

 

[OzFab]

So, you tore down the entire engine, x-rayed all the parts & found no microscopic cracks anywhere? You also tested the conrod, cam & gudgeon pin for straightness with zero deflection?

Unless you answered "yes" to everything above, you can't say with absolute certainty that nothing is damaged...

 

[B_Bimmer]

This is a 80cc engine. You sir take yourself far too seriously.

 

[Hellion]

Can you show us the engine in an overall pic, or is it in pieces? Who's the manufacturer?

Chances are, you can find a new crankshaft and get it running again. Everyone here seems to be super efficient and not want to take the effort to fix broken things--everything is indeed throwaway but only to a sad few.

 

[B_Bimmer]

Might take me a day or two but I'll get you a whole engine picture. It's loosely assembled to keep track of parts with socks in the crankshaft holes to keep dust out.

 

[OzFab]

This is a 80cc engine. You sir take yourself far too seriously.

I was merely pointing out that, IIWM, given my experience, I wouldn't be taking the chance & throwing time & money at it just to have something else break; I'm the last person to throw something away without attempting to fix it but, sometimes, there's simply no point trying... been there, done that...