Pulling apart my lifan 140

[90Gabe]

Ok so I drained the oil in my bike for the first time(probably should have done this first up) and I found a couple of chunks of metal as well as some finer metal pieces. I decided it would be fun to pull apart the motor and see if i couldn't track down the issue. Also I have been reading through the tutorials and have wanted to pull down the head and cylinder. I'm really happy because it was really interesting to see how it all worked. So ive got a few noob questions:
1. Why is the cylinder so damn heavy?
2. Why is it finned?
Probably really stupid questions but im new to all this.

 

[Nuts 4 50s]

1. The cyclinder is very heavy because it is made of metal which is a heavy material. Another reason is that the cyclinder needs to be strong, this means having lots of metal around it, as this is a part of the bike that has moving parts in it Eg The piston and its rings. This is a main area that has friction, and therefore needs to be durable. This is why you need to regulary need to change the oil to get minimal friction, which mean less ware and this lengthen the lifespan of the motor. This is one reason why Two stroke engines need to be rebuilt alot, because of the piston moving faster in the cylinder, creating more ware.

2.The fins is a cooling mechanism. These fins provides more surface area on the motor, therefore the motor can repell more heat, cooling the motor. These fins are found around the head and cylinder of the the motor as this is where the most heat is produced.

Theres some info, hope this helps you out.

 

[The_GDFP]

The finer stuff is very common. Chinese gear manufacturing techniques lack the de-burring process. The larger chunks are likely kicker gear parts, and rarely need the cases split to cure. Chinese gears lack effective materials and heat treat procedures.

That monstrous lump of iron cylinder can be swapped for a TB 57mm alloy one and a 2-3mm spacer, since the 140 was a stepping-stone to the bigger engines and uses an odd jug height. You'll need a wristpin bushing to use the TB 13mm pinned piston, or a 15mm Akunar to get the deal right. Add some better valve springs and you end up with a decent runner.

 

[90Gabe]

Thanks so much for the help guys. I thought that might be what the fins were for. How much lighter would the alloy cylinder be? When I picked it up the weight just shocked me and I was thinking surely there must be lighter stuff out there. Is that one of the main differences between your bottom and top end parts? Like weight as well as strength? Are there any other designs that don't use fins and cool the engine in another way?