Crankcase/Crank compatibility

[knappers]

I been given a pile of China bike parts, 156FM 163FM push-rod engines. As a project wanting to build up an engine, do as much tuning as possible and use it in one of the other rolling chassis I have. Before I strip and split the cases I wondered if anyone knows if the cranks are interchangeable between the cases of both engines. I realize the rods are different due to stroke. Any other info would be good. I see there is a big bore kit for the 156FM engine which brings it to 150cc. I'm looking for something 200+cc. I know there are lots of engines readily available but as I say I wanted to see how far I could take it as a project. Thanks for any info

[TurboT]

I been given a pile of China bike parts, 156FM 163FM push-rod engines. As a project wanting to build up an engine, do as much tuning as possible and use it in one of the other rolling chassis I have. Before I strip and split the cases I wondered if anyone knows if the cranks are interchangeable between the cases of both engines. I realize the rods are different due to stroke. Any other info would be good. I see there is a big bore kit for the 156FM engine which brings it to 150cc. I'm looking for something 200+cc. I know there are lots of engines readily available but as I say I wanted to see how far I could take it as a project. Thanks for any info

I would expect if the stroke is different, the crank will be different. Or, machined to a specific stroke. The journal diameters may be the same, but the counter weighting and stroke would be different, and hard to tell by eye.

[knappers]

Thanks for the reply. I didn't see the balance as being a problem if the crank would go in the cases, as the rod and piston should balance out any extra weight. I could be wrong though as I'm no mechanic. Any more info would be good. Thanks [/i]

[TurboT]

Thanks for the reply. I didn't see the balance as being a problem if the crank would go in the cases, as the rod and piston should balance out any extra weight. I could be wrong though as I'm no mechanic. Any more info would be good. Thanks [/i]

Well, the weight would probably be very minor. These aren't the best of balanced engines anyways.

In theory, you could take the rod and crank from one, and put it in the other as a set, if the main journal diameters are the same. I could see that working more than mixing and matching rods and cranks. I guess the only reason you would do this is if one crank is damaged etc. I don't see a huge HP gain here.

It could offer you clearancing issues somewhere, but I really don't know. I don't have a whole pile of experience on motorcycle engines myself. :)

A good portion of your power would be made in the cylinder head. More fuel, more air, more power. :)

[knappers]

Ordered a 150cc kit for the 156FMI engine, brings the bore out to 62mm from 56.5. Was wondering if the motor would loose low down torque? Heard from others there is a noticeable increase in power???
Its really the 200cc motor I'm interested in so not that bothered if it doesn't work out quite right as the kits are really cheap.
Again, if anyone has any more info about these motors especially head, carb and pipe work id be most Interested. Ill post how it goes when I get the stuff. Thanks again for all the help.