Sunday, January 13, 2008

190cc Bajaj Mod

Roy wrote an article on how he designed and built his 190cc kit on "All things Bajaj." Comments are posted there as well.

Here's what Roy wrote:

a lot of research went into this and those so inclined may benefit from this. first i decide on the maximum size that the cyl could be sleeved to this is determined by the engine case as it can only be opened so far (70 to72mm) that sets the piston size at (63 to 67mm) working with Marvin at tel 888-697-4343 (tell him roy rhodes set you) we decided on 65mm this allows for two over bores if needed and gives a displacement of 189.1cc if you went the max at 67mm you would have a full 200cc. but no room for boring. the piston i decided on is a Honda ATC200 81-86 std size 65mm this piston has a dished top and must be machined down in a lathe also the skirt must be shortened this is also done on the lathe the piston pin dia is 15mm the stock pin is 17mm i machined a sleeve on my lathe and locktited it into the rod small end. the cyl head must be mounted on the lathe and a recess cut to match the new cyl dia this is then blended into the combustion chamber and additional material removed from the chamber to bring the cr down in my case 10.75 to 1 at this cr the electric starter just will turn the engine over but if its up on compression i must jog the starter or kick it past top before it will spin the motor. Marvin supplied a custom cut copper head gasket and i used 2 stock base gaskets to seal the cyl you can only raise the cyl so much before the cam chain becomes tight. and that is how i did it doing all the lathe work and cyl head work myself, is there a better piston to be used?, or Marvin said that a custom piston could be ordered but cost is a factor. total cost for this work was $380.00 but as Marvin now has all the info on hand the next customer may do much better also if you supply your own piston they can be had for less im using a ProX2430 cast piston which Marvin supplied.

one thing i forgot is that the engine case must be opened up to accept the larger cyl liner this can be done by stripping the entire engine and having a machine shop do it but i stuffed the engine case with shop towels cotton balls more shop towels and then sealed it with modeling clay then i made a guide from 2in thick oak and used a 2 3/4in hole saw to open the engine case up a little clean up with the dremmel and then remove and clean the engine just for good measure i flushed the engine with a parts cleaner pump and cleaning fluid and then did the final assembly.

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