yamaha 70 ces

[mobil1]

I want to get the flywheel lightend, and have a few questions about it.
It has 3 rivets in it, when i drill these out will it seperate the ring/gear from the flywheel?
Also my engine has the 6j2 pistons in it, as I have read these are not the best.
How long will these last? Engine has not much hours...

Engine will be ported and 90hp carbs.





Grt

[mobil1]

Or if someone can offer me a link to an exploded view of the flywheel...

[mobil1]

To me it Looks like the rivets holds the starter gear in place...
If you have experience with these motors feel free to post...

Im planning to drill the rivets out, machine the starter gear thinner myself.
Then let someone cnc machine circular forms in it to lighten it some more.
Make the rivets self and press it back togheter.

[phillnjack]

so your just going to make it a 90hp then ?
isnt it just the carbs that is the difference in the engines ?

Dont forget when you lighten the flywheel you will need to re-balance with the starter ring back in place.
a lighter flywheel will cause a lot of differences, especially at slower speeds.
if its purely a drag race engine then fine, if you use it for recreation its not a good idea at all.
It would be cheaper for the factory to sell the engine with a lighter flywheel, !!!!!!!!!!!!

i can never understand why people buy new engines that are just big engines with small carbs.
when secondhand yes its fine as the engine will probably never have been tested to its normal limits.

phill

[Fast Fred]

the starter ring is pressed on the hub, the rivets hold the rope ring on . weld the crank or lose the press. the stock high ring pistons are ok, i was not able to get new rings for that piston, once the rings wore out i'd change out the pistons. 17-18deg MAX advance, pull to 7800rpms, not the same as a 90hp powerhead.

[mobil1]

Got the flywheel back today, shaved 1.2kg of the total wheight.
If you want, it can be more... tomorrow i will balance it.
Also mounted the 90hp carbs on the intake and matched them together.
Soon i will start the porting work.