250-500cc Top end rebuild now backfires!!??

[DargoRider]

Hi guys,
Just completed a top end rebuild (shattered piston) on my 07wr250... Case split and cleaned by the shop, and re assembled yesterday... Problem is it started 4th kick, over revved due to throttle cable being stuck... Now all I can get is backfires, kick backs and no action.... I have pulled the carby, cleaned it, inspected reeds which are fine and checked plugs which are all good.... Everything moves as it should...
I am suspecting a woodruff key detonating.. Timing seems out of whack...
. Has anyone had similar problems?

I don't have a puller yet... But will source on ASAP...

Any thoughts?
Cheers
Steve....

 

[2premo]

timing slipping is a decent guess, your mag only relies on the woodruff key for alignment
did you assemble it yourself?

 

[justintendo]

if you assembled the top end...is the piston backwards?
how long did the bike rev up with the throttle stuck?
when you say it backfires, is it firing thru the exhaust or back thru the intake?

 

[DargoRider]

Thanks guys,
Finally worked it out - detonated woodruff key! Assembled by shop and missing the washer behind the nut on the crank, so wasn't tight enough.... A quick rev must have had enough torsion to shear the woodruff when the flywheel was loose.... Probably a $1 fix, just need to find a new key now.....
Thanks heaps guys... Will let you know how it goes...
Nice amount of compression now!

 

[2premo]

Thanks guys,
Finally worked it out - detonated woodruff key! Assembled by shop and missing the washer behind the nut on the crank, so wasn't tight enough.... A quick rev must have had enough torsion to shear the woodruff when the flywheel was loose.... Probably a $1 fix, just need to find a new key now.....
Thanks heaps guys... Will let you know how it goes...
Nice amount of compression now!

something to remember the key is for alignment
before you install the key and the mag use lapping compound and lap the mag to the crank stub, wipe off the lapping compound and install the key and torque the nut

 

[DargoRider]

Thanks 2 premo, will do.
I'll have to wait to get the key, at least it's sorted....

 

[DargoRider]

I've found the key online, but does anyone have the specs / dimensions for it?

 

[johnnyboy]

If your desperate just find a large washer or a bit of steel and make one that fits - 15 minutes with a hacksaw and a file and your good to go, dosnt even need to be pefect as its only as stated above for alignment and you have the two halves to copy

 

[DargoRider]

Cheers johnnyboy... A bit of shed time doesn't go astray!

 

[gazmcfaza]

in case this ever happens to me, what is a wood ruff key? Is it the thing on the lh side of the engine where the magneto is?

 

[justintendo]

in case this ever happens to me, what is a wood ruff key? Is it the thing on the lh side of the engine where the magneto is?

yes, shaped like half a circle. used to index the flywheel

 

[juicypips]

Come guys your on the second most powerful tool in the world and you cant be arsed to log onto another page and search for the woodruf key?
The most powerful tool is you! just incase you were wondering.

 

[justintendo]

hahaha, but its soooo hard to look things up on google

 

[Hammerz]

Measure the width of the slot in the crankshaft go down to your local engineering supplies store and tell them you need a woodruff key that size don't file a washer this isn't the 1970s