'81 390 or 420 KTM

[JohnnyO]

Does anyone know the bore size of a 390 ktm? Mine has a 83mm bore which seems big for a 390 and i thought maybe it's a 420? Also the transfer ports don't go close to lining up with the crankcases so maybe it's had another barrel fitted.

[oz555ktm]

 

Dose youe Engine No# start with??

560 = to be a 420cc with  85 mm piston

561 = 350cc with a 77.5 mm piston .also engine #  560*****A

562 =390cc with a 82 mm piston also engine # 560*****B

541 = 250cc with a 71 mm piston

[JohnnyO]

My engine # is 5603413 B. I guess that means it's a 390. Why don't the cylinder ports match the crankcases, it's not even close. Is that normal on these engines?

[holeshot buddy]

maybe its a maico barrel

[JohnnyO]

Ha ha.. if it was a maico barrel i'd be keepin it just to roost your 465.

[holeshot buddy]

na maicos dont turn remember

 (i can say that i am not in maico forum)

[JohnnyO]

I'll call the maico police..

[oz555ktm]

What you have got is a 420 bottom end with a 390 top end .
dont worry  about the ports you will have all the power you need to
wipp your maico mates