I am re-building the motor on an IT400 which the PO holed a piston. Trying to check the timing and getting nowhere fast. Can anyone talk me thru the process? Not new to bikes but this one very confusing to set the timing. It is a 1977 model. Thanks, lizard

Have you got a strobe lamp lizard? if the bike is 6v you may have to connect the strobe lamp to a 12v battery depending on its type?

This may be some use and a parts list / service manual if you can find them

http://www.ebay.com/itm/Yamaha-OEM-Service-Manual-IT250D-IT400D-/180959413898

Yes I have all the tools to do the timing with. My problem is the method of static timing the motor. There are 3 timing marks on the rotor, 1 mark on the stator and 1 mark on the crankcase. I understand from the Clymer manual that the timing mark on the stator should be lined up with the mark on the crankcase. When I do this with the micrometer reading 2.7mm BTDC the center mark on the rotor lines up with the mark on the crankcase which is lined up with the mark on the stator. If this is correct, it is 10 or 15 degrees off what the PO had it set on. That may be why he holed the piston but I really would like to make sure this is the correct timing before starting it and ruining another piston! Thanks, lizard

does the clymer book not say what the mm BTC should be?

The usual method is to turn the rotor until the correct mm BTDC then hold it there, tthen adust the stator mark to align with the central rotor mark this should also align with the casing mark...if it doesnt, then make a new casing mark...This is how my DT is and I doubt your IT would be any different. Incidentally did the PO have it further advanced than that you didnt say. if he did then that would explain the holed piston

If you do have to re-position the stator you'll need a flywheel puller and a means of holding the rotor when torqueing back up...

I havent any info on the IT400D but the 76 C model is 2.7mm BTDC so that would no doubt be the same for yours

Yea I have got the marks on the cranckcase, the mark on the stator and the center mark on the rotor lined up at 2.7mm BTDC. Sounds like I have got it right. The PO had it way advanced according to that. Thanks guys. lizard