Scooterotica

Can anyone help with this one. I have always set my timing by dial gauge at 2mm BTDC which equates to 19 degree's and never had a problem, until recently when an engine I built last year holed it's Piston after about 4000 mile, although a new stator was fitted at the IOW in august. I told the owner of the engine, a MUGELLO 225, to take it up to Martin at Chiselspeed for him to check out the Bore etc. When he returned he said Martin reckons the reason for the hole is the timing is out. Now when setting with the Dial Gauge I always get the Piston as soon as it reaches TDC and then back the 2mm. Dial Gauges do not measure the dwell of the Piston at TDC whilst the Degree disc does. Do folks with degree Disc's go to the centre of the dwell and then back the amount of degree's they require or, like me do they turn back as soon as it reaches TDC?

call me old fashioned........but i still prefer the positive stop method...........i still think its the most accurate way to find TDC..................

How does the Positive stop method work?

stickys manual..........page 112./113............explains it ,
the spark plug way is ok ,but i prefer to do this without head on..........using a bar bolted across two studs.............

I use the posative stop system to . I bought a tool years ago the screws in to cylinder hea to do the job . It would be possible to make one using an old spark plug.

With the degree disc it is crucial to find true TDC before measuring the degrees back to the firing point. As a dial gauge is measuring piston travel as long as the gauge is zeroed anywhere in the dwell period then 2mm back will equal 19 degrees BTDC (on a 58mm stroke, 107mm con rod crank).

Just to add to this there is a good mm to deg and deg to mm calculator on scooter help .com , it has a long list of con rod lenths etc.

Positive stop and degree disc does it for me. made a stop from an old spark plug

same here.........

as above