Strange timing marks?

[Fux]

I`m building up a new motor and alarm bells are ringing as to where my timing marks are compared to where they were on the previous owners build.

I have a 60x110 crankshaft compared to the 58x107 that was in there previously but I wasn`t expecting such a huge difference.

Heres the picture..



I don`t know which of the million marks that are on the mag housing were used on the previous build but I found TDC by the positive stop Method and following the marks on the new BGM flywheel 17 degrees is where the flywheel arow is on the pic.

Surley, somthing is amiss here? -what have I done wrong now?

[slangen]

I had the same feeling building up an engine with bgm ignition a few months ago. Regardless of crank tdc would be the same right?
Anyways my thinking was they put the arrow on the flywheel a bit anti clockwise just to get a clean area for new marks...?

[Adam_Winstone]

TDC and timing marks will change any time you change a flywheel or crank as the arrow on the flywheel may be in a different position and the slot on the crank's taper will differ from crank to crank. As such you must NEVER rely on existing marks on the mag housing.

You should never trust existing marks and any that are close enough to confuse you should be totally ignored, to the point that it may make sense to put a totally new TDC mark on the flywheel and mag housing somewhere opposite existing, then find the correct firing point in relation to the new TDC mark.

Basically, ignore any existing and trust your own work... providing it is accurate enough.

Adam

[corrado]

I dremmel all the old ones off when fitting a new set up. Saves the confusion.

[RICSPEED]

if any thing is changed .. ie flywheel /crank ect then any timing marks must be dissregarded and tdc re checked

[slangen]

In my little experience, changing cranks and flywheels around you always end up around the same but with the BGM flywheel the arrow on flywheel is way anti-clockwise related to crank taper groove, think that's why FUX heard the bells ringing... Just saying, had the same experience. Happy days!

[Fux]

Ok, I was up early and had a re-check and my New marks are correct.

Iv`e built quite a few motors and like Slangen here, my tdc marks have always been in the general same sort of area.

It must simply be either that the Arrow on the bgm flywheel is in a differnt area compared to other flywheels, and or the Woodruff slot is in a different pos. to whats "normal".