Merc 402 Timing Mark

My engine is a 1978 Merc 402.

The initial problem was the engine would not run. With the help of some people on the forum, Laddies, I narrowed the problem down to some very brittle wiring in the wiring harness and stator as well as a bad switch box.

I replaced all the brittle wiring, purchased and installed a new CDI switchbox. In the process of replacing the wiring on the stator I removed the flywheel to get as much of the brittle wire as possible The replacement wiring is making good contact. I marked the flywheel with the a marker for Top Dead Center, TDC, also using a screwdriver in the #1 cylinder to confirm.

In order to remove the flywheel I had to use a puller which required removing the bolts from the hub and a lot of effort since it has been on there for almost 30 years. I was careful as I could be not to rotate anything when it finally came apart.

Everything is back together and I have strong spark on both cylinders. I am preparing to fire it up with fuel.

I noticed tonight that the mark that I made with a black sharpie as TDC is aligned with the mark on the edge of the flywheel with 2 dots with the timing pointer. See the attached photo.

There is another line on the flywheel 5 gear teeth on the edge of the flywheel to the left in the photo, or clockwise.

Question: Are the 2 dots on the edge of the flywheel, TDC or is TDC the mark on the edge 5 gear teeth clockwise? Using a screwdriver in the #1 cylinder, there is enough play to believe it could be either one. If I did manage to rotate the flywheel from its original position what problems might I encounter.

Thank you.

Re: Merc 402 Timing Mark

I wouldnt think the you should encounter any problems there as long as the timing is right the flywheel postion shouldnt matter and if you didnt unbolt the flywheel completly from the the crank the flywheel is keyed and will only go one way so i would think that you should be fine

Re: Merc 402 Timing Mark

Thanks, do the 2 dots mark TDC for the flywheel?

Re: Merc 402 Timing Mark

Thank looks correct. There may be an additional mark on the flywheel that lines up with the engine centerline on the plug side.

You an also test by:

1. Dropping the lower unit
2. Inserting a piston stop into the upper cylinder plug hole
3. Rotate flywheel in 1 direction until the piston hits the stop, mark this on the flywheel (to your timing reference).
4. Rotate flywheen in other direction until the piston hits the stop, mark this on the flywheel
4. TDC is halfway between the marks.