How to set Timing on Rotax 185

[rayjb60]

[Guest]

2 additional questions. 1. Is the point gap important..? I had to set mine wider to accomplish step 7. 2. Regarding step 7., I thought I read somewhere that the points should 'break' at .16 before TDC...you mention 'close' at .16 before TDC..? Also, shouldn't the prop be backed off from the right direction to get .16 before..? Thx

[rayjb60]

As far as I know, the point gap is not important, but the "break" is.

My terminoligy is incorrect when I refer to "points should close" I like the term "break" better.

The spark should fire at .16" before top dead center.

So now that your done hows your engine running now?

I notice mine ran smoother...less vibration at all seetings, especially just above idle.

[Guest]

Ray what RPM's are your engines turning up ?

[Guest]

Thx So, the spark fires right at the break of contact..or .16" BTDC..? And lastly, at what distance BTDC would your spark fire before the piston made it to TDC... .17"...18"....19"....20..?

[Guest]

According to the manual .13" BTDC is the mark.

[rayjb60]

Just to clarify, the spark fires when the piston is 0.13"(according to manual) before the top of its stroke travel (BTDC).

Have not measured my rpms, but it sure sounds sweet and smooth when they are at full speed.

I had both flintstone brakes straining on the ground practically lifting the entire plane to hold it in place while sitting in the seat at full power.

Those engines are powerfull and sing sweetly together....Lovin it!!!!!!!

[Guest]

Ray - Ignore my ignorance. .13" BTDC is a distance. Do you mean, with points breaking at .16" BTDC, another .03" and the spark fires..? I'm trying to understand this timing thing logically and need to know when the spark is created. At the break of the points, a little after the break of the points, or when the break of the points reaches a gap of .14 inch..?

[Guest]

The points should contact and FIRE somewhere between .13-.17" BTDC. 16"-17" BTDC seems to be the best setting.

[rayjb60]

That measurement .13-.17 inches is the distance from the top of the piston, to the top of its travel.

You set a gauge in the spark plug hole and zero it, when the piston is at the top of its travel......then you bring it down .15 of an inch and then you adjust the points so that they close (contacts touch).

You use a continuity tester of some sort to determine exactly when the contacts touch, on the points.

Do be sure that the piston is in the BTDC position....I believe the roation of the prop is clock wise when looking at the front of the engine.

If you time it to the After Top Dead Center, your engine will run very poorly if at all.

If you still dont understand then I will draw a picture and paste it in the post, that should help clear it up.

I think your confusion lays in what that measurement is..... It is NOT the points gap, it is a measurement from the top of the piston to TDC through the spark plug hole.