1931 Harley VL timing

[Buster]

Just put a new set of Truett and Osborne flywheels in my stock motor. I have run this motor at around 30 degrees advance in the past. The timing mark on the new T and O flywheels is at 35 degrees btdc. My understanding from the Riders Handbook's description of how far the piston should be down in the cylinder, full advance would be around 30 degrees. I am familiar with the Shope Dope which states that timing should be advanced due to higher octane fuels. Is 35 degrees advance too much for this motor. Should I be closer to 30 degrees.

[Peter Cooke]

That's not a timing mark Buster. It's related to a starting point for the flywheel machining process. T&O told me no issue with using a center pop to transfer the timing mark from an OEM wheel to the new one.

[Buster]

Thanks Peter, do you know if 35 degrees is too much total advance. My flywheel sounds possibly different than yours. I called Truett and Osborne today to confirm and they told me the solid line timing mark on the flywheel is 35 degrees advanced btdc. The mark is actually stamped vertically on the side of the perimeter of the flywheel like on a later model motor and I had to extend the mark around to the outer perimeter so I can view thru my timing hole. Truett and Osburn also stamped a second mark which is a row of dots which is top dead center. Can you tell me how many degrees total advance you motor is set at. I'll try to post pictures of the two marks if I can. Thanks.

[Peter Cooke]

I'm still assembling so am behind you Buster. They did say the mark was 35btdc and that the left wheel is also used for OHV engines, so just transfer the mark from the OEM wheel. That's what i'm planning on doing and then just time as per the owner's hanbook. I'm on the road until the weekend so will post the exact response from T&O and a pic when I'm home.

[Steve Slocombe]

There is plenty of timing adjustment in the left hand twist spiral so I would not get too worried about setting the static ignition timing. Harley said the timing mark should be to the right of the timing hole for high compression motors, maybe 33 degrees, so I would be OK in setting it to 35 degrees today. As you ride the bike it settles down to a happy spot on the timing so that you know where to set it for starting and for regular running.

[joe fxs fxr]

If you want to make a mark at 30 degrees, just measure from the 35 degree mark using this formula:

Wheel circumference (inches or cm) / 360 is how much for each degree. 5 x that amount is your offset.

[Buster]

Rather than make new mark, I decided to use the Truitt and Osborne 35 degrees mark. When I timed it with a light, I adjusted so mark is at front 1/4 of hole, which should approx. 32 degrees. Waiting for weather to ride and test.

[Peter Cooke]

Be interesting to hear how the test ride goes Buster. As promised, here's the response I got from T&O when asking about the mark.

"Yes, the mark on the flywheel is 35 degrees before the Top Dead Center mark. Feel free to make other marks for your use. These start the machining process as the same part is OHV left flywheels and get modified later in the process to be for the VL, but they already have the marks at that point".

[Buster]

Interesting on the mark for machining purposes. Got to wait a few days for weather to warm up for test ride, but I will report back.