Hello all;
I'm trying to set the ignition timing on my stock standard XB33 motor,
using a degree disc on the main-shaft
Would any-one have the figure for the degrees of rotation back from TDC for when the points should just start to open.
Thanks Keith
Keith
26 deg BTDC is what I do my M20 at.
If you know the rod length , stroke and piston height from the pin to the crown then there are a lot of desktop calculators out there, usually an excel spread sheet.
The one I use is on the other computer which is cooked for the time being.
Google Piston drop to crank shaft rotation calculator" and you will get about 100 hits.
Try a few of them as some of the people who posted them have the mathamatical skills of a gold fish and computer skills to match
The rod length is eye to eye ( centers) and the piston height is eye ( center) to crown.
most of them are in mm so be a litle weary.
Thanks for the reply' Yes I have had a look a some of the online calculators.
I tried "stroke" (88mm) Rod length 7'3/8" (eye to eye), and degrees (from which I could reverse calculate to obtain length) but to no avail unfortunately.
I didn't know to include compression height though. (axis of gudgeon to piston crown measurement)The formula using trigonometry with cosine angles and algebra ect, is beyond me at my age.
I will have to try your recommended google search
Thanks again Keith
I just measure mine down the plug hole. Its 7/16 BTC on earlier engines and 3/8 BTC on later, I do both of mine at 3/8 BTC ones an early engine the other a later one. Never had problems its not as if they are race tuned.
