Posted by pete 23 on January 05, 2014 at 16:45:04 from (74.33.68.83):
In Reply to: Mag vs distributor posted by Farmall A Tractor on January 05, 2014 at 15:58:45:
A battery ign unit gives you a variable automatic spark advance. In other words, with the engine running at slow speed you have zero spark advance and when you speed the engine up the spark advances gradually in relation to engine speed. This is controlled with weights and springs,. Each battery ign unit have a maximum advance limit. Most original equip battery used on the letter number IH tractors, ign units were 40 degree units so as you increase engine speed the spark keep occurring earlier in the cycle up to the max limit which should occur at rated engine speed. With a magneto, the spark is retarded (lag) so at cranking speed the spark occurs at or just after top dead center. That is what the impulse coupling does. Of course it also give mag that extra zip for hot spark at cranking speeds. Once the engine starts the spark is fully advanced. Most are about 35 to 40 degrees before top dead center. So, you see, even at low engine speeds the spark plug fires those 35 degrees before that piston gets to the top. This is too early for slow speeds but they get by with it if engine is not working hard at that speed but it makes the engine run less smoothly. Gasoline needs time to ignite and that is why you have to have a advance in timing as engine speeds increases. You always want that charge to have maximum push on piston when piston is going back down, not still coming up. Magnetos have the advantage that no external battery power is needed to run an engine. Some older tractors had a spark control lever to adjust the timing of spark and that was operator controlled.
We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today. [ About Us ]
Today's Featured Article - Oil Bath Air Filters - by Chris Pratt. Some of us grew up thinking that an air filter was a paper thing that allowed air to pass while trapping dirt particles of a particles of a certain size. What a surprise to open up your first old tractor's air filter case and find a can that appears to be filled with the scrap metal swept from around a machine shop metal lathe. To top that off, you have a cup with oil in it ("why would you want to lubricate your carburetor?"). On closer examination (and some reading in a AC D-14 service manual), I found out that this is a pretty ingenious method of cleaning the air in the tractor's intake tract.
... [Read Article]
All Rights Reserved. Reproduction of any part of this website, including design and content, without written permission is strictly prohibited. Trade Marks and Trade Names contained and used in this Website are those of others, and are used in this Website in a descriptive sense to refer to the products of others. Use of this Web site constitutes acceptance of our User Agreement and Privacy Policy
TRADEMARK DISCLAIMER: Tradenames and Trademarks referred to within Yesterday's Tractor Co. products and within the Yesterday's Tractor Co. websites are the property of their respective trademark holders. None of these trademark holders are affiliated with Yesterday's Tractor Co., our products, or our website nor are we sponsored by them. John Deere and its logos are the registered trademarks of the John Deere Corporation. Agco, Agco Allis, White, Massey Ferguson and their logos are the registered trademarks of AGCO Corporation. Case, Case-IH, Farmall, International Harvester, New Holland and their logos are registered trademarks of CNH Global N.V.
