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joe in wi 11-05-2009 04:30:19 64.136.27.231 739836 Report to Moderator	i have seen problems mentioned about front mount distributor engines that have been converted to 12V, but no specific description of what those problems are, or thier cures. i just converted my '47 8N to 12V, but have not started it yet, due to finishing the brake job and am curious as what to look out for and how to cure what pops up. any help with this?? [Reply]   [Send Email]
Bruce (VA) 11-05-2009 05:35:51 24.125.26.10 739850 Report to Moderator	Re: '47 8N 6V to 12v conversion front dist. probs? in reply to joe in wi, 11-05-2009 04:30:19   "....but no specific description of what those problems are, or thier cures." You must not have checked the archives. We get at least two or three of these questions a week. As Zane said, get the resistors correct or you"re going to melt the points & the coil. Technology & materials being what they were in the 30"s, that square coil would melt if it ran on much more than 4 amps for any length of time. (see tip # 38 for an example). In order to get a hot spark at the same time the starter was drawing max current from the battery, a ballast resistor was added in the ignition circuit. What that did was add about .3 ohms of resistance in the circuit, added to the 1.5 ohms of the coil. That got you 3.5 amps or so at start up. As the voltage increased when the engine was running to about 7.5 volts, the resistor heated up, adding more resistance in the circuit. 1.0 ohms hot, plus 1.5 ohms of the coil got you down to 3 amps or so to keep from melting the coil. The same rule (actually, Ohm"s Law) applies to a 12v circuit. I= E/R. Current equals voltage divided by resistance. Until you find out the resistance of the coil, you will be playing a very expensive guessing game regarding the value of the resistors you will need in the circuit to keep from melting the coil. A digital multi-meter has two probes & a switch. Set the switch on resistance. Put one probe on the top of the coil & the other on the pigtail at the bottom. It will give you a reading in ohms. Lets just say it reads 3.0 ohms. Your OEM ballast resistor (which you must use) is about 1 ohm hot. A coil a 3.0 ohms, plus the ballast resistor at 1.0 ohm (hot) gives you 4.0 ohms resistance in the circuit. Your 12 volt alternator puts out 14.5 volts. You need to determine current (amps). 14.5 v divided by 4.0 ohms gets you 3.6 amps; close & probably ok. But, and this is the problem......what if the coil is only 2 ohms? Do the math. 14.5 volts divided by 3.0 ohms gets you 4.8 amps! Not good! And, if the coil is less than 2 ohms (and some are) it will fry quickly. So, to get it to 3.5 amps, you need another resistor in the circuit. Either that, or keep spare $30 coil around. 50 Tips   [Reply]   [Send Email]
joe in wi 11-07-2009 18:32:56 64.136.27.231 740229 Report to Moderator	Re: '47 8N 6V to 12v conversion front dist. probs? in reply to Bruce (VA), 11-05-2009 05:35:51   well, yes i did dig thru the archives quite thoroughly before i decided to convert to 12V. and after the installation, i did ensure that all the values suggested were met. i thought that there mignt be some additional concerns with the front mount to be addressed such as,altered point gap or possibly a slight change in the 1/4" measurement from the mount bolt hole and the drive tang parallel for some reason. since no other issues were mentioned other than the electrical setup, i guess its time to fire up the old girl. thanks for all your efforts to supply us all with valuable technical info to keep our machines running at thier best...   [Reply]   [No Email]
Bruce (VA) 11-07-2009 19:01:15 24.125.26.10 740232 Report to Moderator	Re: '47 8N 6V to 12v conversion front dist. probs? in reply to joe in wi, 11-07-2009 18:32:56   If you you have the correct resistors matched to the coil, you should have no problems. Point gap & timing remain unchanged. Just post back if you need any more info.   [Reply]   [Send Email]
ZANE 11-05-2009 05:03:21 205.188.116.20 739842 Report to Moderator	Re: '47 8N 6V to 12v conversion front dist. probs? in reply to joe in wi, 11-05-2009 04:30:19   Be sure to have enough resistors in the ignition circuit. You should have about 3 volts at the ignition wire at top of the ignition coil with the points closed. Do not allow the ignition circuit to be powered up for more than a minute with the engine not running. If not correct voltage at coil the coil and points will be toast! Zane   [Reply]   [No Email]