How does one change the amount off mechanical advance the easiest way? o No: I got one with to much and one with to little! :stmad: (350 point's distr.) Lars
Lars, If you turn the distributors over, you will notice that the total advance is determined by a peg that rides in a slot in the advance plate. On the peg, should be a plastic or brass bushing. This is the advance limit bushing. They typically fall off, allowing too much advance. You can limit your advance by using a larger bushing. With the MSD billet distributors, this is how total advance is set up. You may be able to fabricate your own bushing, or they commonly come in advance spring kits. Another way is to modify the slot. If you drive out the roll pin holding the distributor gear on, and remove the gear, you can pull the shaft out, to get access to the slot. You can then have the slot welded up to reduce it's size. Then you can enlarge the slot to get the total advance you need. There was a very nice article by Nick Sloop in the current Build Sheet(publication of the BPG). Another good reason to join!:Smarty: Here is a picture of the peg, and slot, and bushing on a V8 distributor.
Larry's pic shows the correct way for a points dist, but...large cap HEI is completely different. However, points distributors have many different lengths of slot that the pin/bushing protrudes through, and some will need a larger bushing than reasonable to stop the degrees down. Just have to play with it, and possibly, braze/weld the slot stop up, reduce the slot length to get the degrees you wish. The HEI uses limiting of mechanical advantage of the center plate curvature as it is interfaced with the weights. In other words, the center flattens out in its curvature and then stops the ability of the weights to move it further, making the mechanical advance curve stop at that point, no definate stop "pin" is involved. The only way to do a large cap HEI correctly is to select the correct weights and center. As one of the best starting points for stock to moderate street engines, use parts from late 70's to early 80's 350 Chevy Suburban, center 375, weights 41. These parts are NOT available new as individual parts, but are in a shaft assembly, but you would want to do the wrecking yard thing far before that. If a person would obtain a 375 center plate, it would be easy to make a two pin jig out of it to modify other centers that had enough meat on them to grind/sand off to make a 375 from it. 41 weights are fairly common. This 375/41 combo is common also to new Chevy Performance crate ZZ series engine HEI's, non-EFI, 350/383/454/502/572, in ZZZ, ZZ3, ZZ4, ZZ430, ZZ383, ZZ454, ZZ502/502 and ZZ527. BTW, between all the different center/weight combinations for large cap HEI, there are over 455 different curves/limits. Have fun finding just that right one for YOU! What...you guys think all this curving business was easy or something???
To the point......... Lucky me? Running points distributor! Thanks again LarryGS72 you helped me before:beer And thank you IgnitionMan you seems to keep an eye on everything that ignites, and you been there for me every time some how.:beer What...you guys think all this curving business was easy or something??? Easy, no way! Not for me any how! uzzled: But the more info one can collect the greater the chance off not doing things my usual way = making things wrong the first time! :spank: The mechanical advance on the distr. I am running (-68 4bbl 350) is not enough only 10-12* mec. adv. Maybe messed up by some one before me? (Actually its on a bench in my garage) On the one I pulled for this one, (It basically worked ok, -71 2bbl 350) But with more initial timing (18*) the total ads up to something like +40* bushing in place! The reason why I changed distr. was a better locking drive gear. And a stripped tread in the plate that holds the points! Think I start with the one with the sripped tread I want 18* mec. +18* initial =36*tot (not including vacuum) this gives 0,005x 18* = 0, 09 movement in the slot, right? All in @ 2600. :laugh: Btw Im running "limited advance" manifold vacuum thanks to IgnitionMan(pix and advice), and a lot of hints from the rest off you people on this board, telling me that this was the way to go! :beer One more thing, will the plate that holds the points from a Pontiac fit? A friend off mine bought a firebird 400engine from a wrecking yard, it rely had fired up. He will give me the light toasted/burned distr. if I can use that plate from it! Any how, this seems like a long timer, trying, rip apart, modify and try again to get it right thing! Join? ... I live in Sweden! will you guys still "talk" to me? o No: Lars
Re: To the point......... Just to let you know, It fit's, replaced it yesterday. and the distr. i thought were from -68 was the -71 and vise versa... Lars
