Tony D Posted October 17, 2011 Share Posted October 17, 2011 We had conventional distributor in our racer (magnetic trigger) with 45 DCOE's and ran it to over 7500rpms. When we went to ITB's we went to a magnetic trigger which was installed in the stock distributor---the smaller wheel in there was good to 8500 rpms (so they said) and as long as we ran the engine below that point, we never had any issues with spark scatter. When we went above 9500 on the L20A, then we started having reliability issues with the spark. Went to true crank-trigger (basically a bigger wheel) and the issues resolved themselves---same system, different trigger point. The MAGNETIC triggers need spacing between the 'peaks' to get a readable signal in the ECU. The opticals work faster and the circuitry is faster so a larger diameter wheel doesn't do much for you other than allow you to use cheaper components and processors in the ECU (think OEM...) With what JeffP found on the conversion of the optical trigger from the Z32 put into a conventional distributor...I think we could have kept it there and not messed with the hassle of making a crank-trigger bracket. Quote Link to comment Share on other sites More sharing options...
duragg Posted October 17, 2011 Author Share Posted October 17, 2011 Just bought a rebuilt single points Dizzy from "510Doc". Ordered solid breaker plate from NISMO. Replacing front pulley Get all the little stuff done and go from there. Thanks again. Tj Quote Link to comment Share on other sites More sharing options...
johnc Posted October 17, 2011 Share Posted October 17, 2011 From maybe 2000 up the timing marks starts to jump around quite a bit. Much higher rpm is steadies a little bit, but not rock solid.[/i][/b] Sorry to be a bit late. Are you still running a vacuum advance? If so, that is most likely the cause of this jumping around. Even if you're not running vacuum advance, take the distributor a part and tack weld the vacuum advance plate so it doesn't move. Quote Link to comment Share on other sites More sharing options...
duragg Posted October 17, 2011 Author Share Posted October 17, 2011 Vacuum advance is gone. Previous Owner fabricated some little arm to lock the plate. I will install this solid breaker plate and do the other mods and report back. Tj Quote Link to comment Share on other sites More sharing options...
duragg Posted October 21, 2011 Author Share Posted October 21, 2011 Pulled and inspected dizzy and everything is tight. Vac advanced plate is fixed. No movement possible. What I did notice is the mechanical advande slot on one side is welded to limit advance, but the other slot is not. So one weight has additional advance it could go if not for the weld on the other side. Perhaps at certain rpm the lack of constraint of one weight is causing vibration of the other and making the scatter I am seeing. Quote Link to comment Share on other sites More sharing options...
duragg Posted October 21, 2011 Author Share Posted October 21, 2011 (edited) Look closely in the picture below, the slot to the upper left has a small "thing" limiting the centrifugal advance. But the slot to the bottom right does not have any limit. I see no reason not to weld both and recut the slots to precisely the same length to give the total advance range I want. Lots of articles on the internets about timing bounce. I think this is (one of) my problem. Perfectly stable until near the centrifugal "all-in" point. Then bouncy. INcreasing further RPM past that and the bouncy lessens (as centrifugal force exerts more control). Soon it will be known. Edited October 21, 2011 by duragg Quote Link to comment Share on other sites More sharing options...
beermanpete Posted October 21, 2011 Share Posted October 21, 2011 Look closely in the picture below, the slot to the upper left has a small "thing" limiting the centrifugal advance. But the slot to the bottom right does not have any limit. I see no reason not to weld both and recut the slots to precisely the same length to give the total advance range I want. Lots of articles on the internets about timing bounce. I think this is (one of) my problem. Perfectly stable until near the centrifugal "all-in" point. Then bouncy. INcreasing further RPM past that and the bouncy lessens (as centrifugal force exerts more control). Soon it will be known. It looks the same as the distributor in our car. It seems to be that way from the factory. Quote Link to comment Share on other sites More sharing options...
duragg Posted October 21, 2011 Author Share Posted October 21, 2011 Hard to see in the picture, but one slot is closed down a bit and the other is standard length. So when the first peg gets to full advance, the second is still being TuggeD on by the other weight. Uneven tugging on the centrifugal advance cannot make timing any MORE stable. Quote Link to comment Share on other sites More sharing options...
beermanpete Posted October 21, 2011 Share Posted October 21, 2011 Hard to see in the picture, but one slot is closed down a bit and the other is standard length. So when the first peg gets to full advance, the second is still being TuggeD on by the other weight. Uneven tugging on the centrifugal advance cannot make timing any MORE stable. They slots are supposed to be different. See page EE-32 in the service manual. EE-32 Engine Electrical.pdf It might not help timing stability, but it is factory. Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 21, 2011 Share Posted October 21, 2011 This is all standard distributor stuff. Polishing of centrifugal weight working ramps, using 'sticky' grease to smooth the advance, altering the weight/spring tension/slot/peg to limit advance/retard... The bouncing will happen as a function of inertia and the springs working against it. The way to get around it, is to go fully digital. That's it. Any mechanical timing device will have a range of advance that is there depending on which point you are at--there is only narrowing the range. You will not make it rock steady unless the mechanical action is eliminated completely. Quote Link to comment Share on other sites More sharing options...
duragg Posted October 21, 2011 Author Share Posted October 21, 2011 You mean to tell me this party's been going on for ages and I just found out about it!! Quote Link to comment Share on other sites More sharing options...
duragg Posted October 21, 2011 Author Share Posted October 21, 2011 They slots are supposed to be different. See page EE-32 in the service manual. EE-32 Engine Electrical.pdf It might not help timing stability, but it is factory. Those pictures are all a "dual points" dizzy. I have a single points dizzy. Would like to compare FSM pictures of the two. FSM says they have different centrifugal system. Quote Link to comment Share on other sites More sharing options...
duragg Posted October 21, 2011 Author Share Posted October 21, 2011 (edited) Pictures. The weights. Except for different springs seem identical. The shaft. Yes, by design it has different slots. But somebody has welded the shorter slot shorter. My issue with this is that when the first weight hits its stop, the other weight is free to continue tugging on the arm. It can't go far, but it can probably bounce around enough to making the timing dance a bit. Machine shop has the parts and they are going to weld and recut so the slots are both equal. Both weights will be on their stops when the advance is all-in. If (or when) this doesn't help or make it worse you an all laugh at me and say "we told you so noobs". Edited October 21, 2011 by duragg Quote Link to comment Share on other sites More sharing options...
NewZed Posted October 21, 2011 Share Posted October 21, 2011 The obvious solution is a tiny shock absorber. Try Hot Wheels or Matchbox. Quote Link to comment Share on other sites More sharing options...
duragg Posted October 21, 2011 Author Share Posted October 21, 2011 The new Hot Wheels are made in China and they no longer use Nitrogen Charged shocks. You tried sourcing NOS N2 charged hot wheels shocks? Insane expensive. Quote Link to comment Share on other sites More sharing options...
duragg Posted October 21, 2011 Author Share Posted October 21, 2011 Fedex ground just came by... Happy FRIDAY! I got one of these because my pully doesn't sit right at Zero-TDC with the piston and cam at TDC. Not certain it hasn't moved. I got one of these too... just in case... Quote Link to comment Share on other sites More sharing options...
duragg Posted October 21, 2011 Author Share Posted October 21, 2011 I found this in my front yard last night, but I don't think it is related to the timing issue. Quote Link to comment Share on other sites More sharing options...
duragg Posted October 22, 2011 Author Share Posted October 22, 2011 Machined the slots in the advance for perfectly equaly engagement at the limit of advance. Didn't do a darn thing. Timing mark still dances above 3000rpm. Maybe they all do that?? Its dead nuts steady just below that RPM. My motor man says the Crane XR3000 is a POS. He is right a lot more than I am. So maybe I will just buy a Pertronix and give that a whirl. I still find it odd that the timing would start dancing like a light switch at a certain higher RPM. Quote Link to comment Share on other sites More sharing options...
duragg Posted October 22, 2011 Author Share Posted October 22, 2011 Why do I need any centrifugal advance at all? This is a Rat-racer driven 5 times a month, mostly all at 3000+ RPM and full throttle. A little cruising and idling around. It stinks, full of holes, stripped interior, NOT a daily drive. If it is hard to start... even better. Running 50/50 100LL and 91 octane fuel. Do I need it for starting? or for pinging reduction? Educate me please. Quote Link to comment Share on other sites More sharing options...
beermanpete Posted October 22, 2011 Share Posted October 22, 2011 Why do I need any centrifugal advance at all? This is a Rat-racer driven 5 times a month, mostly all at 3000+ RPM and full throttle. A little cruising and idling around. It stinks, full of holes, stripped interior, NOT a daily drive. If it is hard to start... even better. Running 50/50 100LL and 91 octane fuel. Do I need it for starting? or for pinging reduction? Educate me please. The only reason I can think of for reataining the spark advance is for starting. I have considered fixing mine as well. On the race track the RPM is high enough the advance is always all-in. A crank triggered system would end the problem but some race group rules prohibit them. Quote Link to comment Share on other sites More sharing options...
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