Main caps

Old 05-16-2007, 04:40 AM
  #1  
demented
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Default Main caps

On my last teardown I happened to see some movement of my main caps on my dart block. Its a 622 bbc with a dart splayed steel cap block.My question is when the caps start "walking" like this does it usually mean that there is too much timing in the motor? This motor is alcohol injected and the plug colors look good. But last year with the same tuneup I had cap walk and a main bearing spin. I am just wondering if it's timing related?
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Old 05-16-2007, 04:44 AM
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topsportsman1
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Some of the time its caused by detination,the chowdering up of the cap surfaces and the block.You got any pics?
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Old 05-16-2007, 06:22 AM
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We normally see this because of three reasons, one mentioned above which is detonation, another which is preignition(or sparatic ignition, not controlled ignitioned) and an out of balance condition. Sit down some time and do the math of grams at 550 RPM on a balance machine and then calculate at 7000 RPM. Don't be overly surprised. But one thing is for sure, look at the bearings and see what story they tell. And you had better take heed, because it is telling you a detrimental story.
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Old 05-16-2007, 01:17 PM
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No I don't have any picks now because the motor was cleaned up,checked and put back together,. I did have to clean up the main cap flats and have it honed. I don't believe its balancing to be my problem although I am just speculating. However I do believe it is ignition related as I have in the past on gas motors run the ignition timing more than I should have. Since I changed to alcohol I have been on a learning curve and have really learned alot the hard way(breaking parts). I quess I need to set the timing back some. Almost all the caps have some sign of movement but the center cap shows the most. As far as bearings They still look good with some almost unnoticable scuffing on the capside bearing in the center where most of the load is placed.I opened up the bearing clearance to .0035 on the last freshen up and that seemed to be better. Any Ideas? Does it seem to be timing?By the way timing is 36 degree's with crank trigger.
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Old 05-16-2007, 03:42 PM
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Gas and alky take the same timing, contrary to what you may hear, you do not use more timing for the alky. we have hundreds of hours of dyno time related to alky engines and did extensive development work with Holley back in the late 70s on there alky carbs.
Assuming you are using the same timing as gas,make sure the polarity of your mag pickup is correct.unplug the pickup from the loom and cut two short pieces of wire.insert one end in the wire loom and cross the wires before plugging them into your pickup. if you have an analog box whichever way gives you the most retarded position on your timing is the correct way.if you have a digital box the most advanced position is correct.if the polarity is backward the timing will scatter above 5500 or so and cause bearing problems.also make sure the mag pickup wires aren't running in the same loom or taped to the orange and black coil primary wires,this will induction fire the coil and also cause bearing problems.Bill
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Old 05-17-2007, 12:58 AM
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I guess it is a little too late to make this post now but here goes;

If your main caps are walking and showing signs on the cap mating surfces of metal transfer, I suggest to look at the crank closely for any color or bearing material on it. If there is or if the bearings show any shrinking find a shop with a Wet Mag Machine and get the crank Wet Magged. Even the highest dollar crnks cn get cracks when they get hot and the main caps move.

Are you torquing the main caps according to the Dart Specs? I suggest to go to the Reher Morrison WebPage and check their specs for their Super Series of engines and torue accordingly.

The example you mentioned of the main cap moving causing a bearing spin? I am wondering which came first. Usually it is a bearing over heated that causes the main caps to move.

Also I hope that you or whomever the machinist is checks the main cap to block register and see if it is still tight. You should be able to measure the distance between registers side to side and measure the main cap and the main caps should be measuring .005 wider. This gives a good tight .005 intrference fit. If you do not have a good tight interference fit, you may have found a part or most of your problem.

I do not suggest to use any oil restrictor in the front smaller than .125.

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Old 05-17-2007, 10:56 AM
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Thanks for the info guys. The first time I had a problem was with the #3 main spinning , The register was screwed up and the bearing did spin and the crank was junk. However after looking at all the parts the outcome of the problem was that I had some stretched main studs. Now after all was put back together with all new parts and machine work(Yes align bored,tightened up on the registers,new arp studs and lunati crank balanced to match my bob weights) and after about 20 runs, I took the motor apart for winter check up. The registers are in good shape the crank in like new shape, journals perfect, and just some slight wear on the lower main bearing half. Like I said earlier, I think I might have too much timing from the minor scuffing on the lower main bearing halves. The motor has run very strong with no indications of problems. But the way the bearings look, It has me concerned.Most guys wouldn't think there is anything wrong with the way the bearings look, but I think I may be on the right track.
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Old 05-17-2007, 11:02 AM
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Assuming you are using the same timing as gas,make sure the polarity of your mag pickup is correct.unplug the pickup from the loom and cut two short pieces of wire.insert one end in the wire loom and cross the wires before plugging them into your pickup. if you have an analog box whichever way gives you the most retarded position on your timing is the correct way.if you have a digital box the most advanced position is correct.if the polarity is backward the timing will scatter above 5500 or so and cause bearing problems.also make sure the mag pickup wires aren't running in the same loom or taped to the orange and black coil primary wires,this will induction fire the coil and also cause bearing problems.Bill
Hey Bill. Can the alternator output wire next to the mag wires cause the same problem? I do have them in the same loom.I have the alt. wire running back to the dash to a juction box, but my mag wires are zip tied along with this wire going to the dash were the MSD box is also.
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Old 05-17-2007, 11:10 AM
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topsportsman1
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Originally Posted by demented
Assuming you are using the same timing as gas,make sure the polarity of your mag pickup is correct.unplug the pickup from the loom and cut two short pieces of wire.insert one end in the wire loom and cross the wires before plugging them into your pickup. if you have an analog box whichever way gives you the most retarded position on your timing is the correct way.if you have a digital box the most advanced position is correct.if the polarity is backward the timing will scatter above 5500 or so and cause bearing problems.also make sure the mag pickup wires aren't running in the same loom or taped to the orange and black coil primary wires,this will induction fire the coil and also cause bearing problems.Bill
Hey Bill. Can the alternator output wire next to the mag wires cause the same problem? I do have them in the same loom.I have the alt. wire running back to the dash to a juction box, but my mag wires are zip tied along with this wire going to the dash were the MSD box is also.
I'm not Bill but I'll put my .02 in on this.

The alternator wire will infact cause interfearance issue.It should have a protective sheild over it just like the wire running from the crank trigger to the MSD box.Or some thing to that affect.
Either or run the wire away from other electronics,as wiring of such,causes "fielding" affects.


Have you ever magnitized a screw driver with a piece of wire wraped around it and a 12 volt battery?
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Old 05-17-2007, 11:31 AM
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The voltage in the magnetic pickup wires,either distributor or crank trigger,is so minute that any other voltage close to it will induce false triggering.
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