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Author Topic: Rebuilt motor tuneup  (Read 4381 times)
bob69
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« on: January 25, 2006, 01:34:33 PM »

I need help trying to figure out why my 302 (30-30 cam ) wants to run at 20 before. It has a MSD dist ( unlite ) that I know nothing about, could this be messing with my setting? It seams to run good at 20 before. I doin't think there's a vacume leak, it idels fine but I only get about 8 lbs. of vacume. the cam was advanced 4 degrees could this be it. And last I think I might have the valve lash to tight ( I doin"t here any noise under the covers ).One more thing is the gas is 6 months old . Any ideas Thanks Bob
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JohnZ
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« Reply #1 on: January 25, 2006, 09:54:23 PM »

Does the distributor have vacuum advance? If so, initial timing is set with it disconnected and plugged. If you don't hear any valvetrain sounds, the valves aren't lashed correctly - if you drive it like that, you'll burn the valves. Click on the box at the top of the page labeled "CRG Reports" and go to the Research Report on adjusting valves with the "30-30" cam. Most 302's only pull about 9"-10" Hg. vacuum at a 900 rpm idle - it's characteristic of that cam.
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'69 Z/28
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bob69
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« Reply #2 on: January 26, 2006, 04:25:54 PM »

Thanks John, I think the valves are to tight,I have rollers and when I adjusted them they seam to compress a little when I pushed down on the rod side of the rocker.So I pushed down on them and gaped them that way. Everything is new and I thought they needed to break in in order to seat.How much drag should I have on the feeler gage? And does a 302 ever have a sweet spot other than at 4 before,like mabe 20 before? Thanks Bob
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Grsmnkey
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« Reply #3 on: January 27, 2006, 07:06:59 AM »

Hi,

Didn't you have the same issue before the motor was rebuilt?  Are you sure you have the correct Harmonic Balancer and the correct timing tab?  When your builder put it togetehr did he check the marks to see they matched at TDC (most builders don't)?  Manually check TDC by putting it at TDC without looking at the timing marks, then look at the timing marks to see if they match.
« Last Edit: January 27, 2006, 02:25:03 PM by Grsmnkey » Logged
bob69
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« Reply #4 on: January 27, 2006, 12:51:25 PM »

I never thought about wrong equiptment, everything else I took off was right,But makes good sence. I'm going to check it out. and yes I am the guy. Bob
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JohnZ
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« Reply #5 on: January 27, 2006, 10:28:11 PM »

If you have roller rockers with a true 1.5:1 ratio, change the recommendation in the Research Report for lashing the valves for your car to .030" cold (the .026" cold lash recommendation is only for use with stock stamped rockers, which are actually only 1.37:1 at initial contact). As noted above, get a piston stop tool and verify ACTUAL TDC vs. what your balancer and timing tab show, and re-mark the balancer with a new timing index line aligned with "0" if necessary. If I had a dollar for every mis-matched balancer and timing cover I've seen in the last 20 years, I could afford to buy at Barrett-Jackson.  Grin
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'69 Z/28
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bob69
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« Reply #6 on: January 28, 2006, 08:54:19 AM »

Thanks again everybody, I'm going to find TDC today. If TDC is off by 20 degees and I adj my valves with the old mark,would that make that much of a differance on the ramps? Bob
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JohnZ
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« Reply #7 on: January 29, 2006, 12:04:48 PM »

I'm out of town this week in Florida, so I don't have my "30-30" crank angle-cam lift diagrams handy; I'd find true TDC, re-mark the balancer, then adjust the valves.
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'69 Z/28
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bob69
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« Reply #8 on: January 29, 2006, 07:56:56 PM »

Well I had a hard time tring to find a piston stop. So I took a piece of wooden dowl rod 1/2" and used it, the piston stoped at the same point both ways( a little over 2" ) so that means my marks are good right? I know you told me not to advance the cam a few degrees, but I forgot to tell the shop. So since it is advanced 3- 4 degrees would that mess with the timing? The only other thing I can thik of is the dist. It was in the car when I got it (mallory unilite ) Thanks Bob
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JohnZ
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« Reply #9 on: January 30, 2006, 09:05:35 PM »

If the two marks from your piston-stop exercise are both exactly the same distance from the "0" mark on the timing tab, your existing marks are OK. Advancing the cam 4* shouldn't have any significant effect on ignition timing - will just move the torque curve down a little.

I don't recall how the Unilite distributors manage centrifugal advance - haven't had one for many years. I run my '69Z with 8*-10* initial advance, 26* in the distributor, all in by 2800 (for total timing of 34*-36*), and a NAPA/Echlin #VC-1810 vacuum advance unit that adds 15*, and is fully deployed at 8" Hg. and connected to full manifold vacuum.
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'69 Z/28
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bob69
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« Reply #10 on: January 30, 2006, 10:57:01 PM »

John, I went with the 45 sparkplug,do you think because I have a high voltage coil the plugs might be to hot. And this could be part of the problem with my timing. I think the problem is in the dist. or the way its set up. I wish I had a set of points to fool with. Thanks Bob
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JohnZ
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« Reply #11 on: January 31, 2006, 10:48:17 AM »

Doubt if the plugs have anything to do with it - I run AC R45S plugs in all my small-blocks for normal driving - 44's tend to foul somewhat in around-town driving, and 43's are WAY too cold for normal driving.
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'69 Z/28
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McKenzieDave
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« Reply #12 on: March 04, 2006, 05:02:24 PM »

This camshaft will prefer a lot more initial timing.  The only problem you'll have is in the distributor.  Most out of the box distributors have 20-24 degrees of mechanical advance.  Add it up--too much timing at higher RPM which will lead to severe pre-ignition and engine damage.  Your Unilite is VERY adjustable, but will require the tuning kit to do it right.  Contact Mallory or simply read the instructions for the Distributor if you have them.  I recommend no more than about 36 degrees of total timing for safety sake.  Good fuel and fine tuning can make a big difference from there.  Dave
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