Distributor Knock ? - Impala Tech
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post #1 of 5 (permalink) Old 10-17-2013, 06:32 PM Thread Starter
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Distributor Knock ?

This is an ongoing nagging issue. I can feel a knock around the #4 and #3 post and the vacuum canister on the HEI cap. I have done a search on this read many posts and with all of their successes they didn't work for me.
What I have done ( before I found noise in cap ) so far is:
Replaced a good timing chain, found rubbing on inside of cover - no fix.
Multiple valve adjustments.
Modified valve cover breather baffle.
Good operation of water pump, fuel pump and rod; fan and assembly.
After I discovered knock in cap I:
Minimized shaft endplay to .0023".
Checked pole and assembly for centering.
No side play in shaft
Rotor and cap show no markings, yes thay are mounted properly.
Cap contacts firm
Gear has normal polished wear but not gouged.
Any else I need to check before I go to a new GM piece?
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post #2 of 5 (permalink) Old 10-18-2013, 01:46 AM
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Possible worn cam lobes. Since it is the slight slope of the worn in flat tappet lifter that keeps the cam from walking forward on deceleration. With worn cam the gear rides up and down as the cam moves fore and aft in the cam tunnel (also accounts for wear in timing chain cover).

Without DZZP in your motor oil the cam will wear away at an alarming rate going flat very quickly.

Big Dave
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post #3 of 5 (permalink) Old 10-18-2013, 09:14 AM Thread Starter
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Thanks Dave, I am running DZZP and VR oil. But it is still possible. As a last resort I'll change the cam gear and go with a GM cap/rotor as these are the highest wear parts in there now.
Not trying to look at that elephant in the room yet.
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post #4 of 5 (permalink) Old 10-18-2013, 03:43 PM Thread Starter
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Just to pass along my experiences to other's. I purchased an AC Delco rotor and cap $26 at Advance Auto. Immediately I noticed the AC cap--made in Mexico, dam* it-- the contact's extended further down the cap than my Canadian made cap by at least .125". I installed both and ran with no knocking issue, just the sweet sound of big block rockers These replaced units were brand new pieces. The Q.C tolerances on replacement parts from one to another is troubling nowadays.
I'm thinking spark scatter from the Canadian cap with shorter contacts.
Now on to that annoying exhaust leak.
Now final timing is stable at 22* base; 35* total; 48* with vac. advance and no labored starter. Nailed down the dist. clamp and now I'll be able to move on to exhaust and bodywork without the mechanical's on the back burner.
The elephant has left the room!
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post #5 of 5 (permalink) Old 10-23-2013, 06:52 AM
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You did good
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