Detonation after replacing timing chain

71FuryGC

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Last week I had the timing chain and sprockets replaced on the 360 in my 71 Fury at a local shop. At the same time the water pump and fuel pump were replaced. I picked it up on a warm afternoon, about 85, and noticed on the way home pinging under light throttle application that went away with more throttle. I was close enough to home when it started that I didn't go back to the shop but called later and the owner told me he didn't touch the distributor or carburetor. I put some Seafoam in the gas and sprayed a can into the carb mouth which helped but didn't completely solve the issue. I was thinking maybe the new timing chain would eliminate any slop from wear on the old chain which had worn nylon teeth on the sprockets. Could the new chain advance the ignition timing slightly if it was correctly installed? Today I decided to remove the air filter assembly to check all of the vacuum lines to see if any were loose. I pushed them all down tight and adjusted the curb idle down a bit as it was a bit fast. I reassembled everything and test drove the car and the ping is almost completely gone. Ambient temperature is in the 80s again today. Any thoughts? Could one of the vacuum lines have been leaking slightly causing a too lean mixture in turn causing engine ping? Car has 87,000 miles and is pretty much stock.
 

70NEWYORKER

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Check the timing!!!!
If somebody adjusted the timing before the chain swap it is most likely advanced with the new chain and no more slop letting the cam and distributor run retarded.
 

71FuryGC

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Check the timing!!!!
If somebody adjusted the timing before the chain swap it is most likely advanced with the new chain and no more slop letting the cam and distributor run retarded.
It was 2 1/2 degrees retarded from stock before the timing chain replacement and wasn't pinging noticeably. I run ethanol free 91 octane. Timing is the next thing to check since the chain replacement. Thanks for the suggestion. I think we're on the same page thinking the new chain may advance the static timing slightly.
 

CBODY67

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One other thing, if the Seafoam might have cleaned the combustion chambers a bit (as you mentioned that it was less after you sprayed the carb), THEN it sounds like a road trip might be in order. Reason? I found out when I was driving the '66 Chrysler home from college once a month, that after each of the 300 mile (one way) trips, the car seemed to run a bit better. Which means that hose long cruises cooked any residual carbon out better than some "one shot" fuel system treatments, or it seems that way.

As you also mentioned that the ping decreased/went away with a bit of thorttle input, then it sounds like the timing is just past/pretty close to optimum for the fuel being used, but that also means that a tweak of the vac advance can's inner spring might do the trick by itself.

For good measure, do recheck the base timing and carb adjustments.

Enjoy!
CBODY67
 

ayilar

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It was 2 1/2 degrees retarded from stock before the timing chain replacement and wasn't pinging noticeably. I run ethanol free 91 octane. Timing is the next thing to check since the chain replacement. Thanks for the suggestion. I think we're on the same page thinking the new chain may advance the static timing slightly.
In my own experience, 91 is not enough -- I need 93 in both Medina's 440 and Poppy's 318, and so that is what I use for all my C-bodies.
 

71FuryGC

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In my own experience, 91 is not enough -- I need 93 in both Medina's 440 and Poppy's 318, and so that is what I use for all my C-bodies.
I went to a local Sunoco station a couple of days ago (where I used to buy race gas for one of my vintage motorcycles) to see if their 93 octane was ethanol free only to find the station closed and the forecourt being dug up!! Thanks for the tip. I'll try 93 too.
Carl
 
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HWYCRZR

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Its disappointing that your mechanic didn’t know enough to check the timing after replacing the chain. Re-setting or checking the timing should have been the first thing he did after starting it up.
 

CBODY67

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Remember, too, that octane availability is related to altitude. In some of the higher altitude areas, only 91 is available, whereas areas under 1000ft elevation can get 93. In the later 1970s, Super Unleaded was 91, too.

When the B/RB engines were introduced, "Premium" gas as 97 Research Octane and "Regular" was usually 93-94 Research Octane. Later, as Premium inched-up to 98-100 Research Octane, Regular increased to 95 Research Octane. With sub-regular (think Gulftane) closer to 91 Research Octane. As in 1974, Phillips 66 FliteFuel had a pump octane of 95.5 in the South Plains area of TX, which would have meant it was just over 100 Research Octane.

So . . . current Regular (87 Pump Octane) would have been the prior sub-Regular grade, current Mid-Grade (89 Pump Octane) would have been normal Regular, and 93 Pump Octane Super Unleaded would have just hit the bottom level of Premium Grade (97-100 Research Octane) from prior times. There are MANY electronic gizmos in modern vehicles which allow them to run well on the lower octane fuels, by observation. There used to be a 100 Research Octane unleaded racing fuel, too, available from racing fuel vendors.

In any event, tune the engine to run well on available fuels for best results.

Enjoy!
CBODY67
 

71FuryGC

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Its disappointing that your mechanic didn’t know enough to check the timing after replacing the chain. Re-setting or checking the timing should have been the first thing he did after starting it up.
I thought the same thing but he test drove it earlier in the morning with cooler ambient temperature and said it drove "flawlessly" :BangHead:
 

71FuryGC

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Remember, too, that octane availability is related to altitude. In some of the higher altitude areas, only 91 is available, whereas areas under 1000ft elevation can get 93. In the later 1970s, Super Unleaded was 91, too.

When the B/RB engines were introduced, "Premium" gas as 97 Research Octane and "Regular" was usually 93-94 Research Octane. Later, as Premium inched-up to 98-100 Research Octane, Regular increased to 95 Research Octane. With sub-regular (think Gulftane) closer to 91 Research Octane. As in 1974, Phillips 66 FliteFuel had a pump octane of 95.5 in the South Plains area of TX, which would have meant it was just over 100 Research Octane.

So . . . current Regular (87 Pump Octane) would have been the prior sub-Regular grade, current Mid-Grade (89 Pump Octane) would have been normal Regular, and 93 Pump Octane Super Unleaded would have just hit the bottom level of Premium Grade (97-100 Research Octane) from prior times. There are MANY electronic gizmos in modern vehicles which allow them to run well on the lower octane fuels, by observation. There used to be a 100 Research Octane unleaded racing fuel, too, available from racing fuel vendors.

In any event, tune the engine to run well on available fuels for best results.

Enjoy!
CBODY67
Thanks again for the input. I'll put some 93 octane in the tank for now and listen carefully. It might contain ethanol however which I believe isn't good for these old sleds! Next will be timing check.
 

71FuryGC

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So today I took a 1/2 inch wrench to the distributor clamp bolt and took a couple of degrees or so out of the initial timing. I guessed at it as I don't own a timing strobe (yet). Good news is pinging is gone and running fine with no overheating. 93 octane with ethanol, which is the only way I can find it locally, didn't eliminate the problem by itself. I'll probably invest in a timing light in the near future. I'll adjust the curb idle back up to compensate for the slightly more retarded timing. Thanks to all who made suggestions.
 
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