Knocking/Rattle
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Senior User
Joined: Nov 2009
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From: TX
Knocking/Rattle
I've been chasing a "marbles in a can" sound in my motor for about a month. The cause has been narrowed down to too much advance, but I would like some wisdom on what's causing it to advance like it is.
Ok, the basics on the motor:
-1972 Dearborn-casted 400 from what I guess is a LTD.
-Motorcraft 2100/2150, 1.08 venturi/287cfm w/50F jets
-Intake manifold is from a 73 T-bird
-Comp Cams magnum timing set set to compensate for the 4* retard in the stock cam.
-Reman. distributor with Accel points eliminator kit.
-Accel Super Stock coil
-195* thermostat
-Hooker headers
-91-93 octane gas
I got a cheap tach, hooked it up with a timing light and no matter how I set the screw in the vacuum can it would always run past 36* before reaching 3000 rpm (actually hit it about 2500-2800). I set the initial timing back to 6* and it still rattles under load. With the vacuum line unplugged the motor will it 34* @ 3000 RPM, will not rattle under load, and has much more power - although the mileage is terrible.
So given this, what do you guys recommend to eliminate the knocking?
Ok, the basics on the motor:
-1972 Dearborn-casted 400 from what I guess is a LTD.
-Motorcraft 2100/2150, 1.08 venturi/287cfm w/50F jets
-Intake manifold is from a 73 T-bird
-Comp Cams magnum timing set set to compensate for the 4* retard in the stock cam.
-Reman. distributor with Accel points eliminator kit.
-Accel Super Stock coil
-195* thermostat
-Hooker headers
-91-93 octane gas
I got a cheap tach, hooked it up with a timing light and no matter how I set the screw in the vacuum can it would always run past 36* before reaching 3000 rpm (actually hit it about 2500-2800). I set the initial timing back to 6* and it still rattles under load. With the vacuum line unplugged the motor will it 34* @ 3000 RPM, will not rattle under load, and has much more power - although the mileage is terrible.
So given this, what do you guys recommend to eliminate the knocking?
Thread Starter
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Senior User
Joined: Nov 2009
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From: TX
Rattles under load, when warmed up and especially when it's hot out - the rattle starts when I have my foot in the petal but not when gradually accelerating. Doesn't rattle under the same conditions if the vacuum can is unplugged and the line is sealed up.
I didn't rebuild the motor so I am unsure of the compression ratio.
I didn't rebuild the motor so I am unsure of the compression ratio.
Thread Starter
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Senior User
Joined: Nov 2009
Posts: 125
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From: TX
Edit: Found this article:
http://www.phoenixcmr.com/Distributor_tech_article.htm
Lead Driver
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Senior User
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From: TX
Yeah I had taken it off. It was pretty lightweight.
BTW guys, what year did Ford start retarding the cams in these engines?
BTW guys, what year did Ford start retarding the cams in these engines?
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Senior User
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From: TX
A couple things I found:
- The shutter was sheared from the rotor on my Accel points eliminator kit. I poxy'd it back together to get to work this morning, and I have a new one coming from Summit.
- Found out that '73 was the first year Ford started retarding the cam in the 400. I was under the impression that '71 was the only block with a non-retarded cam. So my cam has 4* of extra advance through my timing set. I've driven with it like that for the last 4 months/2000 or so miles. Ugh.
- Tightened up a couple loose header bolts
- replaced the 195* thermostat with a 180* one to help it run cooler in the Texas heat.
- replaced the carb gasket between the body and choke assembly, which was in bad shape.
Overall the motor still rattles under load when the vacuum advance is hooked up. I plan to back the advance off today to 6* which will give me 4*+ 6* + 26* = 36* and (hopefully) stop the rattle until I can adjust the timing set this weekend.
Lead Driver
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Is the timing chain at zero, straight up right now ? 36* could be a little much. the initial should be around 10*, as much as it will take without spinning over hard, total might have to be backed off. I don't think the vacuum advance has anything to do with it because port vacuum will go away under a load and the centrifugal will be shut down.
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From: TX
Is the timing chain at zero, straight up right now ? 36* could be a little much. the initial should be around 10*, as much as it will take without spinning over hard, total might have to be backed off. I don't think the vacuum advance has anything to do with it because port vacuum will go away under a load and the centrifugal will be shut down.
Today I backed off the dizzy to about 5* (for a total of 9* initial) and the knocking seems to have mostly subsided for now.
Will it mess up the engine to run it like this for any length of time?
Lead Driver
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I'd put it back to zero, odds are it will always knock in the 4* slot. It won't mess it up but as you have found out it won't run right there. You might want to try colder plugs and thermostat if you don't want to change it back for a while but there is just no real way to crutch it with trying to retard the dizzy.
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