| JayChicago | -- 10-14-2017 @ 7:59 AM |
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40 Ford, all stock I have pinging (pre-ignition or detonation) at high RPM, 50-55 MPH on the highway. Pings slightly at steady throttle, louder with climbing a grade or accelerating. Does accelerate well. The pinging is only at high RPM; engine starts and performs well in all other conditions. Pinging is never heard at lower RPM, even under hard acceleration. The distributor is newly rebuilt by Charlie Schwendler, so I called him for advice. He suggested it could be a lean condition rather than timing, suggested I first verify that the carburator has the correct .051 jets. I went a step further while I had the carburator open, installed over-sized .053 jets as a test. Deffinate improvement with the larger jets. No longer hear pinging under steady cruise highway speed. But the pinging is still heard when climbing a grade or slight acceleration. A second call to Charlie, and he suggested we now retard the timing to see what happens. No change to the symtoms with timing retarded. Charlie has offered to re-check everything in the distributor, but I am thinking the problem is not there, seems to me the tests done so far are pointing to a lean condition causing detonation. So my questions are: Can there be a vacuum leak somewhere that sucks air only at high RPM? Can you think of anything else that could cause these symptoms that I can test for?
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| TomO | -- 10-14-2017 @ 8:45 AM |
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Jay, Try changing the brand of gasoline that you are using. I had a similar problem with one brand of gas. Last year, I noticed that my 40 now needs mid grade after using regular all of these years. If that doesn't solve your problem, try adding tension to the vacuum brake. Turn the adjusting nut in 1 turn and try it out. You can do this until there is only 3 threads showing. I would not tighten it more than that. Tom
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| ford38v8 | -- 10-14-2017 @ 11:26 AM |
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Jay, you do sound certain that it is detonation you hear, but sometimes a symptom can be misidentified as to the actual cause. If you've had your heads off, perhaps shaved a bit, or even a different type of head gasket thinner than the one you removed, the noise you hear may be a piston kissing the head at high RPM. Alan
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| JayChicago | -- 10-14-2017 @ 12:06 PM |
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Tom I failed to say that Charlie also suggested trying premium gas, which I did. Now have 3/4 tank of 93 octane on top of the 1/4 tank of regular that was in the tank. No detectable difference in the pinging. I will turn down the vacuum brake as you suggest. I would think this would have the same effect as retarding the initial timing that I have already tried. But its easy enough to adjust the brake, I will try that. Thanks for that suggestion.
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| JayChicago | -- 10-14-2017 @ 12:31 PM |
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Alan I agree. I can't be sure what this noise is. It sounds like the typical internal combustion pinging to me, but other things could make a similar noise and send me off on a goose chase. I don't know the history of the car, just purchased last summer. It could very well be that the heads were worked some time in the past. So it could be a piston kissing the head at high RPM. But since going to over size jets the noise is not heard at steady throttle, just under load. Would that symptom be consistent with a piston hitting the head?
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| ford38v8 | -- 10-14-2017 @ 1:45 PM |
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Jay, auto mechanics is not an exact science, much of diagnosis is a guessing game, as is brain surgery. Symptoms can be very similar, and intermittent symptoms are the hardest to diagnose. The best advice, obviously, is to search out the easiest fixes before the more drastic, which you already are doing. Brain surgery, by the way, in the old days a surgeon looking to cure a headache would use a large auger on the patients skull to see the demons inside. Alan
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| TomO | -- 10-15-2017 @ 8:16 AM |
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Jay, In light of your reply about using 93 octane fuel, I doubt if changing the vacuum brake will have any effect. Your problem may be caused by a carbon buildup on the pistons and heads. I would try spraying bursts of Seafoam into the carburetor with the engine above a fast idle for 3 0r 5 minutes and then spray enough to kill the engine. Let it sit for at least 12 hours, add 1 can to the gas tank and then drive it aggressively at various speeds for about 30 minutes. This should clean out some of the carbon build up and eliminate the hot spots. If this takes care of the knock, continue with the Seafoam in every tank for a while. It not only cleans the carbon, but acts as a fuel conditioner also. Changing the vacuum brake setting is not the same as adjusting the timing screw on the side of the distributor. The vacuum brake adjustment changes the rate of the mechanical advance and at when it starts allowing the advance. The screw changes the initial timing and total advance. Tom
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| sarahcecelia | -- 10-15-2017 @ 8:40 AM |
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Check the compression; that could possibly tell you if the heads were shaved enough to cause the ping; but I doubtit is highenough to cause it to ping.My 8BA putting out 176 HP +, with Navarro heads, 4BBL Holley 390 Merc crank, MSD ignition, bored with an Isky cam. The GOOD Ford starter ( I built) ouldn't crankit so I bought a high torque starter.} and it spins it right over and I have no ping at all. Try gas with no alchohol, I use it exclusively. I wouldn't ever use that other cr-p!The no alchhol I get is the next higher grade than regular. Regards, Steve Lee
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| supereal | -- 10-15-2017 @ 11:42 AM |
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Pull the distributor and check the internal springs. The stock distributor for your '40 uses flat springs which can be weak or broken. Be sure the weights move freely, and that there is no perceptible slack between the distributor shaft and the bushings. Your problem sounds like the advance is insufficient at high rpms. The vacuum portion reduces the advance by snubbing the point plate as engine vacuum drops to reduce advance. With today's fuel, it usually isn't necessary. If you have a shop in your area with a distributor machine, have the distributor checked to see how much, if any, it is advancing at various levels of rpm.
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| JayChicago | -- 10-18-2017 @ 9:01 AM |
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Supereal You said "Your problem sounds like the advance is insufficient at high rpms." Symptom is pinging. I would think insufficient advance would cause poor performance, but not pinging. Did you mean to say problem could be excessive advance at high RPM?
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| JayChicago | -- 10-18-2017 @ 9:45 AM |
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Follow-up: Thanks for all your ideas on this problem. Simple things first, I tried the Seafoam treatment as suggested by TomO. No change in the pinging at high RPM. TomO and I discussed further at our regional meeting last night. (so nice for a flathead newbie like me to have access to helpful guys with decades of experience!) Tom is still thinking that the problem could be carbon deposits causing a hot spot that triggers pre-ignition under the just the right conditions. And one treatment of Seafoam with no change only tells us that one chemical treatment didn't do it, does not eliminate carbon deposit as a possible source of the problem. Tom had a couple other ideas that I can investigate. I will post a follow-up if I am able to find anything conclusive.
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