| fenbach | -- 06-09-2013 @ 8:51 PM |
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when i accelerate quickly in first gear and reach maybe 20 MPH, i hear a loud noise coming [i think] from the engine - a stock '36 LB. it sounds like something banging very rapidly like a valve hitting the head, but seems faster than that. almost a screeching sound. it only happens in first gear and only when i accelerate rapidly and only after the engine reaches a fairly high RPM. if i let up a little, the noise goes away. if i accelerate moderately, no noise. i recently put headers and duals on, but don't see how that could be part of the explanation. also cleaned the carb and reset the timing - at 4deg BTDC. i thought, too, that maybe it was pinging horribly but the engine doesn't ping at all under a load. it also sounds something like a fan blade hitting the radiator, but i have an electric fan and an alternator. hope someone has a clue. bob
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| 40 Coupe | -- 06-10-2013 @ 3:40 AM |
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If the problem happens in 1st gear and not in 2nd under the identical conditions. Look to the transmission and not the engine. Drain the fluid and see if anything comes out beside fluid.
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| supereal | -- 06-10-2013 @ 4:03 PM |
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Check to see if you have at least an inch of clutch pedal free play. If not, your noise may be from a failing release(throw out) bearing. If the bearing remains in contact with the pressure plate fingers, it will eventually fall apart and make a "horrible" noise. The next best guess would be the transmission input shaft input bearing. They are often furnished with a shield over each side. We remove the shield facing the inside of the box before installation. This insures adequate lubrication. They get noisier under acceleration as driveline tension increases. You may have reduced the free play as you installed the duals, as getting past the clutch pedal and linkage is tough. This message was edited by supereal on 6-10-13 @ 4:04 PM
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| fortyfordguy | -- 06-11-2013 @ 3:40 AM |
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Any chance the fan is hitting something? If so, check all your motor mounts and the stay rods.
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| fenbach | -- 06-11-2013 @ 5:10 PM |
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the noise does sound like the fan rubbing against the radiator. but as i said, i just have an electric fan. all the mounts are snug. i drained a spoonful of oil from the tranny [which is full] and found no sign whatsoever of metal particles. it also sounds like maybe the counter weights on the clutch pressure plate rubbing against the bell housing. but again only happens in first gear or, i discovered, in second if i really wind it out. i reved the engine quite a bit in neutral with no trace of the sound even with the clutch depressed. the engine did get pretty hot recently and i lost oil pressure at low RPM. which made me think maybe i had scored something in the engine. i'll remove the tranny cover one day and hope to better locate the source of the sound. but any other suggestions/guesses are welcome in the meantime. of course, i'll have some of the local boys ride with me to get their opinions. one other thing, i removed the mechanical fuel pump and push rod. not that i can think of any connection to the noise.
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| supereal | -- 06-11-2013 @ 9:24 PM |
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That is the first time you mentioned oil,pressure loss. The noise is likely a spun rod bearing. It usually happens so quickly you don't have time to shut it down. If your LB is a poured block, it is probably toast.
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| TomO | -- 06-12-2013 @ 6:41 AM |
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Could the horrible noise be your alternator belt slipping? Tom
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| fenbach | -- 06-12-2013 @ 8:41 AM |
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thanks to both tomO and supereal for more suggestions. of course, i have to hope it's just the belt and not a rod bearing! i did snug the belt with no apparent difference, however. and the sound is really more metallic. even so, i'm puzzled that i basically only hear the sound when accelerating rapidly in low gear. i thought LB stood for "loose bearing" or "late block" [with insert bearings]. regardless, that is what i have. now i have to ask if the pan can be removed by just raising the engine. and if i could identify a bad rod [or main] bearing without removing the caps. thanks again. i'm glad you fellers don't have better things to do!
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| Stroker | -- 06-12-2013 @ 8:55 AM |
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Fenbach: This may be a "stretch", but is it possible that one of your recently installed head-pipes (between the headers and mufflers) is tapping on the frame under hard acceleration? These usually pass through the oval holes in the frame, and if your motor mounts are soft, contact is possible. I'd look for any evidence of contact, such as a shiny spot on the pipe.
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| TomO | -- 06-13-2013 @ 9:22 AM |
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Before I would drop the pan, I would start looking for spots where two parts are making contact. If I could not find any, then I would start disconnecting easily removed objects, such as the electric fan and alternator. If you did not have the noise before the duals were added, look at the installation of the duals for possible interference points. Tom
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| joe b | -- 06-13-2013 @ 1:08 PM |
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I think Tom O and Stroker might be onto something. I had a similar noise after duals and Smithy's were installed. The pipe on the right side was hitting just behind the steering box. Remember the engine torques over a bit on hard acceleration.
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| trimboulster | -- 06-13-2013 @ 2:26 PM |
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Bob, If you are running a pre '49 flat head V8 engine, you probably have a rod knock. These engines had "floating" rod bearings, one set per throw and two rods per throw. The reason the noise is only heard in low gear on fast take off is because it is under a load at the fastest rpm. If you have a tach, you can check this out. Watch the tach as you go up through the gears. A good way to check for a rod knock is start the engine, put it in gear, hold your foot on the brake and slowly let out on the clutch at the same time, and you will hear the knock. Usually flat head engine knocks are caused by low oil pressure or a low oil level. You can get a correct oil pressure reading by removing an oil passage plug and connecting an accurate 60 psi gage. Most of these engines run about 30 psi oil pressure and below. I had a 40 Ford once that only had about 5 psi pressure when cold and about 15 psi when hot. The rod bearings would only raddle when the oil was low though. I think you have an oil pressure problem and you shouldn't have to do anything to the engine if you get the pressure problem corrected soon. At this point, you can't trust the dash oil gage. Lowell
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| trimboulster | -- 06-13-2013 @ 2:28 PM |
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Bob, If you are running a pre '49 flat head V8 engine, you probably have a rod knock. These engines had "floating" rod bearings, one set per throw and two rods per throw. The reason the noise is only heard in low gear on fast take off is because it is under a load at the fastest rpm. If you have a tach, you can check this out. Watch the tach as you go up through the gears. A good way to check for a rod knock is start the engine, put it in gear, hold your foot on the brake and slowly let out on the clutch at the same time, and you will hear the knock. Usually flat head engine knocks are caused by low oil pressure or a low oil level. You can get a correct oil pressure reading by removing an oil passage plug and connecting an accurate 60 psi gage. Most of these engines run about 30 psi oil pressure and below. I had a 40 Ford once that only had about 5 psi pressure when cold and about 15 psi when hot. The rod bearings would only raddle when the oil was low though. I think you have an oil pressure problem and you shouldn't have to do anything to the engine if you get the pressure problem corrected soon. At this point, you can't trust the dash oil gage. Lowell
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| trimboulster | -- 06-13-2013 @ 2:32 PM |
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Bob, If you are running a pre '49 flat head V8 engine, you probably have a rod knock. These engines had "floating" rod bearings, one set per throw and two rods per throw. The reason the noise is only heard in low gear on fast take off is because it is under a load at the fastest rpm. If you have a tach, you can check this out. Watch the tach as you go up through the gears. A good way to check for a rod knock is start the engine, put it in gear, hold your foot on the brake and slowly let out on the clutch part way at the same time, and you will hear the knock. Usually flat head engine knocks are caused by low oil pressure or a low oil level. You can get a correct oil pressure reading by removing an oil passage plug and connecting an accurate 60 psi gage. Most of these engines run about 30 psi oil pressure and below. I had a 40 Ford once that only had about 5 psi pressure when cold and about 15 psi when hot. The rod bearings would only raddle when the oil was low though. I think you have an oil pressure problem and you shouldn't have to do anything to the engine if you get the pressure problem corrected soon. At this point, you can't trust the dash oil gage. Lowell
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| trimboulster | -- 06-13-2013 @ 2:34 PM |
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Bob, If you are running a pre '49 flat head V8 engine, you probably have a rod knock. These engines had "floating" rod bearings, one set per throw and two rods per throw. The reason the noise is only heard in low gear on fast take off is because it is under a load at the fastest rpm. If you have a tach, you can check this out. Watch the tach as you go up through the gears. A good way to check for a rod knock is start the engine, put it in gear, hold your foot on the brake and slowly let out on the clutch part way at the same time, and you will hear the knock. Usually flat head engine knocks are caused by low oil pressure or a low oil level. You can get a correct oil pressure reading by removing an oil passage plug and connecting an accurate 60 psi gage. Most of these engines run about 30 psi oil pressure and below. I had a 40 Ford once that only had about 5 psi pressure when cold and about 15 psi when hot. The rod bearings would only raddle when the oil was low though. I think you have an oil pressure problem and you shouldn't have to do anything to the engine if you get the pressure problem corrected soon. At this point, you can't trust the dash oil gage. Lowell
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