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Old 05-17-2013, 07:41 AM   #1
Bob from Northport
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Cool Engine noise at 40mph

We just began driving a customers' 1930 4Dr. after 2 years of body, interior and mechanical work. The customer advised that her father had the engine rebuilt a number of years ago, and what records we have indicate the engine sat for over 20 years.
It idles fine and starts great. At 30-35 it runs smooth and quiet. At about 40mph, there is a rattling noise in the engine that get louder as speed increases. I think it is piston pin rattle.


Any suggestions??

Thanks!!
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Old 05-17-2013, 07:59 AM   #2
Dave in MN
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Default Re: Engine noise at 40mph

Did you slow the engine speed when you heard the noise or did you continue to increase the speed? The reason I ask...there is a typical vibration in most Model A engines that starts at that range of rpm. It typically has this vibration for a 2-3 mph range and then settles or quiets. Please give us more info.
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Old 05-17-2013, 07:05 PM   #3
Barry B./ Ma.
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Default Re: Engine noise at 40mph

You wouldn't be hearing the cam or timing gear rattleing would you ? The cam may be walking in and out because of a weak plunger spring in the front. I had a rattle like that after 2000 miles on a rebuild and took the engine all apart (except for the cam) and found everything perfect. I would put a stethoscope along the valve cover toward the front while the engine is running and rattleing to see where it's the loudest. Does it go away when accelerating or decellerating or loudest in the float throttle position?
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Old 05-17-2013, 10:47 PM   #4
Bob from Northport
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Default Re: Engine noise at 40mph

The noise appears at about 42 mph. It gets louder as the car accelerates. I believe it is wrist pin noise. The noise goes away when the car decelerates. We were told the engine had been rebuilt, but a compression check indicates 45 to 50 lbs on all but one cylinder, and oil on the #1 plug.
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Old 05-18-2013, 12:10 AM   #5
Chuck Sea/Tac
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Default Re: Engine noise at 40mph

Maybe a piston hitting the head? Easy check compared to pulling engine/ pan ect ect.
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Old 05-18-2013, 05:29 AM   #6
Tom Wesenberg
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Default Re: Engine noise at 40mph

Quote:
Originally Posted by Bob from Northport View Post
The noise appears at about 42 mph. It gets louder as the car accelerates. I believe it is wrist pin noise. The noise goes away when the car decelerates. We were told the engine had been rebuilt, but a compression check indicates 45 to 50 lbs on all but one cylinder, and oil on the #1 plug.
How much compression one that one cylinder?
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Old 05-18-2013, 10:10 PM   #7
Bob from Northport
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Default Re: Engine noise at 40mph

The compression was as follows.
1. 50lbs 2. 45 lbs. 3. 54 lbs. 4. 62 lbs.

Does anyone know a procedure to verify pistol pin noise??

Thanks!!
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Old 05-18-2013, 11:23 PM   #8
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Default Re: Engine noise at 40mph

I have no idea of how to check for pin noise at 42 mph. I am curious why you think a pin might be the problem. Model A pins are oversized for their application and rarely fail unless the retainer fails or pops out, in which case the noise would be random at any speed.
My first check would be sticking valves. After 20 years of sitting, they may have gummed up. Next would be rings, for the same reason. Try some Marvel Mystery Oil or some other engine cleaner in the gas and oil, and drive it for 100 miles, although I do not normally like additives. Next would be valve lash. Are the lifters adjustable?
Are you sure you are not hearing detonation? Have you moved the spark advance while accelerating to see what happens?
Also check all nuts and bolts up front for tightness including the hood, fenders, radiator and shell, brake rods etc,--sometimes things just rattle per Dave above. Does it make the same rattle when you increase engine rpm to the same speed as 42 mph (approximatley) when standing still? Just guessing at things to check to avoid a teardown.
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Old 05-19-2013, 12:30 AM   #9
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Default Re: Engine noise at 40mph

PC/SR, Dog here,
Iffin' you don't normally like additives, why you hawkin' Marvel Mystery Oil??? It, like most additives, is just a "SNAKE OIL" money maker with a trick UNFORGETTABLE name! In the old western movies them folks sold "SNAKE OIL" too!!! Did they give it to their HORSES to makem' FAST?? Buster T.
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Old 05-19-2013, 01:18 AM   #10
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Default Re: Engine noise at 40mph

Yo Buster T: I don't put much stock in MMO or the other additives, but just trying to think of ways to save Bob from Newport from tearing down his engine and some of the guys here recommend the stuff. My Pop used to swear by CD-2--I don't know that it did any good but pour that in the carb and watching all the smoke was kinda fun for a kid. He also used to flush the engine by running it a few minutes with kerosene after draining the oil, saying you did not need detergent oil, it was just invented by the oil companies to make money. But I would not recommend any of it for horses.
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Old 05-19-2013, 08:08 AM   #11
Bob from Northport
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Default Re: Engine noise at 40mph

The noise I am trying to describe at 40+mph is the sound a diesel engine makes when running. The engine and idles smooth, starts very easily. Changing the spark advance makes no difference in the noise-not detonation. The engine leaks oil badly from the rear main as well as a leak from the front. We did put MMO when we changed oil, but so far no change. The noise increases as the car accelerates above 40. There is nothing loose-brand new fresh rebuild on the entire car. If valves were sticking, I would not idle as smooth as it does.

Bob
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Old 05-19-2013, 08:44 AM   #12
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Default Re: Engine noise at 40mph

Now that you tell us about the oil leaking, It's time to drop the pan and plasti guage the mains. Bet you can quit her down that way. Not the most fun job but very doable.
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Old 05-19-2013, 10:24 AM   #13
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Default Re: Engine noise at 40mph

To check for a wrist pin rattle, just raise the engine speed and keep removing each plug wire until you find the problem cylinder. That'll also pin point a bad/loose piston or bearing, but, they are all different noises. A loose wrist is a double rap.
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