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Tractor Talk Discussion Forum

Engine knock after carb change update

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Morgan in ar

08-13-2019 18:43:19




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I had some time to work on the old Chevy today. I took out all the plugs, hoping to cough out any debris in the cylinder...no change. No plugs appeared damaged. I bought a bore scope, but I couldn't see anything except for the reflection of the light on the camera on the back of the cylinder walls. I pulled the valve covers, and didn't notice any change in the sound, or see anything odd. Three pushrods weren't rotating, but nothing really loose. All valves appeared to be closing all the way. The knock seems to keep time with the valve train. It sounds kind of like a three cylinder Ford or Perkins, to keep it tractor related. Other than the knock, it is running smooth. I tried listening through a hose, and the sound is loudest behind the water pump, and inside the breather on the front of the intake manifold. Camshaft?, Maybe fuel pump lifter? Could be a coincidence, not related to the carb change. What next? Pull the intake?

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rusty6

08-15-2019 06:25:23




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 Re: Engine knock after carb change update in reply to Morgan in ar, 08-13-2019 18:43:19  
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I use piece of rubber hose as a "stethoscope" to detect the location of noises in the engine. A length of heater hose works well.



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Clarence Slydell

08-15-2019 03:09:38




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 Re: Engine knock after carb change update in reply to Morgan in ar, 08-13-2019 18:43:19  
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Yes, but that's way too sensible.



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showcrop

08-14-2019 18:36:44




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 Re: Engine knock after carb change update in reply to Morgan in ar, 08-13-2019 18:43:19  
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Yeah Mutt and Jeff, I have this picture in my mind of a guy in blue coveralls with a broom stick to his ear walking sideways towards a running engine in a car, as he stares off at the ceiling. LMAO!!



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Hobo,NC

08-14-2019 18:19:58




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 Re: Engine knock after carb change update in reply to Morgan in ar, 08-13-2019 18:43:19  
YTDOT police at work... Good grief... Get a life its not that damm hard to do... You can reach down there and grab the fuel pump with your hand if the chain is hitting the timing cover its gonna be near the crank and will rub a hole in it...
BTW in the old days we used water to break up carbon that should drive the YTDOT police crazy as ell... And really drive those that think ATF is the cure all :))))

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sotxbill

08-14-2019 15:52:05




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 Re: Engine knock after carb change update in reply to Morgan in ar, 08-13-2019 18:43:19  
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You need to hire a professional sticker??

Boy did this post go sideways.

meanwhile back at the ranch,,, working on a tractor........



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Hobo,NC

08-14-2019 11:25:07




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 Re: Engine knock after carb change update in reply to Morgan in ar, 08-13-2019 18:43:19  
If its that skeered pay someone to stick.... Good grief



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Steve@Advance

08-14-2019 08:02:24




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 Re: Engine knock after carb change update in reply to Morgan in ar, 08-13-2019 18:43:19  
I would do some more investigation before disabling it.

Start with taking the belt off, start it and listen. Could be an accessory, crank pulley loose.

Then work back, fuel pump next, take it off.

Timing cover, look for the plastic teeth coming off the gear, chain hitting the cover.

If it sounds like 1/2 crank speed, could be timing gear or cam failing. Usually the front lobes fail first.

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Hobo,NC

08-14-2019 04:42:29




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 Re: Engine knock after carb change update in reply to Morgan in ar, 08-13-2019 18:43:19  
If its the pump you would hear it with a long metal rod are wood rod held again the pump. My first go to is a long handled wood screw driver are a long 3/8" drive extension...

305's use to be bad for this along with a worn timing chain hitting the timing cover.



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Sprint 6

08-14-2019 04:19:57




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 Re: Engine knock after carb change update in reply to Morgan in ar, 08-13-2019 18:43:19  
I would run it without the fuel pump. I have also seen a fuel pump push rod break on a small block one time. Also, if you have any pushrods not turning while running on a flat tappet cam, that lobe is on its it's way out. You need to be planning a cam change. Does the noise change if you pull one plug wire at a time? If it changes volume, the knock is likely lower end. Valve train and things on top of a piston won't change that much by killing the cylinder.

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rustred

08-13-2019 19:10:17




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 Re: Engine knock after carb change update in reply to Morgan in ar, 08-13-2019 18:43:19  
pull the fuel pump. then start it.



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Morgan in ar

08-13-2019 19:22:36




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 Re: Engine knock after carb change update in reply to rustred, 08-13-2019 19:10:17  
Good idea! It would run for several seconds.



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ffreeb

08-13-2019 18:52:36




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 Re: Engine knock after carb change update in reply to Morgan in ar, 08-13-2019 18:43:19  
Back when I worked at the truck garage I did a tune up on a fairly new truck. This was back in the points and condenser days. When I was test driving it after it started knocking something awful. I hadnít done anything with the carburetor. Just by coincidence a screw came out of the throttle shaft. It ended up on top of one of the pistons. I had to pull the head and dig the screw out of the piston. Is it possible something got into the intake while the carb was off?

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Morgan in ar

08-13-2019 18:56:46




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 Re: Engine knock after carb change update in reply to ffreeb, 08-13-2019 18:52:36  
That was my first concern.



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gab

08-13-2019 18:51:44




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 Re: Engine knock after carb change update in reply to Morgan in ar, 08-13-2019 18:43:19  
Lay a broom stick between your ear and the fuel pump, that might be your noise.



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Mutt and Jeff

08-14-2019 05:29:57




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 Re: Engine knock after carb change update in reply to gab, 08-13-2019 18:51:44  
Nothing hurts more than a broom handle used to listen to a running engine accidentally placed in the path of a rotating or moving mass (fan pulley belt alt/gen fan or otherwise) and rammed through your ear an into your skull

for under $10 you can get a mechanics stethoscope

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gab

08-14-2019 07:32:10




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 Re: Engine knock after carb change update in reply to Mutt and Jeff, 08-14-2019 05:29:57  
I've had a stethoscope for probably 30 years, old news. An uncoordinated guy could probably get the fan belt off in five minutes to disable the fan.



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Mutt and Jeff

08-14-2019 10:40:39




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 Re: Engine knock after carb change update in reply to gab, 08-14-2019 07:32:10  
Doesn't mean he would.



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teddy52food

08-13-2019 18:50:03




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 Re: Engine knock after carb change update in reply to Morgan in ar, 08-13-2019 18:43:19  
Maybe a chunk of carbon on top of a piston. Have it idling & flood it out with ATF & let it soak a few days to soften it up. I had that on a 2 cylinder Onan one time. After soaking a while, the knock was gone when it was started again.



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