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Well after all the work sorting out the DRT-08 carb and getting the car running very decent it decided to throw more at me. Today when moving cars around it developed a knock. I was pulling it back in the driveway when it started and got in the garage quickly and shut it down.  Removed the fan belt and started it up and sure enough, there it is at the front of the motor. Had 35-40 PSI oil pressure and been driving it after an oil change 2 weeks ago. Had it out last night no issue. This morning, not so good.  It sounds like it is coming from the front of the motor low and quite pronounced. Don't know much about these early 4 cylinder motors but guess I am about to learn.  The inside of the pan was very clean with no sludge I could feel so am thinking it was rebuilt sometime fairly recent. Had not had much time to enjoy the car as the carb crapped out 2 months after getting it.  So where is a good place to start ? Any books around on chrysler corp 4 cylinder motors ? I have a good idea of what I need to start on but want to be sure.

Edited by Brooklyn Beer (see edit history)
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I redid my 32 PB 4cyl myself in 1986?, except for having the bare block bored 30 over. Everything else including grinding valves I did myself. Very simple engine without requiring a specific PA/PB manual. My bearings and crank were perfect and held up fine, even with the new pistons which have more drag during break-in.

 

I find it odd that a rod bearing could start knocking while moving the car around, not even hot?, especially after a road run prior to that day, and it had no noises.

 

I'd suggest pulling one plug wire at a time and see if there is any change at all.  If that does not change the noise in anyway at all, take the belt off again for safety, and use a very long screwdriver or long dowel as a way to listen to different areas, like multiple engine block areas and also timing cover area.  Just hold it to your ear, it works well; but be careful near the spinning lower pulley.

 

I'd do that before pulling the pan.  Yes, the pan comes off easy, but it would help to isolate the noise first in case all the rods are good after pulling the pan without listening first.

 

also, decades ago on some random engine brand, I had a broken tooth on a timing gear that made a steady knock.  Keep an open mind when chasing noises, rather than assuming a knock must be a loose rod.

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Thanks for the advice. I always let the engines in my cars warm up and always do a quick drive of a mile before putting them up. This time I was just moving from garage to garage so only did a quick spin to the dead end (1/4 mile) so I could line up coming into the driveway and garage. It started knocking (more of a tap to start which I thought was a fan blade hitting something really) as I was 100 yards from the garage. Pulled in and shut the engine down and looked for something hitting. Nope.  Some I pulled the belt and the fan spins freely but with a little in and out play. Gen spins free.  So put belt on and started it up. (like a dream she starts now Grrrr) and heard a different sound which now seemed like more of rapping. Shut it down and removed belt and started up again and that is when it sounded really like a rod knock.  I am running over tonight to pick up an engine stethoscope. I had recently changed oil to my summer oil in TX. 15w40 HD. For winter it was 10w30.  Idle oil psi is 32-34. Gets 100 here. It was 96 when I did the oil change on operating temp oil. I have no sludge in the pan but no paperwork on when the motor was done. Only had the car for 6 months.

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I had that happen to me. My car had been sitting for quite some time. I got the car running and after about 200 miles it developed a rod knock. I took the bottom end apart and found that No 4 rod had too much clearance. I rectified it and put it back together. about 300 miles later it developed another rod knock. I was disappointed to say the least but I was determined to find out what was going on.  After a lot of looking and some swearing I finally found the problem. While it had been sitting water had run past the spark plug into the cylinder and down the rod and had rusted a flat spot in the crank Luckily i found it before I lost my mind! Anyway, after that I decided to do a complete engine rebuild. I had to bore it .060 over to clean up No 4 cylinder, had the main caps rebabitted and the rods redone, put that sucker back together and it was on of the best engines and quite powerful for a car of that era I ever had.

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Going to get into it today and do the checks as recommended. I know odd things happen with old cars but this one is truly odd.  Drove it, parked it. Got up, drove it and a tap started that sounded as first like a lifter and when I got the last 1/4 mile home and parked it was a slight rapping.  35-40 psi oil. Turned it off and checked bearing in water pump and genny and started it back up (still hot motor) and it was knocking.  I am really not blowing my own gasket over it as in a month I was going to start a rebuild on my first flat head motor for my 46 Dodge that has lots of blow by.  This just gives me a motor to do that would have to be done. Sad part is that I spent a lot of time working on the stupid carb and getting that sorted out. Just began enjoying the car after some months !.  Have never rebuilt a flat head before and took a long break from cars for 20 years when I was in the military,  The babbiting, etc is new to me. Going to be more sourcing a machine shop here is TX then anything else.  But that is getting a head of things. 

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OK, so this morning went out and checked oil.  Broke out the scope (I can only hear out of one ear) and with high hopes wished that the elves came and fixed things and chased away the gremlins.  Half choke and fired right over and idled down quickly.  TAP TAP TAP and not the rap rap rap I thought I was hearing. Scope and it sounds about the same all over. A tap tap tap. Motor at 180. So I started pulling plug wires and did not notice that much of a change till I got to number 4 and that was a much noticeable decrease in rpm. Oil pressure 35-40.  When I got this car it had a bad manifold gasket which I changed. Not seeing any leaks from it. That was 3 months ago.  Didn't start really driving it to 3 weeks ago with the carb issue. My untrained ear on flat 4's has me hearing valve train noise. This just started out of the blue. One day to the next. Once it cools down I am going to do a compression check on each cylinder. Now am wondering if a collapsed spring, broke keeper, wiped out lobe? Trying to get a vid shortened enough to load.

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2 hours ago, JACK M said:

Just thoughts,

Fuel pump, exhaust leak.

Got me thinking.  I did smell gas in the oil when changing but was thinking it was blow by on a ring.  Really need to do a compression test now for sure to see if the fuel pump is not leaking through.

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alright here is what I got and some good news.  The tap tap tap is now less them half of what it was and you can pretty much easily diagnose it being in the lifter area with the scope, even with me only having one ear to hear from. At RPM the sound is all put gone.  Did a compression test on the cool motor and came in at 81, 76, 80, 79 front to back. Can live with that expecting 8-10 higher when hot. Vac test from manifold (wiper) port. 18-19 with a little flutter.  But 15 at rpm.  I found that interesting.

 

I want to change this fuel pump anyways so not going do much with it. I do want to get an oil pan gasket and drop the pan and check the pick up screen. Running 30-35 hot at idle. Old cars are wierd at times for sure. no idea why the tapping was so pronounced and now it is so much less.

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That's good . Your numbers all seem fine . You don't by chance use hearing aids , that could have skewed your hearing ?

   Another thought was the insulation wrap you just added . Manifold maybe causing over heat of valve area . As it swells from heat maybe affecting . I would remove from manifold and just leave on pipe until fuel pumps repositioned .

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Hearing aid won't work for being everything was basically destroyed on that side.  I will try that idea with the insulation.  The 31 is supposed to have a heat shield too I see listed in parts.  Found a correct fuel pump.

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Sounds high up to me, possibly piston/gudgen pin ?

 

If the noise decreases when you pull a plug wire that's indicative of lightening the load on a particular piston and subsequent noise reduction, also it might account for the now you hear it, now you dont symptom due to the piston/pin moving around.  

 

Certainly doesn't sound like bearings or crank issues, perhaps you could start investigating by dropping the oil, put a stocking or something over the catch pan and see if there are any metal bits floating around. 

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