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#1
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help needed with engine noise
i thought i could figure this out by myself, but again looks like i need advice from more experienced people. problem´s here: knocking coming from nr.4 cylinder. noise disappears after pulling wire off. gets worse when turn idle down. disappears if i turn advance on distributor. most noticeable when engine cold. i thought it would be piston pin, but well known and recommended shop checked rings, piston, connecting rod+bearing and piston pin, no problem there. lifters seem to be ok and rocker arms+pushrod aswell. cam (hydraulic) looks good too. cylinder´s exhaust valve was darker than others when i took head off. no problems with compression test. car was tuned in dyno. i use high octane gas. any idea
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#2
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what engine is it?
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#3
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engine specs.
oops, sorry.
it´s 1971,383, engine rebuilt 700miles ago, stock heads, edelbrock performer intake, 750edelbrock carb, new mopar performance 272 hydraulic cam, mopar electronic ignition, cylinders honed, old pistons but new rings. all new bearings. new lifters and pushrods. crankshaft milled, polished and balanced. no visible damage in piston i took out, it was measured ok |
#4
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Double check the wires on the distrib and make sure there not cross fireing. Check plug.
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#5
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Sounds like a piston rocking back and forth.
Too much clearance, scuffed maybe? Some mopar distributors have bad cap/rotor phasing which can cause misfire and scuff piston/s. [not to say this is your problem] but u can find out by looking at the contacts to see if there burnt off to 1 side. |
#6
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just did:new dist.cap, new plugs, new coil, no cross wiring, already checked wires for cracks, just got dyno tuned. could low oil pressure cause this? few months back shop installed cam bearings, they´re not perfectly alligned with oil passages. all of ´em are open but some passages about 1/3rd overlapping. somebody might remember that from my earlier posts. i think i might just get new piston/pin/rod bearing before i put the engine back together. if it still knocks, i´ll take car to shop. only thing is that i´d like to fix it myself rather than have someone else do it for me.
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#7
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Coronetcustom
When did this begin? Right after tuning? Sounds like TOO MUCH timing advance causing detonation at idle? Check for correct timing!!! (total advance) |
#8
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ì´m not experienced about timing, it was tuned for me and i think guy who did it said it´s 30`to 40`advance on full throttle(i´m not sure how them degrees work and i could be wrong here, how much should it be?). funky thing being that when turning distr. to advance takes the knock away. turning retard no effect. sound is most clear when engine is cold and i adjust low idle. when engine warms up and there´s more revs, there´s less sound. car was driving great and no audible sound in cockpit when driving/accelerating/high
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#9
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Counterclockwise
Coronet custom
Are you sure you are turning the distibutor for advance? Big blocks distributors rotate counterclockwise, so advance increases with a clockwise rotation of the distributor! I believe 35 degrees advance at 2000 rpm is a baseline for big blocks total mechanical advance. |
#10
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Yea pretty much if u retard the timing the piston knock [if thats what it is]
will go away. Thats funny about the ignition kits these days, they tell you dis rotation is clockwise. When I helped a friend of mine break in his 440 we were debating over which way was advance, when he showed me the instruction sheet I couldn't believe my eyes when it said ,from mopar, clockwise. |
#11
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yep, i knew timing works counter clockwise/how to retard-advance timing.
i think i will replace all moving parts on problem area. 2lifters, 2rocker arms, 2pushrods, piston/rings, wrist pin, connecting rod/bearing. |
#12
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For shts & gigls check the rod journal on crank and the rod for straightness and the big end correct size and if pressed make sure the piston flops back and forth easily cause if pins too tight it will hurt the skirt/bore.
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#13
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An exhaust leak at the cylinder head to manifold / header can sound an awful lot like a metallic noise. Pulling the wire off you no longer have pressure there and cold things tend to be looser and they get tighter when hot.
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#14
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Check to make sure you don't have a vaccum leak on that cylinder... of course if you have the motor apart, IDK how this could be verified.
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#15
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"cylinders honed, old pistons but new rings."
My guess is you have too much piston to wall clearance which allows piston to rock and make a hollow knocking sound. The fact that you reused old pistons with a rehone of already worn cylinders makes this much more likely. -Bob |
#16
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Quote:
Whether it is the reason for the noise or not, the exhaust valve has been running hot and that's an issue. Lean mixture caused by intake air leak would look like this. On engines where exhaust temperatures for each cylinder are constantly monitored this is easily observed before the valve is burnt. Could the valve be occasionally hanging due to a bad lifter, causing by pass and heating? I haven't seen it on these engines, but a burnt valve is normally the result of this kind of an issue. Fix the found issue first, the noise could just disappear. |
#17
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hello Mecki,
i can send you short videoclip with engine noise. you sent me picture of steering unit few weeks back. could i use same email address? |
#18
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Yeah, thats OK!
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#19
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Sounds like a ticking lifter to me, but it's hard to recognize exactly from a video. Regular clicking noise witch decreases when revs increase? Low oil pressure at idle? Did you check the pump, old or replaced, when you assembled the engine?
You have had the piston, rod and bearing checked. Check the piston to bore clearance when you put it back together. Still have the miss coloured valve. Is it the material that has turned dark or is it deposits on the metal surface? |
#20
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Fuel Pump ...????? Knock......Cam Speed Knock
Sounds like Piston slap or Wrist Pin to me...... Crankshaft speed knock. Keep Digging....You will find it. |
#21
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"I have re ringed many engines and haven't had a problem with this so far."
Re-ringing a race motor that may have only a hundred 1/4 mile passes is one thing. Re-ringing a street motor that has several thousand miles on it is just not good mechanics. I don't see how, after rehoning an already worn engine, your piston to wall clearance is anywhere near decent spec. Horrible practice IMO and could easily be the cause of what is happening. -Bob |
#22
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Yeah, what is the skirt to wall clearance? Could be piston slap, if over about .005".
How did the upper half of the rod bearing insert look? If it shows copper, it's detonation. |
#23
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Quote:
Can you say at what clearances you have experienced noisy piston slap? I haven't, but .008 has still been working fine. I'm not saying that I'm happy with loose clearances, but a garage fix good for 10 or 15 more years for a hobby car is pretty cost efficient, especially if I already have all the measuring and honing tools needed. IMO bad practice is if you don't know what you are doing and what to expect. If I can run our wheel loader over the winter and get the snow job contracts fulfilled with a similar weekend home workshop fix for pocket money instead of taking it out of service with all the consequences of that I'm happy, the customer is happy and my bank manager is happy. It can be horrible practice, but I dont give a f**k. |
#24
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"IMO bad practice is if you don't know what you are doing and what to expect. If I can run our wheel loader over the winter and get the snow job contracts fulfilled with a similar weekend home workshop fix for pocket money instead of taking it out of service with all the consequences of that I'm happy, the customer is happy and my bank manager is happy. It can be horrible practice, but I dont give a f**k."
Some people are satisfied with nothing but the best and some don't really care what they have. Sounds like you fit in the latter. For someone with your expertise why are you posting on this board looking for answers? Remember, you are the one with the engine noise that stems from something not being correct. Running a motor 200,000 miles, reaming the ridge(which had to be more than .004 by the way or you wouldn't have needed to do it) then honing and installing the same pistons and calling that good enough-well you(or someone else) can solve the problem because I have better things to do. -Bob |
#25
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Dear Bob!
Different problems need different solving methods. Some times getting a job done within a certain time for a certain goal with a certain cost and in a location where you only have what you have with you put some limits on what is "good enough". Funny that you are saying that I don't care about what I have. All the people who knows me are saying that I'm a perfectionist who is newer satisfied and always wants better and demands too much quality. That's true, I know my self and I like to execute that on my hobbies too. But I have also learned that the world does not work that way and to get things done, some short cuts must be taken and you can't press your employees to be perfect either. Life is just compromising all the time. The most important IMO is that you know the risks with the decisions you make and are ready to take the responsibility for that action too. OK, this is not about an engine, but I think you should not make conclusions about me so fast. I'm sorry if I have insulted you, I dont know what kind of a guy you are and what your experiences are. I was just telling what I have experienced about piston slap and what I got out from one of my engines by re ringing it. I was surprised that the result was so good with those measures. Other results also confirms that out of round and taper is more critical than clearance if you are not aiming for an engine that will last 200k miles more. FYI I'm posting at this board asking questions and reading other threads to get information. I want to get as much information on a subject as possible before I evaluate it and then decide what to do. This is a great place to collect facts and info. My experiences and skills are what they are and only doing more will increase them. It's obviously better to keep them to my self. BTW, it's not me having the trouble with engine noise, I was just stupid enough to get involved in this discussion. Have a nice day! M. Eriksson PS. I asked a question I honestly would like to get answered. By anybody who has experienced it. At what clearances has piston slap noise occurred? |
#26
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Answer.....When the clearance becomes enough to make the noise....
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#27
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Custom,
The only way to fix this is to open it and find the problem.... |
#28
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Wait I have to chime in here again. This sounds eerily similar to a noise I was chasing in my 440. Does the motor get sluggish or hard to start (by this I mean does the starter have a hard time turning the engine over?) when it gets up to operating temperature. I finally tracked down my noise, it was caused by a vacuum leak. The valley-pan had a crushed spot, and it was causing detonation on #8 cylinder only. Unfortunately for me, it had already ruined the piston (crushed ring lands, and scored cylinder wall, and piston skirts) by the time I found it. See if you can check for this. Cause like you I was attributing the noise to loose tolerances, because I had forged pistons. My noise was worse when it was cold, or when you would barely rev the motor, like in the 1500 - 2200 rpm range. I also didn't have any signs of detonation on my spark plug, it wasn't until I seized the motor and tore it down, when I found the problem. Hope my tragedy can help someone else. BTW I didn't have a problem with piston slap. I have heard the "piston slap" diagnosis multiple times, I for one however have not seen a single instance of this actually occurring. Everytime I hear of this diagnosis, I cover my head, because inevitably there is fixing to be a thrown rod. Also another dead giveaway for me, is that valve that is different than all the others, this is the exact thing that happened in mine too. See when the ring lands crushed it allowed that cylinder to let oil pass by, which turned straight to carbon. All my other exhaust valves were a nice brown color, that one however was black black black. BTW my compression test revealed nothing unusual with any of the cylinders.
That's just my experience though. |
#29
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Quote:
But really, have you had this problem and could you give some figures? I think it would help coronetcustom too to have some figures to compare his observations with. |
#30
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Quote:
Rampage, I enjoy reading your posts, your observations and facts have given me a lot of information before also. You don't mix facts and quesses and you don't make premature conclusions. You must have been writing a lot of reports in your job. |
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