Can't figure this out

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SirDan

SirDan

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So I was out beating on my car about 2 months ago and it felt down on power, got it home and it was idling slightly rougher. Then i noticed I had a knocking noise from 1800 rpm and up. I have also noticed when it gets warm the passenger cylinder bank smokes out the exhaust. A compression test had the lowest cylinder at 108 and the highest at 120. Which is about the same as when i tested it a year ago. I checked for vacuum leaks and there is none, checked timing and it is good. distributor advance is free and smooth.

Not too sure what is really wrong here. If it just knocked id say i had a rod knock, but it smokes and feels a bit down on power. Then i think maybe its a head gasket leak but the compression test seemed OK.

any ideas?:dontknow:
 
I don't consider a variance of 108--120 to be "all that good." You did this with the plugs out?

Google up a homemade leakdown tester, the key is a .040" orifice, and that will allow you to also look for

bubbles in the coolant

air leaking out the exhaust

air leaking up through the carb throats

air leaking through adjacent plug holes

air leaking down into the crankcase

Use a length of scrap fuel hose, etc, for a stethoscope

You also could have something like a damaged valve, or a damaged piston/ broken ring(s)/ broken ring land.
 
Could be a broken lifter, push rod, or valve spring. I'd pull the valve cover on the bank that is smoking.
 
A valve guide or and seal is leaking and worn maybe to make it smoke, white smoke or dark ??
 
FWIW i checked the compression a year ago and it was the same it is now. drove the piss out of it for a year with no issues. that is the only reason i say the compression seems okay. tested with all the plugs out and the throttle wide open.

plugs look wonderful

Will pull the cover maybe thusday or friday. should i turn it over with it off as well?

what do you think the chances are I have a rod knock and another issue that happened at the same time?
 
Rods usually knock when you let off the gas(no load). Mains knock under hard load(deep knock). The noise, is it with valve train(twice as fast) or with rpm of the crank?

Pistons slap cold, broke rings burn oil, some times compression is not off that bad(been there).
 
Check your converter bolts.
I have had then come loose and make a knock sound.
Broke motor, trans mount allowing headers / exhaust to hit the chassis will cause noises also.
 
It sounds like it goes with the rpm of the crank. It sounds like for every rotation of the crank someone hits a hammer against something metallic.

The knock like i said comes on from 1800 and up. If you hold it at a steady rpm it knocks still, if you rev it up and down a bit i think it knocks a bit worse.
 
pull your oil filter off and dump the oil out of into a white clean container. Then cut the filter open and take a look. If its knocking, and there is ANY kind of metal in the oil filter, your done.
 
had a 383 that started to knock above a certian rpm, 2 weeks later it threw a rod. not tryin to scare you here , it may be something else, but either way, as im sure you are well aware, no internal mechanical knock is good.
 
I guess it might be time to build a new engine. FWIW this thing is likely the original to the car. I really wish i had the money to build another one though.
 
I would break out the mechanics stethoscope and crawl around listening to different spots to determine where the noise is coming from. 108 -120 compression is not that great, but you don't have a variance of over 10% and it has been running well on the same compression for a year. I guess I can't see that as being the problem. You have to track down upper or lower noise, and then pinpoint the source. If you don't have one, spend $15 on a stethoscope. They are incredibly handy.
 
So I pulled the number 4 sparkplug wire and the noise goes away. Pulled the plug out it looks good not oily or wet, not pitch black or anything. with the sparkplug out of the engine i plugged it back into the boot and started it up. seemed to have fine spark. What do i look for next?
 
did you drop a valve? i would pull the rocker cover and make sure the valves are opening and closing over your #4 just a thought, im not sure why the knock would go away with out spark. maybe a wrist pin? without combustion, maybe there is not enough force to cause the knock. just throwing ideas out there.is it firing on all 8 all the time?
 
SirDan said:
So I pulled the number 4 sparkplug wire and the noise goes away. Pulled the plug out it looks good not oily or wet, not pitch black or anything. with the sparkplug out of the engine i plugged it back into the boot and started it up. seemed to have fine spark. What do i look for next?
Click to expand...


Sounds like a spun rod bearing to me--sorry

Keep a look out for a short block for sale--here or on ebay
 
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