Mystery engine knock

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Paul2426

New member
I have a 1966 1100a with a 266 v8. It has abt 89k miles on it. I notice a knock in the engine the other day. Oil pressure is normal, temp is normal, and it only occurs once the engine is warmed up. Wanted to see if this sounds like a rod knock to anyone, or if it could possibly be a simple exhaust leak. There is definitely exhaust leaking just can't tell if that's the noise. The knock follows the rpms...
 
Does not have to be under load. It is noticeable at idle or engine acceleration once the engine is warm. Not as noticeable while being driven, but May be because I am inside rather than outside listening
 
Also... More of a knock than a tick. Doesn't sound like lifters or valves. I tried removing each individual plug wire, but it didn't make much of a diff from what I could tell
 
It could be piston slap but that would go away or get worse if you pulled the wire to it. If std trans, it could be the flywheel bolts being loose too.
 
Thanks for the input. I'll check the flywheel out. I should be able to hear it if I crawl under if that's the case. I'm just hoping to avoid having to pull the pan, but May anyways. I would rather catch a bad bearing earlier than later... If nothing else, I can rule a bearing failure out
 
From your description is seems to be a light knock. On many IH engines there is a bit of a knock from the cam gears. On several of my engines when the cam bearings spin (common problem) the tips of several teeth are chipped off which makes a louder knock. But if you oil pressure is good warm at idle it might not be a cam bearing. IH engines will run 1000's of miles in this condition. A loose damper wheel can cause a knock in the front cam gear too.

Can you tell where in the engine it is coming from?
 
Isolating the noise has been the headache. It has an old rotted out glass pack for a muffler along with a swiss cheese'd collector pipe which makes it extremely loud... I have used a stethoscope to rule out the upper engine so all I can figure is that it's bearings or a bolt on appendage like the flywheel as previously suggested.
 
I would definitely repair all of the exhaust leakages before committing to breaking open the engine.

To many other non issue components can do make similar noises. So the other leak sounds May very well be masking the true culprit.

What oil viscosity are you running and what exactly is your hot idle oil pressure? You will need a known accurate mechanical pressure gauge.

I can say for sure that if you have a bearing/s that is loose enough to knock, your oil pressure will be in the tank.
 
I use 30w oil as required in the manual. I used a mechanical oil pressure gauge which read 20 at warm idle and 40 at acceleration. Per the manual, this is right in spec.
 
You really need hot oil pressure which takes a
10 min drive down the road to achieve. If your idle pressure holds I stand by my recommendation to fix the exhaust leaks them re-evaluate.
 
paul2426 said:
I have a 1966 1100a with a 266 v8. It has abt 89k miles on it. I notice a knock in the engine the other day. Oil pressure is normal, temp is normal, and it only occurs once the engine is warmed up. Wanted to see if this sounds like a rod knock to anyone, or if it could possibly be a simple exhaust leak. There is definitely exhaust leaking just can't tell if that's the noise. The knock follows the rpms...
Click to expand...

If the knock seems to be at the front of the engine, try removing all the accessory belts and check for a cracked belt. Start the motor without any belts and listen for the knock. 10 - 15 seconds without the belts shouldn't matter.
 
Thanks everyone! It looks like I will have my weekend cutout for me. I am having the fuel tank refurbished (again, long story...:mad5::mad5:) beginning today, so can't test drive until I get it back. I have been running the engine by placing the fuel pickup line into a gas can... Once I get the tank reinstalled, I will check the oil pressure with a mechanical gauge while driving. I checked the belts and they do not seem to be causing the knocking noise. I May also replace all of the plugs, wires, cap, etc... This weekend. The vehicle sat in a field unused for about 10yrs before I snatched it up. I already verified that there was plenty of spark, even with the old components, but they could just as well be the culprit. Also, I need the check the vacuum advance. It could be that it's not working properly and causing the timing to be off once it warms up...
 
My mystery knock with a similar description turned out to be a grooved lifter. Cam was jumping between a high side and low side.
 
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