Engine Knock & c4 Auto

[ski4evr]

Sometimes when I start up (cold or hot) I here a 'knocking' sound. It goes away. I also get a similar noise when I'm in third gear (c4 auto) going slow up a hill and trying to accelerate. It seems to only happen at low rpm under load. Is this a timing problem or som other "serious" issue? I have no clue as to what degree from TDC my timing is set to. I've tried to set the timing to 12 degrees using a timing light in the past, but it stalls (my timing mark pointer seems to be misaligned). So, I just set it by ear (iterating between timing and carb idle speed).

Also, are c4 auto transmissions the same between 8 cylinder cars and 6 cylinder cars? In all of the parts catalogs I've seen, there is no differentiation between 6's and 8's. Are the "Shift Kits" the same?

 

[Anonymous]

I have a 66' bronco w/170 I6 and it would bog down going up hills and knock a little. The remedy was a new vacum advance. check the old by pulling the little hose to it and lightly suck. if you can suck air then the diaphram is tore. If not then its fine. Try premium I guess... I got a new crane cams vacum advance (this was 7 years ago) from summit or jc whit.. and it came w/several color coated springs for tuning the advance to where ya need it. This is a cheap and easy fix, just grab your repair book.... I hope this helps.. [/b]

 

[MustangSix]

A clatter or knock when cold at idle could be piston slap. The piston slap will diminsh as the engine warms. It is caused by excess piston clearance due to worn cylinders bores.

The clatter under load is probably an ignition related knock. Better fuel, less timing, or cleaning the combustion chambers may help.

Try to determine true TDC in relation to your timing mark by inserting a wire hanger into the #1 spark plug hole and rotating the engine by hand.

 

[ski4evr]

I've now determined that there is two noises from under the hood:

- one is when I first start the engine. It is a clank noise. It has a hollow tone as if thin metal is involved ( I don't know it that description helps any). When I first start the car, this clank happens for about 5 secs (about 10-15 clanks) and then stops. I will usually here the clank again when I stop the engine (but only one clank). When I'm under the hood and open the throttle quickly and release, I'll sometimes here one clank. I think I've narrowed the noise down to the rear of the engine. Any suggestions? Is there something in the transmission that could be causing this? I have a green-dot c-4.

- second noise is a ticking noise (@ ~ rpm frequency) when the car is in drive. It's from the very front of the engine. I don't hear it when the car is idling in neutral/park. Timing gear or chain? I'm fairly certain that the noise is coming from just below the water pump. I felt uncomfortable sticking the one long screw driver I have just behind the fan blade with my ear resting on it. I've had a slight miss forever. Is it possible to have slack in the chain to cause this kind of a noise and a slight miss? Broken timing gear tooth? Or would the car not even start/run if there was slack in the chain or a broken tooth/gear?

 

[MustangSix]

Noise one could be a loose or fractured flexplate. Check the nuts holding the torque converter first. I'm not sure if you'll be able to determine if the crank bolts are loose without pulling the transmission out, but try to see if you can rotate the engien back and forth even a fraction before the flexplate begins to turn, which would indicate a loose flexplate.

Noise two could be timing chain slapping around. They get very stretched out and are known to do that. To determine if it is excessively stretched, remove the distributor cap and watch for the rotor to rotate as you rotate the engine back and forth. You should not be able to move the engine more than a few degrees before the rotor begins turning.

 

[ski4evr]

Thanks Mustangsix. I'll check for timing chain slap by pulling the dist cap today. I don't know when I'll have the time to pull the transmission. Hopefully I'll find the smoking gun.

 

[Anonymous]

You might also ck crankshaft end play

 

[Anonymous]

I had a similar problem with regards to issue 1 and it turned out that my flexplate bolts were not properly torqued.

You do need to remove the transmission in order to check these bolts.

I hope this helps.

Kurt.

 

[ski4evr]

I removed the inspection plate and checked for cracks in the flex plate and could not see any. The noise was definitely louder with the inspection plate off. The noise lasted longer than usual with the car up in an angle (use jack stand to get under the front end easier). It made me think to check the transmission fluid level. Guess what - it was low. I feel like such a dork. I started it up again and the noise is gone. I'll run it later to see if that really was the problem. Sometimes I think too much

 

[ski4evr]

The fluid level in the transmission is fine and the noise is still there. It was a coincidence that the noise went away last night and I got really frustrated. I'm going to try checking for the flex plate to crankshaft bolt tightness. When checking earlier for a broken / cracked flex plate, I couldn't get the torque converter to move without bumping the engine with the ignition. Any suggestions? Big wrench at the front of the crankshaft with the transmission in neutral?