loose timing chain cause knock?

[bigbadchev84]

I just bought a new truck and i noticed it has a knock at about 2500rpm and up, i thought it was a broken flex plate i pulled the motor and found it was not the flexplate, the truck also had a vacuum leak , i found that the p o pinched a ground strap between the manifold and the intake, i started to tear into the engine last night and found the timing chain was about to fall off it was so loose, could this be causing my knock some how?

 

[dyeager535]

I doubt it.

I've seen timing chains so bad they would skip teeth, get it to fire, run for a split second, die, move distributor, repeat ad infinitum. No knock when it would run though.

Under a constant load, the timing chain shouldn't be moving. When engine RPM varies (as in letting off the gas abruptly) is when I've noticed loose chains, as the oil pressure drops for a split second.

Pinging I could perhaps see, since timing would change, but knock I'd think not. Might be more to it than what I'm thinking though.

 

[bigbadchev84]

could it be causing the valves to hit the piston?, i mean it would run great i could still drive it as a dd but the knock was bothering me, so i dug into it, the only time it would know is in the upper rpms and it dosent really sound like a rod knock, it is fairly faint, but it is a knock

 

[diesel4me]

noisy chains??

I thought I had a loose timng chain on one 350 I had,I have heard a loose one slap against the cover before(one had actually worn a hole in the timing cover and caused a leak!)--but I found out it was a bad fuel pump ,the arm on it had broken the casting where it pivots--replaced the pump,no more noise--new timing chain and gears stayed in the glove box and were sold to the new owner!..

You could have a lot of things making noises--bad bearings,loose wrist pins,a bent pushrod, rocker arms,pistons loose or a cracked skirt,--its possible to isolate what the noise is by using a mechanics stethascope or a peice of vaccuum hose stuck in your ear and probing around to hear where its the loudest--pulling the plug wires off each plug one at a time will help tell which cylinder has the problem if its a bearing or wrist pin,the other noises usually stay the same regardless..be careful if you use the vacuum hose in your ear trick!--if you touch it to a plug wire with it running,the carbon black in the rubber hose makes a good enough conductor to give you a good shock!..

 

[dyeager535]

I had the bolts on the crank pulley back out, and even though it never made any noise through the belts, it sounded like the engine was on its way out. Good excuse to build the motor I have now, but didn't need to. or

 

[beater_k20]

yes, a worn timing chain could very easily cause a knock. in a normal running engine the ignition fires at precisely the right time, igniting the air/fuel mixture and making the engine continue on its merry way. the distributor is driven off the back of the cam, so when you add slop to the chain, not only does cam timing change, so does ignition timing. you can very easily cause an engine to detonate (ping, whatever you want to call it) just by adjusting the ignition timing, throw in funky cam timing, and you can definitely create some serious problems, possibly ones that could threaten the life of the engine.

 

[Fierospeeder]

When the pistons hit the valves, the valves start bending at the stems. Usually, the engine will not run under most circumstances.


I would crawl underneath while its running and listen through the oilpan and see if you can hear anything knocking down there.

take note of the clutch fan or electric fan while under there, dont wanna lose a finger.


Does the knocking happen while at idle, or both at idle and driving the vehicle?

Another thing to try is remove the serpentine/accessory belt and see if it goes away. Your knock may differ from the way a knock sounds to us.

 

[bigbadchev84]

the motor is already out, and i did pull all the belts off and let it run, it never did knock at idle only at rpms above 2500-3000rpm, i have the motor out now, i got an rv cam for it and new timing chain, the old cam was pulled out last night and i had 3 really worn lobes, it was amazing that this thing still ran as good as it did!

 

[bigbadchev84]

i also forgot to say that i pulled the heads off just to check the pistons, and there is no evidence on the valves or pistons that they have been hitting, i tok the heads into the machine shop today just in case and everything was great.