402 engine problems???
 

My BB 402 idles ok but a low thumping noise is present. It increases frequency and volume as rpm goes up. Here's the story of how the noise started... I installed a set of summet headers on the engine a few months ago and the truck sat for a few months till I saved enough to do exhaust( dual 40 series flowmaters with H pipe by the way...) After and before exhaust mods the engine ran good. I drove the truck after finishing the exhaust with no problems until the new headers heated up and melted through some of my spark plug cables...then it ran like crap because the ignition was sorting all thre time. I replaced the cables with a new set with 45degree boots and fiberglass boot covers and replaed all spark plugs. After all that the noise is there...what do you think it is ? what did I break?

P.S. I'm running a MDS 6AL ignition if that helps-:chevy:

Re: 402 engine problems???
 

Sounds like # 5 & 7 plugs wire are crossed.

Re: 402 engine problems???
 

It increases frequency and volume as rpm goes up.

That would make it my guess, re-check your plug wires.

Re: 402 engine problems???
 

nope...I re-checked all wires right. 1-8-4-3-6-5-7-2 firing order...does it matter where you put #1 wire on distributor? because mine goes #2 just left of Hei coil then 1-8-4-3-6-5-7.

Upon further checking.. with truck in park and idle it's a faint clicking then still faint if I rev engine in park. In any gears it gets louder, like a brushing noise..like a belt falling apart and flapping around sound...

I also recently swapped trannys from a 350 to 700r4

Re: 402 engine problems???
 

Make sure your torque converter isn't loose on the flex plate.

Re: 402 engine problems???
 

Check to make sure the bell housing bolts are all up tight and there is no gap between the engine and bell housing. It sounds like the torque converter is hitting something.

Re: 402 engine problems???
 

I looked at trans bell housing, it all seems secure...no gaps or loose bolts. I'm gonna have shop that installed tranny check it out torque converter today.

Thanks for your help!!

Re: 402 engine problems???
 

You might want to do a visual under the hood when it's dark...see if you have arcing/cross-firing.

Re: 402 engine problems???
 

I know this might sound crazy but.. tighten up the header bolts or make sure the header gasket is still good. My buddy's engine started making a noise that we swore was valvetrain but ended up being the gasket was blown out and the headers were loose.

Re: 402 engine problems???
 

:agree:

Re: 402 engine problems???
 

that same thing happened to me a couple of days ago

Re: 402 engine problems???
 

Sounds like the Torqe Converter may have blown a thrust bearing.

Re: 402 engine problems???
 

Exhaust leak can sound just like a click or valve train noise...just got a new one in my exhaust that has previously been running fine for three years. was worried that I had a valve train issue until I listened closer.