Thread: Broken pushrod on 400sbc-what else to look for...

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Hey guys, I got a question about the valvetrain. I recently added a adj. vac advance. I got everything hooked back up plug wires...etc. when I tried to turn over the engine and fire it- she wouldn't fire. I let it sit for a few minutes, checked the connections and tried to fire it again. While cranking the engine over it made a huge backfire and then started and seemed to run allright. I then took off my drivers side valve cover and noticed that my #7 cylinder roller rockers were off and one of the pushrods were broke. I took off my intake and located both the pieces of the broken pushrod and found the other one in the lifter valley as well. Also both lifters came out of their bores too. I had some new ones so I just replaced them. My questions are below.

1) what could have caused my pushrod to break?
2) what else should I check before reinstalling my intake manifold?
3) was the loud backfire associated with the broken pushrod?
4) do hardened pusrods break like mine did...In half?
5) are heat treated pushrods the same as hardened?

sorry so many ???'s but I don't have anyone to help me out.

C'mon I know someone has some good input on this.....Should I pull the head off and check for damage to the piston or a bent valve etc...... I would like to put my intake back on but don't want to until I know everything is square. Is there another method for this???

Originally posted by onemangang
C'mon I know someone has some good input on this.....Should I pull the head off and check for damage to the piston or a bent valve etc...... I would like to put my intake back on but don't want to until I know everything is square. Is there another method for this???

I am no expert but my boys 350 roller rocker engine started missing a ticking and we pulled the valve cover off and found one bent push rod we replace it with a set of the best we could find at PAW and put it back and set the valve adj and worked fine ever since. I believe these where hardened tipped one. Sounds to me that the temper was wrong for the push rod to snap like that, they were over hard and brittle. good luck hope someone that knows more will help you. Ed ke6bnl

anybody else have anything to add for the questions I have above....

Thanks fellas I'll try that Hopefully nothing else is bent or broken.

Just a shot in the dark here,,,,your motor could have run backwards,,you said you installed a new vac advance dist, it's possible that it could have been off by a tooth and started running in reverse,,,i've seen it happen to a brand new rebuild 396cu. and yes,,, if not stopped imediately the motor will eat some parts.

check the fireing order you probly have some wires crossed that would cause it to backfire
good luck bill

I guess I don't how that could have happened. I verified my rotor on my dizzy was running clockwise before I attempted to start the car. I'm really puzzled as to why the pushrod broke. They were supposedley hardened but I replaced all of them with ones I know were heat treated (from crane). Anyway I got it back together today but I'm afraid to start it again. Maybe I was trying to start it with to much advance 19 degrees.

double check the firing order it should be 18436572

The firing order could cause the engine to break a pushrod? I did get the engine started after the huge backfire so I know I got my order right.

backfire will break a pushrod. how was it running before you played with distributor?

Well at this stage of the game,,i would double check my distributor, for proper installation,, also check the cap for tracking marks,,and i would be checking the Cam as well.
You had problems starting it to begin with,,so something was out of whack. hence the backfire.
And make sure you take a magnet to the inside of the oil pan to pick up any stray metal bit's.
Forewarned is Fore-armed.

Well it's all back together now. The only thing I'm not totally sure about is the distributor installation. I believe I have got it right though. this is how I installed it.

1) Brang the motor up on the compression stroke
2) turned the oil pump gear in line towards the #5 cylinder
3) Aligned the balancer mark to 8 degrees BTDC
4) dropped in the ditributor all the way down w/ rotor pointing directly towards #1 cylinder and vac advance at 45 degree angle.
5) Routed plug wires 18436572 on dist. cap

This is exactly what I did last time and it didn't fire until AFTER the huge backfire.