Push Rod Issue

Reply Subscribe

Thread Tools

Search this Thread

Aug 21, 2005 | 06:15 PM

Glass Act

Thread Starter

Melting Slicks

Joined: Jul 2005

Posts: 2,545

Likes: 3

From: 406ci SB, AFR 180 Heads - 490 HP @5,600 RPM 529 lb-ft @ 4,100 RPM

Push Rod Issue

I just completly rebuilt my motor and have approx. 1000 miles on it. The other day I bent a push rod on exhaust valve side. I checked my lifter, spring and valve, everything looked ok, I did not remove head to check, just external test pushing on lifter and valve. The spring was not broken, valve seemed to move freely in both directions, so I installed another push rod and set the valve again. After running the engine for about an hour at idle, I bent the same push rod again. Now my only option is remove the head and see what is going on. I need your suggestions incase I have over looked something before I tear down the head. My guess so far is a valve sticking because it's bent, or the valve guide is a bit tight. Everything else is working perfect with all the other valves on this head. I'll also mention this is a L-82 motor.

Aug 21, 2005 | 06:29 PM

MotorHead

Race Director

Joined: Apr 2000

Posts: 17,676

Likes: 201

From: Who says "Nothing is impossible" ? I've been doing nothing for years.

You let it sit there for an hour idling ? That can't be good for anything.

Any way we need more info, what was the buildup, everything stock ? Does it have guide plates ? Same rocker ratio as stock ? Are they stock length replacement pushrods ? What head works was done, if any ?

Aug 21, 2005 | 06:45 PM

Boofers

Drifting

Joined: Nov 2002

Posts: 1,665

Likes: 1

From: Ontario

fascinating...

Aug 21, 2005 | 07:02 PM

Glass Act

Thread Starter

Melting Slicks

Joined: Jul 2005

Posts: 2,545

Likes: 3

From: 406ci SB, AFR 180 Heads - 490 HP @5,600 RPM 529 lb-ft @ 4,100 RPM

This is a complete stock engine I built for my wifes Vette, all componets were set to GM specs. The heads have new valves, springs, retainers, guides, pushrods and rockers. The heads work perfect except this on that likes to bend rods now after 1000 miles of running for some reason. The engine ran perfect until this little set back? I guess I'm just hoping I don't have to remove the head, but my gut feeling is I will be.

Aug 21, 2005 | 07:05 PM

stingr69

Le Mans Master

Joined: Mar 2004

Posts: 7,502

Likes: 1,510

From: Little Rock AR

Bent pushrods are a sign of mechanical interfearance.

What method did you use to adjust the valves?

-Mark.

Aug 21, 2005 | 07:08 PM

big_G

Le Mans Master

Joined: Jul 2005

Posts: 5,752

Likes: 4

From: Austin Texas

Usually coil bind is the cause for broken pushrods. (too much lift for the springs)

Aug 21, 2005 | 08:41 PM

Glass Act

Thread Starter

Melting Slicks

Joined: Jul 2005

Posts: 2,545

Likes: 3

From: 406ci SB, AFR 180 Heads - 490 HP @5,600 RPM 529 lb-ft @ 4,100 RPM

Quote:

Originally Posted by big_G

Usually coil bind is the cause for broken pushrods. (too much lift for the springs)

Big_G, I thought of this, but since it only happens on one rod while all the others are fine I ruled that out. All componets are the exact same, rods, springs, valves.

Stingr69, I listen for clicking to start, and make a quarter turn. On my engine that I rebuilt in the spring this worked fine, except mine's not a stock motor like this one.

Tomorrow night I see myself removing the head and replacing all the componets. I'm just stumped with why after 1000 miles it showed up on this cyclinder only.

Aug 21, 2005 | 08:53 PM

Rockn-Roll

Melting Slicks

Joined: Dec 2000

Posts: 3,407

Likes: 2

From: Carmichael CA

It sounds like you have an interference problem...just because only one push rod is receiving plastic deformation doesn't mean that the others aren't getting some elastic deformation which returns the push rod into it's original condition after flexing.

Did you shave the head or mill the block? The most likely problem is that the piston is hitting the valve. Can you use a flashlight and look inside the spark plug hole to see if you can see any signs of contact? Though, I'm not sure it will leave any marks actually. When building an engine you should always check for interference. I had to use two shims on each head to avoid contact between the pistons and valves due to my having to shave both the heads and mill the block. The shims are a dead-soft copper.