Bent push rods again!!!

[marine6212]

I put new push rods in the 390 about 1 week ago. drove it all last week with no problems!! went to start the truck and take it for a drive yesterday and it had no power and was smoking alot. today I pulled the valve covers and 4 push rods are bent again. What is causing this. I have been very careful not to rev the motor and have driven it like a 80 yr old man. just putting along. never getting above 50.

any suggenstions would be helpful!!

Semperfi,
Marine6212

[bumpside]

Wrong pushrods ( TOO LONG)
Stretched timing chain
Cam lift too high for springs ( binding )
Valve lash set way too tight
Valves hitting pistons
Ignition timing too advanced
Cam indexed improperly
Finnagin pins and chrome muffler bearings binding on do-dads next to the framble rods

Hope this helps

[bumpside]

I just checked in a PAW catalog and there are different length pushrods overlaping in years from 1961 to 1976.
The lengths are--------9.620
9.590
9.157 with adj. rocker arms
9.564
9.584

Some of the lengths are close enough to look the same at a glance, but cause the troubble you are having. Check the new ones against the old ones.

[taylor351]

Do not forget to replace the canuder valve when you get your new chrome muffler bearings. The framble rods always wear those little buggers out, but you have to buy that left handed screwdrivers, otherwise you will never get them back in.

Keith

[BobbyFord]

The reason the pushrods are bending is tight, gummed-up or dry (lack of oil) valve guides. Remove the spark plug from the suspect cylinder(s), stuff a length of cotton rope in the cylinder, carefully rotate the piston to the top of the bore and pull the valve spring off. Rotate the piston down the bore a little (but not enough to let the valve drop into the cylinder) and see how easily the valve slides up and down in the guide.

[427]

They could possibly be rubbing against the intake.The holes might need to be opened up.

[two-bit]

I had the same problem in my 390 T-bird block when i rebuilt it.
Turns out .509 lift is to much for stock valve springs. I had spring bind, bent pushrods, a very unhappy truck.
Got some better valve springs, new pushrods, and then i had a happy truck

BobbyFord may be onto something, my concern would be why are the guides starved for oil?

I am not sure of your engine background, fresh rebuild?, rework an old one? If you are reworking old parts, you might want to check your oil passages.

This stuff can really hard to diagnose on line. There are so many things a seasoned mechanic can spot by hearing an engine run or even looking at it for a few minutes.
Keep feeding us info. Eventually it will get figured out.

Two-bit

[BobbyFord]

The pushrod is the weakest link. When the guides are gummed up with sludge or tight or dry, the cam pushes the lifter up but the valve is hung up in the guide, resulting in a bent pushrod.

[Dragon]

They could possibly be rubbing against the intake.The holes might need to be opened up.

I worked and work exclusively on FEs since 1969 (well a couple of SBFs and BBCs and Pontiknocks a Few Hemis and 1 440) and I never saw them bent from intake manifolds rubbing. I have seen them shiny when the high lift cam angled the rocker so far that they rubbed.

#1 stock engine bent pushrod cause! Overrevving
#2 Binding rocker arms on shafts.
#3 Sticking valves especially with sunken valves.

If cam is stock check by rotating the engine that all the new push rods open the valves with out bending/binding at all. Without push rods use a pry bar and test valve freedom of movement and with the rocker shafts off inspect them for tight rockers and slide them sideways and look for burnt blue rocker shafts under the rockers. That is an indication of clogged oil passages to the shafts.

[BobbyFord]

They could possibly be rubbing against the intake.The holes might need to be opened up.

I worked and work exclusively on FEs since 1969 (well a couple of SBFs and BBCs and Pontiknocks a Few Hemis and 1 440) and I never saw them bent from intake manifolds rubbing. I have seen them shiny when the high lift cam angled the rocker so far that they rubbed.

#1 stock engine bent pushrod cause! Overrevving
#2 Binding rocker arms on shafts.
#3 Sticking valves especially with sunken valves.

If cam is stock check by rotating the engine that all the new push rods open the valves with out bending/binding at all. Without push rods use a pry bar and test valve freedom of movement and with the rocker shafts off inspect them for tight rockers and slide them sideways and look for burnt blue rocker shafts under the rockers. That is an indication of clogged oil passages to the shafts.

Hmmm, I'd have to disagree with the over-rev theory...I've hit 6500 a couple of times on missed shifts in my Mustang without a bent pushrod.
I'll go with the binding rocker arms, however. Unless somebody missed tight rockers during assembly (?) I'd say lack of lube would be the cause of hung up rockers.
My bet is still on sludgy guides.

[Dragon]

Mustangs yes Trucks have different spring sets and I hit 5300 in my 390 and again bent push rods. It is a 65 Car 390. My 360 bent them at 5100. My 67 Super Stock Factory Stang hit 6800 once on a missed shift and never had coil bind or bent push rods.

[BobbyFord]

I still gotta disagree with the over-rev. The 390 in my '63 Uni shifts at 6,000, when mashed and hasn't bent a push rod in the 25 years that I've owned it. Same heads and springs on 4 different engines.

[Dragon]

I have overrevved my stock truck engine and had the engine get instantly sick. Upon arriving home raised the hood and #4, 7 and 2 had bent intakes and 8 had bent exhaust push rod.

And like I said trucks. You are still talking cars. This is a truck forum.

[BobbyFord]

I have overrevved my stock truck engine and had the engine get instantly sick. Upon arriving home raised the hood and #4, 7 and 2 had bent intakes and 8 had bent exhaust push rod.

And like I said trucks. You are still talking cars. This is a truck forum.

My '63 Uni IS a truck. With D2TA heads. Shifts at 6,000 rpms with stock valves, springs and pushrods.

[Dragon]

Your point? Mine does it, yours doesn't. So where is this argument going?