Straight 8 pushrods bending

I have a 320 straight 8 in a 1952 roadmaster that is bending pushrods. This car sat for a loooong time. When i brought it home from a farmers field i found 3 bent pushrods. I replaced them and disassembled, cleaned,and oiled the 3 lifters for those bent push rods and adjusted the valves per the 52' manual. Life took over and the car sat in a garage this time for about 2 years. I made an attempt to start the car a week ago. The car fired right up. I made sure to watch all the rockers for proper movement through 2 -3 heat cycles before installing the valve cover. I even drove the car around the block. I shut the car down. I Went to restart the car the next day and it had a serious miss because it was running on 6 cylinders due to 2 more (different) push rods.

I ran a compression check with surprisingly good results. I was able to purchase push rods but don't want to replace the parts until i figure out whats going on. I don't see where a stuck lifter would bend a push rod. Any ideas?

Stuck valves bend the push rods. I had the same problem on a '56 Special that sat for a long time, and also on a 1950 Pontiac that sat for 32 years. The old gasoline deposits are like tar. The valve stems and valve guides are full of it, probably. Pour Marvel Mystery Oil over the valve stems and springs and let it sit overnight. Put a quart of Marvel mystery Oil in the gas tank, so the new gas will have the oil in it. So what, if the engine smokes out the exhaust on that tank of gas. You are saving your push rods and valves. On the Pontiac (flathead straight eight) I had to remove the cylinder head, valves, and pushrods, and ream out their holes with a reamer, to get rid of the tar-like deposits. On the '56 Buick, I was able to unstick the valves with lots of Marvel Mystery Oil as described above.

P.S.: I am envious of anyone fortunate enough to own a '52 Roadmaster! The trials and frustrations will be worth it in the long run.

Pete Phillips, BCA #7338

Leonard, Tx

A bent pushrod is caused by either the valve sticking in the valve-guide, or by interference from either valve spring coils binding or piston interference. I don't believe this engine is an interfence design where the piston tops can hit the valves if the timing is off, so that leaves valve spring bind.

Check for broken valve springs; if a spring is broken a piece of the spring coil can wedge itself into the rest of the spring such that it binds when the valve is opened.

Are the bent pushrods on intake or exhaust valves, or both? Exhaust valves run hotter and are more prone to sticking than intakes when hot. Usually caused by insufficient valve stem to guide clearance. This can happen if the guides were replaced and not reamed to the proper clearance, or from rust or severe carbon or hardened gum buildup.

Pete, The check is in the mail for the push rods you offered to sell. I only paid $1000 for this roadmaster and it is a 2 door. However it is very rough but it does run and now stops thanks to a very complete brake rebuild. I can't believe how well the car handled when driving on very short trips. I am excited.

If you dont know the mechanical history of the car, there is another possibility.

There are left and right rocker arms. If someone worked on the rocker shaft and rocker arms, they may not have got the orientation right. The manual spells that out. If the rockers are assembled wrong, the pushrod will go in, but rub the hole where it goes through the head, bending and eventually breaking. I found that to be the cause of a "miss" on a '38 Buick.

….. Here is a link to enlightenment. "Same holds true for 52"

http://forums.aaca.org/f162/how-do-series-learn-how-we-322149.html

Well, i found a little time to spend out in the garage this evening. I was able to collapse all valve springs/valves easily. I then sprayed each valve with wd-40 several times and let that set for 2 hours. Finally i used a "zoom spout oiler" with transmission fluid to direct the tranny fluid to the valve guides as well. I will let this set for a couple of days. I may do it again after that.

I'm sort of stumped now as all the valves exercised up and down with seemingly no interference whatsoever. Even before lubing the valves.

Tonight i took a suspect sticking intake valve, then i removed the spring and retainer. I brought the piston to tdc. I mic'd the valve from fully seated position to as low as it would fall. The valve only fell off seat .215

I believe the camshaft valve lift is .347. This tells me my valve isn't opening enough. Or does the hydraulic lifter cushion this to some extent?

Hydraulic lifters don't really "cushion" the valvetrain, they just take out the lash automatically.

You need to compare this valve opening with the other valves. Is it stopping before fully opening, or is it not returning to fully closed?

There could be carbon/coke buildup on top of the piston, on the face of the valve, on the backside of the valve, or all of the above causing some kind of interference. Try backing off from TDC a bit and see if the valve opens further (but not so far as to allow the valve to drop into the cylinder). Check the height of the valve stem tip when closed; does it match the other valves?

Hydraulic lifters don't really "cushion" the valvetrain, they just take out the lash automatically.

You need to compare this valve opening with the other valves. Is it stopping before fully opening, or is it not returning to fully closed?

There could be carbon/coke buildup on top of the piston, on the face of the valve, on the backside of the valve, or all of the above causing some kind of interference. Try backing off from TDC a bit and see if the valve opens further (but not so far as to allow the valve to drop into the cylinder). Check the height of the valve stem tip when closed; does it match the other?

I backed off tdc to where the piston is about an inch below the valve when it's .215 off seat. The Valve seats fine. It appears to be opening .132 less than it should based off of the advertised lift of .347. I need to compare it to some other valves tonight.