I have a 390 bored 30 over. Edlebrock heads, Comp Cam with a 268 lift. The problem is I have bent the same pushrod on the same cylinder (#7 cylnder big valve) on 2 different times. I've changed cams and lifters twice but the problem still comes back. This is a rebuilt enginge with less than 100 miles and I am using stock pushrods.

I'm going to have my heads checked for a bent valve if anyone has any suggestion please help.

 

Are you still running the stock non-adjustable rocker arm setup?

 

Yes I am. Stock nonadjustable rocker arms and stock pushrods.

 

You'll probably want to upgrade to the adjustable setup. The only other option is custom pushrods.

To upgrade to adjustable, you need the adjustable rocker arms and pushrods. Both are available at DSC.

 

So you dont think nothing is wrong with the heads or cam. why would the motor only bend the same pushrod and not all the rods. The other side runs fine.


Thanks?

 

Well the way they built them, they used varied length pushrods to compensate for a non-adjustable system. If you have it apart, you have to keep the pushrods in order. I'm guessing a longer pushrod went where a shorter one should have been. Then when the lifter pumps up at higher rpms, the valve stays slightly open when it should be closed. Combustion occurs, and the valvetrain takes the load the valve seat should take. Kaboom, bent pushrod.

That's the problem with the stock system. You cant set lifter preload. If you get the adjustable rocker system, you can set lifter preload to where it needs to be to avoid problems like this.

 

How much would an adjustable rocker arm system cost???

Thanks

 

They have 'em at DSC. Follow the link.

 

I took the heads to the machine shop nothing was wrong with the valves. He suggested that I check the length of the pushrods. It was common for people to change the length of the rods, and I may have a couple of long ones.

Thanks for the help.

 

your going to have for fork out id say $270 to do it right. You need the 427 Ford adjustable rockers, and the HD pushrods to go with. Rocker adjustment also depends on how close your machine shop got your installed valve height to stock specs. If you want your motor to run perfect, you must do it right. Also you can run those Ford adjustable rocker assemblys up to a little over .600. With your 268 cam, that would make a valve train that is dialed in perfectly, and indistructable. I just did the exavt setup on my FE motor. The way i like to adjust them is get the cylinder to TDC, have oil in the pan, and build pressure with a 1/4" deep socket and externsion and a speed wrench to prime the lifters, You know the lifter is ready when you cant push in the lifter plunger with the pushrod. Then imidatly crank down on the adjuster untill the pushrod cetches a slight drag, then go another turn and a half. THat will get you the correct lifter preload. If you dont prime the lifters after every cylinder, you will be able to push in the lifter plunger with the pushrod, giving you varying results. It just take a few turns of the oil pump to get it. Before you install the rockers, either make sure your lifters are primed(not spongy) or back off all 16 adjusting screws. Also only install the rockers with the crank 1/4 after #1 is at TDC, this puts all your cam lobes at their lowest lift for ease of install. If you crank down on your rocker stands, with a collapsed lifter, the pressure of the valve spring and smash that lifter plunger spring and damage it. Anyone have any other tips, id like to read emm. Im sure i missed some stuff tricks, i dont do it very often.

 

Ok thanks for the advise

 

jazzy66! Ford sets hydraulic lifter preload at .60. Sometimes due to variations in the valve train a lifter using the standard length pushrod will clack. The fix is to install a longer pushrod to achieve .60 preload on the noisy lifter. You have already replaced the pushrod twice so I think the problem is elsewhere. If the machine shop checked the valve and guide for binding and there was no problem, I'd check the rocker arm and rocker shaft. When you remove the rocker shaft on FE motors you should set the vibration damper on the xx symbol under the tdc indicator. This relieves valve spring pressure on the rocker shaft as you remove it. Take the rocker shaft mount bolts off one turn at a time until the rocker shaft is loose. Then use a straight edge or a sheet of glass to check the shaft for straight. Does this pushrod contact the intake? (You did buy a new pushrod..right?) Adjustable rockers are nice and provide a better valve to rocker ratio but not necessary for a smooth running truck. And sometimes for no apparent reason these FE pushrods just bend! There is a tech article here on FTE about this.