Ok I am a little concerned here. My new stroker, bent both push rods on number eight cylinder. I took her out for a little stretch Saturday morning, at about 5000 RPM in first gear i felt and hear something let go. A loud bang or snap, scared the shnit out of me to tell the truth. The push rods bent so bad they came out of the rocker and lifter seats, and now look like a couple of stainless bananas!!! What a pain in the a$$ to get them out of the lifter valley, but i managed to get them with one of those flexible claw things. the valve stems look healthy and the locks and retainers are OK as well.

Anyway I have some questions on how to make sure I have the correct valve geometry, when i order the next set of push rods. I have the CC306 cam, with Crane gold 1.6 rockers. New standard oem lifters, the heads have been milled .010" the block was decked about .010" as well. I am using the standard fel-pro 1406 head gaskets. I had used the 7808-16 Crane hardened push rods when i assembled everything. should i just use the 7608-16 chrome moly rods and be done with it . or should i use a different length than stock? 7.200" I think. My springs are supposed to be good to .600 lift, says my machinist, not sure of the brand or part numbers though, but they are the single coil variety. I did notice that the push rods flex a lot when I spin the engine over by hand. Help me out a little Oh Might Stroker Gods!!!

 

Things that may cause bent pushrods include overreving, inadequate piston to valve clearance, coil bind, retainer to guide interferance or inadequate slot length on the rockers. Weird things like a loose bolt under the valve cover, etc. can do it also. Of course, a defective pushrod could bend under normal loads.

You need to figure out what went wrong before starting it up again. Who put the motor together? Was the piston to valve clearance checked?

Rich Krause

 

Thanks Rich for chiming in, I appreciate the knowledge of some of the board members that post in the advanced tech section. The short block and the heads were assembled by Nelson Brothers in Largo, FL. They came highly recommended from local gear heads, and did an outstanding job I think. The piston to valve was not check as I did not have my mind made up on what cam when they did the work. The pistons are SRP -18cc Dish with valve reliefs cut in them. They are set at TDC to be about .020" below deck height. I did the cam install and the heads on an engine stand.

The car had about 300 miles on the block when this happened and had seen life at 6000+ RPM a few times. What may have happened is I had just finished adjusting the rockers. and was doing a little road testing. Maybe a rocker was loose. That could have been the case I guess. I did notice that one of the rocker arms looks like it was smacked by the retainer bolt. it has some minor cosmetic damage to the top of the bolt slot. I also suspect that the bent push rod interfered with the neighboring rod causing it to bend as well.

 

silly question-
are you sure they are the correct size pushrods?
they didnt go with a different size b/c of a smaller base circle cam or anything right? Did you mill your heads a good amount and keep stock sized rods?

I know both of the above happened to my friend and evenually a lifter went

just thought Id state the obvious

 

As Rich said, there are a lot of possibilities. I have two suggestions. First, I would mark the valve stem with a black permanent marker and spin the engine over several times. The rocker should rub off the ink right in the middle, about 1/8". Second, raise the exhaust on a cylinder to max lift and check coil bind. Sounds funny that the springs are "good to xx lift". Springs have a number of specifications, and max lift isn't the most important of those. I would find the sheet for those springs

 

Update: I checked the valve stems and the contact area is to the outside of center with the edge of the contact being right in the middle of the valve stem. Is this OK? I tried to check coil bind but that is a little sketchy to me. I used a feeler gauge that was .0025 thick and at full lift it slipped between an exhaust springs coils just fine. I dont know what kind of springs my machinist used. But I will try to find out tomorrow. I know that from what everybody says about Nelson Bros he does good work. I did tell him I would be using a cam with .550 to .575 lift so he could get me a good set of springs.

Nosfed you refer to specs of springs and that "max lift" isn't the most important of specs. Just to clear things up a little what is important about your springs specs. seat pressure? lift pressure at .xxx lift? a little more information on springs would probably help me understand what your talking about.