Hello all,

I just recently finished my 400, and upon starting it have bent the intake and exhaust push rods twice now on cylinder 8. What could be the likely causes of this happening, and what am I looking at for a remedy?

Any help Appreciated.

Thanks

Milton

 

Check your valve train geometry. Always do this after a rebuild. Spring bind or improper lifter preload can cause that problem. Check ALL of your valves! Hope you have not ruined your camshaft.

 

There's really only 1 cause of bent pushrods and that's from the action of the cam trying to force the pushrod against an object that doesn't have any give. Bottom line as Torque1st said, either the cam has too much lift for the valve springs and they're "going solid", the lifter preload is set too high (only possible with adjustable rocker arms) or the pushrods are too long for the application (can happen with non adj. rocker arms if the block/heads have been machined).

Since you didn't give us any other specifications such as cam profile, RA type, machine operations performed, it's rather difficult to try to help you diagnose the problem.

 

The cam is a Crane Energizer with a .508" lift. The pushrods are stock length, and the lifters are the stock lifters, torqued to spec. The problem has only occurred on the intake and exhaust of cylinder 8, no others. and "appears" to occur anly after the engine get warm.


I am confused as to the term geometry, as the installation of the rockers as they are on the 400 seems bone simpple, and impossible to screw up, which doesn't mean I'm not, just that i don't see what I could be doing wrong if I install to spec only.

I appreciate your answers to this point, and look forward to any further insights you may be able to offer.

Thanks

 

If you're using the stock springs then you're probably on the ragged edge with all of the cylinders. I don't recall the exact specs but stock springs go solid in the .490" range. Slight differences in lifter & RA specs are probably the only thing keeping you from bending more pushrods. It's also very possible you've wiped the cam.

If you're using the springs that Crane recommends with the cam then did you have the machine shop check the installed height of the valve? Did they deck the block and/or heads? If so how much?

 

The seats were probably worn bad in that cylinder, so the valves got sunk farther making the stems stick out more than the rest. Always make sure the machine shop you choose controls their valve stem heights. You can either try to shim the stands or get shorter push rods. Like Torq said your going to have to check the geometry.

 

OK, so my own bumbling has created the problem, as I suspected. While I did change the cam and lifters, the stock springs were used, so there is an apparent .018" difference in the lift now as compared to standard. Since the engine has less then 20 minutes running time on it, I am going to proceed from this piont in the hopes that the cam hasn't been wiped. Assuming such, if I shim the rocker arms, how do I determine how much they are to be shimed to acieve a decent geometry? It seems that shims come in only .030" and .060" thicknesses, allowing up to .090" total shimming if both are used. NOw, I am certainly no math wizard, especially when it comes to engines, but it seems that if I just place one .030" shim under the rocker, that will translate into either .015" list difference, or possibly even only .0075" difference. But I don't know. Can someone point the way to the correct method of determining shim height, or is it simply trial and error?


Thanks again in advance

Milton

 

Check your service manual. It has a detailed process for setting lifter preload and checking valvetrain geometry. There are many factors involved. You may still suffer premature cam failure due to the tremendous pressure that was put on the #8 lobes. Check that service manual and go over your engine to make sure you have not made any other mistakes.

There may have been instructions with the cam and they may be available on the manufacturer's website.

 

My advice would be to go get the correct springs for that cam. Shims are useful for getting the correct lifter preload not band-aids for having the wrong springs. The bottom line here is that the cam is trying to open the valve farther than the spring is designed to allow. Opening the valve more is a performance enhancement because it allows more A/F mixture into the cylinder. What's the point in having a high lift, high performance cam if you're not going to use it?

 

Your right, of course, but this and other things are just a few of the things I didn't know when I decided to build my first..and probably last...engine.


I am going to replacce the cam with a stock cam, since I have probably either wiped or seriously weakened a couple of lobes at least, if not all. I will return to engine to the factory specs, and see how it runs, before I decide whether I want to tear it down yet another time to upgrade the cam and springs.

Thanks for all your guys help, it has been much appreciated.

 

Forget going back to stock. Do yourself a favor and just get one of the Comp. Cams K kits. Comes with everything you need; cam, matched springs, retainers, and a timing chain. If you don't need the timing chain, get the cheaper kit, it comes with the cam and matched springs............they take all of the guess work out of it for you. Check with Summit or Jegs. The big kit is about $340, if I remember right, and cheaper if you don't need the timing chain. They even offer the 255 cam and 265 in the same type kits. Do yourself a favor and do not put the stock one back in. Go check the comp cams website and pull the kit part numbers. And call jegs or summit, whoever you want......... and get a price. The prices will be comparable to a stock set up, but you will be further ahead and much....MUCH happier.

Don't get discouraged from your first rebuild. Live and learn. You can even buy an engine rebuild book for the 335 series engine from those same suppliers. I don't care who you are, there is nothing wrong with building something by following the directions. Once you've done it a bunch of times, you'll know what you're doing.

Good luck, and keep us posted.

 

I was about to say the same thing !!!