I'm starting to think pushrods might be my thing.

I'm not sure why it broke.  I replaced them, made sure the valves were opening and closing as they should.  It's running good.  Performance is the same so I guess nothing else is wrong.  I think the bent one is the result of firing the engine with the exhaust valve closed.

Should I replace this rocker arm? 

Lawrenceville, GA

Charlie,

      recently there was a thread concerning the same thing. I also have been experiancing the same problem. New motor, about 1200 miles on it, all new push rods from NAPA, and rebuilt rocker assemblys. Sure can't figure that out. I'm going to start adding Marvel Mystery Oil in the fuel and see if that makes any difference. I also though of going to the larger diameter rods through Murmmunt  but don't know if there will be any problem with the "G" rockers that have using the bigger ones. I have a very boring stock cam too, nothing loopy.

                                        Michael

Michael

Sandy Valley, NV

I wonder if the rocker and the cup mate together properly. If the ball is too big for the cup, they will break like this. You might clean up a rocker and a push rod real good and mark the ball with a lead pencil and then mate the two together and see where your contact is. This is the old fashioned way I cut valve seats and check seat width.

Kenneth

Fredricksburg, Texas

I don't think that is the problem. I look at all of the pushrods with a mirror to make sure they are seated properly when I replace them. Every one looks the same. The wear pattern appears to be the same as the others. The adjuster screws all look the same.

This set of pushrods was installed about 2 Labor Day Weekends ago. Since then, I must have put at least 3000 miles on them. If it was a mismatch such as that it seems like it would have shown up sooner.


Lawrenceville, GA

Charlie,  Do my eyes deceive me or is there a black area in the base of the cup at the break.  The shinny surface appears to be a new break while the dark area could have been a defect in the pushrod cup.  The lower area looks shinny, but it could have been from gouging the rocker.  If this lower part was also dark to start with (no way of knowing), there could have been a crack in the cup from the get go.  These things wouldn't be something you would look for prior to installing and short of a magnaflux you probably couldn't tell.  I sure am interested because I often wonder why my pushrods hold up as well as they do at 6500 + rpm for a couple of minutes with stock rockers.  We use hp push rods from Mummert and so far, so good.

I talked at length with Mummert on rocker/pushrod geometry and he feels that it is very important, but difficult to change on a Y-Block outside of pushrod length.  It is my personal opinion that valve spring height will change the geometry and along with the higher lift cams, it is very possible that the base circle is a smaller diameter and therefor might start the rocker/pushrod angle at a stressful position with too short a rod.  Therefor short of shimming the rocker towers, like Mummert says, pushrod length is the key.  We check the geometry very carefully and make sure we order the correct length of pushrod.

Defective pushrod?  Stressful geometry angle?  At least it is something to think about.

Charlie Burns Laton, Ca (South of Fresno)



BurnsRacing981@gmail.com

Charlie,



I don't think this is your problem but thought I would throw it out there anyway. When I first installed Dove Rockers the push rods were hitting the bottom of the rocker when the valve opened, shorter push rods solved the problem...





Johnson Rod



Southern California

It is black where it broke. I thought that looked kinda weird, too. I could see where the rockers contact the valve when I had the shaft off. It's a narrow contact patch, in the center of the valve. Other than noticing that, I haven't done anything to check geometry.



When I had a failure the first time, just after installing the Doves, JM told me about the shorter pushrods. But when checking with my mirror, there is plenty of clearance when the valve is open and closed. There are no signs that the cup is contacting the arm.



Hopefully it's just a good quality American pushrod that slipped by quality control - they can't catch them all - and not some Chinese crap.


Lawrenceville, GA

The patch of contact on the valve stem shouldn't be effected by the rod length.  This is what Mummert was trying to help me understand.  The reason is that the fulcrum point of the rocker on the shaft and the distance to the roller tip (or contact point of the rocker) and the head is constant no matter what the rod length.  With the valve stem height fixed and the lash at the desired spec, you just cannot start the rocker earlier or later with rod length.  What is desired is that the angle of the adjuster and the rod should be identical but opposite angles at the heal of the cam lobe and at full lift.  Too short of a rod will create a much larger angle while the valve is closed and therefore putting it in a bind to start the lift.  If you need shorter rods to clear the rocker, then you have no choice, unless you modify the rocker.

Sorry about the drawings............they won't get any better!  Also note that too short a rod will require more adjuster showing below the rocker.  Adjustable rods to calculate the correct length are available from CompCams and I have seen some very effective home made units.

I feel brave with these comments, remember, Tim has the final word on our builds.  I guess he is just letting me ramble here.

Charlie Burns Laton, Ca (South of Fresno)



BurnsRacing981@gmail.com

Are you using shims under the springs?  Are they stock springs?  If they are aftermarket, what is the shut-height?  Is the pushrod free of obstruction in its entire stroke?  Can you insert a feeler gauge in the spring coils when collapsed?

Your pushrod has a radial break under the cup (a sign of excessive compression).  Your valve came to a sudden stop, but the lifter kept pushing on the rod.  Somehow, either the valve got stuck and couldn't go down any further (not likely), or your valve ran out of stroke from something else like a collapsed spring, or from too much shim, or the lash adjust was too tight.  The pushrod collapsed at the weakest point, and came to a violent end from excessive pressure.

Dave.

Royal Oak, Michigan (Four miles north of Detroit, and 12 miles NORTH of Windsor, Canada).  That's right, we're north of Canada.

Ford 292 Y-Block major overhaul by simplyconnected

Charlie,

The drawing makes sense to me.

When I've watched Don build engines, he seems to adjust the rocker arm height to get the patch centered on the valve. Then he proceeds to check for the pushrod length by installing a dial indicator on the spring retainer and adjusting the pushrod until he gets the maximum lift. Then he checks that the rocker arm is close to a 90 degree angle at half lift. I've never asked him how he does it. It's just my observation. And, he usually asks "does that look like 90 degrees to you?"







There are shims. Springs are not stock. Have not measured the spring height. It does not look any lower than the rest of them. The pushrod is free of obstruction. I haven't tried to insert a feeler gauge. I can see when the valve is open that there is space between the coils. Nothing is apparent that could have stopped the valves motion. There is not enough valve lift for there to have been piston contact. With perfect geometry, lift will be .457". You're safe up to about .500" and my pistons have reliefs.


Lawrenceville, GA