Question about push rods

[MGTF1250Dave]

Aloha All,

I have just finished putting my engine back together after repairing a damaged exhaust valve. It is great to have power from all four cylinders again. The push rods are hollow tubes with a ball fitting at one end and a cup fitting on the other end that appear to be either pressed in place or spot welded to the tube. I noticed that three of the push rods had the either one or both of the fitting loose enough that there was movement in and out of the tube, but not to the point that they would come free. Should I have these replaced or repaired? How would these be repaired?

Safety Fast,
Dave

 

[Matthew E. Herd]

Definitely replace them immediately! I can't state this with enough force! I had some custom made ones which were hollow and of similar construction on my midget. The cups spread and then finally one of the cups broke free, falling onto the block and causing a series of loud bangs. I was terrified, but upon removal of the valve cover discovered that no harm had been done. Aside from the metal debris all over the pushrod area and evidence that every single rod was failing in a similar manner, the engine was fine. There was insufficient oil flow, but I feel that that was not the only reason for the failure. If they aren't 100% solid, get rid of them. You don't want to risk wiping out a cam should parts drop down past the lifters (unlikely, but if it did happen, terrible). I went over this in another string under the spridgets section. Don't remember the name of the thread.

 

[Dave Russell]

Wow - Don't get so excited.

Literally tens of thousands of tubular aluminum pushrods with pressed in steel ends have been & still are being made & used successfully. The advantage is a lighter & stiffer rod. No doubt a few have been of inferior design, materials or construction, but many more are excellent. If there is anything to be learned it is to use parts that have been well proven. If this means solid to you, so be it. Obviously the cups on your pushrods were faulty, not the design itself. Custom made does not always mean better, it sometimes means that it hasn't been done before.

School of race car & motorcycle building 1954
D

 

[MGTF1250Dave]

Aloha Dave and Matthew,

I agree that experience is a very helpful tool. Matthew's tells him to go with solid push rods. He was very lucky that he did not face a major overhaul as a result his push rod failure. In, my case, these push rods have been in the engine since at least 1972, and probably before that and may well be 50 years old. This type of push rod seems to have worked well in this early 50s vintage engine.

I cleaned and inspected the push rods for wear and cracks before reinstalling, the end fitting were in good condition and the only thing I found that some of the end fittings could be moved. They did not rotate in the tube, but could move in and out of the tube slightly (1/16 inch or less).

Dave, do I need to be concerned with the movement or since the specified valve clearance is .012", it would seem that when installed the end fitting can not move any significant amount. Also, this condition could have been there for some time since the push rods have been in place since 1999. Your advice is greatly appreciated.

Safety Fast,
Dave

 

[Matthew E. Herd]

No, I have no preference for solid rods, its the manner of construction. Mine were insufficient. I feel that hollow rods are desireable, so long as their construction is adequate. I'm simply saying that if they're not perfect, don't reuse them!

 

[MGTF1250Dave]

Aloha Matthew,

I misunderstood your post and didn't mean to put words in your mouth by inferring an opinion. I'm glad that your engine was not severely damaged because of the failure you experienced. Your input is greatly appreciated.

Safety Fast,
Dave

 

[Dave Russell]

[ QUOTE ]

Dave, do I need to be concerned with the movement or since the specified valve clearance is .012", it would seem that when installed the end fitting can not move any significant amount. Also, this condition could have been there for some time since the push rods have been in place since 1999. Your advice is greatly appreciated.
Dave

[/ QUOTE ]
Normally engines are designed so that there is never any tension on the pushrod & there would be no forces present to un-seat a loose end, & Yes the .012" clearance would probably prevent a loose end from popping out.

However;
If the engine is revved high enough to cause valve float, the normal .012" clearance could be greatly exceeded & the rod end might pop out.

Now for the really odd part;
Some British engines had an early form of hydraulic tappet quitening. The clearance of the rocker arm ball & pushrod cup was purposely made so tight that oil had to be squeezed out of the mating surfaces to take up the set .012" valve lash. The rockerarms would have a low pressure feed to the ball ends. Result - quieter tappet operation. When the cam dropped off the lobe, the pushrod weight plus the slight oil pressure feed would open the gap again to feed more oil into the joint. This is why it is recommended on some engines to force the rocker ball down before measuring the lash. (To squeeze the oil out of the joint)

What I am getting at - There could be a slight ball to pushrod separating force which could cause a loose pushrod ball seat end fitting to work up & down in the tube & create some wear & more loosening. The cure is to throughly clean the joining surfaces & assemble with Red Loctite. If you were "spooked" by the prospect of an end coming loose, replace the pushrods with new ones of the same type construction. Or if "really spooked" use solid pushrods.
D