Broken Pushrod - Mystery Solved ???

[PC Rat]

UPDATE on 7/31/07, see post #14.
If you have seen my thread about the broken pushrod, I may now have the answer.
I took another close look at all of my pushrods and noticed the #8 exhaust had three rings around the end. I have used different colored arrows to identify the rings.
http://www.***boat.com/image_center/data/520/3256No_6_and_8_pushrods_post_1.JPG
After looking at the corresponding rocker arm, I noticed a small spot where the blue coloring was worn off of the body of the rocker. When you put the two together as they would be a full lift, a contact point is visible (Red Arrow).
http://www.***boat.com/image_center/data/520/3256Pushrod_and_Rocker_Post_1.JPG
In this next photo I have attempted to draw (in Blue) a cross section of what the inside of the pushrod cup looks like in the rocker arm. Again, with the pushrod and rocker in the full lift position, it is evident how the last two rings (Orange and Green Arrows) correspond with the chamfer in the pushrod cup.
http://www.***boat.com/image_center/data/500/3256Rocker_post_1.JPG
So, I assume that the pushrods with the ball ends will take care of this problem. What about the contact point in the rocker body described by the Red Arrow?
Also, as a side note, to check ALL engine components, as in my case the majority did not seem to have clearance problems.
Brian

[obnoxious001]

How about a photo of the valve stem tips? How long are your pushrods, and what are the rest of the particulars, standard or tall deck,,,, roller or flat tappet,, I forget,, and which heads? Looks like that pushrod may be too long?

[SmokinLowriderSS]

Yes, geometry problem somewhere. The pushrods shouldn't hit there and side-load them.

[MikeF]

Does the rocker from the pushrod that broke show the same signs of damage in the same position? Take one of those really good close up pictures of the pushrod cup of that damaged rocker. :boxed:

[rrrr]

PC, it appears that the geometry of the pushrod and the rocker is off. Check your pushrod length.
Rio
That's what I thought to begin with. Sometimes the obvious answer is the correct one.

[roostwear]

I would also check the valve stem height to ensure they are all the same (and correct). If the contact surface on the valve tip is off, it can remedied to a degree with lash caps, pushrods, or a combination of both depending upon what you find.

[GofastRacer]

Measure, check, check, measure, check, double check, triple check, and one last time just to make sure!... :)

[steelcomp]

I think the push rod would have to be way too long,,,he's not running that much lift. My bet is that it's the Isky rockers. They're way beefy, and probably just a little too thick right there. I'd just take a small cartridge roll and oh so slightly relieve the rocker. No harm done.

[GofastRacer]

All part of the building program!.. :)

[Weaverman]

Couldn't help noticing your rocker trunion shaft is rotated such that the flat for your lock is not facing up (toward the lock). Is that just from handling?

[PC Rat]

Yes

[PC Rat]

Smith Bros sent me a couple pushrods with a different end, they have a lot more clearance.
The machine shop was the one that figured out what length of pushrod I needed. I questioned about his method and he puts the roller in the center of the valve. I think I am going to do it myself using a mid lift/shortest swept area. My pushrods are 9.800" and 8.700" which seem very long and I think produced a very small angle between the rocker and pushrod.
Will I be able to get a mid lift geometry to work with rocker studs and not push the roller to the extreme edge of the valve?
Brian

[PC Rat]

UPDATE:
Last weekend I started putting my engine back together again. I've spent the last two evenings checking the pushrod length.
My intake pushrod length needs to be 9.000" (previously 8.700").
My exhaust pushrod length needs to be 9.700" (previously 9.800").
A couple areas of concern that I have is:
1. The roller contact pattern on the valve tip. The valve stem diameter is 0.340", the contact pattern is 0.040" wide and starts 0.074" from the outside edge ( 0.074" + 0.040" pattern + 0.226" = 0.340" dia).
Is 0.07" too close to the edge?
2. The longer intake pushrod puts the rocker so high that is only leaves 0.3" of stud thread engagement for the rocker nut.
Is 0.3" enough engagement?
The studs are Manley 42288 which are 2.810" long, with 0.740" into the head. The only longer studs I can find, also put more stud into the head - which sticks down into the port.
3. When the valve is at max lift, the angle between the rocker arm body and the pushrod is so tight that there is less than 0.010" clearance between the rocker body and pushrod.
Will I gain much clearance by going to a steel bodied rocker instead of the blue aluminum Isky 1.75:1 rockers that I have now?
I was considering the Crower Stainless 1.75 ratio rockers, any other suggestions?

[Rexone]

You can relieve the Isky rockers with a small sanding roll as mentioned above. They are way beefy (good thing imo). I've ground on them before myself for various clearance issues. You might consider stud girdles too. It creates a situation where all the studs share the load, stabilizes them, and any one is less likely to fail.

[PC Rat]

It has a stud girdle.

[steelcomp]

It's typical for the roller tip on the rocker to be somewhat towards the outside of the valve tip. Not to worry. The .300" of engagement on the stud isn't too bad, either. Again, typical. And what Rex said above. Just add a little clearance where the PR gets close to the rocker, and you'll be fine. Just make sure you clean the rockers thoroughly when you're done.

[gn7]

was the push rod that broke an intake or exhaust? you said the in were to short ans the ex were to long. be really surprised if this happened with a rod too short because the problem is only gunna get worse. If the .300 thread engagement really bothers you, throw a head bolt washer under the stud between the stud and guide plate. if the threads in the head make you nervous, get and long thread exhaust stud and cut the head side threads down to the length you need.

[PC Rat]

It was an exhaust pushrod, so the shorter ones should help a little. I will be using the pushrods with the shaft rocker style ball end.
Brian

[gn7]

yep, as long as your buying new push rods thats prolly the best idea