Quote:
Originally Posted by Gaz64
I would say the pushrod cup seat has been starving for oil.
Many of this type of rocker system does not have continuous oil flow.
The cup and pushrod tip have pounded themselves away, the rocker has increased it's rocker ratio, and possibly driven the valve to coil bind, allowing for the increased valve clearance.
I would be looking at replacing any/all of the pushrods and rockers.
I would also run the engine with the valve covers off checking for oil flow after reassembly. And do as olddog above has mentioned about flushing the engine.
Gary |
I was thinking the same thing initially, Gary. What changed my mind was the lack of heat discoloration that usually accompanies an oil starvation failure. My suspicion is, if the pushrod cup had a scratch or perhaps a hairline crack that was the weak link and it finally gave up the ghost with all the attendant carnage.
The more probable (big) contributing factor, was very likely poor rocker geometry attributable to too short of a pushrod for the pieces being used that never was investigated, measured or corrected. The short pushrod as already noted would put the full load of opening the valve on the side of the pushrod cup instead of in the center. The abuse does not take a long time before it extracts its pound of flesh.
When the pushrod is short the rocker fulcrum has to be lower to make contact with the pushrod. As you lower the rocker fulcrum the existing pushrod increasingly pushes on the side of the cup. Cups are pretty hard little devils. Push on the side instead of the approximate center long enough and you can induce this type of failure.
Determining the correct pushrod length to obtain the correct rocker geometry is
always the responsibility of the engine builder and something that needs to be done anytime you build an engine from parts. I suspect that step was overlooked or just not known to this builder. In fairness all the other rockers could be at the same risk of a similar type of failure and there is no way to know w/o checking the geometry.
Here is a teaser with respect to the geometry issues off the T&D website, T&D's focus in their explanation is prevention of premature guide wear;
The main thing we are looking for in geometry is the pattern on the valve stem to ensure that valve guide wear is at a minimum.
The roller tip needs to start towards the intake port side of the head when the valve is closed. The rocker should then roll out to just past center towards the exhaust side of the head at half lift. Then from half lift to full lift, it should roll back to where it originated on the intake port side of the valve stem. The amount of tip travel will be directly affected by how much lift there is at the valve.
Example: If you have 0.550” lift, the roller tip should start 0.020-0.025” before centerline of the valve stem. If you had 0.650” lift, this pattern will roll back towards the intake side of the head and be 0.025-0.030”.
The OP's engine looks like it may have had very short pushrods. With stud mounted rockers an uniformed engine builder would just snug down the adjuster until the pushrod made contact with the rocker. This is high stakes poker no matter how you cut the cake.
There are several good videos on YouTube. I did a quick search and found this one, from Prestige Motorsports, click here
Rocker Geometry (you need to wait for the YouTube commercial to finish). The video is fairly well organized and presented. By far the best explanations I have seen come from T&D in their tech literature that accompanies their products. I did not check but I would not be surprised to discover that you can download their installation doc.
Ed