This one has me puzzled. After replacing the camshaft with a mild performance one from Crane cams repeated problems with the same valve in the same cylinder. First, the stock rocker arm broke in half so I replaced all the rockers with comp cams heavy duty roller rockers, checked the valve springs and replaced the keepers. After a few hundred miles valve stem broke right below the keeper. There was no indication of trouble before either failure. Certainly dont want to just replace the valve without understanding what'sz happening. Help! thanks in advance.

 

You say "mild" but what is that actual lift now, compared to the stock
To me it shows that you did not take the rest of the valve train into consideration
1 broke push rod, broke rocker arm, valve stem
Is the cam the only thing you changed?
did you change springs?
just a few thoughts..
Hope you get things working
Best

 

You are correct, I didn't take any other components into consideration. I needed to replace the cam in my 289 and didn't want to buy an off the shelf one being fearful of a low quality Chinese part. So I contacted Crane Cams and they recommended a cam they described as a mild performance cam that would work well with existing stock components. So I purchased it along with a new lifter set from them..BIG MISTAKE! Now, in retrospect, I can see the cam wasn't so mild, the sales guy would say anything to sell it, even though I told him I wanted as close to stock as possible. And the lifter set was bad. One lifter did not have the oil inlet hole drilled in it so wouldn't pump up. When that was resolved and the engine restarted a second lifter disassembled right in the bore. Replaced with Comp Cams lifters with no issues. So in my instance using Crane Cams was a bad move and caused all the problems. Of course, over the phone they said it was my fault for not seeing the lifters were bad. Holy Cow!

 

I would not be say it was a bad mistake.

Like all of us, you want to get something done, but we need to look
down the road sometimes.
Of all components on a car the inside of the engine is the most
time consuming and costliest. I think you can see that when you see
the prices of "crate' engines, one is $2500, the other $4000, you see
where I'm going.
And your not a TV show, with dozens of mechanics waiting to fix
the mistakes before it airs.
I've never been one to "rebuild" my motor, as opposed to to buying
a Long or short block. Time is one issue, but you know that engine if
coming for a reputable builder is right, he might dig into your block
and find real damage, either cost you a lot more money or you going to
end up buying that off the shelf motor..
Anyway, good luck on the situation, keep us informed.
Best

 

Did you resolve your problem? Do you have screw in studs and full roller rockers? How did you set lifter preload? Did you verify rocker tip to valve stem geometry to make sure you have the correct pushrod length?