This is the second set of 461 heads this has happened to. Both times, it happened about 1000 miles after putting them back on the truck. Both times, the #2 exhaust valve tip was flattened to one side. This time, most of the exhaust valves were dimpled, pitted, worn, scuffed, damaged. Surely this has happened to other hambers, so please let me know what the root cause of your issue was so I can troubleshoot my problem and get my '61 chevy truck back on the road! Important details: -1968-69 327 block -bored .060 with 350 rods -no clue what cam, but rough measure shows about .480 valve lift -no, I didn't build it; trying to fix po's handy work After a bit of interweb searching, here are the most likely causes: -pushrods are too long causing rocker to valve tip alignment issues -it's an oiling issue and there's not enough lube at the top of the motor (but why would this only happen on exhaust valves?) -weak springs causing valve float (springs are new and head was built by Brooks Eliot); Also, i think the max rpm this motor has seen is mayby 5K, and that's only when i smoke them in 1st.
Yes. That makes me think it might be pushrod length. The rocker is experiencing some lateral pressure and cut into the side of the stud. Heads are at the machine shop now, but I don't want to put it back together until I investigate all potential points of failure. @squirrel, have you seen anything like this before?
I saw something like that on a similar engine, I don't know offhand how to fix it...although getting good rocker studs would be a place to start.
I wonder about the pushrods with the groove in the stud? Do the pushrods show wear on the side where they go through the hole in the head? Also wonder if you've checked alignment on the pushrod to ensure it's centered on the valve stem? Length issue? Are all the pushrods the same length? Oiling could be an issue, but not if it's just the exhaust valves. I'd pull all the pushrods and see if someone used different lengths on exhaust vs. intakes.
All pushrods are the same length and have gone back in the same valve they came out of when putting back together, both times! I think they are stock length, but can double check tonight. The first time this happened, the pushord gouged the guide in the head, so I opted not to have those heads rebuilt, and went with a "new to me" set from a trusted friend. The pushrod guides in this set look normal, with just slight, and what appears to be normal wear.
let the machine shop cut out the factory guide holes, and install screw in studs and guide plates. make all the improvements you can afford springs , retainers, keepers and such... roller rockers might be of some help too
My experience with those particular heads in the past is that the pressed in studs are not always square to the world as they should be. Hand tapping the hole may repeatedly produce similar results. They need to be machine tapped square in a competent machine shop. Charlie
+1 on this - we did a set of these on my buddy's '63 split window and the studs were all over the place....
Usually the pushrod length being too long [ rocker sitting higher ] causes the furthest point of the rocker to make contact. If this was the case the tip of the valve would be concave. To wear like in the photo supplied, shows the valve is not rotating.
What's the rocker look like ??? If there are no "rotaters" on the exhaust valves [like factory] , they don't rotate. dave
I'll bet the pushrod is reeeal shiny where it goes through the head. Guideplates and screw in studs. You drill out the pushrod holes in the head, you can "aim" the rocker square over the valve by moving the guideplates before the studs are torqued down.
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