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I'm looking into the possibility of running 1.6 rockers* on my -461 heads. Will the stock, as-cast pushrod holes in the heads likely need to be elongated to allow clearance for the slightly changed angle of the pushrods?
*(I'd prefer to run full rollers, but since they must fit under OE stamped steel valve covers I'll probably have to compromise with Comp Magnum roller-tip rockers, which I'm quite sure will clear the valve covers.)
Yup, you're going to have to do a bit of enlarging on the holes with the bigger ratio, at least on most of the old OEM heads things got a bit too tight.
Are you running the engine under a class rule that requires stock height covers??? We had to do the same thing back a decade or so ago. The rules said you had to have stock height covers, but they didn't say a ting about running valve cover spacers under the stock height covers! Had plenty of room for big rockers.....
Thanks Dave.
Is this a common, straighforward job that can be done when the heads are being redone at the machine shop, or will I need to mock up the engine and mark exactly where the pushrod holes need to be enlarged first? It looks like there are some simple tools available for doing this but I don't think I'd attempt it myself at home (especially on iron heads) without a drill press:
Pushrod Slotting Tools - Tools & Shop Equipment - SummitRacing.com
No, it's not a racing engine; it's the original "numbers matching" motor out of my '65 Impala SS. I'm going to rebuilding it soon and plan on some internal upgrades while keeping a stock appearance. I saw a pic of those valve cover spacers; I think they're available up to an inch thick. While they would allow me to use full roller rockers, they'd look kinda goofy on an otherwise all-stock engine :-)
Could check them first with the long rockers before you take the engine apart...If you're not installing guide plates, just make sure you don't get the slots too wide!