1.75:1 Rockerarms on 301 & 426
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URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=84864
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Topic: 1.75:1 Rockerarms on 301 & 426
Posted By: Big Orange
Subject: 1.75:1 Rockerarms on 301 & 426
Date Posted: 14 Feb 2014 at 10:12pm
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Can you use 1.75 :1 Rockerarms on 301 & 426 without needing to flycut the pistons?
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Replies:
Posted By: O.P.S. Heads
Date Posted: 14 Feb 2014 at 10:45pm
Posted By: Big Orange
Date Posted: 17 Feb 2014 at 9:32am
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OK then. How much of a relief do the pistons need to clear & run.
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Posted By: O.P.S. Heads
Date Posted: 17 Feb 2014 at 4:42pm
That depends on your cam lift and timing as well as where your valves are set for recess or protrusion in relation to the head surface. If you plan to use the stock cam with the faster ratio rockers and stock valve size and depth you could probably get by with a .100" deep relief. If you use a reground cam with the faster rockers and .050 or more protrusion you may need as much as .350" deep depending on the cam grind and where you time it in relation to the crankshaft.
No matter what the combination be sure to measure clearances correctly before final assembly. Use an old piston for machine purposes and install it. Roll the engine over by hand far enough to where both valves open and close with everything assembled and the valve lash set. Use silly putty or whatever you want as a measuring device. Once you decide what is needed you can machine the pistons you will use correctly. You should have a minimum of .060 clearance on the intake and .080 on the exhaust valves. More is good. Too much is not necessary.
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Posted By: Big Orange
Date Posted: 17 Feb 2014 at 6:50pm
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Thank you, I just thought maybe somebody on here may have done this, so I wouldn't have to do all of that. I have done this on race car engines before.
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