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Jul 21st, 2025 | | | | Joined: Aug 2019 Posts: 240 'Bolter | | 'Bolter Joined: Aug 2019 Posts: 240 | Has anyone here measured the pressure on their old valve springs? Before I ripped off my cracked cylinder head the engine actually ran pretty good. It's valve springs exert about 54 pounds (just below the minimum 235 spec) when compressed to the 1.844" test length (see page 8.8 of the manual). My replacement springs test ~83lbf (wayy to high for a 235, but pretty close for a 261) and now I'm having a hard time deciding which spring to run. I like the idea of the soft old springs being gentle on my cam, although I am planning to upgrade to a 261 cam... I'm speculating that the stiffer spec for the 261 might have been chosen because those trucks originally had such low gears that the engine would spin fast more often. Since I have tall gears I'm thinking I could get away with the soft springs?
Last edited by Ott3r; 08/18/2019 3:11 PM.
'59 Chevy Suburban, NAPCO
| | | | | Joined: Feb 2004 Posts: 28,674 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 28,674 | Use the heavier springs. Neither one is particularly extreme- - - - -I'm accustomed to running triple spring setups with 300+ pounds of seat pressure on round track race engines. If you ever happen to get into an over-rev situation and float some valves the soft springs might allow some valve/piston contact and bend a few valves. That soft spring pressure might not seal the valves properly under compression, also.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Aug 2019 Posts: 240 'Bolter | | 'Bolter Joined: Aug 2019 Posts: 240 | Thanks for the tips hotrod... you're on a roll lately!
83lb doesn't seem so stiff now that you mention those other springs.
'59 Chevy Suburban, NAPCO
| | | | | Joined: Jan 2013 Posts: 1,518 'Bolter | | 'Bolter Joined: Jan 2013 Posts: 1,518 | The soft spring might work ok on the smaller exhausts but with the bigger intake valve's mass and any kind of rpm above 3000-3500 might not be enough to seat it, without float
1953 Chevrolet 3100261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done In the DITY GalleryVideo of the 261 running1964 GMC 1000305 Big Block V6, sm420, the next cab off restoration
| | | | | Joined: Feb 2017 Posts: 83 Vintage Truck & Tractor | | Vintage Truck & Tractor Joined: Feb 2017 Posts: 83 | I just had a head rebuilt and used 110 lb springs
Current project; 1961 C20, 235 I6
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