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post #9 of (permalink) Old 06-17-2016, 11:15 AM
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Join Date: Mar 2012
Location: Newman Lake, WA
Posts: 1,069
Wow... 3/8" from AFR, huh? They must use 3/8" on the smaller heads. My AFR 210's came with 7/16". No matter... I just needed to know the thread pitch of your rocker studs. Yours are apparently 3/8"-24. This is important for adjusting the preload on your lifters.

When I worked at a large Chevrolet dealership in the 90's, we used to do valve guide seals on the 5.0L and 5.7L truck engines on a daily basis...literally hundreds and hundreds of sets of them. Of course, you would have to pull the rockers to change the seals, then readjust the valve on the way back together. I have tried pretty much EVERY method of adjusting SBC rockers, as well as pretty much EVERY amount of preload. With stock 1.5 rockers, and stock 3/8"-24 rocker studs, I found 3/4 turn past zero lash to work the best. I had them start clattering after a test drive at 1/2 turn, and I had them hang valves open after a test drive at 1.0 turns. I never had any problems at 3/4 turn past zero lash. Now, this if for 1.5:1 rocker arms on a 24 thread/inch rocker stud. With 7/16"-20 studs, and/or 1.6:1 or 1.7:1 rocker ratios, you'll have to do the math to get your lifter preload correct. I always set up hydraulic lifters (roller or flat tappet) at appx. .050-.060" preload, unless otherwise specified.

I asked about the bottom end because the LT1's were notorious for coming in with an upper end tapping/knocking sound that sounded for all the world like a lifter tick, except that it was at crankshaft speed. Almost without fail you would find a spun rod bearing on either #7 or #8 to where the rod would let go of the bearing shells, and they would both end up stacked together in the big end of the rod. So you had the empty rod cap on one side, and a double-stack of bearing shells on the other side riding against the crank journal. Oil pressure would read normal, but you had this tick/knock sound that was actually the piston lightly kissing the bottom of the head on that cylinder due to the extra bearing shell in the big end causing the piston to come out of the hole at TDC and hit the head. I've seen this literally dozens of times with these engines. That's why I have such a hate/hate relationship with the rods in a stock LT1. They're heavy, weak, and don't hang onto their bearing shells well at all. ANY build should include a new, decent set of rods...

1995 Camaro Z-28, M6, 396 stroker, Scat forged 3.875" crank, Scat Ultra Q-Lite 6" H-beams, Icon forged pistons (4.030"), splayed 4 bolt w/ARP studs, 12.25:1, AFR 210 heads (2.08"/1.6", 58cc), Comp Ultra Pro Magnum XD 1.7:1 rockers, GM847 cam (234/242 .611"/.632"), Edelbrock LT4 air-gap intake, Spec Stage 3+ clutch, Fidanza aluminum flywheel, 24x conversion, 0411 PCM, TPIS 58mm, Bosch III 42# injectors, Aeromotive 340, Kook's stepped LT's -- SOLD TO MYSTERYBIRD
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