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I am currently building a Vortec 350 for my 1977 Corvette. Its bored .030 over with flat top pistons, forged Eagle rods, reconditioned crank (balanced assembly), zero deck, and a .028 gm gasket. I am also using an LT4 hotcam. The heads are 062 Vortecs that have been minimally decked, valve job with back cuts, mild porting and polishing on the exhaust side and LT1 screw in studs installed. I am also using Straub Technologies 1.26OD valve springs with 115# 1.8 installed height with a max lift of .550 on unmachined Vortecs (which mine are). I also drilled out the pushrod holes to 1/2" to use a set of Comp Cams 1.6 roller tip rockers. I was going to use the stock 7.18 in pushrods as nothing has really changed than a little decking. Upon start up (1/2 turns lash on primed lifters), The engine immediately bent 12 pushrods. Upon removal of the pushrods, I inspected the lifters and cam lobes and they are in perfect condition. I purchased a valvetrain geometry tool and an adjustable pushrod. I dont have a solid roller lifter or a way to make one, but according to the blue plastic geometry tool and the adjustable pushrod, the 7.18" pushrod is .18 too long. The only rods I can find are 7.05. Before I pull the trigger on anything else, I would like for yall to take a look. I have a buddy with a bore scope. we will check for damages. Here is a picture of the stock 7.18" rods with the plasitc tool showing the gap.
Here are some pics of the New geometry with the adjustable rod at 7.00", the pushrods clearance through the 1/2" holes (the darker rod is the adjustable one) and the installed height difference at 1/2 turn lash.
These are pictures of the valve at full lift with the 7.00" adjustible rod in place. The contact patterns are of the adjustable rod on the right and the stock rod on the left along with the LT1 rocker studs.
Never seen pushrods bend to almost 90*. Somethings fishy there. First off, if you have zero deck, then you gained .020-.025 on the pushrod geometry length. And I believe a std headgasket is .040 thick. So there is another .012. I believe you either torqued the valvelash to tight on a empty lifter, then it pumped up. Or your timing chain sprocket timing marks were never dialed in and could be way off.
After viewing your additional photos I notice the rocker nut with the checker tool installed has more threads showing than its neighbor.
Also, are those heads suppose to have guideplates? That would raise the rocker up considerably.
Can't tell for sure, but looks like the key in the keyway is two pieces? Almost looks like it shifted, but might be the camera angle.
And when the sprockets are dot to dot, I believe that is the firing for number 6 cylinder. H-m-m-m-m-m-m-m-m-m..
And when you say "primed lifters" you mean they sat in a bucket of oil overnite, right?
After viewing your additional photos I notice the rocker nut with the checker tool installed has more threads showing than its neighbor.
Also, are those heads suppose to have guideplates? That would raise the rocker up considerably.
You know, even though they are LT1 rocker studs that arent supposed to be used with guide plates, perhaps the machine shop didnt know and machined them for guide plates. I dont recall telling them, w
hich is my fault, but they usually request to have the plates there to check their machining.
Bingo! I think we have clue number one (of many). Something looks different about the rocker stud pads all right.
And it wouldn't hurt to check the length of the rocker studs too. Who knows what somebody torqued in there. Not sure what the length should be.
If you didn't bend a valve, dent a piston, crack a piston, chipped a valve head, then quick! Run to your 7-11 and buy a Lottery Ticket lucky.
Bingo! I think we have clue number one (of many). Something looks different about the rocker stud pads all right.
And it wouldn't hurt to check the length of the rocker studs too. Who knows what somebody torqued in there. Not sure what the length should be.
If you didn't bend a valve, dent a piston, crack a piston, chipped a valve head, then quick! Run to your 7-11 and buy a Lottery Ticket lucky.
Just measured a spare Vortec head I had on hand and here is the difference in the stud boss heights.
Rocker studs. You set the valve lash-preload actually. Shouldn't make any diff if rocker studs raised by being installed on top of guide plates or lower cuz mount boss machined down. You screw the rocker nut down to zero lash. Doesn't really matter where the top or bottom of the stud is. But zero-decked block plus machined heads plus thinner head gasket has the valves closer to the pistons. Then OP threw in 1.6 rockers to make matters worse. I don't think shorter pushrod is gonna help. And bending pushrod that hard, you have bent valves.
Last edited by derekderek; 06-22-2018 at 11:10 PM.
Did you check retainer to top of the valve guide clearance at max lift? I was thinking Vortec heads needed the guides cut down to run any real lift?
Pull a spring off....reassemble retainer and keepers on valve with no spring and measure distance from bottom of retainer to top of guide to be sure and compare against cam lift specs.
Did you check retainer to top of the valve guide clearance at max lift? I was thinking Vortec heads needed the guides cut down to run any real lift?
Pull a spring off....reassemble retainer and keepers on valve with no spring and measure distance from bottom of retainer to top of guide to be sure and compare against cam lift specs.
Too much lift for those heads. Bent pushrods are from valve train interference. Ran out of clearance between the top of the guide and the bottom of the retainer. Need to cut down the top of the guide for more clearance.
Guided tip rockers OR pushrod guide plates required for Vortec heads - You have to have one OR the other BUT NEVER BOTH. I do not see either one.
Vortecs are rated for max lift of .420. Stingr and 427HR nailed it. "Straub Tech valve springs max lift of .550 on unmachined vortec heads." That statement bit you on the ***. Valve springs don't lengthen the distance between valve seal and retainer. I have hand cut .050 or so of big block guides for clearance, but you need closer to .100 extra clearance. They sell cutters for this purpose that will do the trick. They register in the guide so you don't need fancy machine work to do the job. Probably cost less than having it done. I would have a word with Straub about that statement they made. Pull heads. Check valves. Check pistons for valve dents. Then, remove springs and reinstall retainers. You can measure valve lift with a set of dial calipers or even a tiny steel ruler. Here is a Super Chevy magazine article on the process. http://www.superchevy.com/how-to/148...ads-valve-lift
Last edited by derekderek; 06-23-2018 at 08:30 AM.
Too much lift for those heads. Bent pushrods are from valve train interference. Ran out of clearance between the top of the guide and the bottom of the retainer. Need to cut down the top of the guide for more clearance.
Guided tip rockers OR pushrod guide plates required for Vortec heads - You have to have one OR the other BUT NEVER BOTH. I do not see either one.
+1. Vortec heads cant handle the lift of a Hotcam. A solution may not be that expensive.
Last night, I ran a bore scope in all off the cylinders and saw no contact marks. I sprayed carb cleaner in the intake ports and they held fluid, even until the morning. I pulled the passenger side head this morning and saw nothing on the pistons. There are also no bent valves. I removed the valve springs and found no damaged valve seals, spun the valves on the seats and they are perfectly concentric. Measured the retainer to valve seal distance and got .570+- which leave enough room for the .525 lift of the cam with 1.6 rockers. The Comp Cams rockers have little ears on them and are self aligning and the LT1 studs are not to be used with guide plates. I am stumped.
I believe guide plates are acceptable instead of self-aligning rockers. Can't use the 2 together. As long as calipers are out, double check by measuring spring seat to retainer. Then measure again with retainer touching the seal.
Last edited by derekderek; 06-23-2018 at 05:47 PM.
06-22-2018, 07:02 PM
Bent Pushrod Query/Mishap
