labrat Posted May 24, 2002 Share Posted May 24, 2002 Well, after rebuilding my carb, sending both heads to the machine shop, and reassembling everything, my car seemed to lose a bunch of power(!?!) and was "popping" gas out the carb when i tried to start it. pulled the intake off, and i now have 4 bent pushrods. Not bent badly (ie. no right angles), but bent enough that they wobble when rotated in place. Now, I never had the timing chain off, and i've never been able to get the motor to run good enough to hit the rpms needed for valve float, so I don't think valves met pistons. What could have caused this? I don't want to repeat my mistake this time. Could really, really "off" ignition timing cause this? I did have the dizzy 180 off the first time i cranked it ( and two plug wires crossed). As always, I bow to the powerhouse of chevy knowledge here on HybridZ, and any help is greatly appreciated! Bill Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted May 24, 2002 Share Posted May 24, 2002 the most common causes are (1)badly miss-adjusted valves (2) coil bind mostly from trying to run a high lift cam without checking your clearances or useing stock springs or heads without the retainer to valve guide clearances checked (3)running stock stamped rocker arms that have rocker stud mounting slots that are too short to allow full travel with higher than stock cams. (4)retainer to rocker arm binding from useing stock rockers on larger vavle springs/retainers (5)valve to piston clearance problems, if you did not make sure there was at least .100 clearance for 20 degs on both sides of TDC on both valves you may have problems,just being able to spin the engine by hand is NOT CHECKING. (6)push rod to head binding, if you changed to 1.6 ratio rockers this happeneds quite often, (7) cam installed 1 tooth off the correct indexing, yes the engine still runs but your down on power and your much more likely to have valve to piston clearance problems do a compression check, if you bent a valve youll be down in the 30-60 psi range on that cylinder if its only slightly bent, check your cam lobes for excessive wear (yes you will need to pull the intake and pull each lifter out and carefully look it over and reinstall it in the same location, to check, if even one looks bad you need a new cam ! things will only get worse if you run it that way, and go through the check list again BEFORE STARTING THE ENGINE AGAIN, you MUST ALWAYS CHECK ALL CLEARANCES Quote Link to comment Share on other sites More sharing options...
Michael Posted May 25, 2002 Share Posted May 25, 2002 A very similar thing happened to me with my 454, when I installed a Comp Cams XE-262 flat-tappet hydraulic camshaft complete with the kit (springs, locks, retainers, timing chain set) on an otherwise stock engine from a 1978 Suburban. I used stock pushrods, stock rockers, ... - everything stock, basically. The cam was installed with the timing chain set dot to-dot (not degreed in). I did NOT check the spring pressure (open or closed), but I did check for coil bind and for sufficient length in the rocker slots (both passed the "paper clip test"). I didn't check the piston-to-valve clearance either, since I did not pull the heads when I installed the cam. The vavles were adjusted by tightening until the pushrods could no longer be spun by hand, then tightening one half more turn. The installation was done in the presence of a guy who has been racing big block Chevies for some 30 years, so I figured that he knew what was going on - although we were pressed for time. The cam was broken in for 20 minutes at 2000 rpm. But very soon after the first drive, the engine started to make noises that sounded like a spun rod bearing, though oil pressure was always at least 10 psi for every 1000 rpm (never exceeded 3000 rpm, by the way). I did a compression check in each cylinder and found 130+ psi everywhere, with maybe 20 psi variation (at most). What eventually happened was that one pushrod (#4 intake) was broken in half, and several other pushrods were in various stages of bending en route to buckling. The engine backfired severely. Several cam lobes look like some one took a grinder to them. The corresponding lifters are so badly worn that they won't come out of their respective lifter bores. However, the valves are in good shape, as are the pistons - which I checked when I finally removed the heads. This whole adventure basically destroyed my confidence in doing any engine internal work.... Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 25, 2002 Share Posted May 25, 2002 Well as far as the bent pushrods go,did the valves stick in the guides .This can happen if they don't have lub on start up. Ask the machine shop to pull out aa couple off Valves and look for metal transfer to the stem. As for why the big block ate the cam . Big block Chevys have always had a lifter bore alignment problem . One thing we found was if the cams were ground with .002-003 taper we had better lucky with cams . Good Luck TM Quote Link to comment Share on other sites More sharing options...
labrat Posted May 25, 2002 Author Share Posted May 25, 2002 Well, what I think is crazy about this whole thing, is the head that has the bent pushrods was not changed one little bit from the way it was before when it ran fine, i just cleaned it up. The opposite head went to a machine shop for valves, guides, and springs, but not this one. The cam never came out, timing chain was not removed, basically i only pulled the heads to change headgaskets, but one head had 2 burnt valves with pounded in seats, so i had it worked. Put the whole mess back together, and didn't get 500 miles out it... I did swap the heads side for side (left head now on right bank) but that shouldn't change anything, should it? I will pull the heads probably tonight and inspect the pistons and valves to see if there was any contact..... Thanks! Bill Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 27, 2002 Share Posted May 27, 2002 Sounds like thr lifters may not have bleed down . This could have caused the springs to go into coil bind if you just run the rocker nuts down to the same height for a rough valve adjust. Good luck TM Quote Link to comment Share on other sites More sharing options...
labrat Posted May 28, 2002 Author Share Posted May 28, 2002 That makes sense, i thought i reassembled the motor quick enough not to have the oil drain out of the lifters, so i adjusted them accordingly. I guess they were adjusted while they were bled down and then the lifters pumped up when I sarted it. arghhhh... oh well. Learning curve..... That also explains the way it was running, no compression with the valves open... Bill Quote Link to comment Share on other sites More sharing options...
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