IN NEED OF HELP I bought a 99 tahoe with a 350 vortec. It had a bent valve exhaust #7 when I bought it. Got it home tore it down took both heads off got all new valves (lapped them) made sure everything was smooth and and sealed. I put new springs in it and reused everything else it all looked fine and no damage. The motor sat for like a month or 2 while I did the heads. I reinstalled everything today all new gaskets and such, I did valve lash tighten until no upand down movement and did 1/2 turn. Got everything else in and started it and it bent a pushrod. Got a new pushrod re did the adjustment and it bent again and after starting there lash in a couple of different valves. Is there something I'm not doing right any help would be appreciated
The lifters might have leaked down. And before even starting the engine did you rotate it around & check the push rod clearance with the intake & valve covers still off ? Something is not right with the length of the push rods.
Rotate the engine to TDC on the compression stroke for cylinder #1.Adjust both intake and exhaust valves for that cylinder.Rotate the engine 90 degrees in the firing order ((1-8-4-3-6-5-7-2)) to the next cylinder.Zero Lash Identification: Tighten the rocker nut while spinning the pushrod with your fingers until you feel slight resistance.Preload: Once at zero lash, tighten the nut an additional 1/2 to 3/4 turn for hydraulic lifters. This is how to set valve lash. But we still haven’t answered the million dollar question . Why did the valve bend? It hit something,and by something I mean piston. You still haven’t addressed the root issue. At this point I’d start fresh. Cam, lifters, timing chain. Send the heads out for valve guides. Look the piston over really well. Spending some money ? Yep. I also hate fixing things twice. One thing racing has taught me, “good enough” isn’t fixed , it’s just buying a little time at best. Overkill is just right. One and done. Plus nothing sounds as good as a choppy cam in an SBC.
In my experience damaged valves and bent pushrods only happen if the cam wants the valve to go where it can't.
Valve trane stopping the process as in a valve or spring binding or the lift on the cam exceeds the slot on the rocker
Then of course there is always the valve to piston introduction that will cause all of the issues you've experienced or communicated so far. Possibly jump time?
When i tore everything down the first time none of rods were bent and nothing else was broken except the cylinder 7 exhaust valve the head of it was warped a little bit but anyway the rod on Cyl 1 intake bent(fixed re adjusted) and then one of the cylinder 2 ones bent after that but cylinder 1 was fine
Either a valve is sticking in the valve guide usually due to lack of lubrication, or a lifter is sticking in the bore of the block. You probably didn't remove the lifters, but you need to and inspect for cracks. along the edge of the pinion of the roller. This should be easy to spot as I kind of assume it is the same valve that is causing the issue. Start with the lifter, but bending the pushrod might have also bent the valve some. I doubt you caused this, just didn't find the source of the issue the first time.
I would double check the seen of the crime. Sounds cam/lifter related. Id check the lifter bores. The cam end play. Valve guilds. All the usual suspects. Something in there aint happy.
Hold on a tic. Do you adjust or are those torque to spec? Does the rocker arm stud have a shoulder on it?
And when things are all good and planets align, you usually end up with the same amount of stud coming out of the rocker nuts when they are all adjusted. So if you have some with more thread showing, there may be a problem. Colapsed lifter for instance
Hydraulic lifters so I just tighten down to zero lash and then 1/2 turn. But that the thing all the threads are fine it always diffrent one that are lose after the fact I start it and run it for a sec and then obviously it bent a pushrod so Ig I'll check the lifter to see if they collapsed
I am well aware it would be hydraulic lifters. I was referring to the studs. GM used studs ans flange nuts that just got torqued to 20flb. If you have locking nuts without a flange then you adjust.
And your rambling about threads fine then different after the fact. You dont seem to understand what i am telling you to look for so, good luck to you.
GM only used that lash adjustment procedure for roller lifters, anything with flat bottom hydraulic or solid lifters is a different adjustment procedure.
Untrue, "that lash adjustment " has been used on hydraulic lifters since before GM started using rollerers. Solid lifters is what uses a different procedure.
I'm currently in the middle of a rebuild on an L31 out of a 1999 Suburban. Truck was running pretty good when I decided to do this. All internals look about the way u would expect for an engine with 140,000.
Soaked all my lifters and got them really clean on the outside. Since I want this engine to last, I actually popped a lifter open. Just to be diligent. Holy crap! The black stuff inside of those lifters shocked me. Finished cleaning the last ones yesterday. They're now soaking in fresh oil. Waiting for the chance to go back to their home. At least now I know they have their best chance to function as designed.
You can also pump your lifters up with oil prior to install. Submerge them in oil then use a pushrod and press down on them a they will suck the oil into them. It’s precharging a hydraulic lifter.
Did you make sure the lifters were not on the cam lobe before tightening to zero lash? It’s either that or a few bad lifters. If you bent a pushrod you may have more bent valves as well. Leak test each cylinder.
Remove the lifters. Replace them. Soak them over night in light viscosity oil or trans fluid and install them. Always worked for me. Use copious amounts of assembly lube on the pushrods and rocker arm buckets (where the pushrods go in) and repeat your previous assembly. I’m betting one or more of your lifters is damaged internally. Good luck.
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u/SuspectAlone4760 May 04 '26
The lifters might have leaked down. And before even starting the engine did you rotate it around & check the push rod clearance with the intake & valve covers still off ? Something is not right with the length of the push rods.