The Stovebolt Site Forums The Shop Area Engine Shop 350 Tearing Itself Apart

I had this engine torn down and overhauled over the last year. For the past 2 months, I have been consistently bending pushrods in an attempt to set lash at zero. Either the engine clacks, or it bends pushrods, no in between. Today, a new development arose; The engine is now snapping rocker studs. What gives? This sounds like lifters, But I really do not want to tear off the intake manifold again. Any thoughts?

are you bringing the piston in each cyl. to top dead center on the compression stroke before installing the push rods and rocker arms, Sorry this might sound like a dumb question !

I did that twice. Third time, I removed lash as the engine was turned. Fourth was with the engine running.

Check the piston to valve clearance on every valve with the valves on overlap. If you don't know how to do that, drop me a PM. You're probably headed for a full engine teardown, not just a manifold removal.
Jerry

What kind of lifters are you running, solids or hydraulic?

I doubt the valves are hitting the piston, the bending rods are almost at random, the only similarity is when I tighten it to a certain point (they still rattle) and it bends. The lifters are hydraulic.

OK- - - -do it your way. I tried! BTW- - - - -I know exactly what's going on, but trying to help people too stubborn to listen isn't the way I do things.
Jerry

Good to know, Hotrod. So tell me, what exactly is going on?

Why? You didn't want to listen to my first suggestion. My email is in my profile- - - -or send me a PM.
Jerry

Only one thing bends push rods or pulls rocker studs---interference. Could be several things but spring coil bind or valve to piston are the most common. First turn engine to point of maximum valve lift and see if a thin feeler gauge will slide between spring coils. To see how much clearance you have put a piece of solder between coils when valve is closed and make two revolutions of the engine, remove solder and measure how thick it is where crushed. We have a home made tool to work the rocker to check valve to piston clearance but I think they make them for sale. With a magnetic mount dial indicator you can find the point of the least valve to piston clearance then assemble with push rod and see if rocker gets moved beyond the known interference point. None of this should be necessary if the engine builder didn't have his head buried in a dark odorous place. I am not a teacher and Jerry was for a number of years so his explanation would have been much better so make note of lesson learned.

When you are sitting the valves, are the lifters full of oil?

Has it been setting for a while?

Are you setting each cylinder one at a time, INT & EXH?

Please give as much information on your procedure so maybe we can figure out if it's your method or mechanical.

Snapping and bending parts is real sign or something to tight.

When the engine runs, does it run OK? just noisy, sluggish, hard starting?

What are the spec's of this engine? cam lift, rocker ratio, head type, etc...........

If you are not doing so already, I would strongly recommend using a poly-lock nut on each rocker stud. They are much easier to adjust lash with then a stock Chevrolet lock nut. I suspect you are running a 3/8" stud, it would be a chore to be breaking the 7/16" big block studs.

I would start with #1 cylinder, bring it up on the compression stroke ( both valves closed, piston TDC ) and set the lash to zero. Using poly-lock nuts, you can get zero lash by using your finger tips on the poly-lock. The pushrod should just touch the lifter and have a very slight drag. Even if the lifters are not full of oil, you can still find zero lash if you are careful on the adjustment, again, this is where poly-locks come in handy. At zero lash #1 cylinder, loosen the other 14 rockers so as to not bend or damage anything else. Rotate engine till the intake valve is fully open. You may have to rotate a few time till you are sure you are at full valve opening. Use the belts or a wrench to rotate ( pull the spark plugs ), NOT THE STARTER! Now, just as Evan said in the above post, check to see how much more the valve will open. Use a pry bar, screw driver, what ever it takes, to compress the rocker to it's maximum travel. If there is zero travel, or you can't even get to full lift, you have mismatched parts or poor machining. If you do have more travel, then set the other 14 rockers with zero lash and check each cylinder as you go. .060" or more is needed between each coil of the spring at full valve lift. If you cannot figure out how to pry the rocker to maximum opening, at least measure the gaps between the coils of the spring.

The engine should run with zero lash, it may be noisy but should run. If you are 100% sure you have hydraulic lifter, give each nut, 1/2 more turn from zero lash. It should run with no lifter clatter.

If you cannot get to fully open valves on #1, pull engine and take back to who ever built it!

Get a set of "long-slot" rocker arms. The rockers are bottoming out on the studs before you get the adjustment right. That bends pushrods and breaks studs. The kids in my high school classes made that bonehead mistake on a regular basis. "Higher lift" does no good unless you do everything it takes to make it work. Bolting a bunch of mismatched parts together is not engine building. Now you're going to need to change all the studs since the ones that haven't broken already have been overstressed and they're going to break soon. Run- - - -do not walk away from whomever built that engine!
Jerry

This is the way I have adjusted lash for almost all the engines I have done, Assuming you have the matching parts that are supposed to be in the engine.
Setting valve lash
Works 100% of the time.
There seems to be as many ways to adjust valve lash as there are posters, Best bet is to listen to the guys that rebuild engines for a living or work on them for a living.

Good morning Casey. Along the way many of us have had experiences similar to yours. It’s probably the origin of the saying “If you want something done right, do it yourself”. Bending pushrods and breaking rocker arm studs requires a lot of force and that force came from physical interference between parts. As others have pointed out the likely suspects are valve to piston interference, valve spring coil bind and/or rocker arm slot too short.

All of those things can be checked without removing the heads. But if the valves have collided with the pistons the valves may also be bent and the heads will have to be pulled to correct that. If the broken rocker studs are screw in types they are easily replaced with the heads in place. If they are pressed in studs it’s probably possible to machine the heads for screw in studs without removing the heads if you use some ingenuity but would you really want to risk machining chips falling into the engine? I doubt it.

There are some excellent “How to” books to help you through this. A couple of examples are:

How To Rebuild your Small-Block CHEVY by David Vizard and SMALL-BLOCK CHEVY Engine Building by the editors of Chevy High Performance. It’s great to have that information to refer to while you are doing the work.

I would bet that when you start carefully inspecting that engine you will find that the guy who put it together made some other serious mistakes also that haven’t shown up yet. The books mentioned above will help you to find and correct the other guy’s mistakes.

Good luck!

Is it possible the timing gears are off a tooth or so, causing his bent push rods and other problems?

Rick

I second Yar's recommendation of David Vizard's "How To Rebuild Your Small Block Chevy". I used that book to rebuild my first SBC back in the mid 70's. I still used it as a reference when I rebuilt my latest SBC (1963 327) 2 months ago.

It not only tells you how to assemble the engine, but how to disassemble, inspect, refurbish as needed, determine when to replace instead of refurbish as required, then put it all together and fire it up.