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Zero lash
#1
Hey all, I’m having trouble setting zero lash. When I do it per the instructions the rockers are really sloppy. I have a newly rebuilt 351 Cleveland. I have 71 closed chamber heads on my 72 Q code block. It’s .040 over with 10.3:1 compression. I have a Crower flat tappet cam with Crower cam saver hydraulic lifters and Crane gold roller rockers. 
The engine started running crappy and I went through the ignition and carb systems first but all was good there. So next I pulled the valve covers and found quite a few rockers loose. 2 were really loose so I removed the rockers and checked them and the pushrods, they look good. So I reset all the valve lash settings but some of them are still really sloppy. Not sure what I am doing wrong. I sent a video of how bad they are to my engine builder and he said he’s never seen this before.
So as far as I know about setting zero lash you tighten the arm down till you feel a slight resistance when spinning the pushrod. When I did this I got the same results, some of them are so sloppy loose that there’s no way I would even try starting the engine back up. I, along with the engine builder must be doing this wrong. What should I do? I haven’t done this for 25 years or so but I remember that I would just kinda rock the rockers back and forth to just take up any lateral play, then tighten the adjusting nut 1/2 turn. As they are now I can lift the rocker up off the valve stem, which seems to loose to me. Any help surely will be appreciated, thanks!

run_horse Run Horse Run!
John 72 Q Code
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#2
John, I can't offer anything on this issue, but look at it this way, you now know your timing, ignition and carb are all good.
Geoff.
 PS, if I had to guess, I'd say bad lifters. When I went through my engine wows, re HV oil pump, the first two rockers were loose because the lifters were worn hollow from low oil flow. Could be a similar issue. Just a thought.

I learn something new every day!
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#3
I'm assuming you have screw in studs and guideplates? Or do you have the bolt down rockers with the adjusters on the pushrod side?

For studs, I used either 1/2 turn from zero lash or 3/4, depends on the cam manufacturer. You want just enough pre-load to allow for expansion of the parts when hot. I'd run through the whole engine and set them a 3/4 turn, then drive it. If they loosen up again, you have either a failing cam, or the poly-locks are loosening up on the studs. I use the ARP studs on my engines as they have a ground face for the polylock to seat. Some other brands are as-forged and have a rough face which causes the set screw to loosen, and then the polylock.


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#4
(10-30-2019, 10:32 AM)Hemikiller Wrote: I'm assuming you have screw in studs and guideplates?  Or do you have the bolt down rockers with the adjusters on the pushrod side?

For studs, I used either 1/2 turn from zero lash or 3/4, depends on the cam manufacturer. You want just enough pre-load to allow for expansion of the parts when hot. I'd run through the whole engine and set them a 3/4 turn, then drive it. If they loosen up again, you have either a failing cam, or the poly-locks are loosening up on the studs. I use the ARP studs on my engines as they have a ground face for the polylock to seat. Some other brands are as-forged and have a rough face which causes the set screw to loosen, and the the polylock.
Yes sorry I didn’t mention that. I have arp screw in studs. All the polylocks were tight. If I had a failing cam wouldn’t I be seeing some metal shavings or evidence of that in the oil? I even pulled my distributor to make sure that the gear was good. Everything looked fine.
When the lifter is adjusted correct should I be able to easily lift the roller tip off the valve tip?

run_horse Run Horse Run!
John 72 Q Code
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#5
Are you pushing down on the wrench when adjusting them? Which could make it seem like the rocker has reached zero clearance, when it hasn't. Are the studs firmly set in the heads with locktite so they aren't loosening?

If you can move the rockers that much after it feels like you have zero'd them either something else is loose, or they have not been zero'd.

I would spin the oil pump while wiggling the rockers, to see if that tightens them up. If so, I would suspect something wrong with the lifters they shouldn't bleed down that much that fast. The spring in the lifters should keep contact with the push rods, rockers, and valve stem.

Have you tried cranking it while observing the valve train and how much lift you're getting. This is a crude and inaccurate way of doing it, but I would turn the engine by hand until the lifter is at bottom, make a mark on the pushrod, turn it over by hand until the lifter is on the top of the lobe, make another mark on the pushrod and see if the difference between them approximates the specified lobe lift. You can use the valve cover gasket surface as the guide for making the marks.

Either the cam is going away, the lifters are bad, or the rocker studs/poly locks are moving, or you're not actually getting zero lash.

EDIT: As to your last question, no, you should not be able to easily lift the rocker off the valve stem.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#6
(10-30-2019, 10:30 AM)Stanglover Wrote: John, I can't offer anything on this issue, but look at it this way, you now know your timing, ignition and carb are all good.
Geoff.
 PS, if I had to guess, I'd say bad lifters. When I went through my engine wows, re HV oil pump, the first two rockers were loose because the lifters were worn hollow from low oil flow. Could be a similar issue. Just a thought.
Ya all the stuff I was hoping was bad was good, lol. 

I have a std. volume melling oil pump with good pressure. I think I may have gotten a few bad lifters too. I picked these because they are supposed to be a good one and I think they are made by johnson? Anyway I’m bummed out, this sucks.

run_horse Run Horse Run!
John 72 Q Code
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#7
Are you on the base circle when adjusting each valve?

When setting lash, I remove all plugs and put a breaker bar on the crank so I can turn the engine by hand. I make sure each cam lobe is on the base circle, and then I prefer to move the pushrod up/down while I slowly tighten the poly lock, and then set the lash.

The up/down method makes it easier for me to tell when I take the slack out  of the valve/lifter assembly. The real key is making sure you are on the base circle and not partway up a cam lobe.
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#8
(10-30-2019, 12:42 PM)71coop Wrote: Are you on the base circle when adjusting each valve?

When setting lash, I remove all plugs and put a breaker bar on the crank so I can turn the engine by hand. I make sure each cam lobe is on the base circle, and then I prefer to move the pushrod up/down while I slowly tighten the poly lock, and then set the lash.

The up/down method makes it easier for me to tell when I take the slack out  of the valve/lifter assembly. The real key is making sure you are on the base circle and not partway up a cam lobe.
Yes I’m on the base of the lobes, but I’m going by the shop method so I only have to move crank to 3 different positions.

 I was doing the up down method too, but there’s quite a few that feel really spongy. I’m afraid that I may get them to tight. I can push down on them by hand easily. I just talked to the machine shop that did my engine and he said I shouldn’t be able to push them down like that.

run_horse Run Horse Run!
John 72 Q Code
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#9
(10-30-2019, 03:31 PM)jpaz Wrote:
(10-30-2019, 12:42 PM)71coop Wrote: Are you on the base circle when adjusting each valve?

When setting lash, I remove all plugs and put a breaker bar on the crank so I can turn the engine by hand. I make sure each cam lobe is on the base circle, and then I prefer to move the pushrod up/down while I slowly tighten the poly lock, and then set the lash.

The up/down method makes it easier for me to tell when I take the slack out  of the valve/lifter assembly. The real key is making sure you are on the base circle and not partway up a cam lobe.
Yes I’m on the base of the lobes, but I’m going by the shop method so I only have to move crank to 3 different positions

This may not be accurate enough with a performance grind camshaft. Try doing it using the EOIC method.

73 conv. 460, D0VE large valve heads, Performer RPM manifold, Voodoo 227/233 cam, Holley 950 HP carb, C6 trans, 3.25 trak-loc.
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#10
+1 on Tommy K's post. Chuck
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