Question on valves closing all the way

[troy.70R/T]

I was wondering if anyone has any suggestions on a problem I have I just finally got my Charger running awhile back. It is all stock except for my Holley 750 Vac secondaries.  I have a Vac guage hooked up to my engine and It is not stable at all it bounces back and forth about 20 inches of vacuum. The guage is hooked up to the intake. I also can not seam to get the car idle RPM to stay stable. I only had about .030 milled off the heads but is it possiable that the valves are actually open a little bit. I see they make rocker shaft shims, but not even sure if that is my problem   I sprayed starting fluid around the intake and carb while it was running to check for a vacuum leak and could not find one.
Again it a 440 .030 over, stock cam and cast intake I don't remember the cam specs but it was a stock replacement. Any ideas. Thanks

[elacruze]

Pull the valve covers and check to see if your lifters are bottomed out. You should be able to find play in all of them when they're closed.

[A383Wing]

I had the same issue back in the 80's with my 318...heads were milled, seemed like valves were not closing...so I put some decent thick gasket material under the rocker shafts where they bolted to heads. Just made sure the holes were there for the bolt & oiling holes.

Worked great, steady vacuum again

I doubt you will find "play" with a hydraulic cam, you might be able to twist the push rods, but no play should be present

[elacruze]

Right, I meant that you should be able to turn the pushrods by fingers. If not, they're bottomed.

[Cooter]

Took .030 off heads right? Did you install .030 shim under Rocker shafts to compensate?

[troy.70R/T]

No I did not. I did not think it was that tight of a tolerance. How long are stock pushrods supposed tobe? Also how much of  a margine of error do I have whith  hydraulic lifters?

[John_Kunkel]

The lifters should be able to compensate for a mere .030" IF the lifters are new....if they're used, they could have a varnish ridge that isn't allowing the top disc to move.

This is one of the few times a leakdown tester is of real value.

[troy.70R/T]

They are new lifters. I know I had heads milled .030 but could not be sure that they were not milled before. I had them cc ed but have since lost the paper work. That is why I was wondering about what the push rod length should be.I have some shims on the way but want to make sure I have the right length push rods to start with. What exactly is the idea behind hydraulic lifters over mechanical? Is it just that they are self adjustig. By that I mean they just dont need to be adjusted every 12000 miles.

[Cooter]

With the stock style hydraulic lifters, there is a certain amount of lifter preload. Meaning, the pushrods are 'supposed' to be down in the lifter about .050 when everything else is correct and rocker shafts are bolted down. However, with mass produced engines like the BB Chrysler, when was the last time you saw anything remotely near what it was supposed to be?

Anytime you swap heads, rockers, mill heads/block, etc; you should always check lifter preload. Yes, the hydraulic lifter is self-adjusting whereas the solid lifter requires aftermarket, adjustable rockers, different pushrods, as well as higher rate valve springs. No, you cannot simply substitute solid lifters on what was originally a hydraulic camshaft. Same with roller lifters.

Solid cam= solid lifters
hydraulic, flat tappet  cam= hydraulic flat tappet lifters

Solid roller cam = solid roller lifters
Hydraulic roller cam = hydraulic roller lifters

[b5blue]

I've got a new set of shims here somewhere....I'm going to install adjustable push rods so I won't need them. Want me to see if I can find them? (PM me.)

[troy.70R/T]

Thanks for the help guys. Thanks for the explination Cooter. Thanks b5blue. but I ordered some shims last friday so I would have them for the long weekend. Its a set of .010, .015, .030 10 of each shim from Mancini Racing. I also bought the reusable valve cover gaskets. I hope they prevent leaks

[John_Kunkel]

Before you go shimming things, ascertain that the valves are indeed not closing.

[troy.70R/T]

I was hoping some one would tell to do that and then explain how to go about doing that.   Also one othe question I have my brake power booster hooked up to the same intake port as my vacuum guage. Is there anyway if my brake booster is bad that it would cause this? I will unplug my booster and block it off before I get into the whole shimming project. Any other sugestions on what to look for??? thanks again John

[A383Wing]

just clamp the booster hose with pinching pliers and see if vacuum needle stops bouncing and the idle smooths out

Bryan

[firefighter3931]

It's possible that you might have a burnt valve....that can cause erratic vacuum readings.

The lifters could also be pumped up and not bleeding down.


Ron

[troy.70R/T]

Well the heads are rebuilt. The engine has only about 40 minuites of run time on it. The vacuum guage had acted that way the whole time. I am going to be able to look at it on Sunday.

[firefighter3931]

While you're in the investigative mode ; have a close look at your ignition system. Bad plug, ignition wire, cap etc... will make the engine act funny.

The idle bleeds on your Holley could be partially clogged....hit them with some carb cleaner.

From my experience, it takes quite a lot of changes to require a different length pushrod. Lots of milling and a much bigger cam before you need to look at pushrod length. There is at least .060 travel with most hyd lifters before they bottom out. It's easy enough to check ; get the cam on the base circle and tighten down the rocker shaft then observe what's going on with the lifter plunger. 


Ron