Hot Rods Small block 305 cam and compression question

I have a small block 305 2 pc rear seal 1979 variety engine. Engine refurbished by me, heads done by pro shop. The original cam was reused. I had a no compression issue on cylinder #7. To test, I put air into the plug hole using my home shop air supply. I rotated the engine until I had the valves closed. I had no compression. I loosened the nuts on the rocker arms and I had compression. I readjusted the valves on that cylinder and again no compression. I used the 1/2 turn on the nut to set preload. Air was coming from the intake on the air test again. I loosened the intake rocker nut 1/4 turn and now I have the correct compression on that cylinder. Does that indicate that the intake lobe is worn on that cylinder? The lifters and pushrods are new.

 

Maybe you just have to wait until the lifter bleeds down?

If a lobe is worn, the valve won't open as far as it should. That does not seem to be your problem.

 

I think you should use a compression gauge to see in lbs. what that cylinder is doing.They dont cost a lot,and everyone should have one.They answer a lot of questions.

 

Sounds possible, but if I adjust the intake valve using the finger spin or up and down movement way..when I turn the 1/2 turn to set the preload, no compression until I back off 1/4 turn no matter how long I wait for bleed down. Only on #7. This has me stumped. All cylinders are within 2 lbs or so of spec, so I will go with it to see what transpires.?

 

I remember a lot of those 305s were recalled for cam replacement. They had a bad run of cams that weren’t properly heat treated, I think. They just went flat and would barely run after awhile. May or may not be your particular problem.

 

I've owned and used several in the last 60 years since I was 17. I guess you didn't read the post. Thanks anyway.

 

Does it run OK? or is there a problem with the engine? I can't really tell from what you've posted....

 

Doesn't sound like a cam problem. Could be a bad lifter. If it's collapsed it can't bleed down and any "preload" just keeps the valve open.

 

After the engine assembly the first time when I only did a simple valve grind, cylinder #7 was dead. I sent the heads out for a rebuild and after reassembly, valve adjustment ect. cylinder #7 still no compression. After putting some air into the plug hole to see where it leaked, I found that the intake valve was open when it was supposed to be closed. Only a 1/4 turn out on the nut seated the valve. I haven't started it yet but all cylinders have correct spec compression now so it should run ok. The issue is, I can't adjust that valve by any tried and true ways because it leaves the valve slightly open. All the lifters are new...unless that one sticks or has some other issue.

 

That sounds reasonable. The lifters are new so it would not be likely, but possible. I think I'll run the engine and see what happens with that specific valve and lifter after some run time. Thanks

 

So it's possible that the lifter is not moving inside? I'd take the lifter out and take it apart and see if something's wrong with it. Maybe someone put a solid lifter in with a set of hydraulics? or????

 

Well, that could be another, different, problem. New lifters on a used flat tappet cam is the recipe for quick destruction of both.

 

Could it be the lifter is empty of oil and causing a faulty zero lash setting...?

 

could be, you'd notice that the adjusting nut was down pretty far, I'd think.

 

Give that lifter a gentle tap with a plastic mallet [on the rocker] that particular lifter could be binding at the bottom of the lifter bore.

I know everybody uses the "finger spin" method on the pushrod, I haven't had much luck with this method due to assembly oil on the pushrod ends.
I got a piece of brazing wire and bent the end 90 deg , then hammered it flat until it reads 0.030" on a micrometer.
I drop this down beside the pushrod and slip it between the lifter pindle and the circlip [using it as a feeler gauge]
This method doesn't require re-setting the lifters after starting.

 

So maybe there is a lifter issue. In the picture you can see that there is more thread showing on the #7 stud than the others and that is typical of all the rocker studs. It's not a lot but maybe it's sticking. I'll try the mallet on it and see it that changes the amount of thread showing.

 

One random solid lifter in the mix?

 

Good idea to check it .
I believe I would rather fix it while it’s on the stand,,, than already in the car .

Tommy

 

That seems like a collapsed lifter with the adjustment nut down so far.

 

Looks like zero lash was exceeded before preload was set. I'd carefully re-adjust it making sure not to exceed the zero lash adjustment. If the lifter does not have sufficient oil in it, it's easy to go too far.

 

I remember it being the 307 engines in the early 70s that had this. Don't recall the 305 having this problem.

Agree, that is a plausible explanation of the problem.

 

Collapsed lifter for sure. Thanks to all who offered ideas and solutions. It moved me forward to remove the lifter to see what was going on. This exactly why you want to be in groups like this. Excellent help!
I'm probably not the first to do this, but I removed it through the distributor hole in the manifold using a magnetic tool and a camera. I'll replace it the same way. Summit Racing is only a few miles from me and a single replacement is waiting for me to pick it up tomorrow. I'll make sure to soak it to prime before installing.
Again, thank you very much to everyone!
Bob

 

Junk parts. Seems you did everything right. Glad you found the problem!

 

Did you take it apart, and see why it's collapsed? It's a fun mechanism inside...might just be a bit of dirt making it stuck?

 

Not yet, but I will tomorrow just to see if there is something to see! lol

 

you might be able to unstick it. Also clean and carefully inspect the check ball and spring at the bottom of the plunger.

I think the first time I took apart a set of hydraulic lifters was when I overhauled my first engine, age 14, 1975.

It's not rocket surgery, fortunately.

 

Good find, congrats on pin pointing the cause of your problem.

 

I remember the first automatic trans I took apart. I had steel balls rolling down the driveway and my dad had to put it back together. 1960, I was 15 lol.

 

I did my first automatic at 15, I put a part in backwards, and the third time I took it apart I took the drums to a transmission shop, and the guy there spotted my mistake immediately.

 

The rebuilt engine by me, had a dead cylinder. I was so focused on things like compression rings aligned and not offset, head gasket leak or maybe the valve grind I did on it, that I missed the real problem and never considered that new parts would be the culprit. Thanks to the guys here, they made me focus and realize it had to be the lifter being collapsed. Great people on here and always ready to help when someone gets in a fix. I really appreciate everyone for saving the day for me.