hydraulic lifters

[Jeremy MacDonald]

Hi all. I have a small issue here: I replaced the cylinder heads on my 440. I did it with the engine still in the car. The replacements are a later version of the head (from the tnt version, but I'm not trying to increase the power - just run new heads) and I replaced all the exhaust vales and installed new valve springs. I didn't touch anything else - didn't pull out the lifters because I wasn't having any lifter noise before this job. Well, after replacing several of the rocker arms, I then installed the pushrods and tightened down the rocker shaft. As I did so, I noticed that it was pushing down slightly all the vale stems - even those for closed valves. How far down? Not far - I'd say about 1/16" but I can see the valve stems moving down that distance as I tighten the rocker arm shaft bolts. I decided to do a compression test to find out if the valves were all closing and sure enough I only get about 125lbs right across all cylinders.

So I need the lifters to bleed down, I wouldn't have had any issue if I'd thought to pull out each lifter and collapse it before re-assembing then engine.

So here's my question: will the lifters bleed down by themselves to the correct level once I get the engine going and the oil warms up?... or do I have to pull them all out and manually collapse them in order for them to pump back up the the correct zero-lash position?

Many thanks!

 

[twostick]

If that is a late model 440, 125 psi is likely normal. The fact it's consistent across 8 cylinders tells you the valves are closing properly.

It stands to reason you will see valve movement when tightening the rockers down as the valves are mostly all opening or closing at any given time. They are only both closed briefly and then only 1 cylinder at a time.

Kevin

 

[Jeremy MacDonald]

If that is a late model 440, 125 psi is likely normal. The fact it's consistent across 8 cylinders tells you the valves are closing properly.

It stands to reason you will see valve movement when tightening the rockers down as the valves are mostly all opening or closing at any given time. They are only both closed briefly and then only 1 cylinder at a time.

Kevin

The compression test showed ~165 on every cylinder before, so I know the valves aren't fully closing now...and lots of valves are closed for a long duration, e.g. between the intake stroke and exhaust stroke there's a long duration with both closed while the piston travels all the way up to compress and all the way down during the next (firing stroke). The thing is, the closed valves shouldn't be pushing down at all into the cylinders when the lifters are on the backside of the cam lobes.
I know if I pull all the lifters I can collapse them and then they'll pump up to the correct position but does anybody out there know if they'll simply bleed down to the correct posn if I just run it for a few mins?

 

[Big_John]

Your valves are closing otherwise you wouldn't get 125PSI.

They may not be sealing 100%, but I'd run it before making any judgement.

In answer to your question, yes, everything will take care of itself. You are overthinking it.

 

[Jeremy MacDonald]

OK - I just did a quick test a few mins ago: I loosened the rocker shaft bolts until there was lots of slack on the (now fully closed) closed valves and I now get ~160 lbs compression.

 

[65sporty]

Like Big_John said tighten it up and run it, the lifters will bleed off the oil. The only way you will have a problem is if the lifter is bottomed out, it will take a lot more than 1/16th of movement to do that. In fact most Hyd lifters are designed to run at about half of the lifter travel.

 

[Jeremy MacDonald]

That's what I was hoping to hear! Ok - will do. I'll button it up this morning and then run it until the oil is good and warm - and then I'll pull some plugs and take new compression readings - and I'll post them here, in case anyone else comes across this situation again.
Many thx!

 

[Big_John]

OK - I just did a quick test a few mins ago: I loosened the rocker shaft bolts until there was lots of slack on the (now fully closed) closed valves and I now get ~160 lbs compression.

Since there is no valve timing coming into play, I would expect that figure to be higher. Either way, it's "apples and oranges" because your "before" readings were taken with the valve train connected up.

A leak down test would be better and you do that with the valves closed, but you have no baseline to tell you if you are better or worse.

Run the car and then take your compression test.