I recently had a tap in the valve train on my 85 D-150 and after changing the lifters in the suspect cylinder, the tap remained. Pulled the head, had the valves ground, seats ground, and replacing both #1 valve guides and exhaust guides on #2. (#1 exhaust was way sloppy) Put the head back on, ran for three minutes and then developed a squeak that sounded like a wrist pin. Replaced the pistions, rings, and rod bearings. Reassembled, and then a miss.

Compression test resulted in zippo in #1, 50 lbs in #2, 160 in the other four. Pulled the head of my working 84 van, put it on the truck, same readings. Attached a dial indicator to #1 exhaust valve and seen the when the rocker shaft was tightened down, the valve would open .100 inches.

Replaced lifters with new, all the while changing heads and trying changes I was bending pushrods left and right. Seven total.

Now, after changing the original head with new valves in #1 and #2 I have zippo compression in cyl 1, 2 and 3. The lifters have appearently locked up and will not bleed down. Oil pressure is 60 psi after the change, 45 before.

Other notiables: Surface of the block has been decked .060 four years ago. The head in question only has 65k miles on it and had been running on that block for 2 years. Before I pulled the head for the initial tap, I had comp readings of 180 on 2 through 6 and 150 on #1 and it was running fine. Comp Cams RV cam intsalled.

So: Why do the valves open when I tighten the rocker shaft into position after a simple valve job? And why do they do the same thing with a different head? I'm seven weeks into swapping parts, new and used and cannot figure this out.

What do I need to be looking at???

Troy

Is the Comp cam new in this buildup? They've been known to send out incorrect cams (solid-lifter cams when hydraulic is needed or vice versa...)

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Too many people who were born on third base actually believe they've hit a triple.

The Comp Cams has been installed for more than a year with no problems noticed.

Troy

Is this the original hydraulic lifter motor that came with your truck? Otherwise it would sure seem like tight rockers on a mechanical set-up. Dan's guess seems pretty good, maybe put a dial guage on your push rods or the tip of your rockers to try and get an accurate lift measurement from your lobes. Roll it over by hand to get your max lift then compare it across the board.

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Known block is an 86. Known head is an 82. Current cam has worked on this setup for over a year married together. I keep boiling down the problem to bad lifters that lockup or over length pushrods.


Troy

At this piont you need to verify the camshaft is good. Checking for lift at the the lifters out edge of the body ( not off the center where the plunger is).


The lifters get there oil from the rocker arms. Any times when a lifter start tapping on these engines it is the rocker arms, or pushrods that are stopped up to cause it most of the time.


I expect its was either one of these was stopped up in the begining, or the camshaft lobe is warn off, that was causing your tapping.


Now after changing a head, it may be that the head you have installed was cut or shaved enough to cause the rocker arms to be tighter on the valves and holding them open. This may be what caused the pushrods to bend.

Anyway after having the other head repaired, it may be that it was cut some, and or the valves are setting up higher in the head because after a valve job the valves sink in the head, which causes the stem to be higher if they did not cut the stems down to allow for the amount the valves sank. You may even have some valves that stuck in the guides because they may have been to tight ( the new ones).


Like I siad you need to verify if the cam is good. Even if you have to pull all the lifter and inpect each lobe. That and possible stopped up rocker arms will probably be the starting of your trouble. If a cam is warn a lobe off it can cause compression problems.



Jess

The lift of the cam is fine. The fact of the matter is that is the valves will open as the rocker shaft is tightened down, the take and exhaust valve causing no compression.

need shorter pushrods.....

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Yeah....Im the one who destroyed this rare, vintage automobile.....

New shorter pushrods seem to be in order. Is there a good place somewhere on the East coast or should I stick with Smith Brothers?

It still boggles my mind that I can take a good running engine with a tap due to a worn #1 exhaust valve guide, grind the seats and valves, not shave the head surface and end up with the valves opening .200 when the rocker shaft is tightened down.

I have noticed that the valve stems are not all the same height (rocker shaft off).

I'm now wondering if I should spring for new valves and install new seats to lower the installed height of the valves or get a set of custom pushrods built that may or may not be correct. My gut feeling is that the lifters are locking up for some reason.

Any good suggestions or comments?

Troy

Sounds like you've got the wrong lifters.

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Official Cookie and Mater Tormentor.

Thought that same thing, so I pulled 6 lifters from my slanted van, installed them into the truck and got the same results. And, the van runs fine with the new lifters.

Troy

Who ever did tthe head work screwed-up.
All the valve stem heights must be the same on a hydraulic SL6.

Did the shop resurface the head along with the valve job?
.060 off the block, something off the head, some new (longer) valves, tighter valve guides, "sink" the valves as the seats are reground... all this adds-up to the hydro lifters being bottomed-out, with no more travel.

Shorter pushrods will fix the problem but if all the stem heights are not the same, what new length should you get?
Take the head back and have the stem heights evened-up.
Then get your shorter push rods and you should be back on track.

Want to do a test? put a set of solid lifters, pushrods and adjustable rocker shaft in it, adjust the lash to .006 intake and .012 ext. and see how it runs.
DD

DD, I agree all the stem heights should be the same. I had the same problem with my oversize'd valve head and this same machine shop cured that problem.

The head wasn't milled, and has only 76k orginal miles on it so it's doubtful it's ever been touched. The guides and seats were still cast iron so nothing has been replaced in the head in it's lifetime untill now.

As far as the lifters are getting bottomed out: I rigged up a dial indicator to #1 intake valve at TDC and rocker shaft loose. Tightening the rocker shaft down, the valve opened .200 of an inch. Twenty minutes later, the lifter had 'bleed off' and the valve was back to the first (free height) measurement.

Logically thinking, wouldn't a new valve lower the stem height, since the valve seating surface is thicker than a ground valve?

And why, when swapping with a different head is the problem duplicated?

The only constant in this problem is the cam, which has been installed and ran for the past two years, and the new engine oil, 10w-40 installed after the new pistons, rings, and rod bearings were installed.

Troy

so if i understand it , the cam, head and block were running as an assembly with a tapping noise like a loose pushrod or rocker. you replaced lifters, two guides and then a complete re-ring/bearings in engine, and now you have no compression on #1#2#3 cyls and can measure the valve on these cyls being open when it is not there time in the rotating cycle,first with new lifters having trouble bleeding of pressure the valves will be held open to long ,so you have to fine what is stopping them from not bleeding off(rockershafter or arms blocked or weak valve springs). second with bent push rod on a low compression engine and the guides are good and not binding the valves then your cam timing must be way off because there is to much clearance between the piston and valve on a low compression engine with a r.v. cam to interfere with each other and bend a pushrod.

Here's something I've been thinking about all weekend:

The bottom line is the lifters are locking up and not bleeding down like they should to take up the clearence/slack in the pushrod-rocker arm-valve connection.

What if: once I changed the rod bearings to new (.040) and noticing the oil pressure jumped from 45 to 60 at idle, that there is not much leakage through the crank bearings and cam bearings causing an extra amount of volume of oil to be pushed through the rocker shaft and into the lifters?

Just looking for guesses here.

Troy