Valve lash?

[Maverick H1L]

I've been busy working on a number of things on the Bird, getting parts together for various things, and I'm still chasing that blasted exhaust leak I've had for as long as I've had the car.

Anyways, I need to go back a bit. Back in late 2005, I noticed I had a compression loss between cylinders 3 and 5 and deduced the problem to be a bad head gasket. So I replaced the gasket, and set the valves. Back when I set the valve lash when I replaced the head gaskets, I used a compression gauge afterwards and got an average of 162 PSI in all cylinders (except for cylinder 6, which has leaking valve guides and was at 180+). A few weeks ago, I started chasing noises again, and one appeared to be loose valves. So, knowing my average compression, I did compression tests again, and noticed that the compression in each cylinder was about 30 PSI lower. I pulled the valve covers, and, sure enough, the valve lash was loose again. I reset it to where I remember setting it when I did the valve covers, and ended up with noisy lifters (1/4 turn past no play, too loose, apparently, but tight enough to bump the compression back up). I just went and set the lash according to the GM FSM for the 92 Bird, which is 1.5 turns past no play, and got a scary noise. I'm going to go ahead tomorrow and check the pushrods for bending and such. The lash spec in my Haynes manual is 1/2 turn past no play, and I've seen 3/4 turn and 5/8 turn from members on this site and others. I'm !

In the meantime, I was wondering what the lash spec for the 3.4 and the FWD 3.1/3100 with adjustable valves is? Is there a torque spec for the later adjustable valves, like there is for the 2.2 in the J-body and such (22 ft/lbs)? Or is there another number of turns? I'm trying to find a later spec, hoping that maybe GM corrected it's mistakes some time?

[3400beretta]

Unless your lash is so far off that the valves aren't even opening, theres no way a loose rocker will cause low compression. Too tight, yes, because then you could be keeping a valve slightly open and bleeding off compression.

You know that you must set the lash with the corresponding cylinder at TDC, correct? And when you do it, you must let the lifter pump back up if you've tightened it down too far before trying again.
Also, if you have a collapsed lifter you'll never get it right.

I found it much easier to do with the engine running. IIRC on the LT1 it was 1/2 - 3/4 turn past no noise while running.

[Maverick H1L]

I found out that the noise was the #5 cylinder's exhaust valve hadn't been done up...

Yes, a valve not opening far enough (loose) will lose compression as the engine won't suck the correct amount of air and fuel into the cylinder. Found that out doing a compression test while adjusting the valves on my 2.8 before it blew. No, I can't really adjust the lash with the engine running. My RWD requires the intake to be completely torn down to the lower manifold (3 piece intake) for the valve covers to be removed, as the middle and upper plenums are in the way of the upper cover bolts AND allowing enough room to allow the covers to be removed. It's an MFI engine, not a TBI nor an FWD with easily removed valve covers.

And the GM FSM is wrong ... With the valves set according to the manual (set half the valves with #1 at TDC and the other half with #4 TDC), I'm floating valves, no compression at all. I don't know how it started earlier, but it did. I'm going to back out half a round tomorrow morning and more if necessary.

Still looking for the later specs...

[Rootie524]

what exactly is valve lash? lol

[3400beretta]

I checked my 94 fbody gm service manual, and it says the same thing you say for the 3.4L, 1.5 turns past zero lash. You sure you have the engine in the right spot? #1 tdc you do exhaust 1,2,3, and intake 1,5,6. #4 tdc is exh 4,5,6, and intake 2, 3, 4.

The only other thing it can be is if your lifters are compressed. I can't see every single one being compressed though.

Edit: I just checked my 94 Lbody service manual as well, and it says exactly the same thing, that is for a 3100. So it has to be correct, no way they are all wrong.

[pocket-rocket]

what exactly is valve lash? lol

A hydraulic lifter, also known as a hydraulic tappet or a hydraulic lash adjuster, is a device for maintaining zero valve clearance in an internal combustion engine. The conventional means of adjusting valve actuation always requires a small clearance to be left between the valve and its rocker or cam follower to allow for thermal expansion and wear. The hydraulic lifter was designed to ensure that the valve train always operates with zero clearance, leading to quieter operation and eliminating the need for periodic adjustment of valve clearance.

The hydraulic lifter consists of a hollow expanding piston situated between the camshaft and valve. It is operated either by a rocker mechanism, or in the case of one or more overhead camshafts , directly by the camshaft. The lifter is filled with engine oil intermittently from an oil gallery via a small drilling. When the engine valve is closed, the lifter is free to fill with oil. When the valve is opening and the lifter is being operated by the camshaft, the oil feed is blocked and the lifter acts just as a solid one would, oil being incompressible.

http://en.wikipedia.org/wiki/Hydraulic_tappet

It's adjusted on ball pivot rockers (stamped) by how far the retaining nut is tightened down. The rocker is "held up" by the valve tip (which is held up by the springs) and the pushrod by way of the lifters. Think about your roller rockers for a minute, then instead of holding them down on the pedestal, think about a nut with a half round washer under it sucking it down against the valve tip and the push rod. How tight you tighten that nut is how you adjust lash. Too tight, valve sticks open, too loose, rocker rattles around and you don't get full valve lift because of the slop in the valve-train.

[Rootie524]

if im on the same page as you i tightened the rocker arm bolts to haynes torque specs so it should be good then right? i dont need any shims or seats or anything? right..just tightening of the bolt?

[pocket-rocket]

Yours is a 99, IIRC. That means you have roller fulcrums with the pedestals. Those only need torqued down to spec and you don't have to worry about lash adjustments. Lash adjustment is mainly ball pivot rockers like in the pics I posted. That's why I posted pics, so you would see what ball pivots look like.

[Rootie524]

oh ok now i understand..haha..gotcha

[60dgrzbelow0]

I checked my 94 fbody gm service manual, and it says the same thing you say for the 3.4L, 1.5 turns past zero lash. You sure you have the engine in the right spot? #1 tdc you do exhaust 1,2,3, and intake 1,5,6. #4 tdc is exh 4,5,6, and intake 2, 3, 4.

The only other thing it can be is if your lifters are compressed. I can't see every single one being compressed though.

Edit: I just checked my 94 Lbody service manual as well, and it says exactly the same thing, that is for a 3100. So it has to be correct, no way they are all wrong.

Here are some supporting scans to precisely back up Mr. Pink's information and give you something you can print out and use...

[3400beretta]

Not Mr. Pink.

[Camarohead]

I have the same problem as maverick.....Im putting my 3.4 liter together and when i lash the valves the GM way...1+1/5 turn after zero lash...Im getting interference somehow....Any ideas???I'm doing the lashing on the #1 TDC and the #4 TDC...Anyone done this before????I'm lost and need to get this car put together for my mother...(She always wanted a T-Top)....

[Maverick H1L]

I have the same problem as maverick.....Im putting my 3.4 liter together and when i lash the valves the GM way...1+1/5 turn after zero lash...Im getting interference somehow....Any ideas???I'm doing the lashing on the #1 TDC and the #4 TDC...Anyone done this before????I'm lost and need to get this car put together for my mother...(She always wanted a T-Top)....

You'll need to back off each nut a full turn... Found that out on another site. Don't know why GM wanted everyone to float the valves, but they do (maybe it's with the lifters not being full of oil, IDK).

[Camarohead]

Then do i tighten them 1/2 turn after zero lash???And do i use the GM method of #1 TDC and #4 TDC to lash the valves or the way ALL the cam manufactures say with lashing the intake valve right when the exhaust valve starts to open and lashing the exhaust valve when the intake starts to close???BTW thank you for some help...

[Maverick H1L]

Do the GM factory method but tighten the nuts only a half turn instead of a turn and a half.