5.3 Valve Lash

[apocalypsesrt]

Hello,

I am new here but i have a 2001 5.3 vortec tahoe. It is having some valve knock or lifter rattle on startup and i want to lash my valves. does anyone have a guide on this or the exact torque specs and lash chart? thanks.

[rob71]

These engines use hydraulic lifters so there really isn't any adjustment to be done on the valvetrain, all you can do is check the rocker arm bolts for tightness (do not over tighten!) or replace faulty lifters.

Here's the functional description of the valvetrain from the service manual:

Motion is transmitted from the camshaft through the hydraulic roller valve lifters and tubular pushrods to the roller type rocker arms. The nylon valve lifter guides position and retain the valve lifters. The valve rocker arms for each bank of cylinders are mounted on pedestals (pivot supports). Each rocker arm is retained on the pivot support and cylinder head by a bolt. Valve lash is net build.

"net build" is gm-speak for you just bolt it together and it works without any adjustment (other than the correct torque on the bolts).

The service manual does not have a valve adjustment procedure, however this is what it says about installing the rocker arms:

Rotate the crankshaft until number one piston is at top dead center of compression stroke. In this position, cylinder number one rocker arms will be off lobe lift, and the crankshaft sprocket key will be at the 1:30 position. If viewing from the rear of the engine, the additional crankshaft pilot hole, non-threaded, will be in the 10:30 position. The engine firing order is 1, 8, 7, 2, 6, 5, 4, 3. Cylinders 1, 3, 5 and 7 are left bank. Cylinders 2, 4, 6, and 8 are right bank.

With the engine in the number one firing position, tighten the following valve rocker arm bolts: Tighten
Tighten exhaust valve rocker arm bolts 1, 2, 7, and 8 to 30 N·m (22 lb ft).
Tighten intake valve rocker arm bolts 1, 3, 4, and 5 to 30 N·m (22 lb ft).

Rotate the crankshaft 360 degrees.
Tighten the following valve rocker arm bolts: Tighten
Tighten exhaust valve rocker arm bolts 3, 4, 5, and 6 to 30 N·m (22 lb ft).
Tighten intake valve rocker arm bolts 2, 6, 7, and 8 to 30 N·m (22 lb ft).


Before you do all that, have you changed the oil and filter? Using the wrong viscosity oil or having dirty oil and a dirty filter could give you some trouble.

[apocalypsesrt]

Thanks rob for the writeup. I have changed the oil and filter and this has only been a problem in cold starts in the mornings. I use 10W30 V High Mileage Syn Blend. I am pretty religious with my changes. Sometimes in the summer i will go heavier to a 10W40. But not all the time.

I live in san diego right now on military orders and i bought the tahoe out here. it has been really REALLY good to me. i only noticed this before my last deployment in 2010. It sat and now im back and need to get on this.

It only seems to happen till the engine is warm enough or the oil gets in the lifter or rocker making the noise. I am going to tighten them as a preventative measure. As with any piece of moving machinery held together with nuts and bolts they will stretch and loosen with time.

thanks again.

[Max]

Mine make a bit of noise but everything is perfect and it runs strong with 120k+. The 00-02 trucks seem to have more cold start knock but I wouldn't worry about it as it is quite common on these trucks. Synthetic did seem to quiet mine up a bit but I honestly don't care cuz compression is perfect across all cylinders and she runs perfect. Just drive it and enjoy :cheers:

[gtwhoa]

Check your oil pressure, is it a little low? There is a rubber o-ring between the oil pump and pickup tube that has been known to get soft over time and leak off oil pressure.

[chauncey0337]

Round here we call this 'piston slap' which some mechanics laugh at.:roflsquared: