Hi,
I have a vortec 6.6 lt stroker with a comp 224r cam. My question is how much preload should I run. Is 1/4 turn from 0 lash be ok ? I have that at the moment and when it gets hot it has bad idel issues. I've been told it should have 3/4 to 1 turn. Has any one have an opinion ? Thanks. Anthony.

 

What type of problem are you experiencing at hot idle? Normally, hydraulic lifter lash problems are evident as soon as when the engine is started. Typically clicking valve train noise at idle is evidence of too loose a lash while stumbling/misfiring is evidence of too tight a lash.

A description of the problem at hot idle would help. (BTW the preload you described in your post should be sufficient if set properly although I've found through trial 'n error that 1/2 turn down from zero lash works best for me.)

 

1/4 turn is no good. Need about 1 turn.,

 

I always use 1 Turn to 1 1/2 and been fine

 

as soon as the oil gets hot it starts to hunt, if you give it a rev it will start bouncing, and it hangs a bit.

 

Try re-setting zero lash as recommended by Slowhawk, and see what happens. Again, I'm not convinced that your problem is related to valve lash unless your lifters are bleeding down too quickly/collapsing because of thinner oil once it reaches operating temperature. (BTW, what weight oil are you using, and what is the oil temp when your problem occurs?)

 

I'm not sure what the temp of the oil is. The oil is 20w50. It's got a lsxrt manifold on it and the only other thing I think it could be is the manafold is flexing when it gets hot and causes a air leak. I've had 4 different tuners look at it and couldn't fix it, so I don't think it's in the tune.

 

If you do have a vacuum leak, you can try spraying a little WD40, ether (starting fluid), or throttle body cleaner around the area you suspect is leaking. (BE CAREFUL! All these items are highly flammable so take precautions to prevent an engine fire from occurring and have a fire extinguisher handy and ready to go.)

If the idle smooths out with the application of the one of these products, you've found the leak.

BTW, I use 10W-30 in all my Chevy engines (LS6, L98) w/o any problems. Did your engine builder recommend 20W-50 or are you using a heavy weight oil to reduce oil consumption? Just curious.

For reference, our summer time temps are typically in the high 90's F, and my normal oil temp during the summer is 190F. During stop & go traffic or while auto-xing, the oil temp jumps to 215F or higher. On track, the oil temp stabilizes at 230F with an oil cooler.

 

Vac leak the lash has nothing to do with the idle problems.

I was fighting the same thing a couple weeks ago on mine.

Tim

 

my engine builder recommend 20w50, but now he's thinking 5w30. were in winter now & its around 18 degrees c. doesn't snow where I am.

 

What kind of tolerances were built into the bearings? Your oil should be chosen off that.

Either way 1-1.5 turns is standard. Somewhere around .050". It's something like .046" per turn.

 

If that is the FAST truck manifold- thats the problem. I've tuned a few of them and refuse to tune another. Nothing but serious idle problems with them.