This is where you have to be very gentle and rotate the rocker and listen for "tick" "tick" against the valve stem. If it does, then lengthen the adjustable pushrod a small amount. You can't use the old spin the pushrod method. If the lifters are new and the plunger is easy to depress, it can be tricky and you have to be very gentile in your measurements. I do both intake and exhaust several times to make sure I get the same readings.

 

hey guys, I'm in a bind and trying to figure out what i did wrong with my set up. I have gm cts-vr lifters comp cams push rods, yella terra non adjustable rockers set in TEA stage 2.5 317 heads. The lifters did not come with a preload spec so i set them to about .070. I ordered a set of -.050 pushrods and checked the preload with a dail indicator set up on the top of the push rod cup on the rocker arm with the indicator following the angle of the pushrod. I assumed this preload was ok, but when i started the motor it is running real bad, very rough and will barely idle and sounds very crackly through the pipes. It also kicks a P0101 code or something for MAF or VAF. Is it possible the preload on the lifters is wrong and it's holding the valves open? Does anyone know the preload for that lifter? If its like .005 and i preloaded .070 would the lifter overpower the valve spring when it filled up with oil and hold the valve open

by the way i found zero lash with the dail indicator as well. very easy to find that way so i'm sure i had that right.

I don't know a bunch about this stuff and i'm learning as i go and from reading posts like this....so any help would be great.

Thanks
Brad

 

If you want to change the wipe on the rocker to valve stem you raise or lower the rocker. A longer pushrod will increase crush on the lifter not on the valve spring. How deep the plunger ends up is where it stays. If you place a long pushrod in with .080" preload that means the extra length of the pushrod is taken up inside the lifter. If I run a 50 thou shorter rod and get 30 thou preload the overall distance between the cam lobe and the rocker is the same in both scenarios hence not effecting the wipe at all. The hydraulic lifter acts as a buffer, and going up and down in pushrod size won't change the distance between the cam lobe and the rocker arm(unless you bottom out the plunger).

When running a solid cam the wipe pattern will change with different pushrod lengths. The lifter is of a fixed length it is not variable like a hydraulic lifter.

You can go a 7.400 pushrod and if the wipe is incorrect u can try a 7.450" etc.

The only way to do it with a hydraulic is shim or mill the rocker arm support.

I don't use moment formulas when adjusting preload. There are variables. I use a dial indicator on the rocker tip. Find zero lash then wind the rocker until it just nips up measuring the distance with the dial. You can feel for zero lash with a bled down lifter. I can still feel the spring, or move the rocker back and forth listening for a click. There should be one lifter that is bled to get an accurate reading. I normally do one ex lifter and one intake lifter as the base circles on camshafts can vary on both. Especially running big split profiles that are used commonly.

 

How did you measure for the pushrods?

 

i put the stock push rods in and checked the preload with a dail indicator. It was .100 that way. So i ordered .050 shorter push rods and then re checked the preload the same way.

The motor sounds like it has a bad vacuum leak, very bad idle but i can't find any hoses off or hear a leak for that matter. We pulled the PCV and could hear the vacuum and it really didn't change the way the motor idled either.

is it even possible for these lifters to hold the valves open when they pump up. if they have so much pressure that the piston moves back the top of the lifter(therfore no longer having the .060 preload) either the push rod bends or the valve opens .060, but i have no idea if that is possible.

Thanks!
Brad

 

What intake are you running?

 

Check your compression values, you may not have enough preload if the rods are too short, but I doubt that- would just run noisy.

Before doing anything else too radical, put the stock pushrods in and see how the car runs on those.

Did this car run OK before, or is this a fresh motor? What makes you think its the valvetrain causing the problem?

 

it's the stock Lq9 intake,

The motor ran great before this. The only reason i'm questioning the valve train is because thats the only problem i can think of. I changed the head gasket to .040 thick, put the new lifters in, new push rods and new rockers. I left everything else alone so i thought i must have messed something up in there, and lifter preload/pushrod length is the only questionable thing. Everything else is bolt and go. The code says MAF but i never touched it and i don't know if a MAF problem could cause the truck to run this bad....

 

Your pushrod is only -0.0500" off stock, which should be tolerated by the hydraulic lifters. With non-adjustable rockers, you don't really do "lash adjustment", and preload per-se. You should just bolt and go. Did your torque your rocker studs to 25 lb-ft. ?

To take off the heads you probably removed your intake, valve covers, wires etc.

Check all your harness connectors. Are your plug wires OK, plugs OK? Do you have a smoker to check for vacuum leaks- nothing caught in the intake o-ring seals? Once again- is the compression OK?

 

yep i torqued the bolts to 25 foot pounds when each cylinder was at TDC on the compression stroke. I've checked the wire harness 3 times and all seems to be good, i even hand checked every injector plug and the coil plugs as well as unplugging and replugging in the MAF. I checked all the MSD wires and found 2 wire that have high resistance but the truck ran fine with them before all this, but i ordered a new set anyway and it will be here tomorrow. I put all new plags in, tr-55 v-groove and made sure they are all at .055 gap. i also unplugged all the MSD wires again and made sure i felt the snap as i plugged them back in. and i also sprayed carb cleaner along the intake ports with the truck running to see if i could see a leak or hear the idle rev up and nothing.

But

i tried some new things tonight and got some more info that might shed some light and here is other info i thought was unrelated. I did check compression right before and right after this change(glad i did), here are the numbers before the head gasket change and bare in mind i checked each cylinder 2 or 3 times: stock MLS gasket, 69cc heads
1=180psi
2=185
3=205
4=215
5=180
6=215
7=175
8=175

here are the numbers after the .041 head gasket. I did this right after the lifter install so there is almost no way the lifters where pumped up with oil if that would make a difference:

1=205
2=230
3=225
4=225
5=240
6=235
7=240
8=225

i didn't think anything of it but i called my tuner and he said that was an unreal increase for just a .01 thinner head gasket. We also talked about maybe the MAF was not working so i used my scan gauges and verified i was getting an IAT reading and at a very bad rough idle i was getting 3.5 lb/m. He said that was way off also. I pulled a plug and my new plugs are dead black which goes along with the very the strong fuel smell in the exhaust.

so maybe the preload is not the problem and somewhere i got a bunch more compression and it threw the tune way off? Does this sound like a possible problem? Maybe they sent me the wrong head gasket and it was the .030 one?

thanks for all the help, and sorry for the hijack

Brad

 

Compression measured under the same conditions?

I am convinced it has nothing to do with the valvetrain. That's a big jump in compression.

I think you need to retune the computer for the "new" engine. Take MAF off line during the tune to see what happens. Also check the coolant temp sender signal to the pcm- might be defunct.

 

Is it a bad idea if Im unsure of what pushrod length to run, (im in the correct ballpark though) but I run it for the first 100 miles while I break in my engine, then I check the length?

I was told by many people my lenth is good..

7.400" pushrods, 5.3 stage 2.5 heads, milled .002 from TSP (standard), milled about .005 from another machine shop, TSP 402 with -10cc pistons, TR custom cam (I know base circle is smaller than stock)... .040" COmetic gasket, APR studs..

LS7 lifters, Harland sharp rockers torqued to 21ft lbs

 

thanks a lot for the help, I just have to wait for saturday now so he can look at it.

Brad

 

hey guys
thanks for all the help and advice! When zippy hooked up to it he found the problem right away. The MAP just picked a real bad time to go bad and it was causing the over fueling which caused the crackle in the pipes. when he hooked up and told it what to do it idled pretty good. we put a new sensor in and she fired right up with minimal adjustment to the tune.