5.3 cutty

iTrader: (2)

fresh rebuild with used ls7 lifters and 243s milled 40,xxx stock size comp pushrods.my problem is when the rocker is torqed down 2 cylinders have no compresson( only 2) back off the bolts on the 2 rockers a hair and they have compresson shop said it mite be the lifters not pumping down...anyone have an idea whats up with this...

PowellSixO

iTrader: (1)

You have milled heads and stock length pushrods? Did you measure for the pushrods? I would say that your pr's are too long, and you are holding the valves open.

Starkey

X2. If you mill them more than 20 thou, you're gonna have pushrod problems.

What kind of rockers? If stockers, are you using the GM rocker cradle?

5.3 cutty

iTrader: (2)

No i did not check the pr's to make sure it was right...but i know a guy thats running the same set up in a silverado on performance trucks.even if its only doing it on just 2 cylinders would make then to long??? Seems like none would have compresson not just 2.and i am running stock rockers and stands.Iwas told that those two lifters are pumped up and should let go when i spin the engine over to prime the oil pump.Would it make a diff if i put plugs in it and then spun it by hand to c if they will let go???

Grimes

iTrader: (3)

i would save yourself a big headache later on, and just make sure you measure for the right length push rods right now.

5.3 cutty

iTrader: (2)

Ya rookie mistake on my part

5.3 cutty

iTrader: (2)

if i used the heads with out milling i would have needed a 7.450 pr but i milled the heasd 40,xxxs + useing the ls6 small base cam every thing should be right.
and if none of the cylinders had comp i would say its the pushrods but its only 2 im haveing problems with.also my comp cams is stock size.

Heres the post from gray matter from truck performance>>>>>
I also have dished pistons
Heads milled .040 with LS7 lifters used stock pushrods

The z06 cam has a smaller base circle which requires a shorter pushrod BUT milling the head takes up that space which is why i run a stock pushrod
Valve train is quiet.
I am sure it makes 310 at the wheels if not a lil more .
It runs just as good as my 212/218 and tr220 cam did
I made 300 with the 212/218 cam on stock heads 706 castings not the 243s
__________________

Grimes

iTrader: (3)

dont remember how much smaller diameter the ls6cam base circle is off the top of my head. dont forget the pushrod length to make up for that diameter will only be half of the diameter though.

mcdonald77

iTrader: (21)

When I assembled my heads L92's and block lq9 with the ls6 cam, I used 4.350. The engine was not decked and I was told the heads were not either. With 4.350 my valvetrain is a little nosiy on the interior using longtube headers, outside its not bad. I got 1.24 turns from 0 lash to 22ft pds.

(I used the comp cam magnum tool, then after installing the pushrods, bought the other comp cams push rods tool. The one thats 6.8 closed with .050 turns and it was still 4.350, I did measure not once, not twice, but more then three times)

PREDATOR-Z

Sometimes I wonder why you guys even mod your cars. Paper calculations are mostly just that, good on paper only!
Guys for the love of the Big Guy, MEASURE. MEASURE

Grimes

iTrader: (3)

Pretty much. All the time spent online searching and posting, the actual measuring could have been done already!

PowellSixO

iTrader: (1)

You can read posts all day long that say this or that, but it doesn't mean that they are right. You really should measure for the pr's, especially if you milled .040" off of the 243's. Also, if the heads were redone the valve lengths could be different on every single valve if they didn't know what they were doing. Hell even if they are stock heads they could be different. I just rebuilt a set of 799's that were 100% stock. After removing the valve stem seals, springs, and retainers I went through and measured the height of every valve, in the location that they originally came from. I measured from the spring seat to the top of the valve. The difference between each valve height varied .020" from one to another. After I cut the valve seats and refaced the valves they all stuck up a few more thousandths. I then went through and cut the top of every valve so that all of the valves were at the same height and matched my original overall average valve height. Moral of the story, if you milled .040" off the heads, and a couple of the valve lengths are off by .020", and you used 7.4" pr's when the stock length is really 7.38", then you could easily eat up all of your preload and hold a valve open (.040 + .020 + .020" = .080").

lizeec

iTrader: (57)

When you say you only have NO compression on 2 cylinders, is it the same 2 cylinders each time you check, or if you rotate the engine which rotates the camshaft which will put some lifters on the base circle of the cam and some on the lobe ramp which will then create no compression in another cylinder due to the pr's being too long and holding the valve open? If you ask for help at least try to listen with open ears.