Curious_George

I am almost finished with my 350 build for my '87 IROC Camaro. My question(s) concerns the VTG. The valve train consists of the following new parts (Except for lifters):
1.) http://www.lunatipower.com/Product.aspx?id=2005&gid=261
2.) Standard length OE pushrods - 5/16", 7.2"
3.) OE 1.5 ratio stamped steel rocker arms, non self-aligning
4.) 081 heads with Summit screw-in studs. No guide plates, using OE slots in head.
5.) Stainless steel valves are correct length (Same as OE steel valves)
6.) Used OE roller lifters in good shape (Taken apart, cleaned and reassembled).

Note: I have an extra roller lifter that I converted to a "solid" lifter for checking VTG with the proper preload. I also marked the valve stem tip with a Sharpie marker to verify the sweep movement.

With everything assembled, I proceeded to check the rocker arm sweep (With my test lifter) across the valve stem tip. With the lifter on the base circle, the rocker arm is slightly off center toward the intake manifold. At full lift, the rocker arm sweep is toward the exhaust, but more toward the end of the valve stem. See picture for reference.

Everything I have read, would indicate that a long pushrod length will cause this condition. However, I am having a hard time understanding this because of the cam I am using. To get the additional lift that the cam affords, it has to have a smaller base circle than a stock cam. This will place the lifter deeper in the lifter bore. If this is the case, and I am using OE length pushrods, how can my pushrod length be too long to cause the above condition?

CG

BASSETT IROC 85

iTrader: (2)

Have the heads are block been milled?

Curious_George

The block was decked 0.02" The heads were cleaned up prior to me getting them, but my guess would be they had 0.01~0.02" shaved off to clean them up.

I am using a 0.041" thick (compressed) head gasket.

thewizard

iTrader: (43)

That's exactly what I was going to ask.

Did you verify your lash adjusting process was completed properly?

How many turns after zero?

Curious_George

Yes. 1/2 turn after zero lash.

CG

thewizard

iTrader: (43)

I'd say get one of those pushrod length measuring tools to see what info it has to offer.

Curious_George

After pondering this situation a little more, I have answered my own question (which is usually the case).

Obviously, from my earlier information, my pushrod length is too long. Tolerances add up and you cannot take it for granted that everything will end up as it should be until you measure everything.

My block was decked 0.02". I assume the heads had 0.01~0.02" shaved off of them when they were rebuilt (Bought them rebuilt). I am using a 0.041 (compressed) head gasket. The OE head gasket is 0.028". The difference between the OE head gasket and my head gasket is 0.013" (.041" - 0.028" = 0.13") So, if we add this up 0.02" + 0.02" = 0.04" - 0.013" = 0.027"

What does all this mean? My VTG is off by at least 0.027", which does not seem like that much, but it is enough to throw things out of whack. Factor in my Lunati cam and it is even more out of tolerance.

I made a variable length pushrod today out of an extra OE one I had. I cut the pushrod about 2" from the ball end and drilled and tapped it for a 1/4 x 20 threaded rod about an 1" long. Cleaned up all the edges and assembled it. I adjusted the pushrod for a length of 7.150" (verified with my precision caliper) and installed it. After checking the rocker sweep with the modified length pushrod, it was exactly in the middle of the valve stem.

Now that I have identified the proper length pushrods, my OE rocker arms are now dangerously close to hitting the rocker studs when the valve is closed. When the valve is open, there is no issue. I could open up the rocker slot with my Dremel tool and the appropriate bit, but I am not too crazy about this idea. I am not certain what the long term effects of this will be.

In a nutshell, I need 7.150" pushrods and long slot 1.5 rockers. I am intentionally using stamped steel rockers for this build and may go to 1.5 roller rockers at some point in the future. I don't really care for the additional valvetrain noise with roller rockers.

CG

1986Z28OWNER

iTrader: (1)

081 heads are tpi, They are meant to locate with self aligning rockers, not the slots.

Curious_George

Well, in this case, the 081 heads I have are built for non self-aligning rocker arms. These particular heads have the "guided" slots from the factory.

thewizard

iTrader: (43)

Have you looked into those aftermarket sets of stamped rockers with roller tips? They are less than $100, and normally have elongated slots.