Slayre

Im near completion on my build and Im at the point of checking things twice. Im running a Comp cam # 12-254-3 its Hydraulic 250/256 @ .050 lift is 519/523. Im running Comp cam pro full roller 1.6's. Heads are dart sportsman 2's. I have a few books that show you how to pre-adjust valves for start up, after doing that I looked at the location of the roller tips where they land on the valve tips, most are in the center where they recomend however there are a few that seem to ride on the end closest to the lifter valley side. Another thing that concerned me is on the number 3 intake the pushrod seems to be alittle tight, to the point it comes off the lifter pocket when the lifter is furthest down into the block, it would be on the base side of cam. I looked at that guideplate and noticed its not centered and rubs one side of the guideplate with a noticable gap on the other side. Kinda long winded for the intro but Im thinking Ill need longer pushrods. I have to get the tool still but I was wondering if anyone uses longer pushrods or have had simular problems? What lift cam are the pushrods necessary, I didnt think my cam was big enough to need them. Do the 1.6's cause you to need a different length pushrod? My heads were built by a reputable shop who has done work for me before and a few of my friends. My block is a pre-79 350 .030 over.Any advice or tips would be apreciated.

Vader

The smaller base circle of the cam, the differences in how the valves are installed, variation in rocker arms, and all the possible differences in heads makes it nearly impossible to predict what length you will need. It's always good to check.

Slayre

Thanks Vader, I kinda figured that. I was just wondering if there was a rule of thumb. I talked to my machinest today he's got the tool I need and is going to check it for me.

1989GTATransAm

iTrader: (3)

Regarding #3 pushrod. You might be able to slide the guide plate a little to help on the clearance. Also check the head to make sure you have good pushrod clearance at that point. Bottom line is you have to fix the tight pushrod or it will cause you problems.

onfire

Slayre,

I had to do the same thing when I got my new cam installed. I went from a 206 211 450 480 112 cam to a 219 219 560 560 112 cam and had to roll the motor over like you have done to check for the proper possitioning/contact of the roller rocker folcrum.

You are correct in stating that the most "ideal" is to have the wear mark in the center of the valve stem. It is not unheard of to have one size push rods on the intake and another on the exhaust.

The general rule of thumb when it comes to the proper length pushrod like vader said ----> run the test and check it.

You dont want to assume the length and be wrong. You have put all the time and effort into this motor it would be a shame to damage internal components due to rushing it. Trust me I also fell victim to the rush factor.

Take your time and enjoy the process.

Rabi C>

Damon

Remember that when using 1.6 rockers the pushrod cup on the under side of the rocker arm is moved slightly closer to the rocker fulcrum (that's how they get the higher ratio). This can cause problems with the pushrod rubbing against stuff in the valve-closed position, which sounds like the problem you are having. You need to correct that or, like was said above, it will cause problems. Longer sticks are not always the answer. Moving guideplates around is common practice regardless of cam or raocker ratio but remember the purpose of doing that is to center the rocker tip on the valve stem- not to fix a rubbing issue. If it's rubbing on something you need to "clearance" whatever it's rubbing against whether that be the bottom of the guideplate slot or a part of the head casting.

I've done such clearancing with the heads installed by using a rat-tail file and making VERY sure to clean all the shavings afterwards. It's better to do it with the heads off the engine before assembly, but I know sometimes the real world calls for more creative solutions.

When things are properly "clearanced" you should be able to drop on the rocker arm in the valve-closed position and have the pushrod just drop right into the cup on the underside of the rocker using ZERO force getting everything to line up. The weight of the rocker arm should be enough to center the pushrod tip in the rocker arm pushrod cup.

Slayre

Thanks agian folks.
Maybe I can go into more detail about the #3 rocker situation. I did grind a very little amount from the guideplate, it seem to help the pushrod to drop right in, as before it did not. I gave it a 1/4 from zero lash then turned the motor thru a complete cycle until the valve was closed again. At first prior to grinding, the pushrod seemed it was being held by the rocker arm itself raising it from the lifter pocket.Almost as if it was in a bind. As far as moving the guideplate, I think that may cause the pushrod it shares to bind Im not sure but I will look into that. Ive been working on it this all weekend and I have got the pushrod to stay in place without any binding, or raising from the lifter. Everything seems ok but I will have it checked before I go any further. I have learned from the past to do it right the first time.
Damon,I can put the rocker arm on and have the pushrod line right up without any force like you said. Only after I cycle the motor did the problem occur. The pushrod is not bent thats what led me to believe I needed longer pushrods.
Thanks again for the input folks, I am a " Do it yourself " kind of person so any information that I can use before I have to take it to someone else will be greatly appreciated.