I need help with pushrod length advice.

Heres the deal. The cam is a hydro roller.

Comp cams says the cam needs .030 preload as ideal.

I am running stock hydo roller lifters. I bought an extra, took it apart, took a 9mm shell casing turned it down on a case lathe and inserted it into the body and reassembled without the spring. The shell casing (spacer was cut to length to allow the plunger to set .030 down from the snap ring which should be perfect per comp cams as for mocking up a lifter as running with "ideal preload".

Now the issue...

My installed height on the valves has some variance. I could not find my feeler gage but with a strait edge and eyball I guess the variance is about .040 with the exhaust valve being shorter. I will take better measurements tomorrow.

Is this enough variance to warrent two different length pushrods. To set the rub pattern perfectly on all valves would require 16 different length pushrods.

To determine proper length..
I have used an adjustable pushrod and a plastic "mock rocker arm" pushrod length checker.

The checker will measure that I have the correct length pushrod, on certain valves with a 7.192 OAL pushrod...

But the wear pattern (roller tip witness mark on sharpie painted valve tip) says they are too long. Does the wear pattern need to be dead nuts center?

Adjustable pushrod set to about 6.90 will yield good wear mark, but is determined to be too short per plastic checker.

How critical is this measurement. Camshaft is a COMP CAM XR294HR 242/248 @.050 and lift of .540 /.562.

 

The location of the witness mark isn't as important as it's width. The correct pushrod length is the one that has the rocker tip moving back and forth across the valve stem as little as possible over the full motion of the cam. Pushrods are available in .100" increments, so don't get too hung up over trying to get an exact length smaller than that.

 

Thanks for the reply!

I checked again today with some week test springs vs the regular springs.

A length of 7.132 put the witness mark dead nuts center with only a thin rub line !

I also checked piston to calve clearance and the intake was tight at .072 exhaust was over .125.

Engine has hypo cast pistons. Will .072 be enough clearance? I will check again tomorrow.

 

You're a little uncomfortably short on clearance on the intake side. It should be at least .080", preferrably more.

What method are you using to measure the clearance?

 

Method for measurement...

Hydo Lifter modified to be fixed.

Set to zero lash / zero preload

Lightweight test springs.

turn engine over by hand push rocker arm down with fingers until it hits piston

Inset feeler gages

 

So you're measuring clearance only at one point of the rotation, TDC? Or at many points, and taking the smallest clearance?
I'd use the play-doh method. That ensures you've got the smallest clearance.

 

Just make sure you don't use real play-doh for the play-doh method, it's too elastic. Modelling clay is a better.

 

You are going to be fine get your self some modeling clay and double check you will see you have more clearnce than you think. I use to check pisyon to valve like that had one real tight tried the clay method and found I had pleanty of room you are basicly throwing the cam timing out using that method.

 

I am checking it at many points turning by hand. .072 was the tightest. I am going to do again tonight with deree wheel attached

 

Trust me use modeling clay.

 

You're doing it with the timing chain on?

 

Yes, The timing chain is on. I am checking it as if the engine would be running. How else can I do it. Is there another way?

 

Ross,

Why will the clay method yield different results? I don't Understand the throwing the cam timing out statement.

I would rather not pull the heads off. If I do this will I have to replace the gaskets? The have not been run.

 

You're measuring clearance in perfect world conditions. I'd want to know what'd happen if the timing chain snaps, or skips a tooth, etc. I'd want the piston at TDC, then push the valve down until it hits the piston, measure the distance, subtract valve lift, and that'd be my number.

 

The method you're using now is fine. When is your clearance the lowest? What heads and pistons are you using? Has the engine been rebuilt?

 

Engine is a brand new ZZ4 shortblock never in a car.

Heads are AFR 195 with 62cc chambers. These were on an expired engine and now have new valves and new valve job.

 

I'm surprised you don't have more clearance than that. What head gasket are you using?

 

I got different results because the piston and valves all move together. I have used cams in the .650 to .680 range with out cuting pistons It does depend on your cam degine also I find the better pistons seem to have more clearance such as JE, SRP, Weiscos. And as for pulling the head if you dont have enough clerance you will have to pull the heads to have the pistons cut or change a cam to get the clerance you need.

 

pretty big cam for a 305 isnt it?

 

A ZZ4 is a 350.

 

Head Gaskets are FelPro 1003s

Cam is properly degreed per cam card. I checked open and close at .006 tappet lift and confirmed 106 intake centerline with degree wheel and dial gage.

 

Guys, THANKS for all the great advice!

I used the clay method and ended up with plenty of clearance!

I gained about .100 on both valves.

I don't understand why the measurements came up so differently.

My next question is what do I do about reusing my Felpro 1003 gaskets. The engine was never fired. Am I ok to reuse?

Also what is the best way to clean off the thread sealer from the block threads and the bolts. It is still stickey.

THANKS A MILLION!!!

 

Your not the first to do that as I stated before.Its all in the cam timing remember the cam moves at 1/2 the speed of the crank.

 

Get some copper coat spray the head gasket both sides. Run a tap into all the head bolt holes to clean them and wire whell the bolts. Put some fresh sealer on the bolts and bolt it together.

 

realistically you need to shoot for .125" piston to valve clearance fyi.

~Couch