lane_change

I just got done installing the new MAST 305cc heads on my RHS 447 and I was trying to measure out my pushrod length. I am using the competition cams 7901 pushrod tester which is 7.500 in length fully closed. Each rotation equals .050 on this tester. My issue was that my measurements from intake to exhaust were significantly different from one another with the cylinder at TDC.

The exhaust pushrod requires around 4 3/4 rotation for just a bit of side to side movement, but no up and down movement (no tapping sound, but not so tight that it can't slide a bit side to side). As close to zero lash as I could get it. Based on the 4 3/4 turns this exhaust measured out to 7.8175 including .080 of preload for the lifters.

The intake pushrod requires around 4 rotations to be nearly the same, with the smallest amount of up and down tapping, but 4 1/4 turn was so tight that I had no movement whatsoever so zero lash is somewhere in between I think. Based on 4 turns this intake measures out to 7.780 including .080 of preload for the lifters.

Also, I measured the spring height of the other valve springs and you can clearly see that the valve springs on the intake side are taller by .020 or so, so with a 1.8 rocker, I'm thinking that makes up for (.036) or the .040 difference in pushrod height requirement.

The lifters in the car are Lunati Linkbar Hydraulic lifters if that makes any difference. So my question is what pushrods should I order? If I split the difference I'd be running 7.79875 ~ 7.800 pushrods. But that makes the intake side .0200 too tight and the exhaust side .0175 too loose. Will that matter? I'm thinking the preload should make up for these variances but I'm not certain and need to order the new pushrods this week, so I would like to order the right ones.

Thanks in advance.

0FederalPerformance

I just got done installing the new MAST 305cc heads on my RHS 447 and I was trying to measure out my pushrod length. I am using the competition cams 7901 pushrod tester which is 7.500 in length fully closed. Each rotation equals .050 on this tester. My issue was that my measurements from intake to exhaust were significantly different from one another with the cylinder at TDC.

--There is your first problem- you cannot measure pushrod length with anything @ TDC-- measure the intake while the exhaust valve is just opening and measure the exhaust when the intake (on the same cylinder of course) is just closing--


The exhaust pushrod requires around 4 3/4 rotation for just a bit of side to side movement, but no up and down movement (no tapping sound, but not so tight that it can't slide a bit side to side). As close to zero lash as I could get it. Based on the 4 3/4 turns this exhaust measured out to 7.8175 including .080 of preload for the lifters.

--what lifters are you using?? .080'' is a ton of preload- unless that is what the manufacture told you to use?? Ok now I read below and see what your using. Check with Lunati i always use comp short travel lifters and use just .030 of pre load always better to error on the less preload side IMO --

The intake pushrod requires around 4 rotations to be nearly the same, with the smallest amount of up and down tapping, but 4 1/4 turn was so tight that I had no movement whatsoever so zero lash is somewhere in between I think. Based on 4 turns this intake measures out to 7.780 including .080 of preload for the lifters.

Also, I measured the spring height of the other valve springs and you can clearly see that the valve springs on the intake side are taller by .020 or so, so with a 1.8 rocker, I'm thinking that makes up for (.036) or the .040 difference in pushrod height requirement.

The lifters in the car are Lunati Linkbar Hydraulic lifters if that makes any difference. So my question is what pushrods should I order? If I split the difference I'd be running 7.79875 ~ 7.800 pushrods. But that makes the intake side .0200 too tight and the exhaust side .0175 too loose. Will that matter? I'm thinking the preload should make up for these variances but I'm not certain and need to order the new pushrods this week, so I would like to order the right ones.

Thanks in advance.

--Final word of advice: with aftermarket heads and valvetrain the intake and exhaust pushrods are rarely the same length so you will end up with 8 of one size and 8 of another. Don't get them mixed up --
-Seth

lane_change

I will contact Lunati tomorrow to verify.

From a quick search on here, Hinson was recommending that preload should be between .030" - .050". So I can lower the figure in my calculation once I confirm with Lunati. I will also be in contact with MAST tomorrow as well for verification that two different sized pushrods are commonly used on their head setups.

As far as how I checked the way I did, I simply followed the steps I had been using below. I did not know to check them the way you are suggesting. I will confirm everything with Lunati and MAST tomorrow and then re-measure if need be.

_______

Step 1: Pick a cylinder; you’ll do this for each head. First turn the engine over manually until the cylinder is TDC. This can be done by placing a paper towel in the spark plug hole of the cylinder and when it blows out you are TDC or placing a wire in the hole and when the piston its it you are TDC.

Step 2: Loosen both the intake & exhaust rockers. Pull push rod out & set aside.

Step 3: Take your Adjustable pushrod checker and open it up to 5 full turns. Next install it into the intake pushrod cavity.

Step 4: Checking for Zero Lash. There are two ways to check this next step.

1. Now reinstall the rocker arm and tighten it down but don't torque it. Now feel for play (tap the rocker) at the tip of the rocker arm, if you hear a tapping sound the pushrod is too short and should be readjusted by rotating the checker one full turn at a time and rechecking it until there is very little play and the tapping sound goes away. Rotating one full rotation = 0.050”

If the pushrod is too long there will be no play at all, meaning not even to the side, a proper length pushrod will have no play up and down but will have some side to side at all and the pushrod will need to be adjusted 0.050” smaller at a time until the proper side is reached.

2. Instead of tightening the bolt down, remove the bolt from the rocker and press it on the pedestal. Hold it firm with one hand while tapping the rocker if you hear a tapping sound the pushrod is too short and should be readjusted by rotating the checker one full turn at a time and rechecking it until there is very little play and the tapping sound goes away. Rotating one full rotation = 0.050”

If the pushrod is too long there will be no play at all and the pushrod will need to be adjusted 0.050” smaller at a time until the proper side is reached.

Doing this method eliminates the possibility of torquing the bolt down effecting the measurement of the checker. I’ve done both ways and each came to the same measurement.

Step 5: Once you find the correct length remove the pushrod. Next count the turns it takes to fully close the pushrod. Write down your count. We’ll get to the math formula later.

Step 6: Repeat steps 4 & 5 for the exhaust, remember to write it down.

Step 7: Repeat steps 1thru 6 on the other cylinder head.

Step 8: Calculating Push Rod length:

Take the # of turns and multiply that number by 0.050” Add 7.50”. (This is the length of the checker) Now add lifter preload* This is your pushrod length

Looks like this: 5 (turns) x 0.050 = 0.250 + 7.500 = 7.750 +0.050 = 7.800

lane_change

Just spoke with Lunati and they recommend a .020 preload for their high rpm lifters.

A .020 preload would give me ~7.750 exhaust and ~7.720 intake lengths @ TDC with zero lash, but I still need to confirm with MAST and possibly re-measure using Seth's advice "measure the intake while the exhaust valve is just opening and measure the exhaust when the intake (on the same cylinder of course) is just closing"

lane_change

Well after measuring every cylinder on the passenger bank, I got measurements ranging between 7.733 - 7.758 including .020 of preload for the Lunati Signature Series High RPM Lifters. After calling around to order pushrods, I can only get a 7.725, 7.750, and 7.775....so I just went with the middle of the road and got the 7.750 which splits the difference as best as possible. I figure the 7.725 are shorter than I need for all valves and the 7.775 are longer than I need for all valves. Hopefully this all turns out good in the end.

inspector12

Looks like you got it now Scott. But yeah what Seth was telling you is to measure them on the base circle is correct. The problem doing it with hydraulic lifters with the motor assyembled is what you found out. Inconsistent results. It best to do it with a solid lifter to get correct length. But I'm sure it will be close enough like you said.

lane_change

Comp 7901 was not very accurate. You would think a tool that is 7.500" long that if I rotated the nut a full 5 rotations (each rotation is .050) that my new measurement would be 7.750" which is what I ordered and received. Nope.

I assumed that was correct, but I found it they are not. I know a caliper is not the most accurate tool in the world compared to a micrometer, but I feel they can be pretty accurate, they claim to being within .001" of accurate at least. New Comp pushrods measured out at 7.750. Comp 7901 tester with 5 full rotations, 7.660. That's nearly 1/10" wrong, or .100 in pushrod length. WTF? Thanks Comp! Excellent product. Time to do this all again with an accurate tool.

Unreal

There is different ways to measure pushrods. What you order and what a caliper measures are different.

Actual length is different from gauge length.

http://www.compcams.com/Products/CC-'Pushrods'-0.aspx