The rocker arm needs to be in a certain position on the stud in order to press straight down on the valve stem. If the pushrod is too short, yeah, you can tighten the rocker down, but then the rocker will be in a position where it isn't pressing straight down on the valve stem, but is actually pushing downward and outward on it. This will quickly wear out the valve guide. The only solution is the correct length pushrod.

In this instance, "lash" can be interpreted as "slop". You are taking the slop out of the valvetrain. Then that extra 1/2 turn is just a little pre-load in the system. Does that make sense to anybody?


Scott

 

Wouldn't that be barely visible if you looked hard enough as it would not "line up" with the other rocker arms?
Elaborate a little more on "slop" vs. "lash" plz

 

Any change in heads, cam, gasket, valve length rockers ect require setting up your valvetrain geometry correctly. You likely need different than stock pushrods. You will also need guideplates. Slow down.
http://www.compperformancegroupstore...y_Code=PSHRDTL

http://www.compcams.com/catalog/COMP...11_292-311.pdf

 

I hear ya here, I will have to try and understand the measuring process. I do have guide plates. I will measure an let you know what I figure out. Thanks for the info!

 

Just to try and clarify this whole mess...

As has been mentioned already, generally when cylinder heads are changed (esp. when stock ones are replaced with aftermarket types) valvetrain height typically changes with it. A minimal change can generally be lived with, but anything significant will either result in rocker arms that hit the sides of the valve retainers (pushrods too short) or tips that trip off the ends of the valves (pushrods too long).

If you have a local speed shop that has 'checking' pushrods, you can replace a stock set of pushrods for two of these and adjust their length until you arrive at a length that properly centers the rocker arm tip on the valve stem throughout its up-and-down travel. Once you have that figured out, you can purchase a set of pushrods in that specific length, install and adjust those, and you'll be good.

Summit and others sell pushrods in different lengths; you may find that whatever length you need is so close to what you arrived at with your 'checking' pushrods that you can install an 'over-the-counter' set. Otherwise, you can have a set custom-made by any one of the well-known cam grinders (Comp, Crane, or any of the others).

Obviously the ideal situation is to carefully examine your rocker arms throughout their range of travel and discover that they are nicely centered on the valve tips throughout their range of motion...if that's what you're seeing you can safely move to the next step!

 

You can find it on YouTube on how to check the rocker sweep its called but basically you just color the valve stem top, adjust the rocker and turn the motor until you get a full rocker movement and check for rocker to valve spring contact. Then take it apart and the marker should be worn off in the center of the valve stem.

I believe this is over kill on a mild build. You can even turn it over and just eyeball it for contact.

 

I'm part of this group - there will be people who will think that's the 3rd worst thing (anti-christ and the devil being the first two), however, as long as you're starting close to the center and it doesn't ride to the side at full lift - you'll be fine.

 

and just to keep the antichrist away here's a reminder. Fatcat's block is stock (was not decked) the heads are new (never milled) so valve geometry should be extremely close to stock OEM specs.

 

Ok, on my lunch today I called the company I got my heads from and they said the valves are longer and chances are I should go with a longer (100th) push rod. He also said I may get away with my rods based on the cam specs in my engine.

 

it's so easy to measure them.... get a black marking pen, mark the top of the valve. put one lifter in, one rocker and one push rod. turn the crank over twice.
pull the rocker and look at the witness mark - if it's centered you're golden.

if it's not, you can either guess how much longer, you can buy a measuring pushrod from Summit, or you can make one with a 3/16 pan head screw, a tap and a pushrod.

I still don't think needing .100 longer will be an issue... but it's easy enough to check - and a good practice to get into.

When you do get into the practice, put all your specialized, engine building tools in a bag or toolbox.... trust me on this, if you don't, you'll end up buying more than one tool because the learn to walk - even when you're the only garage user.

 

things are different. longer valve. head chamber could be lower or higher, gasket is different thickness, different cam and lifters. Those telling you it isn't a big deal are steering you wrong. Don't guess. Spend $15 and get a pushrod length checker and do it right. Improper valvetrain geometry has taken out a lot of cams and valveguides well before their time. I have had a new set of heads need new guides in under 5000 miles because the pushrods were the next size too long.

 

Fatcat, I'm with the others here in that this IS something that you DO need to check, especially if the head manufacturer/ seller did indicate that these heads have longer valve stems. Again, you don't need to have dead-on perfect geometry here, but you DO need to spin the motor over a few times and make sure that-

(a) The underside(s) of your rocker arm(s) aren't hitting the edges of your valve retainers when the valves are fully closed or-

(b) The rocker arm tips aren't riding clear over on the inside of your valve stems, or (worse still) 'falling off' of the valve stems on full lift. What you want here is that the rocker arm contacts the valve stem near the center portion of the stem throughout its full range of travel; from fully closed to fully open...

As long as you're not seeing any of these kinds of clearance/ geometry issues you'll be fine with this motor, but you definitely want to check before you go any further with this thing, since if you do need longer pushrods now is the best time to change them...

 

Ok, I called Grand Prix $15 for the tool is cheap peace of mind and insurance. I will pick one up later this week and let you guys know what's up. Thx!

 

ttt, when is this engine gonna be up and runnin'....?

 

Sorry been sick for a few days... Hope to get the pushrod issue settled tomorrow and try to finish this thing up!

 

FC... I'm beginning to question your loyalties. First you allow family time to come in the way,finances, then wife time, now health?!!! Come on, man, stop being such a goody-two-shoes and set your priorities straight... next thing you're going to tell me is you put God above your Corvette too!

 

haha, yeah. I'm starting to think we'll hear from Hillary Clinton on the Benghazi thing before Fatcat is done with his engine...

 

and you would be the only person who wants to hear anything from Hillary

 

hahaha, not that I wanna hear from her....just want someone to take responsibility for at least some of the garbage coming out of washington.

 

Amen! I will have some progress this weekend.