Hi
I have run into a bit of a problem while mocking up my new 512 stroker engine.

I have a set of Crane 1.6 roller rockers to use on a set of Stealth heads,(good things) however the pushrod clearance is WAY off, like more than can be ground safely.

This is only on the inlet side, where there is already a pushrod relief machined into the head.

Stock pressed steel rockers fitted up look fine, with the pushrod pretty much central.

The length of the stock rocker ( rod tip to valve c/line) is more than the ratio roller (something wrong there?)

I cant use stock rockers cos of the rather large mechanical cam.

DO I just need different length rockers?
Anyone else found this issue?

(The Crane rockers sitting on stock heads look just fine pushrod clearance wise...)

Nick

Good Looking 68 Coronet R/T...But a picture of whats going on with your rockers/heads would be much more helpful.. If you can post a picture someone might have a suggestion...

Are the rockers 1.5 ratio or 1.6--1.7?

Hows the contact between the valve tip & the rockers?

I think you will most likely need a diffrent length push rod.


Like RT said a picture of what is happening will tell a lot.

A picture of what the problem area look like at full lift, none, and a picture of the roller on the valve stem during the same sweep will help too.

I'm going to bed early today but This site has a lot of info.

http://www.4secondsflat.com/Pushrod%20Length.htm

This will help too.

http://www.pushrods.net/terminology.html

Thanks guys so far.

The pushrod length isnt the issue, it seems to be the length of the rocker arm on the adjusting screw side.

It has the pushrod up against the casting for the chamber.

The fact the stock rockers seem to be OK will probably answer my question and I will need longer(adjuster screw side) arms.

I thoght I would poat as I checked for previous stuff on it,b ut there isn t anything specific.

Failing that I could call 440 source and ask.... They even speak to durn forroners like me!!

God Bless the Troops.

By your description it sounds like your rockers are probably 1.6 or 1.7 ratio...By moving the pushrod closer to the fulcrum the ratio is increased... Normally you can grind the needed clearance out of the pushrod passage with a die grinder & burr or if f the interferance isn't bad a round file...

I had to change push rod length and add a rocker
bar shim to get things in look right geometry
wise, and rocker to tip contact.
I would guess your talking about push rod clearance at the top side of the intake port ?
If the push rod is laying down and not in line
with the clearancing already made by the manufacturer then your push rod length should
be changed to a longer one. Are you trying to use stock length push rods ?

logan426

Quote:

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The length of the stock rocker ( rod tip to valve c/line) is more than the ratio roller (something wrong there?)

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Well yeah, how do you think they change the ratio ... they shorten the rocker length on the pushrod side !!!

Anyhow, with no pictures to show the problem we're pretty much guessing. However, using the offset rocker should have moved the pushrod in towards the block but only a fraction of an inch. There should be plenty of material there to grind and get enough clearance without getting into trouble.

Pushrod length is worth looking at only to make sure you're using the right length but don't use pushrod length just to correct your problem.

There is also the possibility that the valve height is a little low for correct geometry. You may need lash caps.

How many threads are showing on the push rod side of the adjustor with zero lash?


The way the rocker ratio is changed on arms is by moving the pivot point on the push rod side closer to the fulcrum. This makes the push rod closer to the arm and creates the possibility that the arm base and the push rod may touch. If you put a lash cap on the valve stem this sometimes gives you more room, but please look at everything as this can sometimes cause other problems. 1.6 arms can work but you have to do some work depending on your setup. You may have to just use the 1.5 arms.

Just make sure everything is correct. I think this is the main reason why there are so many rocker arm problems. Too many people assume they are a bolt on and go item.


I think you would get better more qualified answers in the Race forum.

I am using stealth heads and the Crane Iron adjustable rockers (the old Isky style)with a mechanical cam (Comp Cams).

The heads are milled to 79.5 cc chambers had to get shorter pushrods, also had significant clearance issues on the intake side with the pushrods.

I went with a set of Smith Brothers pushrods which appear to be machined to closer tolerances than the Crane pushrods I was using previously. This gave me a bit of additional clearance.

Head work was still required opening up the pushrod clearance with a grinder on the intake side to get things to work.