Pushrod checking

[NE57]

I ordered up a set of pushrod length checkers. (I swear, there's not a part in this basket case that is useable as is...argh). The installed big valves are ofcourse longer so my adjustable pushrods are too long (Duhhh, Neil), even fully closed, add in decking/milling and there you go.

I assume I would measure the length with the proper lifter preload?(flat hydraulic cam) Is that measurement taken off the checker what I need to order or do I add/subtract a little bit? Use the measurement as the MIDPOINT for adjustables??? I'm still not settled on head gasket thickness, would a gasket change of say .020-.040+/- throw the pushrod length out of whack? And then can I order custom adjustables or is fixed length my only option? I think adjustables are the ticket.

Should I shorten the checker most all the way and then adjust it out to fit the required length after the shafts/rockers are in place then remove the rocker/stands to measure the checker? I dunno who it was suggested it but way awhile ago someone said a good use for crap shafts(I have 8 so woohoo) is to cut them down for mockups like this. I might also assume that doing one cylinder should get me in the ballpark for all 8? Or should I check all 16 pushrods?


Come to think of it, with the longer valve stems the rockers will be working at a different angle than stock, any concerns there? That hole in the head doesn't have a lot of wiggle room.

If I sound a tad confused its cuz I am.

Any favorite suppliers? Any pitfalls I haven't thought of?

Don't anybody tell me custom pushrods take 3 months!!! Just don't.



Neil

[mart]

I'm not sure how your adjustable pushrods are
made, but is there a chance that the adjustable
ends are pressed into the pushrod tubing? If so,
*perhaps* you could remove the ends, shorten the
pushrod tubes on a lathe and then refit the ends.

mart
=============================================

[392heminut]

I ordered up a set of pushrod length checkers. (I swear, there's not a part in this basket case that is useable as is...argh). The installed big valves are ofcourse longer so my adjustable pushrods are too long (Duhhh, Neil), even fully closed, add in decking/milling and there you go.


Neil

Anytime you change something it affects 2 or 3 other things, just the nature of the beast!

[DRHEMI]

Bigger valves should not be "of course longer". They should remain the same. Longer valves, even with shorter pushrods, throw off the rocker geometry. You can have all kinds of problems, such as the scuff pattern of the rocker's path across the valve tip. You might also find that the taller valve spring packs will interfere with the valve cover fit. You may want to consider machining the valve length to the correct length, and use lash caps, or lash keepers.
-Andy Carlson
Ojai CA

[NE57]

These heads were complete when I got them last year(meaning I was definitely a hemi numbnuts and just bought something sexy to get started). The valves I believe are HotHeads 2.125 and 1.945 with the .200" longer stems. I just talked with Bob Walker who thinks if the contact between rocker and tip is centered I should be OK.

Hmm. lash caps, that's a new one for me. They look like they extend the valve stem, while protecting it. I can understand the protection but I don't get how they would help with stems that are too long. Or is the real sticking point scuffing, and length is not necassarily a deal breaker??? The hyd flat cam and springs are not radical. I will double check the clearance between rocker and retainers. What else should I be on the lookout for?

This gets more complicated as I go along...but it gets more fun too!

[krooser]

lash caps will slightly increase the diameter of the valve tip giving the rocker a larger target on the valve tip.

To find the pushrod length you need simply install those "checkers" by taking out all the "lash" then use that # as a mean length for the new push rods... you'll then have equal amounts of adjustments to make 'em longer OR shorter...

[NE57]

Ok. Well I see that indeed the geometry is all screwed up. At closed, the rocker touches the stem tip just at the inboard edge of the stem. Even I know that's way not good. Even If I used the suggested lash caps, the contact point would still be nowhere near the center of the stem. Wouldn't that eat the guides up pretty quick?

It looks like if the long stem was cut down to stock length(I have a nearly full set of stock size to compare to) the original keeper groove would be like right there, creating a smaller diameter tip and maybe not have enough meat below it to cut a new groove securely? I don't know about all that. Has anyone been down this road? I mean these longer valves are sold as for a 392 so what do people do to make them work? Are there suppliers who can custom make valves to the dimensions required? Or would the stem regroove OK and use the lash caps for a larger surface? The tip would be smaller diameter so are caps made to fit this situation?

I have heard mention of spacing up the rocker stands but from what I see that wouldn't address the problem of the stem tips, in addition to being higher in the head, are also moved outboard away from the rocker contact point, would need longer rockers and i don't think that's a $ possibility, even if they are available.

Another option I have is to start fresh with another set of unmolested heads that I have on hand. Which would also address the issue of very large exhaust valves(1.94). See my earlier thread, 'should i sell my good heads' or similar. Everything should be simpler, just buy stock sized componants. But they'd be stock heads. And I'd have to stand in line at the machine shop again. But I already had the pistons made with these reworked heads in mind so I'd have to be very carfeul not to screw something else up in the process.



So after I told this to my GF, in layman's terms, she turns to me and says, "I don't understand why you like this hemi stuff so much, its one thing after another". Yeah, and your point?

[NE57]

Ok now i think I know what Andy means. It s not shorten the stems to stock length (about top of groove) and then add the lash caps, its shorten to below the groove and add the caps to come back to length.

Is that correct?

[mart]

"Ok now i think I know what Andy means. It s not
shorten the stems to stock length (about top of
groove) and then add the lash caps, its shorten
to below the groove and add the caps to come
back to length. Is that correct?"

----------------------
Yep.

mart
=================================

[NE57]

OK! Gettin somewhere now.

Are there special keepers/retainers for this application? Obviously(?) the spring installed height will be reduced by the amount the stem is shortened if the same retainers are 'retained' so might there be a special retainer that has more dish to it?

[mart]

OK! Gettin somewhere now.

Are there special keepers/retainers for this
application? Obviously(?) the spring installed
height will be reduced by the amount the
stem is shortened if the same retainers are
'retained' so might there be a special retainer
that has more dish to it?

---------------------
'As far as I know', you need to order valve springs
that are compatable with your actual installed
height. If you're shortening the valves to the
orginal factory length, than springs intended
to work with stock length valves and stock
installed height, would be what you need. Going
the other way and using longer than stock length
stems, you can sometimes 'cheat' a bit by using
shims underneath the springs to compensate for
the the increased stem length. Unfortunately
though, nobody has yet invented a 'negatavive
height' shim to go the the other way. <LOL>

I've been doing a bit of thinking about your
problem and as I see it, if your valve stems are
much longer than stock, to keep the geometry
the same, you would need to shim the rocker
stands to compensate for the added stem length.
That also might make your current pushrods
usable too. Without raising the rockers shafts
and just using shorter pushrods, the angle that
the rocker arm sits and operates at, relative to
the valve stem tip and the pushrod is going to
be changed quite a bit from stock. Going back
to a stock length valve stem - with or without
lash caps - *should* hopefully get you at least
back in the ball park, both for pushrod length
and geometry wise.

mart
================================================

[polyspheric]

2 major reasons for longer valve stems:
1. larger head diameter, without sinking the seat
2. more lobe height - if the original lobe was .280" (= .420" @ 1.5:1 rocker), and you now have .360" (.540") the stem would be extended by 1/2 the lift change, or in this case .060".

Getting the pad centered is only a useful sign if all the parts are stock.