pushrod length/ rocker install procedure?

[BerniniCaCO3]

I'm putting together a build next week, and I've been putting together parts for it.
A couple things I'm uncertain of:

I bought some 302 parts from a fellow who built a 1990 engine with gt40 heads, exactly the same as mine, so I figured they'd be compatible but I double checked and I had a question.
He had some brand new, PBM performance products chrome molybdenum pushrods. They are 5/16" x 6.350.
When I looked up pushrods in rockauto, I'm supposed to have 6.250

Well, I already bought these from him, and I like the idea of installing heavy duty pushrods just because I can: will 6.350 work?
Will my hydraulic roller lifters take up the tenth of an inch difference, or will I cause problems for myself, collapsing lifters or holding valves open, etc.?
whatever the benefits of chrome moly pushrods, if these are not a workable size I don't want to use them. But, maybe they are.


Second question.
I chanced into some brandy new ford racing 1.6 ratio roller rockers.
I'm still running stock rockers, which I believe I simply torqued the bolt down to 25 lb feet or something like that.
I'm confused, though, on how this works... the hydraulic lifters have a range, and are designed to bleed down or pump up to just take up the slack/lash in the rockers and no more (or they'd hold a valve open), no matter what the height, within a range.
So the instructions supplied with ford racing seem to tell me to just torque it down until the pushrod is clamped tight, then back off until I can rotate the pushrod? Without oil pressure to pump up the lifter, I'm really not sure how this works... I'd like some guidance with the proper way to install and possibly shim, roller rockers. Pedestal mount (stock gt40 heads).

Final question.
When I did my gt40 heads as part of a community college rebuilding class, we used a drill-mounted reamer to do the valve guide sleeves. Naturally, they all came out just subtly crooked. When I went to hone the valve seats, I found myself cutting more on one side than the other. So, I sent them to a machine shop, which then reinstalled seats to match my slightly off sleeves so they valve sealed and seated correctly.
This does mean that my valve stem tips, are probably off a little bit with respect to the rockers. The car seems to have been running just fine for the last year.
Will slightly crooked valve tips, do less well with roller rockers than they do with stock stamped steel rockers, is this a serious issue?
My machinist seems to think it'll work out fine, so I'm hoping that's true.



thanks for the answers and advice!
-Bernard

[BerniniCaCO3]

ah, I found something about why these 6.350" pushrods were sold to me as being for a 5.0, maybe they do work. I can't tell from the article, if they're using stock lifters.
I also wish I new exactly how they/ (or I) would determine what the right length is, how to set lash, again, when I was taught in engines 101 that hydraulic lifters always managed 0 lash anyway...


1990 Ford Mustang Head Install - Tech - Muscle Mustangs and Fast Fords

"The only parts we couldn't get before our installation date were the pushrods. A pushrod-measuring tool was used to determine the exact length. It was decided a 6.350-inch-long pushrod would work perfectly in this application. We spec'd out some different lengths, but the 6.350-inch had zero clearance issues with the pushrod holes in the heads, and rocker arm geometry was correct.

The stock 6.250-inch pushrods did work but were a bit close to the side of the pushrod hole. It could have worked, but using Comp Cams' hardened pushrods that were 0.100 inch larger made more sense."

[gadget73]

you have to measure the lifter preload to find out if you need longer pushrods. You also should mark the valve tips with marking compound and roll the engine over to check for contact pattern. it should be narrow and centered on the valve stem tip. Shim as needed to center, and make up for loss of preload with longer pushrods. I'd advise picking up a shop manual and giving it a run through for the proper procedure for checking lifter preload, but basically it involves a dial indicator and a magnetic base, and you want to observe how far the lifter compresses from zero lash to proper torque on the rocker arm and verify its in the proper range.

[zoomie]

get a pushrod lenghth checker they like 15 bucks from summit

[sick88tbird]

Lifter preload is supposed to be around .030", which typically works out to zero lash plus 1/2 turn. This is very easy...install pushrod, bolt down roller rocker until all the play is out of the pushrod....you'll feel all the up and down slack go away and it will turn very freely...if it's not turning very freely, back off a hair until it does-that is zero lash....if the pedestal(the part of the rocker arm that's actually bolted down) appears to be seated in the rail or nearly seated, tighten it down-paying attention to how many revolutions of the bolt it takes to fully seat. If it takes 1 turn past zero lash, then try putting in a .030" shim and checking again.

Take your time and you'll quickly get the feel for it...don't try to mark your valvestems to check the roller rocker pattern until you have your rockers shimmed to the correct height that way when you do check the contact patch it'll be more accurate. If they contact too far outboard of the stem, you'll need longer pushrods, too far inboard and shorter pushrods. You can also use a sharpie marker to on the tips of the stems but the contact mark won't be as strong as using something like machinists dye. I've set up 20+ top end using this method(1/2 turn past zero lash) and it's given the same great results every time.

Good luck,
Don