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Smith
 Post subject: Valve train geometry 101
PostPosted: Mon Jul 30, 2001 4:59 pm 
I am in the process of setting up the valve train of my long rod 225. Used F### small block valves which are slightly longer than stock valves. The rockers now set on the rocker shaft side of the stem tip at rest, and move towards the manifold as the valve lift increases. The rocker pad never looks like it crosses over the center point of the tip. Using stock length push rods, even though the head was cut 0.100"± and the block 0.010". Push rod to rocker appears to be OK, but the adjuster bolt is only exposed about 3/8" or so below the bottom of the rocker (including ball). Suggestions? On small blocks, I know that shims can be used between the shaft and the cast stands in the head. Would 0.060"± shims help? Motor is cammed for 5900-6100 peak rpm, but I don't want any more guide wear than normal. Guides are 11/32" insert solid bronze, and very hard. Also using PC seals due to dual valve springs, so oil control is tight.

Another item, is that the adjuster bolts in the rockers are on the loose side, based on where the push rods are located. Any way to tighten them up? New bolts? Rockers are stock used condition, but are in good overall shape, with no real wear. Same with the push rods, would like to reuse them if possible. Any suggestions on the exposed length of the adjuster bolts?

BTW, using the KB 2.2 pistons (KB268), 198 rods, 0.100" cut head w/ big valves, and 0.010" cut block we get -0.013"± deck to piston height, and 0.120"± valve clearance with a 0.536" exhaust valve lift, at 108° intake centerline and 284° exhaust duration.

I also would like to say that this site has been very helpful from a technical stand point, and enabled us to make fewer mistakes than we may have made building a "non-traditional" slant 6. Thank you

sgw041454@aol.com
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Doctor Dodge (Doug Dutra)
PostPosted: Mon Jul 30, 2001 11:50 pm 
Yup, It is the longer stem length that will move that rocker arm contact point off the valve stem's centerline. Is there enough exposed stem above the retainer to allow you to trim the stem length down some?

The shims are another option but you will need to grind one side of them to make one top edge real thin (.010 or less) and increasing to full thickness by the time you get to the hole. Install the thin side towards the valve to move the shaft / rocker pads closer to v. stem centerline.
(If you use thick rocker shaft shims, *Always* grind / file the top edges thinner then the bottoms, this reduces the "wedging effect" that can crack / split the cast iron head's rocker shaft towers, right through the center tapped bolt hole. ( I have split a few ) If you think about this, the shim thickness only needs to be at the base of the shaft, (or slightly shifted) tapering to nothing as you come up the sides. Here again you can use shim thickness to shift the shaft's position slightly but be sure the shaft, shims and tower saddles "nest together" with-out much force. Don't just smash it all down with the bolts.

As for the adjuster screws, if you shorten the valve stem, the screw will go in deeper. Shims will also do the same so work on that part first.
If you want a "tighter screw", you can get longer "ball-screws" and use a lock nut. You will need to grind the top of the rocker arm so there is a "flat" for the lock nut to rest on. (it does not take much grinding)
Suppliers like Rocker Arm Specialist have the longer ball screws and lock nuts....
Class Dismissed.
DD
Quote:
:
: I am in the process of setting up the valve
: train of my long rod 225. Used F### small
: block valves which are slightly longer than
: stock valves. The rockers now set on the
: rocker shaft side of the stem tip at rest,
: and move towards the manifold as the valve
: lift increases. The rocker pad never looks
: like it crosses over the center point of the
: tip. Using stock length push rods, even
: though the head was cut 0.100"± and the
: block 0.010". Push rod to rocker
: appears to be OK, but the adjuster bolt is
: only exposed about 3/8" or so below the
: bottom of the rocker (including ball).
: Suggestions? On small blocks, I know that
: shims can be used between the shaft and the
: cast stands in the head. Would 0.060"±
: shims help? Motor is cammed for 5900-6100
: peak rpm, but I don't want any more guide
: wear than normal. Guides are 11/32"
: insert solid bronze, and very hard. Also
: using PC seals due to dual valve springs, so
: oil control is tight.
:
: Another item, is that the adjuster bolts in the
: rockers are on the loose side, based on
: where the push rods are located. Any way to
: tighten them up? New bolts? Rockers are
: stock used condition, but are in good
: overall shape, with no real wear. Same with
: the push rods, would like to reuse them if
: possible. Any suggestions on the exposed
: length of the adjuster bolts?
:
: BTW, using the KB 2.2 pistons (KB268), 198
: rods, 0.100" cut head w/ big valves,
: and 0.010" cut block we get
: -0.013"± deck to piston height, and
: 0.120"± valve clearance with a
: 0.536" exhaust valve lift, at 108°
: intake centerline and 284° exhaust duration.
:
: I also would like to say that this site has
: been very helpful from a technical stand
: point, and enabled us to make fewer mistakes
: than we may have made building a
: "non-traditional" slant 6. Thank
: you


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Smith
PostPosted: Fri Aug 03, 2001 1:52 pm 
Since the head is not bolted up yet, I talked to the machine shop who did the work today, and the machinist strongly suggested that grinding the stems to shorten them is the best long term solution to the rocker location on the valve stem tip. The shim idea was a quick and cheap solution, but I really didn't like it. Having spent this much money on the head so far, it's stupid not to finish it right. Head goes back to the shop next week, and the machinist says he will treat me good on bill. Expecting to take off up to 0.100" to get the location correct.


sgw041454@aol.com
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kesteb
PostPosted: Mon Aug 06, 2001 10:00 am 
Quote:
: Yup, It is the longer stem length that will
: move that rocker arm contact point off the
: valve stem's centerline. Is there enough
: exposed stem above the retainer to allow you
: to trim the stem length down some?


Has anybody tried milling the pedestals down and then using aluminum blocks to offset the rocker shaft?


klesteb@aol.com
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