Hi All
Setting up my rockers, Scat 1.25's and w-120 cam. I've lengthened the pushrod but the adjuster is screwed in all the way and no shims. Here's some pics. What would be my options??
No lift
Half lift
Full lift
Rocker geometry??
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- Posts: 24
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Re: Rocker geometry??
need shims under rocker stands valve adjuster should be in line with the valve at haft lift that's what I use with no problems. when using swivel feet on stock rocker I grind the boss down on the rocker between the swivel foot and the rocker for more clearance and adjustment
- Marc
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- Joined: Thu May 23, 2002 12:01 am
Re: Rocker geometry??
What do you mean, the adjuster is screwed all the way in? - they look like they're backed out as far as they'll go without grinding away the underside of the rockers. Looks like the balls may be nearing the limit of their travel at valve-shut, and that'll wipe out the Mazda adjusters in no time (not to mention complicating valve adjustment).
You've got too much angularity with valve closed and not enough with valve open, so as John said the rocker shafts need to be shimmed away from the head; that'll require longer pushrods.
If the second picture is at 50% lift you aren't too far off.
I'd try a pushrod around .050-.060" longer and some ~.030" rocker shims next. Typically, good geometry with Mazda feet requires that you grind at least half of the projected portion off of the underside of the rockers to make room for the ball-socket. You don't need a lot of space between them, a quarter- to a half-turn's enough to allow for .010-.020" adjustment range in the future, which should be plenty. It takes an m8x1.0 tap to chase the threads if you gunge them up on the grinder; a stock adjusting screw with a few crisp slots filed into it should suffice as a light-duty chaser if you just have a few that need attention.
Best compromise between maximum lift and best guide life with stiff springs is for the adjuster to be parallel to the valve when it's ~60% open, don't accept <50% or more than ~65%.
Chopping some off of the valvestem tips would also help but I'd leave that as a last-resort solution, it'll only complicate things in the future.
You've got too much angularity with valve closed and not enough with valve open, so as John said the rocker shafts need to be shimmed away from the head; that'll require longer pushrods.
If the second picture is at 50% lift you aren't too far off.
I'd try a pushrod around .050-.060" longer and some ~.030" rocker shims next. Typically, good geometry with Mazda feet requires that you grind at least half of the projected portion off of the underside of the rockers to make room for the ball-socket. You don't need a lot of space between them, a quarter- to a half-turn's enough to allow for .010-.020" adjustment range in the future, which should be plenty. It takes an m8x1.0 tap to chase the threads if you gunge them up on the grinder; a stock adjusting screw with a few crisp slots filed into it should suffice as a light-duty chaser if you just have a few that need attention.
Best compromise between maximum lift and best guide life with stiff springs is for the adjuster to be parallel to the valve when it's ~60% open, don't accept <50% or more than ~65%.
Chopping some off of the valvestem tips would also help but I'd leave that as a last-resort solution, it'll only complicate things in the future.
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- Posts: 8
- Joined: Wed Sep 14, 2011 12:45 am
Re: Rocker geometry??
Thanks for the replies. Thinking I'd have to grind down rockers and shim them. What's the best method for grinding? Bench grinder,4" grinder or hand file?
Also with the swivel feet what's the best setup on the top of the valves IE centred or offset to oneside?
Also with the swivel feet what's the best setup on the top of the valves IE centred or offset to oneside?
- Marc
- Moderator
- Posts: 23741
- Joined: Thu May 23, 2002 12:01 am
Re: Rocker geometry??
Even with the swivel feet there's still some rotational impetus if the adjuster is offset to the side, just not as much as you get with a stock adjuster "pawing" at the valvestem - so for street use I set them up a little off-center. On purely racing engines that only go a few hundred miles between valvejobs I'll put `em dead-nuts centered.
I've always just used a bench grinder but there's nothing wrong with the other techniques - and a belt sander would be even more deluxe if you don't need much. Don't overheat the metal, if it starts to turn blue on you, slow down.
If these are used rockers, be sure to sand off any "bump" that's developed due to wear of the side where it rubs against the slit in the stand.
I've always just used a bench grinder but there's nothing wrong with the other techniques - and a belt sander would be even more deluxe if you don't need much. Don't overheat the metal, if it starts to turn blue on you, slow down.
If these are used rockers, be sure to sand off any "bump" that's developed due to wear of the side where it rubs against the slit in the stand.
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- Posts: 8
- Joined: Wed Sep 14, 2011 12:45 am
Re: Rocker geometry??
Hi All
Got rockers done. Ground about 0.030"-0.035" off the rocker as suggested. This gave me one and a half turns of adjustment left(006" gap). Added one 0.060"and a 0.030" shim under the rockers. Now have to make some pushrods 0.1476" longer. Next possible problem is the pushrods rubbing on the tubes. Tubes are Scat Wide mouths so I'll have to wait and see how they go.........
BTW These are brand new Scat 1.25 rockers that I've had for awhile but never used....
Got rockers done. Ground about 0.030"-0.035" off the rocker as suggested. This gave me one and a half turns of adjustment left(006" gap). Added one 0.060"and a 0.030" shim under the rockers. Now have to make some pushrods 0.1476" longer. Next possible problem is the pushrods rubbing on the tubes. Tubes are Scat Wide mouths so I'll have to wait and see how they go.........
BTW These are brand new Scat 1.25 rockers that I've had for awhile but never used....