SBC, T&D shaft rockers geometry?

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SBC, T&D shaft rockers geometry?

Postby redliner » Thu Sep 07, 2017 8:13 pm

I am very familiar with the Midlift rocker arm geometry as I previously worked with Jim Miller to retrofit a set of his rockers for my last motor. My question is, what geometry does T&D use? Would I want to shim the T&D system to midlift geometry? (I dont think the rockers have millers midlift geometry built into them so...) Should I just leave well enough alone and follow T&D instructions?

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Re: SBC, T&D shaft rockers geometry?

Postby panic » Thu Sep 07, 2017 10:12 pm

Mid-lift is not an adjustment.

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Re: SBC, T&D shaft rockers geometry?

Postby redliner » Thu Sep 07, 2017 10:40 pm

panic wrote:Mid-lift is not an adjustment.

It has been a number of years since I was familiar with this set up and realize the rockers had a different geometry to them as compared to all others. I do not recall the specifics of the midlift ... something about the rocker arm and the pushrod and the valve being at the same angle at midlift.... anyhow.... I suppose T&D has their own method, I do not understand everything I know about about the T&D

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Re: SBC, T&D shaft rockers geometry?

Postby redliner » Thu Sep 07, 2017 10:49 pm

panic wrote:Mid-lift is not an adjustment.

I just meant shim them up until the roller tip and the fulcrum are 90 degrees to the stem at midlift I wonder if T&D is designed to be 90 degrees at 2/3 lift like Jesel is?

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Re: SBC, T&D shaft rockers geometry?

Postby cab0154 » Fri Sep 08, 2017 7:07 am

you use the height gauge supplied with your rockers. once you get the stand height set the pattern will pretty much take care of itself. make sure you tell them if your valves are longer than stock because for that head because you only want to add .100" of shim under the stands at most. so if you have longer than +.100" you will likely need taller stands. I have +.100 and forgot to tell them, but I ended up at .087" of stand shim to get it where I needed it. google 't&d stand height tool" and you will see how it works. or look for t&d's downloadable instructions.

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Re: SBC, T&D shaft rockers geometry?

Postby redliner » Fri Sep 08, 2017 7:54 am

cab0154 wrote:you use the height gauge supplied with your rockers. once you get the stand height set the pattern will pretty much take care of itself. make sure you tell them if your valves are longer than stock because for that head because you only want to add .100" of shim under the stands at most. so if you have longer than +.100" you will likely need taller stands. I have +.100 and forgot to tell them, but I ended up at .087" of stand shim to get it where I needed it. google 't&d stand height tool" and you will see how it works. or look for t&d's downloadable instructions.

I already have them.... I have not installed them, I will call and see if they will exchange the stands.... Thanks!

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Re: SBC, T&D shaft rockers geometry?

Postby panic » Fri Sep 08, 2017 9:15 am

If you arrange the rocker height to give a 90 degree angle between the fulcrum/roller tip line and the stem axis, you can't get 90 between the fulcrum/pushrod cup line and the pushrod axis.
Is that the best compromise? Opinions vary.

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Re: SBC, T&D shaft rockers geometry?

Postby redliner » Fri Sep 08, 2017 9:21 am

panic wrote:If you arrange the rocker height to give a 90 degree angle between the fulcrum/roller tip line and the stem axis, you can't get 90 between the fulcrum/pushrod cup line and the pushrod axis.
Is that the best compromise? Opinions vary.

Good question! Does anyone know which method T&D uses?

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Re: SBC, T&D shaft rockers geometry?

Postby Abbottracingheads » Fri Sep 08, 2017 11:12 am

T&D will have mid-lift geometry.
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Re: SBC, T&D shaft rockers geometry?

Postby Belgian1979 » Fri Sep 08, 2017 11:29 am

T&D will have to be set according to their instructions and with the tool they supply. After that you have to adjust the pushrod length to get a good sweep over the valve and that is it.

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Re: SBC, T&D shaft rockers geometry?

Postby redliner » Fri Sep 08, 2017 12:41 pm

Abbottracingheads wrote:T&D will have mid-lift geometry.

Really... I like that....

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Re: SBC, T&D shaft rockers geometry?

Postby redliner » Fri Sep 08, 2017 12:49 pm

Abbottracingheads wrote:T&D will have mid-lift geometry.

I just spoke to Sheldon @ T&D and he confirmed the midlift and he says they are very fussy about their geometry!!! Good to know!!!

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Re: SBC, T&D shaft rockers geometry?

Postby cab0154 » Fri Sep 08, 2017 7:18 pm

Belgian1979 wrote:T&D will have to be set according to their instructions and with the tool they supply. After that you have to adjust the pushrod length to get a good sweep over the valve and that is it.


with the pushrod length on a stud rocker this is true because the pushrod determines the height of the rocker on the stud and thus the sweep. but with the shafts (especially the t&d's because they oil through the lash adjuster) there is a baseline setting for the lash adjuster and you can adjust to +1turn/-1 turn (so +/- .050" from baseline for 20tpi) from that or you cut off oil flow to the rockers. so once you get the stand height, you just leave the adjusters alone from their factory setting and measure pushrod length. shouldn't be a lot of variance in the p-rod length since the stand height is set you aren't changing where the roller tip is in relation to valve tip from pushrod length.


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