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slant six rocker arm specs
https://www.slantsix.org/forum/viewtopic.php?t=66971		 Page 1 of 2
Author:  pishta [ Tue Dec 20, 2022 12:14 pm ]
Post subject:  slant six rocker arm specs
anyone know the specs of a stock rocker arm? looking for length of pushrod to valve and distance from centerline of shaft to rocker valve tip, assuming the 1.5 ratio. Thanks.
Author:  CNC-Dude [ Tue Dec 20, 2022 1:28 pm ]
Post subject:  Re: slant six rocker arm specs
I made a 3D model a while back. I'll dig it up for you....
Author:  hyper_pak [ Tue Dec 20, 2022 5:30 pm ]
Post subject:  Re: slant six rocker arm specs
From what I hear, there is a little scatter in the ratio.
How much I do not know.
Care to share what you are thinking about?
Author:  pishta [ Tue Dec 20, 2022 6:58 pm ]
Post subject:  Re: slant six rocker arm specs
Quote:
From what I hear, there is a little scatter in the ratio.
How much I do not know.
Care to share what you are thinking about?
Well, when I saw a set of AL rockers for a slant at $900, and then another at >$1000 it got me thinking. Hot rodding is making something work, ie Honda bearings on Chevy cranks, Chevy Rods on BB Mopars, etc. . How close is another manufacturers rocker to a slants, barring the shaft size? Obviously it would have to be a pushrod style but 4 sets of Jesel rockers out of a SB2.2 Chevy NASCAR head are going for $200 on Ebag with other T&D sets of 16 as low as $79 used from a race team? Granted these are 1.7-1.9 ratio rockers but they are shaft mount (sort of) and they are pushrod style. Custom grind a slant for a 1.9 ratio? Just spit ballin here......Wondering if V8 rockers would be too fat? My slant is buttoned up so I cant get in there and measure myself but I remember them being kinda skinny?
Author:  Charrlie_S [ Wed Dec 21, 2022 3:13 am ]
Post subject:  Re: slant six rocker arm specs
I once made a set of 1.6 ratio SBC shaft mount roller rockers work on a 440 Mopar. However these were not what can be bought, today.
Author:  hyper_pak [ Wed Dec 21, 2022 8:53 am ]
Post subject:  Re: slant six rocker arm specs
Don't forget those Buick Straight 8 rockers.
Author:  DadTruck [ Wed Dec 21, 2022 4:02 pm ]
Post subject:  Re: slant six rocker arm specs
Looking at this as a math problem and using the tools and the parts that I have available, at the moment.

The tools; a Harbor Freight digital caliper, sometimes it is what it is.
The parts; shaft and rocker arms from Mike J that are used on the flow bench

1) Rocker Arm Shaft diameter; .8750
2) Edge of the center of the rocker arm shaft bushing to the outside edge of the adjustor bolt; .9250
3) Adjustor Bolt diameter; .3700
4) Edge of the center of the rocker shaft bushing to the center of the valve side of the rocker; 1.680

* Shaft diameter .8750 1/2 of that is .4375
** Adjustor bolt diameter .3700 1/2 of that is .1850
*** Edge of the center bushing to the outside edge of the adjustment bolt; .9250

.9250 + .4375 = 1.3625 - 1/2 of the adjustor bolt = 1.3625 - .1850 = 1.1775
so 1.1775 is from the center of the rocker arm shaft to the center of the adjusting bolt.


****edge of the center of the shaft to the center of the valve side rocker radius; 1.3680
***** 1.3680 + 1/2 of the shaft (.4375) = 1.8055

from the center of the shaft to the center of the adjusting bolt 1.1775
from the center of the shaft to the center of the valve stem depression radius 1.8055

proof;
1.8055 +1.1775 = 2.983

2.983 / 1.8055 = 1.65 ratio on the intake side.

so why is this not the 1.5 ratio that is commonly quoted?

see photo #2. That is a rocker arm used extensively by Mike Jefferis and myself for slant six head flow testing.
Note that the radius side of the valve has two distinct patterns. I just noticed this today. When measuring from the center of the inside pattern,
I can mathematically get to a 1.5 ratio valve lift. When measuring from the middle of the outside pattern I can get mathematically to a 1.6 ratio valve lift.

This make me think that the variability of the slant six rocker arms, being 1.5 to 1.6 ratio may have a bit to do with the angle of the valve guide and the corresponding valve tip, although the ramp angle of the intake side rocker arm ramp would also come into play. An additional likely factor is valve stem length. I have ran multiple flow bench cycles with valve that have stems longer than stock slant six valves. Certainly Mike J did also.

I think the values presented are accurate, considering the hand tools used. Hope this helps.

Attachments:
rocker shaft parts.jpg
rocker shaft parts.jpg [ 117.42 KiB | Viewed 2213 times ]
valve tip pattern.jpg
valve tip pattern.jpg [ 54.29 KiB | Viewed 2213 times ]
Author:  CNC-Dude [ Thu Dec 22, 2022 5:13 am ]
Post subject:  Re: slant six rocker arm specs
Pishta, pm sent!
Author:  hyper_pak [ Thu Dec 22, 2022 5:55 pm ]
Post subject:  Re: slant six rocker arm specs
Just thinking out loud here.
Could you not use 2 dial indicators, one on the adjuster and one on the retainer.
Turn the cam and record every .25 lift for both umbers.
Then you could use an excel workbook and see the results.
Author:  Dart270 [ Fri Dec 23, 2022 6:49 am ]
Post subject:  Re: slant six rocker arm specs
Oooo, I like that idea, Stan. I got another dial indicator and base/attachments from Seymour, so I could set that up.

Lou
Author:  hyper_pak [ Fri Dec 23, 2022 3:36 pm ]
Post subject:  Re: slant six rocker arm specs
I think it would be neat to see if the ratio changes as it sweeps across the stem.
And then how a roller rocker rolls across the stem.
I only have one dial indicator, right now......
Author:  Charrlie_S [ Fri Dec 23, 2022 4:24 pm ]
Post subject:  Re: slant six rocker arm specs
I haven't tried it, but I don't think the ratio stays constant. The pushrod end of the rocker travels in an arc, and the valve end of the rocker travels in a different arc. I would think to determine the actual ratio you would need to measure the pushrod straight line movement, and compare that to the valve straight line movement.
When I did my 440 1.6 ration chevy roller rocker setup I found that the "ratio" changed depending on the location of the shaft. What I wound up doing was measuring the cam lift, and multiplying that by 1.6 to give me the theoretical valve lift, then moving rocker shaft until I achieved that number at the valve.
Author:  DadTruck [ Fri Dec 23, 2022 6:50 pm ]
Post subject:  Re: slant six rocker arm specs
Agree that for a shaft mounted rocker arm system, you get the geometry right by moving the shaft. But what is the best rocker arm geometry?

I think it is the positioning of the rocker arm to valve stem interface so the travel of the rocker arm across the valve tip is minimized and centered on the valve stem.
Any rocker movement across the valve tip is movement that is not moving the valve tip downwards.

I put a set of the B3 rocker shaft shims in the slant in the 68 Barracuda, and they reduced the travel of the rocker arm across the valve stem by 50%.
This is with roller rockers and valve stems approximately .100 longer than stock.

The B3 shims are custom made and the dimensions for them are derived from measurements taken from the cylinder head and rockers.

The shims required to improve the rocker to valve tip interface on my valve train are approximately .240 thick. They moved the rocker shaft and rocker arms up far enough that I had to modify the stock valve cover so the rockers did not hit against it.

here is a link the B3 info page
http://www.b3racingengines.com/techcorner.asp
Author:  Charrlie_S [ Sat Dec 24, 2022 3:26 am ]
Post subject:  Re: slant six rocker arm specs
Quote:
Agree that for a shaft mounted rocker arm system, you get the geometry right by moving the shaft. But what is the best rocker arm geometry?

I think it is the positioning of the rocker arm to valve stem interface so the travel of the rocker arm across the valve tip is minimized and centered on the valve stem.
Any rocker movement across the valve tip is movement that is not moving the valve tip downwards.

I put a set of the B3 rocker shaft shims in the slant in the 68 Barracuda, and they reduced the travel of the rocker arm across the valve stem by 50%.
This is with roller rockers and valve stems approximately .100 longer than stock.

The B3 shims are custom made and the dimensions for them are derived from measurements taken from the cylinder head and rockers.

The shims required to improve the rocker to valve tip interface on my valve train are approximately .240 thick. They moved the rocker shaft and rocker arms up far enough that I had to modify the stock valve cover so the rockers did not hit against it.

here is a link the B3 info page
http://www.b3racingengines.com/techcorner.asp
That is essentially what I did. However, I did it by observation, and actual measurement (trial and error) of the lift. This was back in the '70's, and I had no idea of the math involved. It just seemed logical to do it that way.
Author:  DadTruck [ Sat Dec 24, 2022 10:14 am ]
Post subject:  Re: slant six rocker arm specs
'It just seemed logical ... " and it is.

I was just offering an example of a system that works well with Mopar rocker shafts to optimize valve train geometry when non OE components are swapped in.
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