All Small Six 68 small log head porting

This relates to all small sixes


Active member
Supporter 2021
Today I got my two different springs back from the machine shop. They measured the springs with a digital scale on a bench drill, so the measurements are estimates at best, but maybe helpful as a guideline. These are the numbers they measured:

Manufacturer reference
Advertised specifications
Measurements from machine shop
Sealed Power 6513-1
(single spring)​
installed height 1.67 --> 86lbs
installed height 1.30 --> 183lbs​
Clay Smith Cams CSC-TOY-SPG
(dual spring)​
installed height 1.68 --> 100lbs
installed height 0.98 --> 232lbs​
installed height 1.67 --> 147lbs
installed height 1.30 --> 242lbs​

Initially I wanted to install the dual springs, but it seems they are a lot stiffer than advertised. I think I will go with the Sealed Power single springs, they shouldn’t be too hard on the stock camshaft and still be able to control the valve with 1.65 rockers.

@pmuller9 the Sealed Power springs have basically the same specs you recommended, that gives me confidence they should work just fine, so thank you again for your input!
Last edited:


Supporter 2018
Supporter 2021
The only question I have is The actual installed height appears to be a lot more than 1.67 according to the picture you posted?


Active member
Supporter 2021
I have to admit the picture I took is not very good, it looks like it’s more but that is just the result of my poor camera angle. When I measured it without the camera in hand I measured ~42.5mm = 1.673”. I also ordered a “valve spring installed height gauge”, should arrive next week, then I can confirm my ruler reading!


Active member
Supporter 2021
The gauge arrived earlier than expected. With the single spring retainer I got an installed height of1.677", with the dual spring 1.661".

It looks like the installed height is close to 1.7"
If that is the case use the Comp 903 spring which will give you 80 lbs closed @ 1.7" and 190 lbs open @ 1.319" or .381" valve lift.
@pmuller9 I did some more research on my single valves, their coil bind is 1.3" (how could the machine shop that measured the springs not realise that :rolleyes:). With my 0.381" lift that is too high, so I ordered the comp 903 springs as you suggested. It's the 3rd set of springs I ordered by now :rotfl: but they are for sure the best choice for my setup!

PS: If anybody needs a set of dual springs with retainers, will sell them in the "buy, sell and trade" forum.


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