An Indian Valve Spring Study

This Valve Spring Study is for pre-war, and post-war Chief applications. Chief and Sport Scout springs (part #39909) are the same spring with 9 full coils, while Scout 741 springs (part #39908) are shorter with 8 full coils. Bonneville Chief Inner springs can be used with either spring for a pressure increase of 25% at all lift points. All (3) of these springs are being featured in this study.

See below for pictures, Valve Spring data, and Spring Pressures.

Also see the data sheet below for Jim Parker's "Custom High Lift" Valve Springs.

Parts Tested:

1) Post War cylinders with (2) new hard seats installed for the exhaust. Front intake seat is only slightly cut lower than factory-new, while the rear intake seat is cut a little deeper reflecting a slightly higher installed spring height

2) Valves are new Starklite Cycle "Black Nitrided" valves for extreme stem hardness

3) Scout 741 (8 coil) valve springs, (1) good used Chief (9 coil) valve spring, and Bonneville Inner Springs

4) (6) original valve spring retainers, and (8) original keepers

5) New Starklite Cycle "Highest Quality" valve guides, with Perfect Circle brand Teflon seals on the intakes only

6) New Starklite Cycle "O-Ring" valve covers (base thickness = .075")

7) Fiber "O-Ring" seals under the valve covers at .062" thick.

Objective:

To test for available valve lift, before valve spring "Coil-Bind" occurs. Coil-bind is when the valve spring is fully compressed. There is limited valve travel available when using standard Chief components, and by varrying the optional components, increased valve lift distances, and valve spring pressure rates may be achieved. I am setting-up a Chief "Hot Rod" motor using Very Hi-Lift cams (.490" lift!), and I need to provide for safe clearance between every spring coil at maximum valve lift. The minimum recommended clearance between coils (at proper spring pressure rates) is .020" per coil for high-reving automotive springs, and .010" should be OK for our slow reving Indians (per recommendations from a spring manufacturer). Standard Chief cams only offer .330" of valve lift, so coil-bind is never a problem. Bonneville cams, on the other hand, offer around .410" valve lift, and coil-bind becomes an issue (especially when using the .062" fiber gasket under the valve cover). On my sample parts listed above, I found that the Chief (9 coil) spring will coil-bind at .445" of valve lift when using the "O-Ring" valve covers without using the .062 gasket under the valve covers. That leaves only .035 total clearance (.005" per coil, not .010"!), and with the .062" gasket installed, the springs will coil-bind in most cases causing damage to the cam lobes, push rods, lifters, and rollers! My data shows that by selecting the correct optional components, that ample coil-bind clearance can be found even when using extreme hi-lift cams.

Observations:

Valve stems are cut with grooves at their end to hold a "keeper and retainer" combo in place while compressing the valve spring under them.

There are commonly known valve spring pressure rates based on the total mass of the valves, springs, and other valve train components, while considering the RPM range desired.

Chief valve train mass moving at a lower maximum RPM range can get away with slightly lower spring pressure rates.

The recommended spring pressure rates (given to me by a spring vendor), based on the total mass of an average Chief is: around 130 pounds with the valve closed, and around 350 pounds when approaching lifts of .500". We can not meet these pressures with Scout 741, or Chief springs, but we can get away with less due to our lower RPM range. We never need to worry about piston, or valve damage by hitting each other when the valves "float", because Indians are "Flat Heads"! Valve float should be avoided, because it can still cause damage to the cams, and lifters.

Consistant spring pressures can be reached from one valve to the next by trying to keep the installed spring heights the same. This can be done by swapping the retainers around, by shimming, or by using "offset keepers".

I found that between the (6) original retainers I have, that I found (6) different installed spring heights when sampled on the same valve position. One retainer offered 1.900" installed spring height between the bottom of the retainer to the guide's spring surface, while another offerred 1.855" (a .045" difference!). All (6) retainers gave me a different measurement. I recorded how much each retainer raised this installed height higher than the shortest one. I took the shortest retainer, and then measured all (4) valve positions to find the installed height per valve location. I swapped the retainers around to come up with a combination where all (4) valves had similar installed spring heights. By doing this, all (4) valve springs have nearly equal spring pressures, and coil-bind clearance.

If you recall, my rear intake seat had been cut a little more than the others, and by swapping retainers around, I was able to compensate for this.

Scout 741 Springs have (8) full coils, where Chief springs have (9). They both use the same wire size, and coil spacing, so the Scout 741 spring is shorter (compressed and free length). The Scout 741 spring is actually stiffer at maximum lift, because the shorter (7) coil spring is made from a shorter piece of wire, and has to torsionally rotate 14% more for a given amount of travel than does the Chief spring.

Bonneville Inner Springs will not coil-bind, and when added to Chief springs, the spring pressures will increase 24% across the entire range. When used with Scout 741 springs, the pressure rates increase by 25% across the entire range.

The compressed (coil-bind) height of the Scout 741 spring is 1.243", and for Chief springs it is 1.390".

The base thickness of the Starklite Cycle "O-Ring" Valve Covers is .075" thick. This is used to calculate for coil-bind clearance.

In the case of my "Hot Rod" with .490" lift, I have an average of 1.880" of installed height. Add .075 for the valve cover thickness to 1.243" coil-bind height (Scout 741 spring), plus .490" max lift, which equals 1.808". Subtract that from the available 1.880, and I have .072" coil-bind clearance. It is a little less than the recommended minimum, but I'll take it!

Problems and Solutions

After the available installed spring height is measured between the retainer bottom, and the guide surface, the components heights need to be added to find coil-bind clearance. Additional clearance can be found by removing the .062" fiber gasket from under the valve covers, and using thin brown paper (grocery bag at .007" thick) with a non-hardening gasket sealent like "Hylomar HPF", or Teflon Pipe Compound that will creep later when the cylinders are installed. Do not use silicone, because the valve cover positions will need to be adjusted later for the valve cover threads to line up smoothly.

The surface of the valve guides where the valve covers sit can be cut down some as a last resort.

Never cut the valve face, or valve seat in the cylinder to extend the valve stem further!

Aftermarket retainers, and offset keepers can be found, also, to raise the underside of the retainers.

Never try to shim under the springs to increase spring pressures unless adequate coil-bind clearance can be maintaned. Note: Increased spring pressures will accelerate cam, and valve train wear!

On the left is the Chief Bonneville Inner Spring. It will never coil-bind. In the middle is the Scout 741 Spring, and on the right is the Chief Spring.

Important-Read Each Catagory Below for Full Details!