Question: Valve springs and AMC heads

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Question: Valve springs and AMC heads

Post by captain_kapow » Tue Feb 13, 2018 12:35 am

Hi all

While fitting some type 1 springs to my new set of AMC heads, I noticed that the springs fit slightly tight around the boss that protrudes from the head.

The springs hang a little bit on installation, then they seem ok once they are in place.

Is this acceptable, or do I need to make some clearance?

I have found many posts that mention type 1 springs on type 4 heads, but no mention of clearance issues.

The springs in question are HD single springs and chromolly retainers.


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Re: Question: Valve springs and AMC heads

Post by Type 4 Unleashed » Mon Feb 19, 2018 3:15 pm

Your referring to the valve guide boss. Do you have another head to check the springs on, to determine if it's the head or the springs ? Did you receive any spring shims with the springs to set installed heights, how do those fit ? How do the retainers fit the springs ?

I like to see the springs slide over the boss without any interference, any spring movement could gouge the boss putting aluminum in the oil.

It may just be the flat portion of the spring to allow it to sit flat on the head and retainer, that is slightly smaller than the I.D. of the spring. I've been meaning to buy a Chamfer Tool, it's used to slightly clearance the inner dia. of the end of the springs so retainers have a correct fit, I have a couple sets of springs I need to chamfer to get retainers to fit properly as an example.


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Re: Question: Valve springs and AMC heads

Post by Clatter » Tue Feb 27, 2018 4:02 pm

This is a really good subject, actually..

They type 1 that your normal 'heavy duty singles' are designed for has a smaller guide boss than the type 4.

The type 4 actually had bigger springs than the type 1 originally had.

Back in the old days, putting the bigger type 4 springs on a type 1 was an upgrade.
Funny, how we have come full circle, and type 4 springs are no longer, and type 1 springs need be fit to our type 4s.

You will find this interference in other areas of spring construction in other applications.
For one, the springs are better if held 'captive' to the retainers.
If you buy a matched set of retainers and springs together, you will see the fit of the spring is tight to the retainer.
This is supposed to help stop harmonics, or the spring ringing like a bell, by dampening the end.

Likewise, you almost always see a set of VW performance dual springs having interference between the inner and outer spring.
A set of new Scat duals I have here are hard to pull the inner out of the outer using just bare hands.
Likewise the retainers trap the inners and outers both.
This all seems well to stop the spring from vibrating, and going into harmonics, slightly bouncing on the spring seat.

Also on that note, you will see shims used underneath the spring, between the spring and head for this reason.
While shims are used to tighten the spring, they are also used to prevent the spring from 'chewing' on the head.
When you run heavy springs on a big cam to high RPM, you can see the metal eroded away from the spring ringing and rotating in the soft aluminum head otherwise.

The downside to all of this interference/captivity is friction.
Dual springs are known to run higher oil temperatures than singles.
Oil analysis will also show microscopic contamination from all of the ringing and chewing with duals..

So there Is a downside, like everything.

Back to our singles on type 4 heads..
IMHO, a bit of this captivity is a good thing.
It will likely help dampen vibration/harmonics when the valve is closed,
When the valve is open, the spring grows slightly 'outward', and likely does not contact the boss during lift.
(This is just my theory - wish someone could prove it).

I have run the typical type 1 'heavy singles' on an un-modified type 4 head successfully for many miles.
Nextime I have one apart, I'll have to look at the sides of the guide boss for 'chewage'.
Or maybe have the oil in for analysis?

Maybe I'm flirting with disaster,
But the theory all seems sound,
So I'll be sticking with the theoretical success.

Just like an engineer... ;-)

If anyone else has anything to add to this,
then please chime in.

I'm sure there are WAY more of these setups out there than just me..
"Oh, You don't need to do all that... The valve seats are just going to fall out of it anyway!"
- Doug Ellsworth

Beginners' how-to Type 4 build thread ---> viewtopic.php?f=1&t=145853

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Re: Question: Valve springs and AMC heads

Post by Bobby74 » Wed Mar 07, 2018 10:26 pm

Just saw this thread.

Just for reference, I am using using HD Singles on AMC heads, with 44x36 SS valves, and EMW Titanium retainers. Using 250/260 @ 050, .500" lift. No valve float to 6K+ RPM..... BUT, I would not recommend it!! Several engine builders recommend Dual springs with the type of cam/valves. Half for valve float, half for elimination of harmonics....imho.

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