Just a quick question,

Do double valve springs require different retainers/collets/seats then single springs?


Cheers

The short answer is no, but.....

There are different types of collets on the A series motor and it really depends on what engine we are talking about and the spring pressure of the valves you are talking about.

I personally would only use the type that have the little spring clips to hold the collets together.

The Doc and others may have different (and valid) ideas and opinions.

Mike

Short answer to the original question- yes, often but not always. Valve caps for 850, 998 etc valves and single springs have no location seat there for the inner spring. Although this could be machined in, it's easier to get a set of top caps for double springs.

The little spring clips on early heads don't do much really, all the racers toss them away. If they don't, they come off and finish up lying on the head.
They are not used on the 1275 and later 998s, and these have the same angle on the collets.

<edit>
It's more important to use them I guess with stock valves and the stock (very weak) springs, if you bounce the valves.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.