[Spridgets] rocker clearance

[Hal Faulkner]

Although it feels strange, I will beg to differ with Ron:  Clearance
is *measured
at the valve*, but you are really setting the clearance *at the cam and
follower*. Because it is not feasible to measure at the cam/follower, if
the rocker ratio is higher you must allow for this and set greater
clearance at the valve to compensate.  Stock rockers are 1.25 or 1.3 or
something like that.  To correct for 1.5 rockers you should actually
multiply the standard clearance by 1.5/1.25 which is 1.2.  1.2 times12
gives us a corrected clearance of 14.4thou.  That said, this is not a
terribly critical setting and depending on the engine build could be a few
thou more.
Hal

On Sat, Oct 31, 2015 at 5:00 PM, Ron Soave via Spridgets <
spridgets at autox.team.net> wrote:

> It doesn't.
>
> Ron Soave
>
> On Oct 31, 2015, at 6:16 PM, Rick Fisk via Spridgets <
> spridgets at autox.team.net> wrote:
>
> Why does increasing the rocker ratio cause a need for more clearance?
>
> Sent from my keyboard
>
> On Oct 31, 2015, at 6:14 PM, Michael Rowe via Spridgets <
> spridgets at autox.team.net> wrote:
>
> I used Minisport roller rockers bought cheap in the 2008-9 crash.  I no
> longer remember, but they probably are 1.5 (red), and I also used a "warm"
> Elgin cam that came in a box of parts.
>
> Where higher ratio rockers
> <http://www.spridgetmania.com/part/C-AHT436/Roller-Tipped-15-Ratio-Rockers-Aluminum> are
> to be used, the required valve clearance can then be assessed using this
> simple formula. For instance when using 1.5 rockers, you obviously need to
> multiply the cam/follower clearance by 1.5. So 0.010-in x 1.5 gives
> 0.015-in for standard/mild cams and 0.012-in x 1.5 gives 0.018-in for
> race/more-modified cams. Interestingly, most re-profiled performance cams
> generally have a suggested valve clearance of 0.016-in with standard ratio
> rockers. To assess required valve clearance where higher ratio rockers are
> used simply work it backwards and multiply by the higher ratio. This works
> out as 0.016-in divided by 1.25 = 0.0128, then x 1.5 = 0.0192" - or 0.019"
> at the valve.
>
> ----- Original Message -----
> *From:* Michael MacLean <rrengineer.mike at att.net>
> *To:* Rick Fisk <refisk at chartermi.net> ; Michael Rowe
> <mdrowe at optonline.net>
> *Cc:* Spridgets <spridgets at autox.team.net>
> *Sent:* Saturday, October 31, 2015 4:49 PM
> *Subject:* Re: [Spridgets] rocker clearance
>
> How about when you have 1.5 rocker arms?  Drove the Bugeye around
> yesterday.  Runs great, still blue smoke on acceleration on a recent
> rebuild.  At leat 1000 miles since rebuild.  I'm afraid the rings never
> seated properly.  Not sure of the cylinder wall surface during the rebuild
> as I did not so that part of it.
> Mike MacLean
>
>
>
> On Saturday, October 31, 2015 1:26 PM, Rick Fisk via Spridgets <
> spridgets at autox.team.net> wrote:
>
>
>
> The 0.029 in. spec is a whole different thing used when you are assembling
> the engine.  If your engine is together and you just want to set the valve
> clearance it should be 0.012 in. set cold.
>
> Sent from my keyboard
>
> On Oct 31, 2015, at 4:06 PM, Michael Rowe via Spridgets <
> spridgets at autox.team.net> wrote:
>
> New 1275 engine.
> Haynes says "Rocker clearance, timing only = 0.029 in.
> My mechanic/tutor says, "that is twice what it should be."
> Bentley says:
> Rocker clearance: Running (Standard) = 0.012 in. cold
>                                 Running (competition work) = 0.015 in.
>                                 timing        = 0.029 in.
> Online sites agree on  = .012 in. cold.
>
> So what is the 0.029 in. for?
>
> Michael Rowe
>
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