[Tigers] Stock 260 Engine Maximum Cam Lift

[Rob Hogan]

I did the measurements as described in paragraph A to quickly and
inaccurately estimate what lift camshaft could be purchased since there was
no timely ability to make measurements with an assembled long block.  I had
either forgotten or discounted the maximum lobe height occurrence before
piston TDC.  Time constraints compelled a decision to purchase a
0.447/0.447 lift Comp Cams camshaft from Summit to safely stay within the
clearance limits of the stock 260.  From what I've read this camshaft is a
significant improvement over the stock Ford 260 cam toward producing low
end torque without venturing into the compromised driveability of a more
aggressive grind.

Thank you for everyone's advice and grind numbers that provided information
assuring a clearance problem won't occur.

Rob

Rob Hogan

On Mon, Apr 25, 2016 at 8:51 PM, Tom Witt via Tigers <tigers at autox.team.net>
wrote:

> *>>>Even with the original 1.67" intake valves, a 0.010 deck height and a
> 0.040 thick head gasket, I don't comprehend where a 0.070" minimum valve to
> piston clearance is possible.<<<*
>
> I don’t know to what extent you are versed in the engine, but I’ll put
> this out there and use as you see needed (no insult to your knowledge
> intended in my comments).
>
> The valves are recessed in the combustion chamber so the total of the deck
> height and the gasket in and of themselves do not determine the piston to
> valve clearance (if in fact that is what you assumed???). Probably the best
> way to determine the actual clearance is to:
>
> A. If the head is not installed remove a larger intake valve spring. Set
> the head on a flat surface with the valve down, then set and zero a dial
> indicator on the valve stem tip. Push the valve up and measure the
> distance.   Add the stated deck and gasket thickness and that gives you the
> clearance. Unless you check them all there is a likelihood that not all
> will be the same. Casting accuracy and seat recession from wear or prior
> valve jobs can change the numbers. But, hopefully the others will be
> “close.”
>
> B. If the head is installed you can bring the piston to TDC, remove the
> valve spring and do similar.  There is the likelihood that carbon build-up
> will give a lower number (but is the actual functional clearance). Also do
> not add in the deck height or the gasket thickness as they are already
> present. DO NOT crank the engine while doing this or you can drop or bend a
> valve. A narrow magnet may be required to pull the valve back up. Narrow
> rope can be fed into the chamber through the spark plug hole to support the
> valve while the spring is reinstalled.
>
> Remember this gives you the total distance until a valve hits a piston so
> the required clearance (0.070?) will have to be subtracted from the total
> number.  Also, Cams ramp up and down the lobe and may not be at its highest
> lift when the piston is at TDC.  Therefore it is possible that the cam lift
> can be greater than the minimal clearance because the piston is not at TDC
> (or near enough) when it occurs.
>
>   People have used talc powder on clay on top of the piston then cycled
> the engine through a few revolutions, and measured (Calipers) the height of
> the clay. Thus getting an “active” rather than a theoretical valve
> clearance.  This requires assembly/unassembly to measure and a very light
> spring so as not to collapse the lifter (if hydraulic). Also consider that
> advancing/retarding the cam from the centerline will also alter these
> “active” clearances. Lastly, the valve stem to rocker tip clearance
> (mechanical lifter – if used) will create additional clearance.
>
> I hope there is something you can glean from this and I haven’t created
> any confusion.
>
> *From:* Rob Hogan via Tigers <tigers at autox.team.net>
> *Sent:* Friday, April 22, 2016 9:17 PM
> *To:* Tiger's List <tigers at autox.team.net>
> *Subject:* [Tigers] Stock 260 Engine Maximum Cam Lift
>
> Does anyone have experience using a hydraulic lifter camshaft with a lift
> greater than 0.440 (Clymer book page 41 maximum) in the flat top piston
> stock 260 cu. in. engine?
>
> Even with the original 1.67" intake valves, a 0.010 deck height and a
> 0.040 thick head gasket, I don't comprehend where a 0.070" minimum valve to
> piston clearance is possible.
>
> Rob Hogan
>
> _______________________________________________
>
> tigers at autox.team.net
>
> Donate: http://www.team.net/donate.html
> Archive: http://www.team.net/archive
> Forums: http://www.team.net/forums
> Unsubscribe:
> http://autox.team.net/mailman/options/tigers/robertdhogan@gmail.com
>
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://autox.team.net/pipermail/tigers/attachments/20160426/e6503f98/attachment.html>