Re:Compression ratio; rusty cams

[Matthew Killick <m.killick@domain.elided>]

Ben says:

>The CRH doesnt list different measurements. it just gives reccomended 
>practice for building a race engine. it simply says: "mill head to 1098mm. 
>standard head gasket is suitable for racing. thickness 1.5mm"
>I have another book that lists the standard head thickness as 1118mm, then 
>goes on to say that in order to achieve a CR between 10.8:1 and 11:1, you 
>need to mill 1.5 to 1.8mm from the standard thickness head.

Ben.  If you have a head that is 111mm (*not* 1,098mm) or thicker, I would
think very carefully before milling it.  The world is full of heads
rendered virtually useless because they are undersize.  I have two of them
in my garden shed.  Skimming under 111mm can cause the valves to contact
pistons, requiring the pistons to be machined to fix them, or the valve
seats to be cut back, in turn requiring the valves to be shortened, causing
the shims not to fit properly and requiring them to be ground............
Get the picture?  High compression may also give pinging under full
throttle, meaning you can't access the extra power that is theoretically
available.  

I'll swap an undersize 1750 head, complete with new valves and seats, and
cover the shipping for a 111+mm thick casting, valve and cam condition
immaterial.

Cheers
Mat

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End of alfa-digest V7 #1071
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